Severe Weather Discussion for April 26, 2016. Issued: 04/25/2016

Highlights:

– Significant severe weather event is possible on Tuesday across central and eastern Oklahoma. Primary threats are tornadoes, destructive hail to softball size, and winds to 85mph.

– Severe thunderstorms are also possible Friday across parts of the state.

Discussion:

Little change to prior forecast. Models are in agreement that a closed low will evolve across Colorado by Tuesday morning as a shortwave trof dives into the base of the larger trof and ejects east-northeast on Tuesday. The timing for this is late Tuesday afternoon into the evening across Oklahoma. However, before this occurs, impressive mid/upper level winds will spread across the state characterized 500mb by 50kts in central OK and a 70kt jet in the panhandle. 700mb jet of 50kt is located in central Oklahoma at 4pm. Wind fields increase significantly across the state by early evening as the 300/200mb winds translate into central Oklahoma. Additionally, 850mb winds increase to 35kts across a large part of Oklahoma.

Forecast issues continue regarding placement of surface features, surface winds and convective initiation. All models develop convection on Tuesday and generally between HWY 81 and I-35. Timing is the big issue among the models, with some developing convection @3pm and others closer to 6pm. This includes a mix of high-resolution models with medium range guidance. While high-end impacts are possible, they seem to be destructive hail to softball size and 85mph given SBCAPE of AOA 4500 J/Kg and MLCAPE AOA 3500 J/Kg. It appears that convective initiation time is still undetermined given model QPF/BREF outputs. Indeed, the 4km NAM has -3 MLCIN at 4pm, down for -112 MLCIN at 1pm. Given approach of strong mid-level winds, I do wonder if this could be enough to breach the cap earlier than 4pm, if only 3pm, just tough to say. Unfortunately this hour makes a huge difference in activities around the metro. Storms should move at 35-40mph, so not as quickly as I originally thought. Either way, they won’t be slow movers. Finally, surface winds may be @180 degrees and not quite favorable 150 degrees at convective initiation. This should change by early evening and the 4km NAM reflects this in the Sharppy data. So, while the tornado threat may not be present early in the event, it should evolve during the evening hours. However, I do think the significance of this event is not isolated to just tornadoes, the potential for some really large hail and damaging winds seems to be quite high. It appears that wind fields will not line up with convective initiation and s/w trof location to promote a high-end violent tornado threat.

Probabilities:

Risk area for any part of OK (valid: 04/26, Day 1):

Slight: 100%
Enhanced: 100%
Moderate: 100%
High: 50%

Chase Status:

Going on Tuesday, target area will likely be El Reno.

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Severe Weather Discussion for April 25 – May 1, 2016. Issued: 04/25/2016

Highlights:

– Severe thunderstorms are likely Tuesday afternoon/evening across parts of Oklahoma.

– Severe thunderstorms are also possible Thursday and Saturday, although Friday is likely the best time for severe thunderstorms.

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

– This discussion will also serve as the Special Weather Discussion 2016-2-2.

Probabilities:

– Severe Thunderstorms: 60%.
– Storm Chase: 30%

Discussion:

Upper system will pass through the northern US today followed by shortwave ridging on Monday. Another shortwave trof will dig into the western US and progress eastward into the region on Tuesday. Models are similar with timing of this feature although there are significant differences relating to surface feature placements. There is significant uncertainty regarding Tuesday and even expected impacts/location of impacts. There are no changes to yesterday’s forecast reasoning and even 18z data didn’t offer much help. Maybe the 00z guidance will provide some assistance for the forecast, but we’ll see. Best guess right now is central Oklahoma will experience the greater impacts, which may mostly be destructive hail to softball size.

Another upper system will move into the base of the western US longwave trof and move towards the region on Friday. Thunderstorm chances will return Thursday and continue through Saturday. There seems potential for severe thunderstorms during this period, with Friday the most likely day. Beyond Friday a cold front is expected to move through the region Saturday or Sunday, which should end storms chances for a few days.

Pulled forecast numbers from NWS, main forecast focus is on Tuesday.

Outlook Probabilities:

Risk area for any part of OK (valid: 04/25, Day 2):

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

Chase Status:

May go Friday.

