Severe Weather Discussion for April 2-3, 2014

Severe Weather Discussion for April 2-3, 2014.
Issued:  04/02/2014.
 
Highlights:
 
–  Severe thunderstorms are expected this afternoon and evening across parts of central/eastern Oklahoma.  Primary threat is large hail to baseball size.  Tornadoes as also possible, but significant activity is not expected.  The threat remains conditional, meaning we’re not sure if storms will develop.  However, if they do, severe storms are likely.
 
–  Significant severe weather day is likely across Arkansas and southern Missouri on Thursday.  This is outside the area I forecast, but worth noting here.  Severe thunderstorms will likely initiate in Oklahoma Thursday afternoon and move east.  Primary threats with any storm in Oklahoma will be large hail to baseball size and a few tornadoes.
 
Discussion:
 
Little change to the going forecast.  Mesoanalysis indicates a very volatile atmosphere across Oklahoma for early April.  CAPE values are in the 3500 J/Kg range with a spot of 4000 J/Kg in west-central OK.  CIN values are < 25 J/Kg, indicating an uncapped atmosphere.  The issue for convective initiation remains subtle to limited forcing.  HRRR and other convective allowing models hint at storms in northern OK, closer to the warm front.  Additionally, a storm or two along the dryline in western section.  Additionally, there has been a tendency for these models to develop storms in central Oklahoma.  Either way, will need to watch the entire area for storms development this afternoon.  Luckily it appears that storms will start after 4pm, but we’ll see there. 
 
Thursday looks quite ripe out east.  I haven’t had much time to do more than look at the SPC outlooks, but they’re hitting the potential hard.  I think Oklahoma will miss out on the really bad stuff but doesn’t mean storms won’t start in eastern OK (near Bartlesville to Durant).  I may issue a discussion tomorrow, assuming I have time.
 
Probabilities:
 
Risk area for any part of OK (valid:  04/03 Day 1):
 
–  Slight:  100%
–  Moderate:  75%
–  High:  0%
 
Chase Status:
 
–  Level 4 – but might go tonight if something is close.
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Severe Weather Discussion for March 24 – 30, 2014

Severe Weather Discussion for March 24 – 30, 2014.
Issued:  03/23/2014.
 
Highlights:
 
–  Severe thunderstorms are possible for central and eastern Oklahoma on Thursday.
 
–  Showers and thunderstorms are possible across Oklahoma on Wednesday.
 
–  Fire danger on Thursday.
 
–  Temperatures will be in the low 60s Monday, mid 50s Tuesday, upper 50’s Wednesday, mid 70s Thursday, mid 50s Friday, mid 60s Saturday, and low 70s Sunday. 
 
Probabilities:
 
–  Severe Thunderstorms:  20%
 
Discussion:
 
Unseasonably cold temperatures will give way to a decent warm up on Monday as a reinforcing shot of cold air moves into the region for Tuesday.  Beyond that, models agree that the persistent mid-level ridge to our west will finally weaken and shift east as progressive 500mb flow develops.  Rex block associated with the western ridge will likewise weaken and the trapped upper system will eject northeast towards Oklahoma on Wednesday.  Moisture return will start as the system moves across the region.  An area of showers and some thunderstorms seems possible across the state with it. 
 
Upper system moves into the western U.S. on Wednesday and progresses eastward into the central U.S. on Thursday.  12z GFS/EC are at odds on how this system will evolve and subsequently translate east.  The GFS is weaker with the lead wave, keeping more energy back west while the EC has a more focused trof with two embedded waves.  I’m siding with the EC for now, since each solutions offers different sensible weather impacts.  Unfortunately this carries into the the weekend, so siding with the wrong model will mess up the forecast beyond Thursday.
 
Aside from the mid-level pattern differences, the models can be used to derive expected surface conditions on Thursday.  Both show moisture return on Thursday in the upper 50s to near 60F range, although the EC has the dryline near I-35 at 7pm Thursday while the GFS is much farther east, owing to the early wave Thursday midday.  Temperatures appear to warm nicely across the state and EC develops CAPE values @1800 J/Kg.  PW values are in the 0.9 inches range, a little low for severe weather.  Something that caught my eye on the 00z EC was the focused shortwave trof and vortmax on Thursday.  This could compensate for lack of moisture, although the 12z EC shifted from that solution.  Deterministic model windfields are favorable for severe thunderstorms with hail and wind the primary threats.  Can’t say I see the other threat at this point and it has been 229 days without one. Thursday appears to be a slight risk and have put probabilities in that area.  The fire threat may be more substantial than the severe weather threat as dewpoints plunge post dryline.  As noted previously, the GFS would argue for far eastern Oklahoma to get storms.  I do not see this as a chase day, although I’m rather interested in finding such a day. 
 
Models do hint at progressive pattern continuing beyond this forecast period.  Temperatures do cool post Thursday’s system, but warm steadily through the weekend.
 
