Severe Weather Discussion for May 9-10, 2015 Issued: 05/09/2015

Severe Weather Discussion for May 9-10, 2015.
Issued: 05/09/2015.

Highlights:

– Severe thunderstorms are likely this morning across much of Oklahoma and again this afternoon across the western 1/3rd. The threat this morning is large hail to quarter size. This afternoon the primary threats are large hail to baseball size, flash flooding, and winds to 75mph. A few tornadoes are possible, especially in far western Oklahoma.

– A few severe thunderstorms are possible on Sunday, currently not expecting much more than large hail and some damaging winds. Flooding rainfall is the greatest threat.

Discussion:

Forecast Changes: Today has been modulated significantly downward re tornado threat, which now appears limited in space and time.

Numerous runs of storms since Tuesday have greatly stabilized the atmosphere in terms of available moisture, cool temperatures and interrupted low level moisture. The issue for today is how much atmospheric recovery can occur and how far north. Current thinking is that west-central and southwest Oklahoma will have the best chance to recover. Even though NW OK will have direct influence of the upper system, not sure this will be enough to overcome the overturned atmosphere. Additionally, effective outflow boundary in Texas will likely move to near I-40 by afternoon, per HRRRR resulting in elevated storms in Kansas. HRRR also has low 60s dewpoints and mid 60s temperatures in KS and parts of NW OK.

4km NAM should arrive shortly, but I anticipate little change from the 12z HRRR. SPC has dropped the moderate risk and this looks good. The enhanced risk is well placed covering much of western Oklahoma for large hail. The 10% tornado threat was kept but may be dropped or moved on the 16:30z update.

Since this event does not reach the medium-end range, this will be the last discussion.

Probabilities:

None – tomorrow will be a slight risk.

Chase Status:

Still thinking of going today, but currently on the fence.

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Severe Weather Discussion for May 9 – 10, 2015. Issued: 05/08/2015

Severe Weather Discussion for May 9 – 10, 2015.
Issued: 05/08/2015.

Highlights:

– Active and potentially significant severe weather event on Saturday. Tornadoes, large hail, damaging winds and flash flooding are all expected.

– Severe thunderstorms are possible across central and eastern Oklahoma on Sunday.

Discussion:

Extremely complex forecast for Saturday, which seems to be the trend this year. Early morning convection has been a problem in recent events and appears tomorrow is no exception. 00z NAM 4km/HRRR both show widespread showers and thunderstorms developing in west Texas and moving east, reaching western OK at 7am. These storms then progress eastward across the state. I have doubts if the storms will be as intense as indicated by the models given the robust activity in Texas/Oklahoma this evening. I do think the atmosphere needs more time to reset, but we’ll see. Of interest is that lack of storm intensity in Texas, compared to last night. Since the early morning storms are likely being driven by a shortwave trof, there should be NVA behind this feature. The 4km NAM indeed shows the Texas panhandle/western OK clearing out by 1pm. As such, intense daytime heating should initiate in wake of this shortwave trof/convection.

Models continue to advertise an intense 500mb closed low will impinge upon the dryline, which surges east by 2pm into the eastern TX panhandle. Dewpoints in the upper 60s/low 70s in strong diurnal heating regime will result in widespread SBCAPE of 2500 J/Kg and near 4500 J/Kg in SW OK. Despite the fact that skies are clear west of I-35 by 4pm, with temperatures in the mid 70s, this model does not generate convection. I believe this is a model error and we’ll probably need to see what 12z runs show before getting a better idea. Either way, I believe that the 4km NAM, backed up the the HRRR point to a significant severe weather event on Saturday with the potential for long-lived supercells.

We’re looking to leave 12:30pm to 1pm or so. Target area is Watonga. This is the best blind of 500mb closed low influences and instability.

Persons across Oklahoma are urged to remain weather aware tomorrow. If I thought tomorrow was more clear cut, I’d go higher with the high risk probs. At this juncture I think a high risk is possible from Clinton northward into the Dodge City area.

Probabilities:

Risk area for any part of OK (valid: 05/09 Day 1, Day 2):

Slight: 100%, 100%
Enhanced: 100%, 50%
Moderate: 100%, 0%
High: 25%, 0%

Chase Status:

Level 2 – Heading out Saturday, Watonga is the spot..

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Severe Weather Discussion for May 4 – 10, 2015

Severe Weather Discussion for May 4 – 10, 2015.
Issued: 05/04/2015.

Highlights:

– Showers and thunderstorms are likely across a large part of Oklahoma Tuesday into Thursday. A few severe thunderstorms are possible.

– Severe thunderstorms are possible across Oklahoma on Saturday and Sunday.

– Temperatures will be in the low 80s Monday – Tuesday, upper 70s Wednesday – Friday and low 80s Saturday – Sunday.

Probabilities:

– Severe Thunderstorms: 45%
– Storm Chase: 30%

Discussion:

Southern stream shortwave trof currently over the SW US will eject northeast Tuesday into Wednesday. Moisture return will result in decent low level flow allowing for PW values near 1.4, with best moisture across eastern Oklahoma. Widespread showers and thunderstorms are likely as this system moves just northwest of Oklahoma on Wednesday. SPC has a slight risk up for Wednesday and this looks good.

Models want to develop a longwave trof out west as another system develops southward into the mean position over the SW US. The western US trof keeps Oklahoma in SW flow aloft with thunderstorm chances Thursday and Friday. Even though there won’t be much upper support, minor trof will likely result in convection. Severe thunderstorms may occur but potential seems limited these days.