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Severe Weather Discussion 2016-2-1

Severe Weather Discussion for April 24 – 26, 2016.
Issued: 04/23/2016.
Highlights:
– Severe thunderstorms are likely across west-central through north-central Oklahoma on Sunday. Primary threats are large hail to tennis ball size and winds to 65mph. However, a few tornadoes are possible.
– A significant severe weather event is possible on Tuesday across a large part of Oklahoma.
Discussion:
Guidance is in reasonable agreement re eastward progression of a shortwave trof from Nevada/Utah to western Nebraska by Sunday evening. Prior surface high moved deep layer moisture to the Gulf of Mexico, with low/mid 60s currently located across the Texas Gulf Coast. Models attempt to return at least low 60s dewpoints northward into Oklahoma by Sunday evening. Temperatures in the upper 70s/low 80s should yield SBCAPE near 3000 J/Kg with MLCAPE near 2500 J/Kg based on a location at Enid. Convective inhibition may be low to nil by 4pm, so storms could start between 4-5pm across northwest Oklahoma. Wind fields will favorable supercells, capable of large hail and strong winds. The tornado threat may not present until 7pm when the LLJ develops. Indeed, moving the 4km NAM time frame to 7pm results in a better tornado threat than earlier in the day, even through CAPE (SB/ML) both decrease. There is a sharp cutoff to the instability axis, with east of I-35 AOB 1000 J/Kg CAPE.
Potential looks decent enough for a chase on Sunday, current plan is to leave at 3pm. Target area remains in-flux due to model differences WRT initiation location. Models usually tend too far east with convective initiation, so am attempting to move this location west. See attached image from Pivotal Weather website, noting potential chase location, along with expected convective initiation zone.
Monday appears quiet, as shortwave ridging moves across the region. Moisture remains across the region, so a few storms may develop. 4km NAM shows a few storms east of OKC Monday afternoon.
Attention then turns to Tuesday, which has serious potential to be a high-end weather day. Sunday’s upper system will move quickly northeast and be absorbed into the northern jet. The next upper system will progress rapidly into the region. Moisture will remain nearby and rapidly return northward as this system approaches. Models indicate upper 60s/low 70s surface moisture with 14C dewpoints at 850mb. 12km NAM does it usual weird 850mb sink, which is a characteristic bias of this model and is ignored. The resulting SBCAPE values are greater than 5000 J/Kg, indicating extreme instability across the region by Tuesday afternoon. Issues arise with the placement of the upper system Tuesday afternoon and subsequent influence on the dryline and mid level jet features. Models (EC/GFS/12km NAM) are quite varied in the location of the dryline and from intra-model time lapse (run to run).
There are several concerns about Tuesday, given the potential for significant severe weather. Dryline location typically shifts westward as an event nears, which is the case for Sunday. However, this westward shift has not occurred and the models have trended eastward with the dryline to near HWY 81 by 4pm. Additionally, the 12km NAM/GFS both erode CIN by early afternoon (2-3pm) time frame near HWY 81, irrelevant of dryline location. The potential also exists for a pre-dryline convergence area to setup near HWY 81. A 700mb speed max of 47kts is located across central OK by 4pm along with a 50kt 500mb jet max moving into this area. Models do tend to agree on these features, although ultimate placement of the upper system and dryline location remain elusive. Additionally I think there is decent potential for storms to develop before 4pm, whether they are just west of OKC or farther west in western OK. 18z GFS again moves the dryline location around but lowers CIN in central OK by early afternoon. All of these considerations will be tracked the next few days. Despite system timing/dryline location, the potential exists for a significant severe weather day across Oklahoma accompanied by tornadoes and destructive hail. SPC has been highlighting the potential for a few days and expect at least an enhanced risk on the morning D3 and potentially a moderate. Second attachment is from Pivotal Weather, 18z GFS valid 1pm Tuesday.
Probabilities:
Risk area for any part of OK (valid: 04/24 Day 1, Day 3):
Slight:  100%, 100%
Enhanced: 60%, 100%
Moderate: 0%, 40%
High: 0%, N/A
Chase Status:
Going on Sunday, Enid to Watonga is the initial target area.
Sunday Forecast 4km NAM Tuesday Forecast 1pm GFS
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Severe Weather Discussion for April 11 – 17, 2016. Issued: 04/10/2016

Highlights:

– Severe thunderstorms are likely early Monday morning across central/eastern Oklahoma and again in southeastern Oklahoma Monday afternoon into the evening.