First guess at temperatures per EC/NAM are little off from going NWS numbers.  I went lower than NWS on Wednesday since the EC and especially the NAM are much lower. Given the upper system moving through the area, I think the lower numbers are a good bet.  Another difference is next Sunday when the EC is very warm, showing upper70s.  Since the normal high will be 69F by that time, I went low 70s.  Hopefully the EC will be right but certainly not the trend this season.
 
 
 
 
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Severe Weather Discussion for March 17 – 23, 2014

Severe Weather Discussion for March 17 – 23, 2014.
Issued:  03/16/2014.
 
Highlights:
 
–  Showers and thunderstorms are possible Friday afternoon/evening – Sunday.  It will not rain the entire time, but chances persists those days.
 
–  Temperatures will be near 60F Monday, upper 60s Tuesday, low 60s Wednesday, low 70s Thursday, near 70F Friday, and low 60s Saturday-Sunday.
 
–  Spring starts on Thursday.
 
Probabilities:
 
–  Severe Thunderstorms:  5%
 
Discussion:
 
Upper system will continue to move east/southeast from the region as another 500mb shortwave trof moves into the region.  Shortwave ridging will dominate on Monday as this system moves southeast and then turns east just north of Oklahoma.  It will then move on east, with little impact to the state.  The greatest concern on Tuesday will be fire danger as the system departs.  Temperatures will cool Wednesday with northerly winds/Pacific surface high.  Another upper system will move through fast northwest flow around the weekend with several embedded waves in the southern jet.  Moisture will try to return on Tuesday but should be limited as the upper system passes to our north.  12z EC has a slight chance of showers for southern Oklahoma late Tuesday. 
 
After this system goes by, little happens weather wise until Friday.  Models indicate moisture will return to the state on Friday with a cold front pushing it back out on Saturday.  GFS and EC have differing solutions re precipitation, so just added pops for much of the weekend.  Models do not indicate widespread significant precip, but this far out last week, they didn’t show what happened yesterday either.  EC shows some CAPE in the state late Friday and SPC has noted the potential for storms at D6.  So, added low severe chances for the week.
 
EC and GFS greatly diverge beyond this week.  The GFS still wants to break down the western U.S. ridge, resulting in a more progressive pattern.  The EC builds the ridge across the western/central U.S. along with a large eastern U.S. low.  Not sure which to believe at this point and luckily beyond the scope of this forecast.
 
EC seems a little low on temperatures this week, so followed the NAM through Wednesday.  After that a blend of the GFS.  First guess at numbers were pretty good, although Thursday maybe a tad low.  Tornado drought is 222 days.
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Winter Weather Discussion for December 5-8, 2013

Winter Weather Discussion for December 5-8, 2013.
Issued:  12/04/2013.
*Significant Winter Weather Event for Oklahoma and Texas*
*Prolong period of bitterly cold temperatures*
Highlights:
–  Ice Storm Warning for a small part of far southeast Oklahoma.
–  Winter Storm Warning for much of Oklahoma except northwest section.
–  Weather Weather Advisory for northwest Oklahoma and the panhandle.
–  Subfreezing temperatures are likely from Thursday – Tuesday.  Single digit and below 0F temperatures are possible Saturday and Sunday mornings.
–  Freezing rain is likely south of line from Pauls Valley to Poteau line.  Sleet and snow are likely from that line north to near I-40/I-44.  Then snow north of I-44.
Discussion:
No change to the prior forecast from yesterday and no need to rehash the meteorological conditions.
There are two caveats to the forecast.  The first caveat will be the potential for freezing rain Thursday morning across central/eastern Oklahoma.  Models are somewhat at odds on this occurrence but it seems likely to materialize.  As such, travel problems are likely during the day Thursday.  Precipitation will increase Thursday evening into Friday across much of central/eastern Oklahoma as the main wave ejects east.  This is caveat two, the going forecast has snow north of the I-44 corridor.  Recent model runs have shifted this south, which would bring the most intense snowfall south with it.  Currently the most intense snow is expected near I-44 with a mixed bag south to a Pauls Valley east to Poteau line.  South of this line, freezing rain is the primary type.
I may need to update the going forecast tomorrow to shift the precip areas, but for now, I’m staying with my prior forecasts.
An addition to yesterday’s forecast is the potential for Texas to get nailed.  Fort Worth NWS has issued a large winter storm watch and parts of it are now a warning.  The main threat is freezing rain, which should cause havoc in Dallas/Forth Worth.
All being said, I-35 from Dallas to Ponca City and I-40 from Oklahoma City to Memphis are bad places to travel late Thursday into at least early Saturday.
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Severe Weather Discussion for November 4 – 10, 2013