EC develops another system into the mean longwave position by Thursday. The system moves into Oklahoma Saturday afternoon. Strengthening winds aloft and impressive moisture return will set the stage for severe thunderstorms. Limiting factor this far out will be strength of the EML (cap) and/or speed of the upper system. Although way too early for these details but either way will have to monitor Saturday very closely. EC shows widespread showers and thunderstorms Saturday morning, which modulate the severe weather threat. Sunday also has severe weather potential, but will be a function of Saturday’s convection.

Chase potential does exist for Saturday and could also see higher severe weather potential. Special discussions may be needed but those won’t start until Wednesday.

Didn’t get fancy with numbers today, they seem to match well with NWS.

Verification:

OKC Temps 04/27 – 05/03

My Numbers: upper 50s, upper 50s, 70F, 70F, upper 70s, upper 70s and upper 70s.
NWS Numbers: Upper 50s, low 60s, low 70s, mid 70s, mid 70s, upper 70s and upper 70s.
Actual: 56F, 66F, 75F, 80F, 80F, 81F, and 81F.

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Severe Weather Discussion for April 24, 2015. Issued: 04/22/2015

Severe Weather Discussion for April 24, 2015.
Issued: 04/22/2015.

Highlights:

– A few severe thunderstorms are possible this afternoon and evening, mainly near the Red River and south. A tornado watch is posted for NW Texas, panhandle and a small part of far SW OK.

– Active severe weather day is still possible on Friday across much of Oklahoma. Forecast issues remain – dryline location, moisture quality and morning/Texas convection.

Discussion:

Forecast Changes: None

Today – Early morning convection greatly stabilized the atmosphere across Oklahoma. The greatest threat for severe weather is along the Red River and south.

Friday – 12z model suite in much better agreement re upper system moving into the region from the SW U.S. The general trend of all models has been to slow the ejection said upper system into the region on Friday. Despite this slowing trend, several of the models still punch the dryline to I-35 by 7pm. As stated yesterday, I am not convinced of this solution, it also leads many to think the best chance for thunderstorms will be east of I-35. The 18z 12km NAM has done the same trick it did yesterday, slowing the dryline Friday afternoon. It also lights off storms over central Oklahoma and moves them east. This scenario is very reasonable and I think far more likely than those pointing to eastern Oklahoma. A concern will be the dryline slowing even more as we get closer to Friday. Again, dryline movement is tied closely to speed of the ejecting upper system. Since this system is moving into the region from Baja Peninsula, it will not be sampled by the upper air network until Friday. Another note is that models have a bad habit of generating convection 30-40 miles east of where it actually will start, again another concern for storms developing along HWY 81 as noted in yesterday’s discussion. Wind fields will be impressive across the region, there is a little veering above 700mb than is expected. Not sure this is a big deal, so will just note and move on.

The primary issues impacting severe weather on Friday relate to moisture quality (hence instability) and morning convection. Lingering surface high from large closed low over the Great Lakes will be parked across the central U.S. Models struggle to return maritime moisture northward due to this feature and there are a variety of solutions on how much moisture will get north. 18z 4km NAM is reasonable in showing moisture trapped in central Texas by this feature and developing surface low over southeast Colorado late Thursday. Moisture return commences Friday morning with serious questions if enough can return for storms Friday afternoon. This trend will have to be monitored but if correct will greatly modulate Friday’s severe weather threat into the low category.

Sunday – technically outside the forecast period but models indicate another upper system moving towards the region. EC and GFS are completely different, with EC favoring cool/dry conditions and the GFS showing better chance for severe thunderstorms.

Probabilities:

Risk area for any part of OK (valid: 04/23, Day 2):

Slight: 100%
Enhanced: 75%
Moderate: 35%
High: 0%

Chase Status:

Level 3 – watching Friday.

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Severe Weather Discussion for April 22 – 24, 2015

Severe Weather Discussion for April 22 – 24, 2015.

Issued:  04/21/2015.

 

Highlights:

 

–  A few severe thunderstorms are possible Wednesday across southern Oklahoma, primary threats are large hail and strong winds.  The event looks to be on the low-end, however if temperatures warm then a more substantial threat may develop.

 

–  Active severe weather day is possible on Friday.  Numerous questions remain re dryline position, clouds and extensive storms in Texas.

 

Discussion:

 

12z model suite has done little to resolve questions re severe weather potential Wednesday and Friday.  There is enough potential relative to severe weather impacts on Friday to warrant special discussions.

 

Wednesday – Large northern stream closed low will be located over southeast Canada with a shortwave ridge just west of Oklahoma.  Southerly flow has commenced across the region, although dewpoints remain rather low.  19z surface analysis shows dewpoints in the upper 50s/low 60s along the Texas Gulf Coast and surface pressure in the 1014mb range.  Prior cold front pushed moisture well offshore and current return flow will take a while to bring even marginal moisture back north.  4km NAM appears to be the best thing going as dewpoints reach the upper 50s along and south of I-40 by Wednesday afternoon, keeping low/mid 60s in Texas.  Additionally, a cold front is progged to move into northern Oklahoma and reach I-40 by afternoon.  As such, the best chance for severe thunderstorms appears to reside in far southern Oklahoma and Texas.  Any storms that do form will have a large hail and strong wind threat.  Tornado potential would seemingly be higher along the Red River and south.  I’m not convinced this setup warrants an enhanced risk, but I’ll let SPC make that call.  4km NAM does light off storms over OKC @2-3pm Wednesday.  Although these are likely to be elevated hailers.