– Showers and a few thunderstorms are possible across southern Oklahoma late Tuesday into Wednesday.

– Severe thunderstorms are possible Saturday and Sunday, at the very least widespread thunderstorms are likely.

– Temperatures will be in the mid 60s Monday – Tuesday, near 70 Wednesday, mid 70s Thursday – Sunday.

Probabilities:

Severe Thunderstorms: 50%

Discussion:

The weather suddenly gets exciting is probably the best way to describe this week. Incoming shortwave trof is expected to cause severe thunderstorms within the next few hours across southwest Oklahoma. These thunderstorms will move northeast into central sections later today. Farther north, thunderstorms are expected along an incoming cold front this evening. Thunderstorms will likely continue into Monday morning. Another chance for severe thunderstorms is present across southeast Oklahoma Monday afternoon into the early evening as the cold front slowly pushes southward. Rain chances will decrease until late Tuesday when another weak southern stream shortwave trof moves through the region. This one should primarily impact southern Oklahoma with a chance for showers and thunderstorms.

Thursday will be quiet across the region, although out west a large trof will start developing. This trof will influence our weather through the weekend. Models offer differing solutions on the evolution of this feature with the EC/UOKMET/JMA developing a large closed low just west of the region over central NM. The GFS is farther north across central CO. No reason to believe one model over the other. The primary considerations will be the availability of mid-60s dewpoints across Texas and Oklahoma Saturday and Sunday. The latitudinal differences among the models make forecasting severe weather difficult, however there is a nontrivial threat of severe weather next weekend. Could be that much of the weekend is wet with lots of rain, we really need it. And, closed lows are not the best severe weather producers. Either way, will need to closely monitor weather trends for next weekend. I went with medium end severe weather potential due to the rainfall and severe weather threat, which are not mutually exclusive.

Did not get fancy with numbers, followed 4km NAM and 12z EC. I did go warm on Sunday, although if the EC is correct mid 60s will be likely.

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Severe Weather Discussion for April 4 – 10, 2016. Issued: 04/03/2016

Highlights:

– Slight chance for thunderstorms Saturday/Sunday.

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

Probabilities:

None

Discussion:

Northwest flow will dominate the region this week with little in the way of sensible weather impacts. The main story will be above average temperatures and fire weather concerns. An Alberta style clipper will dive southeast across the region on Wednesday with some cooler air, will feel cooler after low 80s Monday/Tuesday. Once this system passes, we’ll have a few days of 70s followed by a warmup next weekend. Models advertise a weak southern stream shortwave trof, which undercuts the eastern Pacific ridge, moving into the region on Saturday/Sunday. There is some moisture return ahead of this system, so went with low POPs due to uncertainty this far out.

Attachment is SPC fire weather outlook for this week, ugly is probably the best description right now.

Numbers ended up close to NWS, so no changes.

Screen Shot 2016-04-03 at 9.05.51 PM

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Severe Weather Discussion for March 28 – April 3, 2016. Issued: 03/27/2016.

Highlights:

– Severe thunderstorms are possible across central/eastern Oklahoma on Wednesday.