Severe Weather Discussion for November 4 – 10, 2013.
Issued:  11/03/2013.
Highlights:
–  Showers are likely Monday evening through Wednesday morning across much of Oklahoma.  A few thunderstorms are possible in southern Oklahoma.
–  Temperatures will be in the mid 60s Monday, near 60F Tuesday, mid 50s Wednesday, near 60F Thursday, low 60s Friday, mid 60s Saturday-Sunday.
Probabilities:
None
Discussion:
Primary interest for this week will be upper system taking shape across the western U.S.  This system will translate east late Monday into Tuesday, bringing a decent chance for showers across much of Oklahoma.  Models are in the common 1-2 inches range, so hopefully we’ll get the anticipated rain.  A cold front front will shift southeast across the state late Tuesday into Wednesday.  As such, after a mild Monday/Tuesday, the temperature will drop Wednesday with strong northerly winds.  Thursday morning has a decent chance at a widespread freeze as a warming trend begins across the state.  Friday-Sunday are expected to be pleasant.  A fast moving and small upper system will cruise by on Friday with clouds being the main impacts.  Extended models show another system approaching @13/14th with the GFS being fast and EC being slow.  So, what else is new?
Overall, a decent early November week is ahead for the region.  First guess at numbers matched up with going models/NWS.  Only a few changes.
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Severe Weather Discussion for October 28 – November 3, 2013

Severe Weather Discussion for October 28 – November 3, 2013.
Issued:  10/27/2013.
Highlights:
–  Severe thunderstorms are possible on Monday in northwest Oklahoma and the panhandle.  Primary threat is large hail.
–  Severe thunderstorms are again possible on Tuesday in western Oklahoma.
–  Another round of severe thunderstorms may develop on Wednesday into early Thursday across a large part of Oklahoma.  Heavy rain looks likely at least late Wednesday into Thursday.
–  Temperatures will be in the mid 70s Monday-Wednesday, upper 60s Thursday, near 70F Friday-Saturday, and mid 60s Sunday.
–  Time change Sunday November 3rd at 2am.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  50%
–  Storm Chase:  25%
Discussion:
Model variability has been quite high the past few days with respect to the Monday-Wednesday time frame.  Luckily much of the inter and intra model variance decreased with the recent 06z/12z runs.  As such, the forecast confidence is a little higher.  Unfortunately forecasting severe weather this time of year has greater risks than May.  However, a severe weather setup appears to be in-place for Monday-Wednesday for much of Oklahoma.
All models forecast a large upper system to take shape over the western U.S. by Monday afternoon with a dryline setting up in the Texas/Oklahoma panhandles.  Upper forcing is seemingly absent, but would expect some minor wave to initiate convection Monday afternoon.  SPC has highlighted western Oklahoma into the panhandle with a slight risk.  A 10% hatched area is also present for far northwest Oklahoma, seemingly for large hail.  By Tuesday the upper system moves a little east and much strong winds impinge across the area.  The dryline is progged to be a little farther east (closer to the TX/OK border) by Tuesday afternoon.  Deep layer moisture will be present with CAPE values near 1500 J/Kg.  Models indicate weak or neutral forcing along the dryline.  However, impressive 500mb jet streak moves into the region during the late afternoon and any small waves would seemingly initiate convection.  NAM has 850mb winds veered a little west of 180 and the GFS also does.  This may or may not mean anything for the setup.  NAM and EC are generally quiet while the GFS does develop convection.
Longwave trof ejects east-northeast on Wednesday, driving the dryline well into Oklahoma.  Wednesday has the potential to be a medium-end event or a huge cluster of thunderstorms (low-end).  Very difficult to tell and time of year would certainly favor the latter.  I’m not in the camp of unidirectional shear although the 850mb winds are more veered than Tuesday.  However, these are just model progs and the ultimate solution could be different.  It is important to know that the models are frequently too fast in ejecting this type of system, so changes seem likely.  The upper system will be much better sampled by the upper air  network tonight, with the 00z and 06z model runs improving on the current set.
SPC has highlighted much of central/eastern Oklahoma in the Day 4 (Wednesday), pointing to 30% probabilities and potentially a moderate risk.  Way too many questions right now and I’ve considered special discussions.  For now I’ll hold off but may initiate such tomorrow.
Beyond Thursday, mild and dry conditions will follow in wake of the upper trof.  Temperatures will be average for this time of year.
First guess as numbers were close and only modified Sunday to be inline with the NWS.  I really didn’t care much about D7 as the main impacts this week will be felt Monday-Wednesday.
Chase wise, I just can’t help myself.  Tuesday seems decent if convective initiate becomes more likely.  I’ll certainly keep an eye on Wednesday assuming the threat is farther west than current.
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Severe Weather Discussion for June 10 – 16, 2013

Severe Weather Discussion for June 10 – 16, 2013.
Issued:  06/09/2013.
Highlights:
–  Temperatures will be in the mid 90’s all week.
Probabilities:
–  None
Discussion:
Not much to say this week, luckily!  A 500mb 588dm ridge will take up residence across the region.  This is a typical late spring/early summer setup.  Precipitation should be limited to nil and will not introduce POPs.
Temperatures should be in the mid-90s, running 6-7 degrees above normal.  I’d think we’ll see the longest stretch of warm weather we’ve had since September.  The ridge isn’t particularly strong, so there may be rain chances next week.
Agree with the NWS that temperatures will likely run a little below MOS guidance, so averaged it out all week to the mid-90s.
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Severe Weather Discussion for May 31, 2013

Severe Weather Discussion for May 31, 2013.
Issued:  05/31/2013.
 