 

Friday – Southeast Canadian closed low shifts eastward as shortwave ridging moves over Oklahoma on Thursday.  A southern stream medium wavelength trof is expected to dig southward over the Baja Peninsula and then eject east-northeast towards the region.  Models offer a variety of solutions, mainly regarding timing, of how this system will evolve.  12z GFS/NAM are fastest with the upper system and hence dryline while the 12z EC/UKMET are slower with the upper system.  The JMA from 12z yesterday also is slower than the GFS/NAM.  The slower approach appears reasonable given the southern latitude this system will take before reach Oklahoma.  All that being said, the new JMA is now faster and more inline with the GFS/NAM.  Ultimately the difference is a matter of hours and probably will not be resolved until Thursday.  Further, the upper system will not be sampled by the upper air network until Friday morning.  For now much of this is a guessing game.  Models do indicate that moisture will return to Oklahoma late Thursday into Friday, with mid 60s dewpoints across central and eastern Oklahoma.  Wind fields will be impressive with deep layer share across the region.  Dryline movement remains one of the issues complicating the forecast.  My thinking is a dryline near HWY 81 by 2-3pm, with convection kicking off near that time.  This is in best agreement with the EC/UKMET and potentially the JMA.  The other issue to address is potential for early morning convection in Oklahoma and robust east-west oriented convection in Texas.  Admittedly the NAM is not near as robust with QPF in Texas as the EC.  So, again tough to determine what will happen.  Given all the questions (not really uncommon) there is the potential for an active severe weather day on Friday, impacting parts of central and eastern Oklahoma.

 

Upper system moves by and apparently another develops near southern California.  This latter system ejects in a similar manner to Friday’s system but appears to have a more southern approach (Texas).  Since models do not seem to have Friday handled, I do not expect much agreement about Sunday.  However, additional severe weather appears possible.

 

Probabilities:

 

Risk area for any part of OK (valid: 04/22 Day 1 and Day 3):

 

Slight:  100%, 100%

Enhanced:  75%, 75%

Moderate:  0%, 20%

High:  0%, N/A

 

Chase Status:

 

Level 4 – Monitoring Wednesday and Friday

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Severe Weather Discussion for April 20 – 26, 2015.

Severe Weather Discussion for April 20 – 26, 2015.
Issued: 04/19/2015.

Highlights:

– Severe thunderstorms are possible Tuesday, Wednesday and Friday. There is a chance of thunderstorms Thursday, but severe weather potential looks lower than the other two days.

– Temperatures will be in the upper 60s Monday – Tuesday, upper 70s Wednesday, mid 70s Thursday, near 80F Friday and mid 70s Saturday – Sunday.

Probabilities:

– Severe Thunderstorms: 35%
– Storm Chase: 50%

Discussion:

Southern stream shortwave trof currently over Oklahoma will move east-northeast and phase with northern stream system. This will create a large closed low over the Great Lakes by the middle of this week. Shortwave ridging will dominate just west of the state, with this area in between the Great Lakes low and the shortwave ridge Tuesday-Thursday. South winds are expected to turn as the cold front moves off allowing moisture turn on Tuesday. Thunderstorms are possible on Tuesday with SPC having a small slight risk in SW OK for severe thunderstorms. The threat appears limited but some large hail is certainly possible. Winds are decent on Wednesday and moisture should improve. Models have backed off on pushing moisture way south and now bring 60F + dewpoints back into the state on Wednesday. As such, there is a threat for severe thunderstorms Wednesday afternoon across a large part of Oklahoma. The threat looks to be hail at this point, but additional threats could develop as we get a better idea of atmospheric evolution that day.

Atmosphere becomes progressive on Thursday with Great Lakes system shifting east and southwest US system ejecting northeast towards Oklahoma. EC/GFS agree that SW US system will move across Oklahoma on Friday with impressive winds speeds aloft. The unknown issues are surface moisture and temperature. Currently the EC develops decent CAPE across much of Oklahoma but only a narrow tongue of good moisture. Either way, Friday does have potential to be a higher impact severe weather day and will be monitored. This also has the best chase potential, as long as the threat stays in western Oklahoma. Upper system moves slowly by on Saturday and Sunday. These days look pleasant and rain free ATTM.

Not sure numbers are that good, but don’t agree with models or NWS. So, I’ll just let them ride, Friday may be too high but then again we’ll see what happens.

Verification:

OKC Temps for 04/13 – 04/19 –

My Numbers: mid 60s, low 60s, low 70s, mid 70s, low 70s, low 70s and low 70s.
NWS Numbers: mid 60s, low 60s, low 70s, mid 70s, low 70s, low 70s and 70F.
Actual: 69F, 57F, 71F, 78F, 75F, 78F and 69F.

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Severe Weather Discussion for April 13 – 19, 2015

Severe Weather Discussion for April 13 – 19, 2015.
Issued: 04/13/2015.

Highlights:

– Widespread showers and thunderstorms for much of Oklahoma today and Tuesday. Additional showers and thunderstorms are possible Thursday – Sunday. A few severe thunderstorms are possible.

– Temperatures will be in the mid 60s today, low 60s Tuesday, low 70s Wednesday, mid 70s Thursday, low 70s Friday – Sunday.

Probabilities:

– Severe Thunderstorms: 15%

Discussion:

Upper system just west of the region will slowly move east through late Tuesday and pick up speed on Wednesday as up stream kicker moves into the SW U.S. Models indicate that this next system will also move slowly east across the state. This should keep rain chances going much of the week. Can’t say I like to put POPs in everyday but there seems to be decent rain chances and a reason to do so. Not sure this is a drought buster but will go a long ways for the state, especially if western OK gets predicted amounts.

Severe weather threat is on the low (slight risk) side of the scale all week. At this juncture, do not see anything significant and closed/cutoff lows are not that favorable for severe weather.

Temperatures are based closely to NWS. I think the EC is a little warm given all the precip expected this week.

Verification:

OKC Temps for 04/06 – 04/12 –

My Numbers: low 80s Monday, mid 80s Tuesday, mid 80s, mid 80s, upper 60s, mid 70s and upper 60s.
NWS Numbers: mid 80s,, mid 80s, mid 80s, mid 70s, mid 70s, mid 70s and mid 70s.
Actual: 82F, 78F, 75F, 75F, 71F, 74F and 81F.