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

Probabilities:

– Severe Thunderstorms: 35%

Discussion:

Primary feature of interest will be a southern stream shortwave trof progged to eject across Kansas on Wednesday. Leading up to this, Monday-Tuesday will be typical this time of year with increasing surface moisture on Tuesday, precipitation chances are low although non-zero on Tuesday. Moisture will continue to increase on Wednesday as a dryline mixes eastward across Oklahoma during the day. Models offer a variety of solutions re dryline placement and of course upper system. The most likely location for the dryline @7pm Wednesday will be I-35 to HWY 177. I do not believe the GFS placement of this feature and it has been slowly drifting westward the past few model runs. I have attached the NAM placement at 7pm, although again this may be too far east. SPC D4 looks good and the western edge appears appropriate given EC/UOKMET/GFS/NAM placements. Primary threat is large hail although shear and moisture do support tornadoes. I’m not sure if this will evolve into an enhanced risk, but do think it is possible for parts of eastern Oklahoma. NAM does exhibit a veer-back-veer setup, which would reduce the tornado threat. Although this event is a few days away. Overall, dewpoints in the low/mid 60s combined with temperatures in the 70s will yield CAPE values AOA 2000J/Kg. Good wind shear and long curved storm slinky support organized storms. SHARPpy data for eastern Oklahoma shows tornado as possible hazard type.

Beyond Wednesday, eastern U.S. longwave trof dominates the pattern with ridging across the western U.S. Models show a southern stream system traversing Texas late Saturday into Sunday. Low confidence in this system producing any sensible weather keeps POPs out of the forecast.

First guess at numbers looked good and only adjusted Sunday based on EC/GFS.

Screen Shot 2016-03-27 at 7.44.42 PM

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Severe Weather Discussion for March 21 – 27, 2016. Issued: 03/20/2016

Highlights:

– A few severe thunderstorms are possible Wednesday afternoon and evening across the eastern half of Oklahoma.

– Showers and a few thunderstorms are possible late Saturday into Sunday.

– Temperatures will be in the mid 60s Monday, upper 70s Tuesday, low 80s Wednesday, mid 50s Thursday, low 60s Friday, mid 60s Saturday and upper 60s Sunday.

Probabilities:

– Severe Thunderstorms: 20%

Discussion:

Primary interest this week will focus on expected development of a medium wavelength trof just west of the region by Wednesday. Models offer a variety of solutions relative to timing of this system, which has implication for sensible impacts. EC model is slower than the NAM/UOKMET/GFS. The differences are minor overall, but do shift the dryline west to between I-35/US 177 Wednesday afternoon. For now will go with EC since it is a reasonable solution. If the other models are correct with timing, the threat will be far eastern OK. Marginal moisture advects into the state by Wednesday afternoon characterized by upper 50s to maybe low 60s across eastern Oklahoma. Despite this, CAPE values end up near 2000 J/Kg with PW values mainly 0.9 with some moisture pooling in northeast Oklahoma (EC). SPC has placed southeast Oklahoma in a 15% area for Wednesday. This looks good, although expect more of eastern Oklahoma to be included in later updates if the EC is correct.

Back tracking a little, Monday and Tuesday will see critical wildfire conditions across the state, primarily due to low RH on Monday then a combination of strong winds and hot temperatures on Tuesday. The threat will continue Wednesday west of the dryline but south of a cold front (northern OK). The worst day may be Wednesday as several meteorological parameters combine for a high-end wildfire threat in western/central OK.

Cold front moves across the state Thursday, with cooling expected into Friday. Models differ greatly by next weekend, when another shortwave trof may approach the region. The EC is more amplified with this feature than the GFS, which keeps it more connected to the northern jet. The EC solution has been the overall trend recently and will follow it again. As such, I went with showers and thunderstorms on Easter. If the GFS is correct, limited activity can be expected and mainly on Saturday.

First guess at numbers look good. A little off from NWS during the period, but nothing significant.

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Severe Weather Discussion for March 14 – 20, 2016. Issued: 03/13/2016.

Highlights:

– Showers and thunderstorms are possible Thursday – Saturday, although it will not rain the entire time. Snow is possible in NW Oklahoma and the panhandle late Friday into early Saturday.

– Temperatures will be in the low 80s Monday, near 70F Tuesday, upper 60 Wednesday, mid 60s Thursday, upper 50s Friday – Sunday.

– Spring starts Sunday.