*Significant Severe Weather Event Today*
 
Highlights:
 
–  Active severe weather day is likely across much of central and eastern Oklahoma.  Tornadoes, some possibly large, destructive hail to softball size, and winds to 80mph are likely.
 
–  This is a dangerous weather situation, prepare now.
 
Discussion:
 
A very busy day is likely across much of Oklahoma.  Many of the parameters are in-place for an active severe weather day across Oklahoma.  One key thing may be missing and could keep this from being a  high-end tornado day; that is low level winds.  Models show these winds in the 180 degree area but if they back to 160 degrees or so, then tornado potential will increase.  Instability will be extreme with CAPE values AOA 4500 J/kg across much of Oklahoma.  This will enable very strong updrafts, supportive of destructive hail.  The cap is much stronger today, with a Tc of 97F and lower in the atmosphere.  As such, explosive development is likely this afternoon.  HRRR and SPC WRF show storm initiation by 4pm across west and northwest Oklahoma.  Supercells will be favored given long curved hodograph.  The veer back veer seen on Wednesday is not present, which should allow good storm organization seen yesterday.  One issue yesterday was storm relative shear vectors oriented NW to SE, blowing rain cooled air into the updraft of the storm.
 
Despite all the stuff above, the forecast and models show a significant severe weather event today across much of central and eastern Oklahoma.
 
Probabilities:
 
None
 
Chase Status:
 
Level 4 – some are going.
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Severe Weather Discussion May 28 – June 1, 2013.

Severe Weather Discussion May 28 – June 1, 2013.
Issued:  05/28/2013.
Highlights:
–  Severe thunderstorms are likely on Wednesday.  Primary threats are tornado, destructive hail, and damaging winds.
–  Severe thunderstorms are possible Thursday-Saturday across parts of Oklahoma.
Discussion:
Severe thunderstorm watch is posted for far northwest Oklahoma and the panhandle until 10pm.  Currently an area of severe thunderstorms is located near Amarillo, north-northeast into Beaver County.  This area should progress eastward during the early evening hours and eventually dissipate.
Additional severe thunderstorms are likely across western Oklahoma on Wednesday.   The dryline will mix eastward to the eastern Texas pahandle as an upper system translates into the region.  Wind fields will increase across the entire state with CAPE values @2500 J/Kg.  Models have consistently low-balled CAPE values on Wednesday and this may be due to widespread cirrus.  A narrow ribbon of decent CAPE is expected in the eastern Texas panhandle and far western Oklahoma at the very least.  Models agree that storms will initiate during the mid-afternoon hours.  Models show a strong veer-back-veer profile for Wednesday and this may limit tornado potential.  SPC has a moderate risk up and that may be more for destructive hail; which appears likely in the threat area.
Thursday looks to be much more robust than Wednesday as the dryline mixes eastward into Oklahoma and strong veering profile develops with height.  NAM is a little interesting and somewhat distressing given the dryline about 60 miles west of OKC.  Storms will likely develop by mid-afternoon as has been the case the past few weeks.  As is common, convection the day before will play a major role in what happens on Thursday.  However, this day has the potential to be a medium-end event and I do expect SPC to issue a moderate on the 17:30z 05/29 update.
The threat for Friday isn’t any easier to determine and will be strongly governed by activity on Thursday.  18z NAM shows not as much turning on Friday in the low levels but CAPE values look to be extreme.  Either way, a dryline should be in the area with robust moisture and decent winds.  Anything can happen.
12z EC/GFS, 18z NAM, and a variety of convection allowing models all were used for this forecast.  Models are in decent agreement, although there are a few important surface feature placement details to be sorted out.  I did defer to the NAM given good performance recently.
On a personal note, I’ll try to get these out as I can but I’m working 12 hr shifts/7 days a week.
Probabilities:
Risk area for any part of Oklahoma (valid:  05/29 Day 1, Day 2, Day 3):
Slight:  100%, 100%, 100%
Moderate:  100%, 100%, 0%
High:  0%, 0%, N/A
Chase Status:
Level 4 – Normal – not that  we aren’t interested, just can’t get away.
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Severe Weather Discussion for May 27 – June 2, 2013

Severe Weather Discussion for May 27 – June 2, 2013.

Issued:  05/26/2013.

 Highlights:

 –  Active severe weather week ahead with severe thunderstorms possible Monday-Friday, potentially into the weekend.

 –  Severe thunderstorms are possible Monday-Tuesday, primarily in western Oklahoma.  The main threat will be large hail, but tornadoes are also possible.

 –  Severe thunderstorms are possible Wednesday-Friday across much of Oklahoma. 

 –  At the very least, thunderstorms are possible across much of Oklahoma Saturday and Sunday.

 –  Temperatures will be in the upper 80s Monday-Tuesday, mid 80s Wednesday-Sunday.