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Severe Weather Discussion for April 8, 2015

Severe Weather Discussion for April 8, 2015.
Issued: 04/08/2015.

Highlights:

– Active severe weather day is likely for a large part of Oklahoma today. Tornadoes, destructive hail to baseball size and winds to 75mph are all possible.

Discussion:

Numerous severe thunderstorms are expected later today and tonight. There are no changes to the forecast from Monday.

Area of showers has developed in SW OK and while not completely unexpected, it may change things a little. I will say that these storms are currently limited in coverage and intensity. The current cloud cover is another issue that may tend to limit the overall threat today, but again is unknown if that is an issue. The past few days, clouds have cleared about noon with temperatures warming rapidly into the 80s. So, I do think we’ll see clearing skies in a few hours, which should allow for enough instability to generate severe thunderstorms.

Current indications are that storms will develop between 4-6pm across western Oklahoma and northwest, with supercells favored across the state. Lots of uncertainty right now, but the key is to watch weather conditions today.

Probabilities:

N/A

Chase Status:

Level 1 – Looking to head out today, probably due west or maybe a little NW.

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Special Weather Discussion 2015-1-2

Severe Weather Discussion for April 8, 2015.
Issued: 04/06/2015.

Highlights:

– Active severe weather day is likely on Wednesday with the potential for significant impacts.

– Severe thunderstorms are possible across central Oklahoma on Tuesday, although the threat is highly conditional.

– Severe thunderstorms are likely Thursday across eastern Oklahoma, although the exact area depends on how fast this event evolves.

Discussion:

Forecast Changes – dropped central Oklahoma from Thursday. Little change to forecast reasoning other than adjusting to the speed offered by all models.

Tuesday – high surface based CAPE will be in-place Tuesday afternoon across a large part of central Oklahoma. Wind fields will be decent but not overly impressive. Additionally, models indicate only a small area where CIN may erode across western Oklahoma. This combined with neutral or even downward motion will keep chances limited tomorrow. Any storm(s) that do form will have the potential to produce hail to baseball size and winds to 70mph.

Wednesday – a much greater threat for severe weather is present on Wednesday. Impressive winds will translate eastward across the region overlaying a highly unstable airmass. Models point to dewpoints in the mid/upper 60s with deep layer moisture across the region characterized by 850mb dewpoints at least 12C. 18z NAM appears to shows a characteristic bias by sinking 850mb dewpoints on Wednesday. I have noted this problem for the past several years and it typically isn’t corrected until the night before. The other issue is that the 18z 4km NAM surges the dryline to near Oklahoma City by late Wednesday, placing storm initiation just west of HWY 81. I’m not sure if this surge is related to intense dryline mixing owing to limited 850mb moisture. Either way, the models are trending east with the dryline instead of a west, admittedly not expected. Storm motion looks to be rather quick at 35-40mph, so reaction time will be somewhat limited. A strong cap will keep storms down until mid-afternoon when height falls coupled with surface moisture convergence should breach said cap. I’m not convinced only a few storms will develop, I think more widespread development is possible. I also do not agree with the current SPC Day 3 and I’d think big changes are forthcoming on the upcoming Day 2. Either way, Wednesday continues to be a day to watch.

Thursday – all models shifted the dryline eastward early Thursday with the main impacts in far eastern Oklahoma. Clouds and rain from the night before could keep the threat on Thursday limited. For now, I’ll keep Thursday in the discussion.

Probabilities:

Risk area for any part of Oklahoma (valid: 04/07 Day 2, Day 3):

Slight: 100%, 100%
Enhanced: 100%, 75%
Moderate: 75%, 0%
High: 0%, N/A

Chase Status:

Level 3 – Wednesday appears to be the day.

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Severe Weather Discussion for April 6 – 12, 2015.