Probabilities:

– Winter Precip: 5%

Discussion:

Compact low responsible for the ongoing severe weather east of Oklahoma will move rapidly east the next few days and weaken. Another shortwave trof will approach the region by Tuesday as a longwave trof develops over the central U.S. The initial shortwave trof appears to have little impact on the region, other than lowering temperatures from Monday. The next system will round the base of the larger trof on Thursday and likely result in showers and maybe some thunderstorms Thursday into Saturday. Models have offered a variety of solutions with this second system and more importantly the potential for snow. Recently upgraded EC seems hooked on snow for NW OK and the panhandle, although amounts should not be significant. Will go with slight snow chances given cold upper system and favorable pattern. Elsewhere, mainly a cool rain will occur as this system moves across the region on Saturday. Beyond Saturday, the upper system moves east and shortwave ridging moves into the area.

Temperatures look very nice early into mid week, then getting cooler towards the weekend. Numbers and POPs look good when compared to NWS, so no changes from first guess.

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Severe Weather Discussion for March 7 – 13, 2016

Severe Weather Discussion for March 7 – 13, 2016.
Issued: 03/06/2016.

Highlights:

– Severe thunderstorms are expected Monday afternoon through Tuesday with large hail the primary threat. A brief tornado or two is also possible. Widespread showers and thunderstorms are likely Tuesday into Wednesday, with primary influence shifting south into southern Oklahoma. Some showers and thunderstorms are possible Thursday-Friday.

– Temperatures will be near 70F Monday – Tuesday, upper 60s Wednesday – Friday, low 70s Saturday – Sunday.

– Time change Sunday 03/13, 2am.

Probabilities:

– Severe Thunderstorms: 25%

Discussion:

Developing closed low in Mexico will be the primary story maker this week. Models agree this system will close of and meander quite slowly eastward across central Mexico into southern Texas. By the end of the week, an upstream kicker should eject this system northeast. Primary influence across the region will occur Monday and Tuesday as a lead shortwave trof ejects northeast across CO/NM late Monday. Marginal dewpoints in the upper 50s/low 60s with temperatures in the 70s should create CAPE values @2500 J/Kg. NAM soundings show a veer-back-veer setup late Monday, which would limit tornado potential. Convective allowing models are also rather dry near the dryline, with main precip in eastern Oklahoma near the low level jet. Parameters do favor supercells, although when storms initiate seems to be in question right now. I do think a few severe thunderstorms are possible in western Oklahoma late Monday afternoon into the overnight hours. A better chance of severe thunderstorms moves in early Tuesday morning across parts of Oklahoma as another shortwave trof ejects across the region.

By Wednesday (see attached 12km NAM 500mb image) the closed low has settled into Mexico and much of the influence will be in Texas and southern Oklahoma. This will remain the case through Friday. I left POPs out next weekend as conditions should be dry across the state.

Went with first guess numbers, as they are pretty close and daily temps are going to be strongly governed by convection.

 

nam_z500_uv_vort_west_17

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SPC Day Two Severe Weather Outlook (3/7/16)

day3otlk_0830

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CST SUN MAR 06 2016

VALID 071200Z – 081200Z

…THERE IS A SLGT RISK OF SVR TSTMS SRN GREAT PLAINS…

…THERE IS A MRGL RISK OF SVR TSTMS CNTRL GREAT PLAINS…

…SUMMARY…
ISOLATED TO WIDELY SCATTERED SEVERE STORMS ARE POSSIBLE ACROSS THE SOUTHERN GREAT PLAINS MAINLY ON MONDAY NIGHT…BUT MAY COMMENCE LATE
AFTERNOON MONDAY.

…SYNOPSIS…
A COMPACT SHORTWAVE TROUGH NEAR THE FOUR CORNERS AREA AT 12Z/MON SHOULD SHIFT TOWARDS NEB/SD BY 12Z/TUE…WHILE A MORE AMPLIFIED
TROUGH DIGS ALONG THE SRN CA COAST ACROSS BAJA CA TOWARDS SONORA. A LEE CYCLONE SHOULD SLOWLY FILL AS IT TRACKS FROM NERN CO TO SERN SDA LONG A DEVELOPING BAROCLINIC ZONE. THE DRYLINE SHOULD MIX INTO CNTRL NEB/KS…WRN OK AND THE EDWARDS PLATEAU OF TX MON AFTERNOON. SOME RETREAT TO THE DRYLINE IS ANTICIPATED MON NIGHT WITH A LEE
TROUGH ANCHORED OVER THE PERMIAN BASIN.