 Probabilities:

 Severe Thunderstorms in Oklahoma:  50%

Storm Chase:  50%

 Discussion:

 Models agree that another western U.S. trof will develop and swing into the region @Wednesday.  The trof will then wrap up into a large closed low over the north-central U.S.  Models want to quickly open this system and progress it eastward by Friday.  Time of year, presence of strong winds aloft, and moisture will yield severe weather chances much of the week.  It is difficult to identify one day that has greater potential than any other.  However, placement of the trof will seem to favor Wednesday and Thursday for the higher potential.  A dryline, initially over the Texas/OK panhandles on Monday will be the main source of thunderstorms through Thursday.  This feature is indicated by the models to slowly drift eastward during the week.  By Friday, a cold front will drift into the state.  Models disagree on where this boundary will be during key periods Friday afternoon – Sunday.  Since the boundary will likely be strongly influenced by convection, tough to say what will end up happening with it.

 The issue within all of this is the potential for another medium-end event.  I do not like to forecast multiple high-end events close to each other, although it has been known to happen re blizzards.  For now, do not see a medium-end event Monday or Tuesday, but Wednesday is certainly in the offering.  May need to start discussions tomorrow.  Thursday seems to be the biggest concern right now, but once again tough to totally say either way. 

 Again this week, did not get fancy with numbers.  I’d think cooler temperatures are possible by the weekend depending on convective processes.  I elected to go with mid 80s and just take the hit if I’m wrong.

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Severe Weather Discussion for May 19-21, 2013

Severe Weather Discussion for May 19-21, 2013.
Issued:  05/19/2013.
*Active Severe Weather Day Expected across Oklahoma*
Highlights:
–  Several significant severe thunderstorms are expected across central and eastern Oklahoma.  The most likely area for the most intense thunderstorms will be Oklahoma City north and east.  Tornadoes, destructive hail, and damaging winds are all likely.  A strong tornado threat exists for northeast Oklahoma.
–  Another round of significant severe thunderstorms is possible on Monday.  However, the threat for Monday will be strongly governed by what happens today.
Discussion:
As with yesterday, this discussion will focus on the threats expected today and tonight.
Active severe weather event occurred yesterday but did not develop as expected.  Several limiting factors kept the storms from organizing and otherwise being in clusters.  I think this should have been obvious before hand but not my place to question a moderate risk with a 10% hatched tornado graphic.  SPC noted last night that a veer-back-veer profile was part of the problem and overall weakness in the mid-level flow.  Additionally, the previously noted dewpoint decrease immediately east of the dryline did occur.  Dewpoints lowered into the mid-50s in western Oklahoma.  I think this had a major impact on storms.  They did not get into deeper moisture until near sunset and but then there was way too much anvil debris and surface cold pool for organization.  It appears the storms tried a few times, especially the eastern storm near Lawton but alas RADAR only showed outflow dominated storms.
I really thought that yesterday would have some impacts on today and I’m still not convinced today will evolve like the models and SPC forecast.  However, I’m certainly not talking down the threat or talking it up, I just think the evolution will be different.
12z NAM/00z SPC WRF/12z HRRR all agree that CAPE values will exceed 3000 J/kg this afternoon as a dryline approaches central Oklahoma.  The HRRR is seemingly a little too aggressive with the dryline and lights off storms at I-35.  This model had a bit of an east bias yesterday with storms, so I’m not quite with that right now.  Best guess is the dryline will be just west of HWY 81 as consistently progged by the ECMWF and NAM.  Given that the SPC WRF is also on the same page, that is the going forecast.  The morning OUN sounding was rather impressive given the storms last night.  CAPE value was 1901 with temp 71 and dewpoint 67.  Tc 96F.  The hodo is a mess though and a veer-back-veer profile is obvious.  However, NAM sounding forecast shows a much better hodo developing by afternoon with a long curved environment, although there is a small dip in the mid-level but not going to worry about those items.
SPC seems rather concerned about T/Td spreads and I think this may be one of the items that doesn’t quite evolve like they’re thinking.  Either way, we’ll avoid playing tail-end Charlie as it may not be the best place anyway.  Not just related to T/Td spreads.  Okarche is on the south side of the nader threats but gives us plenty of options.  It also helps that the SPC WRF lights off a supercell at Okarche by 4pm.  12z NAM is similar.  Better likelihood of storms is north, but can go that direction if necessary.  None of the models are all that excited about storm chances south of I-40, so that will be monitored.  Given the close proximity to Oklahoma City and time of day (outdoor activities), there may be little time to react should a storm develop just west or southwest.  I’m still curious if any left over boundaries down south or “rolls” will create enhanced conditions for storm development.  The rain alone should create microscale temperature differences in that area.  And, still gotta wonder what the outflow boundary/heat burst in north-central Oklahoma will do.  As such, fascinating weather today, unfortunately some of it may be rather hazardous.
Tomorrow remains a threat and is very similar to today.  What happens will be strongly governed by today.  SPC has a moderate risk posted and this looks good.
Probabilities:
None
Chase Status:
Level 1 – leaving at 2pm for Okarche.
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Severe Weather Discussion for May 18, 2013.