Severe Weather Discussion for April 6 – 12, 2015.
Special Weather Discussion for April 8 – 9, 2015.
Issued:  04/05/2015.
Highlights:
–  Active severe weather days are likely on Wednesday and Thursday with the potential for significant severe weather.  Finer details are still lacking (i.e. morning convection, Wednesday’s storms, dryline position, etc), however the potential is there per model progs.  This is a good time to review severe weather safety plans and clean out storm shelters, which honestly should be done by now anyway.
–  Slight chance of severe thunderstorms late Tuesday.  Unknown if storms will develop, but if they do severe weather will occur.
–  Showers and thunderstorms are possible on Sunday.
–  Temperatures will be in the low 80s Monday, mid 80s Tuesday – Thursday, upper 60s Friday, mid 70s Saturday and upper 60s Sunday.
Probabilities:
–  Severe Thunderstorms:  > 75%
–  Storm Chase:  > 75%
Risk area for any part of Oklahoma (valid:  04/06 Day 3):
Slight:  100%
Enhanced:  100%
Moderate:  35%
High:  N/A
Discussion:
Models indicate that a medium wavelength trof/closed low will translate into the western U.S. Tuesday and move eastward towards the region.  Maritime tropical air will move northward ahead of this system as a strong cap develops across Oklahoma.  These ingredients will set the stage for one or more episodes of severe weather across Oklahoma.  I have opted to combine the weekly discussion with a special weather discussion re Wednesday – Thursday.
Evening surface analysis shows a warm front across southern Texas characterized by low 60s dewpoints to the north and upper 60s to the south.  Models prog this boundary to move rapidly north tonight and be located in northern Oklahoma on Monday.  Dewpoints will increase across the state on Monday with mid/upper 60s across the state late Monday.  Winds aloft will be marginal although CAPE will be near 4000 J/Kg.  Models show weak shortwave ridging across Oklahoma and at this point, believe storms will not form.  This is supported by the 18z 4km NAM.
Upper system moves onshore Tuesday as moisture continues to increase across the state.  A weak cold front will nudge into northern Oklahoma, potentially reaching HWY 51.  4km NAM shows extreme surface CAPE by late afternoon in the 5000 J/Kg range with low 70s dewpoints.  Shortwave ridging may relax enough for storms to develop and NAM shows some along the cold front.  If storms form, they will be severe given favorable shear.
Models had been in good agreement for Wednesday/Thursday time period and this is the greatest potential for high-end severe weather.  12z GFS/NAM trended much faster with the upper system, although the 00z/12z EC are consistent and slower.  Ensemble members are scattered, so it appears there is great uncertainty re Wednesday/Thursday.  The EC does have a bias of moving systems too slow over the western U.S. but not sure if that issue is at play for this setup.  The EC appears to briefly close the low off near the California coast and the up stream kicker sends it east on Tuesday.  The GFS/NAM do not slow the system down and keep it a trof.  This system may not be well sampled by the upper air network until Monday morning, so I have little hope the 00z runs will clear this matter up.  For now, I am sticking with the ECMWF (EC) as it has been consistent.  It is also the most prudent move, since I’ll keep severe chance going for central Oklahoma on Thursday.
Wednesday – all models agree that the dryline will move into far western Oklahoma by late afternoon, characterized by dewpoints in the upper 60s to the east of this feature.  A strong cap will also be in-place but is expected to be breached given ample daytime heating and potentially a while timed shortwave trof.  Surface CAPE will be in the 4000 J/Kg range with adequate shear and impressive mid-level winds.  The EC has weaker flow at 200mb, but not sure if this is a model bias.  Deep layer moisture will also be in-place with 850mb dewponts near 15c and PW near 1.5.  NAM erodes all CIN Wednesday afternoon, which is likely not correct.  PRIND – severe thunderstorms will develop Wednesday afternoon in far western Oklahoma and move east.  Supercells will be favored, resulting in potential for tornadoes, softball hail and winds to 80mph.  Potential for longlived supercells is there, especially if the GFS/NAM are correct.  It is also possible that weakening upper support and increased capping due to night time will reduce storm intensity before reaching central sections.  At this point, tough to see if central Oklahoma will get storms on Wednesday, but I do think it will be after 8pm if it happens.
Thursday – following the EC, upper system will eject east-northeast as a negative tilt.  A dryline will surge through western Oklahoma, reaching HWY 81 by early afternoon.  Winds will increase across the area with impressive 700mb/500mb flow.  Storm development by early afternoon appears likely and CAPE values will support severe thunderstorms.  Again, supercells will be favored given winds and instability.  If the GFS/NAM are correct, the dryline will surge well into eastern Oklahoma by early afternoon and the threat will be there on Thursday.  Plenty of time to trend the models.  Also, early April does not favor multiple rounds of severe weather, so we’ll see.  I do think we may end up with western Oklahoma getting hit Wednesday, skipping central and eastern getting hit Thursday.
Previously mentioned up stream kicker moves into the western U.S. on Saturday and shifts east into the area on Sunday.  EC has it in Texas, which should be showers/thunderstorms for Oklahoma.  I have not spent much time on this part of the forecast.
First guess at numbers needed refinement based on model progs.  I sided with the warmer EC Tuesday – Thursday than going NWS numbers.  Next weekend is iffy given the bust today.  I’d think we’ll be cooler than models prog, due to rain, but went with upper 60s anyway.
Verification:
OKC Temps for 03/30 – 04/05
My Numbers:  mid 70s, low 80s, low 80s, low 80s, mid 60s (midnight high mid 70s), upper 60s and low 70s.
NWS Numbers:  low 70s, upper 70s, upper 70s, low 80s, upper 60s, low 60s and upper 60s.
Actual:  78F, 86F, 82F, 84F, 73F, 66F and 54F.
Chase Status:
Level 4 – Monitoring Wednesday and Thursday.

 

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Weekly Severe Weather Discussion/Special Weather Discussion 2015-1-1

Severe Weather Discussion for April 6 – 12, 2015.
Special Weather Discussion for April 8 – 9, 2015.
Issued: 04/05/2015.

Highlights:

– Active severe weather days are likely on Wednesday and Thursday with the potential for significant severe weather. Finer details are still lacking (i.e. morning convection, Wednesday’s storms, dryline position, etc), however the potential is there per model progs. This is a good time to review severe weather safety plans and clean out storm shelters, which honestly should be done by now anyway.

– Slight chance of severe thunderstorms late Tuesday. Unknown if storms will develop, but if they do severe weather will occur.

– Showers and thunderstorms are possible on Sunday.

– Temperatures will be in the low 80s Monday, mid 80s Tuesday – Thursday, upper 60s Friday, mid 70s Saturday and upper 60s Sunday.

Probabilities:

– Severe Thunderstorms: > 75%
– Storm Chase: > 75%

Risk area for any part of Oklahoma (valid: 04/06 Day 3):

Slight: 100%
Enhanced: 100%
Moderate: 35%
High: N/A

Discussion:

Models indicate that a medium wavelength trof/closed low will translate into the western U.S. Tuesday and move eastward towards the region. Maritime tropical air will move northward ahead of this system as a strong cap develops across Oklahoma. These ingredients will set the stage for one or more episodes of severe weather across Oklahoma. I have opted to combine the weekly discussion with a special weather discussion re Wednesday – Thursday.