…SRN GREAT PLAINS…
PERSISTENT POLEWARD TRANSPORT WITHIN THE WARM SECTOR BENEATH AN EML WILL YIELD GRADUALLY INCREASING BOUNDARY-LAYER MOISTURE THROUGH THE PERIOD. A PLUME OF MIDDLE 50S SURFACE DEW POINTS SHOULD BECOME ESTABLISHED ACROSS SRN KS BY LATE AFTERNOON WITH LOWER 60S PREVALENT
INTO CNTRL TX. MID-LEVEL HEIGHT FALLS SHOULD BE WEAK DURING THE DIURNAL HEATING CYCLE AS THE REGION LIES IN BETWEEN THE SHORTWAVE
TROUGH PIVOTING NE ACROSS THE CNTRL HIGH PLAINS AND THE DIGGING TROUGH APPROACHING THE NW MEXICO COAST. WITH ABUNDANT LOW-LEVEL
STRATUS PROBABLE E OF THE DRYLINE…DEEP CONVECTION MAY REMAIN QUITE ISOLATED ALONG IT THROUGH EARLY EVENING. BUT A CONDITIONAL RISK FOR SUPERCELLS WILL EXIST GIVEN A BROAD SWATH OF 50-KT MID-LEVEL SWLYS. ALONG THE ERN PERIPHERY OF THE MOISTURE PLUME WHERE THE EML IS WEAKER…LOW-LEVEL WAA SHOULD FORCE SCATTERED ELEVATED CONVECTION BY EVENING WITH MARGINAL SEVERE HAIL AS THE MAIN HAZARD…GRAMS.. 03/06/2016

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SPC Day Three Severe Weather Outlook (03/07/16)

day3otlk_0830

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Severe Weather Discussion for March 7, 2016. Issued: 03/04/2016

Highlights:

– Severe thunderstorms are possible across western and central Oklahoma Monday afternoon and evening.

Attachment:

– 18z 12km NAM – 78 hour forecast CAPE with dryline and dewpoint gradient.

Discussion:

Upper system will move into the western U.S. by Sunday, which marks the beginning of a rather large closed low forecasted across the southern U.S. A lead shortwave trof will eject northeast across northern New Mexico and southeast Colorado Monday afternoon and evening. A dryline will develop and mix slightly eastward during the afternoon, reaching western Oklahoma. Gulf moisture is in plentiful supply, although will be kept mostly south due to residual surface ridging. Despite this issue, models show at least upper 50s to low 60s dewpoints across Oklahoma Monday afternoon. Placement of upper system and surface low indicates good wind shear near and east of the dryline. As such, supercells should be the favored storm type. Earlier progs indicated veer-back-veer, but do not see this as an issue right now.

Models are in surprisingly good agreement, with dryline placement being the main difference. Either way, severe thunderstorms are expected Monday afternoon into the evening hours across parts of Oklahoma. Models do show a rather significant drop off in CAPE at I-35 and east. This appears related to low temperatures on Monday due to cloud cover. While models do show widespread clouds, including some cirrus, I’m not convinced temperatures will be in the low 60s. A few degrees higher, will raise CAPE values @I-35.

I’m not sure this event will rise to a medium-end threat, especially due to the limited moisture. There is a non-trivial threat for tornadoes due to good wind shear and decent moisture. This threat appears most likely west of I-35, but any increase in moisture or temperature would increase severe weather potential across central Oklahoma.

Probabilities:

Risk area for any part of Oklahoma, valid: 03/05/2015, Day 3

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

Chase Status: Normal

20160304

(Forecast CAPE value for Monday afternoon and location of the dry line. Storms would be near or east of the dry line.)

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Severe Weather Discussion for August 24 – 30, 2015

Issued: 08/23/2015.

Highlights:

– Thunderstorms are possible Wednesday – Friday. Overall coverage isn’t expected to be that great, but opportunities for much needed rain. Yes, the rain is needed in southeast Oklahoma.