Severe Weather Discussion for May 18, 2013.
Issued:  05/18/2013.
*Active Severe Weather Day Expected*
Highlights:
–  Severe thunderstorms will develop this afternoon across western Oklahoma.  These storms will move northeast and east, and approach central sections by early evening.  Primary threats are tornadoes, destructive hail greater than baseballs, and strong winds to 80mph.  There is a strong tornado threat in northwest Oklahoma by early evening.
–  The threats for Sunday and Monday continue, but this forecast will focus on today.
Discussion:
An area of elevated convection has evolved across southwest Oklahoma this morning.  This area is likely rooted well above the cap layer and as such presents a strong wind and small hail threat.  The 00z NAM caught onto this but the 06z lost it.  The 10z HRRR seems to have it, although appeared a little too convective.  This area should move north over the next few hours and eventually leave the threat area by early afternoon.  Atmosphere modification is not expected.
All primary operational models develop convection along an eastward mixing dryline this afternoon.  There are differences as to where storms are expected to develop, but several of them are clustered in west-central and northwest Oklahoma.  Additionally, the convection-allowing HRRR develops 3-4 supercells in western Oklahoma.  This model also shows extreme instability with CAPE values above 4000 J/Kg.  Upper level winds will not be particularly strong but decent speed/directional shear in the low/mid levels along with extreme instability will compensate for this.  Storm motion seems to be strongly northeast but a right mover would certainly travel east.
12z OUN sounding is interesting.  At 6am with temp 71 and dewpoint 71, CAPE value is 3137 J/Kg and LI -10.  Convective temp is 99F.  Strong surface heating is expected today, which will likely yield the extreme instability noted above.  The hodo is rather messy, but that was known going into this.  500mb winds will improve today, especially across western Oklahoma.
Models agree that a shortwave trof will move through the region late morning.  There will be subsidence in its wake with a more substantial shortwave trof moving into the region by mid/late afternoon.  As such, explosive severe thunderstorm development is likely by 4pm across western Oklahoma.  Supercells will be favored, with attendant threats.
Latest SPC outlook has maintained the moderate risk and 10% hatched tornado area.  This looks good and see little reason to change ATTM.  They also note the weak wind fields and that these could be compensated for by the extreme instability.
A quick look at Sunday and Monday yield no major changes ATTM.  NAM continues to be an outlier with cold front position late Sunday and subsequent warm front movement back north on Monday.  Time will tell.  Significant and extremely dangerous severe weather is expected Sunday.
Probabilities:
–  None
Chase Status:
Level 1 – heading west to Clinton @1:30pm.  I see no reason to change the intended target area.  There is agreement among the group of where to head.
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Severe Weather Discussion for May 18-21, 2013

Severe Weather Discussion for May 18-21, 2013.

Issued:  05/16/2013.

 Highlights:

 –  A few severe thunderstorms are expected across western and central Oklahoma on Saturday.  Primary threats are hail to baseball size and damaging winds to 70mph.

 –  Severe thunderstorms are likely Sunday and Monday across much of Oklahoma.  Potential remains for a significant severe weather episode one or both days.

 Discussion:

 Operational model suite over the past 24 hours continues prior trends of develop a western U.S. trof by late Friday.  Said trof is then progged to translate eastward into the central U.S. by late Saturday and wrap up into a closed low by Monday.  Models are in reasonably good agreement and will follow consensus for this forecast.  I’m very tempted to use enhanced wording to describe the threat Sunday and Monday, but forecast rules prohibit such this far out.  Also, Monday’s threat will be strongly governed by Sunday’s convection and subsequent surface feature location. 

 00z NAM remains consistent with prior runs and matches up decently with the 18z GFS/NAM along with 12z ECMWF for Saturday.  As the upper trof approaches on Saturday, a surface low will develop across the KS/TX area.  Robust moisture return is ongoing and is expected to continue through the next several days.  NAM dewpoints in Oklahoma show upper 60s common with some low 70s.  This appears reasonable given upper 60s just south of the Red River and Mesonet showing common low/mid 60s across much of the state.  For the past several runs the NAM/GFS have both had very low 850mb dewpoints across much of Texas Saturday morning.  Previously, this has resulted in a lot of mixing in western OK.  The 00z NAM doesn’t show this as much and has 850mb dewpoints near 12.5 C.  Even the 18z GFS backed off some.  As such, CAPE values are near 3000 J/Kg along the dryline and potentially near 4000 J/Kg along I-35.  Upper level winds are not all that favorable, but low/mid level winds are decent.  500mb jet max will remain west but winds will still be 20-25kts by late Saturday afternoon.  I finally get that the models punch the dryline east into western Oklahoma Saturday afternoon and then retreat it by early evening.  00z NAM develops convection from just south of I-40 northward Saturday afternoon.  Degree of instability and modest low-level shear should support supercells.  NAM supercell composite map indicates much of the area near HWY 183 to be marginally favorable.  Either way, the going forecast for some severe thunderstorms on Saturday appears good.  The tornado threat is seemingly low at this point but one or two can be expected.