Evening surface analysis shows a warm front across southern Texas characterized by low 60s dewpoints to the north and upper 60s to the south. Models prog this boundary to move rapidly north tonight and be located in northern Oklahoma on Monday. Dewpoints will increase across the state on Monday with mid/upper 60s across the state late Monday. Winds aloft will be marginal although CAPE will be near 4000 J/Kg. Models show weak shortwave ridging across Oklahoma and at this point, believe storms will not form. This is supported by the 18z 4km NAM.

Upper system moves onshore Tuesday as moisture continues to increase across the state. A weak cold front will nudge into northern Oklahoma, potentially reaching HWY 51. 4km NAM shows extreme surface CAPE by late afternoon in the 5000 J/Kg range with low 70s dewpoints. Shortwave ridging may relax enough for storms to develop and NAM shows some along the cold front. If storms form, they will be severe given favorable shear.

Models had been in good agreement for Wednesday/Thursday time period and this is the greatest potential for high-end severe weather. 12z GFS/NAM trended much faster with the upper system, although the 00z/12z EC are consistent and slower. Ensemble members are scattered, so it appears there is great uncertainty re Wednesday/Thursday. The EC does have a bias of moving systems too slow over the western U.S. but not sure if that issue is at play for this setup. The EC appears to briefly close the low off near the California coast and the up stream kicker sends it east on Tuesday. The GFS/NAM do not slow the system down and keep it a trof. This system may not be well sampled by the upper air network until Monday morning, so I have little hope the 00z runs will clear this matter up. For now, I am sticking with the ECMWF (EC) as it has been consistent. It is also the most prudent move, since I’ll keep severe chance going for central Oklahoma on Thursday.

Wednesday – all models agree that the dryline will move into far western Oklahoma by late afternoon, characterized by dewpoints in the upper 60s to the east of this feature. A strong cap will also be in-place but is expected to be breached given ample daytime heating and potentially a while timed shortwave trof. Surface CAPE will be in the 4000 J/Kg range with adequate shear and impressive mid-level winds. The EC has weaker flow at 200mb, but not sure if this is a model bias. Deep layer moisture will also be in-place with 850mb dewponts near 15c and PW near 1.5. NAM erodes all CIN Wednesday afternoon, which is likely not correct. PRIND – severe thunderstorms will develop Wednesday afternoon in far western Oklahoma and move east. Supercells will be favored, resulting in potential for tornadoes, softball hail and winds to 80mph. Potential for longlived supercells is there, especially if the GFS/NAM are correct. It is also possible that weakening upper support and increased capping due to night time will reduce storm intensity before reaching central sections. At this point, tough to see if central Oklahoma will get storms on Wednesday, but I do think it will be after 8pm if it happens.

Thursday – following the EC, upper system will eject east-northeast as a negative tilt. A dryline will surge through western Oklahoma, reaching HWY 81 by early afternoon. Winds will increase across the area with impressive 700mb/500mb flow. Storm development by early afternoon appears likely and CAPE values will support severe thunderstorms. Again, supercells will be favored given winds and instability. If the GFS/NAM are correct, the dryline will surge well into eastern Oklahoma by early afternoon and the threat will be there on Thursday. Plenty of time to trend the models. Also, early April does not favor multiple rounds of severe weather, so we’ll see. I do think we may end up with western Oklahoma getting hit Wednesday, skipping central and eastern getting hit Thursday.

Previously mentioned up stream kicker moves into the western U.S. on Saturday and shifts east into the area on Sunday. EC has it in Texas, which should be showers/thunderstorms for Oklahoma. I have not spent much time on this part of the forecast.

First guess at numbers needed refinement based on model progs. I sided with the warmer EC Tuesday – Thursday than going NWS numbers. Next weekend is iffy given the bust today. I’d think we’ll be cooler than models prog, due to rain, but went with upper 60s anyway.

Verification:

OKC Temps for 03/30 – 04/05

My Numbers: mid 70s, low 80s, low 80s, low 80s, mid 60s (midnight high mid 70s), upper 60s and low 70s.
NWS Numbers: low 70s, upper 70s, upper 70s, low 80s, upper 60s, low 60s and upper 60s.
Actual: 78F, 86F, 82F, 84F, 73F, 66F and 54F.

Chase Status:

Level 4 – Monitoring Wednesday and Thursday.

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Severe Weather Discussion for March 30 – April 5, 2015.

Severe Weather Discussion for March 30 – April 5, 2015.
Issued: 03/29/2015.

Highlights:

– A few thunderstorms (maybe a severe) will be possible in northwest Oklahoma Wednesday afternoon/evening.

– Severe thunderstorms are possible across a large part of central/eastern Oklahoma Thursday afternoon/evening.

– Showers and thunderstorms (a few severe) are possible across a large part of Oklahoma Tuesday into early Wednesday and again on Sunday.

– Temperatures will be in the mid 70s Monday, low 80s Tuesday – Thursday, mid 60s Friday (after a midnight high in the mid 70s), upper 60s Saturday and low 70s Sunday.

Probabilities:

– Severe Thunderstorms: 35%
– Storm Chase: 10%

Discussion:

Weakening subtropical shortwave trof will progress eastward across Mexico Tuesday into Wednesday. Models indicate that prior cold front will weaken and drift northward on Tuesday setting up a WAA pattern across the state. A marginal risk for severe thunderstorms is posted across much of Oklahoma on Tuesday. Primary threat from any severe thunderstorm will be hail to quarter size, although the vast majority will simply be showers and thunderstorms. Southern stream shortwave trof moves inland on Wednesday as the northern stream system translate northeast into central Canada. 12z EC has a weak shortwave trof ahead of the main system Wednesday afternoon, primarily influencing NW OK and western KS. Moisture should be in the upper 50s/low 60s with decent 0-6km winds but poor winds above. As such, a transient threat for severe thunderstorms seems possible across northwest Oklahoma on Wednesday.