 Upper system will continue to evolve across the central U.S. on Sunday.  A dryline is expected to punch east well into Oklahoma Sunday morning and afternoon.  The models are disagreeing a lot regarding the expected evolution of surface features on Sunday with the NAM trying to drive a cold front through NW OK into central sections late Sunday.  Other models do not agree, but will need to trend this development a few more runs.  It doesn’t seem to mitigate the overall threat as the front arrives near 7pm and after convection has already developed.  As with Saturday, instability will be impressive as dewpoints and temperatures remain robust.  CAPE values are progged @3000 J/Kg across central/eastern Oklahoma.  Winds increase across the state with impressive flow at all levels.  Depending on the actual location of the dryline, storms are expected to develop by mid/late afternoon.  Supercells will be favored and the NAM supercell composite map confirms such. 

 Yet another potential severe weather event is possible on Monday.  Luckily that is beyond the scope of this forecast.  I should note that the 00z NAM at 84 hours (7am Monday) shows this boundary lifting back north through Oklahoma City.  Monday will be heavily dependent on what happens Sunday.  However, winds remain strong throughout the atmosphere.   Warm and moist conditions are expected yet again during the day.  This would seemingly favor the redevelopment of thunderstorms across parts of the state.

 I expect SPC to do a slight risk on the Day 2 and probably the same on the Day 3.  They may go higher probabilities on Day 3.  I think a moderate is in the offering for Sunday at some point, but not sure they’ll do it on the Day 3.  The Day 2 will seemingly have a 15% area with 10% hatched in western Oklahoma.  The bigger threat will be north in KS/NE.

 Probabilities:

 Risk area for any part of Oklahoma (valid:  05/17 Day 2, Day 3):

 –  Slight:  100%, 100%

–  Moderate:  0%, 75%

–  High:  0%, N/A

Chase Status:

 Level 3 – Still interested in Saturday.  Initial spot is Snyder.  Also, interested in Sunday, initial spot is Weatherford to Watonga.

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Severe Weather Discussion for May 18 – 21, 2013

Severe Weather Discussion for May 18 – 21, 2013.
Issued:  05/17/2013.
Highlights:
–  Severe thunderstorms are possible Saturday afternoon and evening across western Oklahoma.  Primary threats are large hail to tennis ball size and winds to 70mph.  A tornado or two certainly seems possible.
–  Severe thunderstorms remain possible Sunday and Monday, with the continued potential for one or more significant severe weather episodes.  Sunday will be strongly governed by Saturday’s storms and Monday by Sunday’s.  Confused yet?  I am!
Discussion:
00z NAM is arriving and appears to be a keeper.  Southerly winds have transported rich Gulf moisture northward with upper 60s/low 70s common across Oklahoma.  Despite my prior thinking, moisture is very robust across the state.  Even though much of central Oklahoma didn’t see sunshine today, instability with still very impressive.  OUN 00z sounding with 75/72 had CAPE value 3778 J/Kg and LI -9.  Holding this down was our friend the cap, with a Tc of 100F.  That’s a spicy meatball!  Low 850mb dewpoints across Texas have now been sampled by the models and this carries northward into Saturday morning.  While period runs gave this a lot of credit, the latest run of the NAM appears to discount the impacts.  As such, CAPE values Saturday afternoon are in the 4000-5000 J/Kg range.  Not sure I’ll go that extreme, but wow.  Medium wavelength trof is sampled over the southwest U.S. this evening with 45-50kt flow on the downstream and upstream sides.
18z GFS, 12z ECMWF, 00z NAM are all considered for this forecast package.  The models are in decent agreement overall, but there are critical differences regarding surface features and convection.  The latter mainly related to impacts on the atmosphere and subsequent convection.  It is bad enough that Sunday and Monday will change as a function of prior days but worse given the multiple severe weather episodes expected across parts of Oklahoma.
For Saturday, models indicate a dryline will form in the Texas panhandle and surge eastward into Oklahoma during the afternoon hours.  The atmosphere to the east will be characterized by dewpoints in the low 70s with temperatures likely in the 80s and 90s.  This may yield the CAPE values noted above.  CIN will remain rather high but dryline convergence, peak heating, and a well-timed shortwave trof should overcome this feature.  As such, thunderstorms are likely in west-central and northwest Oklahoma late Saturday afternoon.  NAM indicates the storms will dissipate by midnight.
The general idea for Sunday remains the same but the big issue is the development of a cold front as shown by the NAM.  The GFS does not show this feature at all while the EC has to some extent.  This remains one of the more significant forecast concerns Sunday and especially Monday.  Relative to Sunday, the front may not be that big of a deal as strong instability once again develops across the state.  The dryline/front may move into central Oklahoma by mid-afternoon.  Models indicate an early morning shortwave trof ejecting through northern Oklahoma with another feature rotating around by late afternoon.  As such, sudden onset of convection is likely by late Sunday afternoon into the evening hours.  The models develop an MCS that moves across northern Oklahoma.  The NAM seemingly uses this feature to reinforce the front and push it southward.  The new run is also farther south than the prior run with the cold front placement.  Either way, supercells are expected to develop by 4-5pm just west of Oklahoma City.  These storms will have the potential to produce all severe weather types, including destructive hail greater than baseballs and tornadoes.
Despite the overall southern change to the cold front, the NAM still lifts this feature back north on Monday and it is north of OKC by early afternoon.  NAM has convection starting by late afternoon, although I think it will be earlier.  Once again, the front location, should it occur, will be key.  Along with any prior convection and associated cold pools.  The current forecast CAPE values of 4000 J/Kg are very much on the “we’ll see plan” given likely atmospheric modification late Sunday.  For now, the only thing to do is trend the models.  Favorable winds will again provide support for supercells presenting all severe weather threats.
Chasing wise, I have toyed back and forth with Saturday.  Given the latest NAM, I’m pretty much in the “go” mode right now.  If anything, we’ll travel west to Weatherford and just hang out.  Been there enough, plenty of good places to eat.
SPC has been rather interesting on the outlooks for this event.  Today’s product suite looked good.  I do think we’ll see some modifications for the new Day 1.  Will that include a moderate for Oklahoma, I’m not sure.  The NAM was seemingly support such an issuance, maybe down to I-40 or a tad north.  I’d think they’ll go to a moderate for Sunday.  The risk for Monday will likely be a slight given that they probably don’t want to lock themselves in given Sunday’s convection and some big differences among the models.
Probabilities:
Risk area for any part of Oklahoma (valid:  05/18 Day 1, Day 2, Day 3):
Slight:  100%, 100%, 100%
Moderate:  75%, 75%, 25%
High:  0%, 10%, N/A
Chase Status:
Level 2 – Watching  Saturday closely, I’m modifying my target area to Clinton.  Sunday, also very interested and target area is El Reno.
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Severe Weather Discussion for May 18-21, 2013

 

Severe Weather Discussion for May 18-21, 2013.
Issued:  05/15/2013.
 
Highlights:
 
–  Severe thunderstorms are expected Saturday late afternoon into the evening hours for western Oklahoma.
 
–  Severe thunderstorms are possible Sunday and Monday across a large part of Oklahoma.
 
–  Multiple severe weather episodes appear possible for Oklahoma during the forecast period, although Sunday and Monday are technically beyond the scope of this discussion.
 
Discussion:
 
Models agree that a medium-wavelength trof will enter the western U.S. on Friday and translate eastward.  This trof may take on a slight negative tilt as it impinges on the high plains Saturday afternoon and evening.  Ahead of this system, deep layer moisture will return northward.  Said moisture will be characterized by mainly upper 60s surface dewpoints with potentially some low 70s.  850mb moisture will be 12.5C range, potentially greater.  Models are in good agreement regarding these parameters.  Winds aloft will increase across the panhandle late Saturday and progress into Oklahoma during the evening hours.
 
18z GFS/NAM/HWRF and 12z ECMWF all agree that a dryline will be located in the eastern Texas panhandle.  As always, there are a variety of viewpoints among the models as to the ultimate location of the dryline.  The ECMWF surges the dryline east into western Oklahoma during the day and then retreats it during the afternoon.  It develops thunderstorms in western Oklahoma as this occurs during the late afternoon hours.  Extreme CAPE develops on the EC just east of this feature.  The GFS and NAM dryline positions are located farther west in the Texas panhandle.  The GFS develops low 850mb dewpoints and subsequently mixes out surface dewpoints Saturday afternoon.  The most recent run finally mixes the dryline eastward as a result of this.  NAM somewhat does the same thing.  Despite this, all models develop QPF somewhere in the Texas panhandle and/or far western Oklahoma on Saturday.  Winds are decent but not overly impressive.  If robust instability can develop, then storms may have better ability to rotate.  Either way, large hail and damaging winds are expected with any mature thunderstorm.
 
By Sunday a large trof is expected across the western U.S. and somewhat into the central region.  Models are in decent agreement regarding the evolution of this trof.  The ECMWF lifts out a small shortwave trof early Sunday and veers the surface flow across Oklahoma.  This is a departure from the 00z run and is different than the other models.  Current trend is for a dryline to setup in western Oklahoma with CAPE values AOA 2500 J/Kg to the east.  Wind shear should be much better than Saturday.  PRIND severe thunderstorms are possible during the afternoon and evening hours across central/eastern Oklahoma. 
 
Monday’s threat is well beyond the scope of this forecast.  But, to trend the models there is decent agreement that a closed low will develop over the north-central U.S.  This would keep a dryline somewhere in Oklahoma along with decent winds aloft.  Models have the dryline near Oklahoma City Monday afternoon with CAPE values of 3000 J/Kg.  Of course this is way far out, but certainly something to watch.
 
Probabilities:
 
Risk area for any part of Oklahoma (valid:  05/16 – Day 3):
 
Slight:  100%
Moderate:  25%
High:  N/A
 
Chase Status:
 
Level 4 – Watching Saturday.
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