Model agreement goes out the window beyond Wednesday and makes the Thursday forecast complex, especially given the possible sensible weather impacts to the region. Models do agree that the western U.S. southern stream medium wavelength trof will progress eastward into the central U.S. by late Thursday. However, differences at the surface/850mb levels are readily apparent. I’m not sure either model is correct (GFS/EC), so I have modified their solutions, especially bringing the cold front/dryline west Thursday afternoon. The EC appears to surge the dryline east as a small shortwave trof ejects northeast Thursday morning and also lifts out the 850mb low. This model places the dryline along HWY 75 at 7pm Thursday. I can’t make much of the GFS surface pattern at the same time, so gave up. Models do show low/mid 60s dewpoints across the area yielding CAPE values @2500 J/Kg. 0-6 winds will again be good and upper level winds will be impressive. As such, depending on how the surface features setup, severe thunderstorms appear likely on Thursday. I’m not sure if this rises to a medium-end event, but it is certainly possible. Of course last Wednesday was, so we’ll see. Special discussion may be needed starting tomorrow, depends on how much of Oklahoma will be impacted. If models trend farther east or where they are, I may not go forward with special discussions.

Models move this system quickly east with a cold front following. Winds will quickly turn southerly over the weekend with warming temperatures. A more significant western U.S. trof takes shape early next week. This is shown by the EC/GFS/FIM9 and consistency has been decent. Models also show upper 60s dewpoints in the state Tuesday 04/07 and Wednesday 04/08. There are differences between the EC/GFS with the GFS faster than the EC. At this point it is splitting hairs but impressive jet streaks appear possible and another round of severe thunderstorms.

First guess at numbers seems close to the NWS and models, I did raise highs Tue/Wed. The trend has been much warmer than models show, so I think for early week this is a good bet. Post cold front Friday I went with the models but the early morning high is a consideration. I warmed things up per the EC and did not follow the GFS. We were much warmer this weekend than the GFS showed and the incoming cold front doesn’t appear near as strong, as the prior one.

Verification:

OKC Temps 03/23 – 03/29:

My Numbers: low 70s, 80F, 80F , upper 50s, mid 50s, 60F and low 70s.
NWS Numbers: Upper 70s, low 80s, mid 70s, upper 50s, mid 50s, low 60s and mid 70s.
Actual: 78F, 81F, 84F, 62F, 57F, 78F and 78F

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Severe Weather Discussion for April 21 – 27, 2014

Severe Weather Discussion for April 21 – 27, 2014.
Issued:  04/20/2014.
 
Highlights:
 
–  Showers are expected across the state on Monday.
 
–  A few severe thunderstorms are possible in western Oklahoma on Wednesday.
 
–  A few thunderstorms are possible in eastern Oklahoma on Friday.
 
–  Severe thunderstorms are possible across the state on Saturday/Sunday, one or both of these days may present a medium-end event.
 
–  Temperatures will be in the upper 70s Monday, near 80F Tuesday, low 80s Wednesday, mid 70s Thursday, low 80s Friday, mid 80s Saturday, and low 80s Sunday.
 
Probabilities:
 
–  Severe Thunderstorms:  50%
–  Storm Chase:  30%
 
Discussion:
 
Weakening southern stream system will continue to pass over the state tonight into Monday.  Ongoing showers and thunderstorms across western Oklahoma will continue to push east, although overall decrease in intensity should occur at sunset.  Moisture is marginal for severe thunderstorms, although a few have occurred. 
 
A cold front will push through the state late Monday and push moisture south again.  A larger system will  move into the western U.S. on Tuesday and start moisture return late in the day.  Models have a variety of solutions for moisture return by Wednesday afternoon.  The GFS/EC look the best as I don’t see the NAM’s far western Texas panhandle prog verifying.  The trof is seemingly well timed but ongoing short wavelength trofs has put a dent in meaningful Gulf moisture.  SPC does have a Day 4 up for western Oklahoma but I see this as a low-end event.  Hence, despite the hint at a moderate risk, I’ll forgo special discussions.  Seems to be the standard this year.  Either way, EC shows CAPE values in the 1500 J/Kg range with decent winds, as such a few supercells seem likely.  Large hail appears to be the primary threat at this juncture and probably the 30% area SPC is hinting at.
 
Upper trof swings through with moisture being pushed into north Texas and poised for rapid return.  EC goes a little nuts with precipitation on Friday and shockingly the GFS seems to hit the same area.  I really don’t want to put POPs in for Friday, but guess I have no choice.  Like the NWS, I went with low POPs. 
 
Attention then turns to Saturday/Sunday as another longwave trof moves into the lower 48.  Models greatly amplify the 500mb pattern across the CONUS and seemingly due to downstream blocking near Greenland.  The models handle this pattern change different with the GFS developing a strong northern U.S./Canada mid level ridge and the EC more elongated to the east.  WPC has also sided with the less amplified EC as opposed to the GFS.  There are important differences going into Saturday/Sunday as the GFS has a much stronger surface ridge nosing southward into the central U.S.  The model then struggles with moisture return into Oklahoma as the warm air gets held up by the 1032mb high.  The EC is much different and certainly leads to a more robust severe weather setup.  WPC’s D6/D7 drawings match up well with the EC and this lends credibility to the forecast.  Admittedly I have seen several good severe weather setups a few days out, only to fall apart.  Wednesday is one such example. 
 
12z EC progs strengthening 500mb flow atop a warm and moist surface airmass.  CAPE values Saturday/Sunday are in the 3000 J/Kg range with a dryline in Oklahoma.  Upper system will swing by on Sunday and appears to take on a negative tilt.  If the EC is correct and that’s a big if, special discussions will be needed starting Wednesday.
 
I went with storm chase probabilities since I’d certainly like to go if my commitments next weekend don’t go into the late afternoon hours.  I won’t know that schedule for a few more days.
 
Number wise, I lined up okay with the NWS.  The EC is rather warm for next weekend and I didn’t go that high.  I’ll say that if the dryline is faster than progged on Sunday, some 90s are likely in central OK.
 
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Severe Weather Discussion for April 14 – 20, 2014

Severe Weather Discussion for April 14 – 20, 2014.
Issued:  04/13/2014.
 
Highlights:
 
–  Snow is likely for parts of the panhandle and northwest Oklahoma.  Accumulations will be limited but a few inches on grassy areas seems possible.
 
–  Showers and a few thunderstorms are possible on Thursday.  And, another chance late Saturday into Sunday.
 
–  Temperatures will be in the uppers 40 Monday, near 60F Tuesday, upper 60s Wednesday, mid 60s Thursday, upper 60s Friday, and mid-70s Saturday – Sunday.
 
Probabilities:
 
Winter Precip:  10%
 
Discussion:
 
Tornado drought is broken, confirmed tornado near Bray, Oklahoma, today.
 
Upper system responsible for the ongoing severe weather will shift east tonight as the main northern stream system swings through on Monday.  Very strong mid-April cold front is plunging southward across the state and this will usher in much colder temperatures for Monday.  A hard freeze is likely for a large part of Oklahoma by Tuesday morning.  Models indicated that a trace to 0.2 inches water equivalent snow will be possible in the panhandle and parts of northern Oklahoma.  Time of year does not favor much in the way of significant accumulations.
 
Much of Tuesday and Wednesday will be quiet as the next northern stream system moves towards the area.  12z EC/GFS are in decent agreement with the amplification of this system as it approaches Oklahoma.  Current cold front will move into the Gulf, closing off moisture return the next few days.  Moisture will try to return ahead of the next upper system, but will struggle.  As such, showers and thunderstorms look to be primary impact as this system shifts quickly to the east.
 
A weak southern stream system will move into the southwest U.S. on Friday and slowly progress across the region during the weekend.  This system will have more moisture to work with than Thursday’s system but will also be a lot weaker.  As such, another  round of showers and thunderstorms will be possible.  Severe weather is not anticipated beyond today.
 
Models do indicate a northern stream system taking shape in the western U.S. @D10-11 (April 23-24).  Hi-Res ECMWF shows low 60s dewpoints in the state Wednesday (04/23) morning with the upper system near Nevada.  70F dewpoints in southern Texas and several more hours to advect moisture all point to severe weather chances.  Of course this is several days out and a rogue cold front could shut down the Gulf.
 
First guess at numbers was close to models, although I made some changes to the weekend.  Forecast leans strongly towards the EC for numbers, although I do think my Sunday numbers may be a little high.
 
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Severe weather discussion – April 7-13

Severe Weather Discussion for April 7 – 13, 2014.
Issued:  04/06/2014.
 
Highlights:
 
–  Showers are likely on Monday across Oklahoma, overall rainfall amounts will be low.
 
–  A few thunderstorms are possible on Saturday across western Oklahoma.  A severe thunderstorm is possible.
 
–  Severe thunderstorms are possible on Sunday across central/eastern Oklahoma.
 
–  Temperatures will be in the low 60s Monday-Tuesday, mid 70s Wednesday, mid 80s Thursday, low 80s Friday-Saturday, and upper 70s Sunday.
 
Probabilities:
 
–  Severe Thunderstorms:  25%
–  Storm Chase:  15%
 
Discussion:
 
Current upper system will impact the region through Monday as multiple waves move through.  By Tuesday, the upper system will be gone and mid-level ridging is expected.  Dewpoints are low across the region due to the system on Thursday.  As such, precipitation amounts will be on the low side.  However, given the ongoing drought, we’ll take what we can get.
 
Mid-level ridging will dominate the region through Friday.  Beyond Friday, models agree that a southern stream closed low will move onshore in the southwest US early Saturday.  12z EC forecasts this system to open up and eject east-northeast into the region on Sunday.  The GFS is a little slower and much farther south.  It also keeps the low closed longer than the EC.  Both models are seemingly correct, however this week I’ll side with the EC.  This has been the ongoing pattern this season.  Current upper system will clear tropical moisture from the Gulf and as such, only modified moisture return is expected on Saturday.  Models do show more robust moisture return on Sunday but not what we had last Thursday.  Despite this, a few thunderstorms are possible on Saturday across western OK near developing dryline.  Residual shortwave ridging will likely keep storms limited.  Models do indicate a thunderstorms or two along the dryline Saturday afternoon.  Time of year does favor a few severe thunderstorms. 
 
Upper system approaches Oklahoma on Sunday and is shown by the EC to shift east of the state by late Sunday.  This isn’t exactly favorable for sever thunderstorms, but a timing change of only a few hours could increase severe weather chances.  EC winds are favorable for organized severe thunderstorms and right now the most likely area is eastern OK.  I added central into the discussion since a timing change is possible.  If the GFS is correct, a day similar to today is likely with cloudy, cool and rainy conditions. 
 
First guess at number is close to going NWS and models, changed Monday.  I left Sunday in the upper 70s, since seemingly it is possible should the cold front slow down.  Either way, beyond Sunday the incoming cold front will knock temperatures back down below normal for a few days.  Models indicate some freezing temperatures in Oklahoma in 7-9 days.  In other news, 242 days without a tornado in Oklahoma and Monday makes eight months. Still 50 or so days from the record, but since 1950 only 10-11 years with no tornadoes Jan-Mar.  The latest tornado for a given year is April 26th.  I don’t see us making that date, but we’ll see.
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