– Temperatures will be in the mid 80s Monday – Tuesday, near 90F Wednesday, mid 80s Thursday, upper 80s Friday and low 90s Saturday – Sunday.

– Tropical Storm Danny is expected to dissipate near Cuba by Wednesday. Erika has not been named but the system behind Danny should become Erika. EC through 10 days has this system recurving without impacting the US. We’ll see on that one, but either way kept tropical storm chances low this week due to no US impacts through the forecast period.

Probabilities:

– Severe Thunderstorms: 10%
– Tropical Development: 25%

Discussion:

Upper ridge will remain displaced west of the region the two days and when combined with today’s cold front, will keep temperatures below average Monday and Tuesday. Shortwave trof rounds the northern side of the ridge on Wednesday and moves across the region Thursday/Friday. Thunderstorms along with cooler temperatures are likely. Not sure I went cool enough but really can’t justify anything lower given time of year. Upper system moves out of the region and western ridge elongates across the region by next weekend. Expect temperatures to warm a little as the ridge exerts some influence across the area. Not sure we’ll reach EC temperatures, so went a category below this model next weekend.

CFS2 shows September being near normal, which is a dramatic changes from a few weeks ago when this model had September much below normal. Given the cool summer, would not be shocked to see September warmer than we have had but still near normal.

First guess at numbers matched up closely across the board. NWS and I are close with maybe a category difference, especially next weekend.

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Severe Weather Discussion for July 20 – 26, 2015

Severe Weather Discussion for July 20 – 26, 2015.
Issued: 07/19/2015.

Highlights:

– Thunderstorms are possible Tuesday and Wednesday.

– Temperatures will be in the upper 90s Monday, low 90s Tuesday – Wednesday, and upper 90s Thursday – Sunday.

Probabilities:

– Severe Thunderstorms: 10%

Discussion:

Subtropical ridge will flatten a little bit on Tuesday, allowing for a surface boundary to move into Oklahoma. Thunderstorms are likely along this boundary Tuesday and Wednesday given marginal upper support and high surface moisture. EC 50 member ensembles are quite varied on how much QPF to produce but given Dolores and the surface boundary, may see more than the models are indicating.

Surface boundary washes out and the ridge expands on Thursday, with a return hot conditions across the state. The ridge appears to remain anchored near Oklahoma through the end of the week. All in all the weather pattern appears typical for late July/mid-summer.

First guess at numbers had disturbing agreement with the NWS, so no changes are made. I did not go with the EC temperatures for Thu-Sun, as it seems to high with 100F. The EC numbers have been too warm (IMHO) in the 4-10 day time frame, seemingly due to model Td issues. I think 100F temperatures are near, but not this week. Once we do crack that threshold, we’re in for a some heat. Although there are hints in the climate models that a cool down may occur towards the end of July, we’ll see.

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Severe Weather Discussion for May 11 – 17, 2015 Issued: 05/10/2015

Severe Weather Discussion for May 11 – 17, 2015.
Issued: 05/10/2015.

Highlights:

– Showers and thunderstorms are possible on Wednesday, a few severe thunderstorms are possible. A similar threat is present on Friday.

– Severe thunderstorms are possible Saturday and Sunday across Oklahoma.

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

Probabilities:

– Severe Thunderstorms: 45%
– Storm Chase: 50%

Discussion:

Upper system current producing severe weather in southern Oklahoma will continue moving northeast into the Great Lakes region by Wednesday. Shortwave ridging will be present across Oklahoma Monday and Tuesday with limited precipitation chances. A weak southern stream shortwave trof will approach the region from Mexico on Wednesday. Moisture will attempt to return ahead of this system but the setup does not appear favorable for severe weather. Wind fields will be marginal and sufficient deep layer moisture. However, the surface features appear to favor showers and thunderstorms more than severe, although a few severe thunderstorms are possible.

Stronger closed low settles into the SW US on Friday and starts eastward towards Oklahoma. This should create a favorable environment for thunderstorms on Friday. Wind fields again are marginal and moisture content remains high given PW values of 1.7. Severe thunderstorms may be more likely on Friday than Wednesday as a lead shortwave trof reaches NW Texas by late afternoon. The greatest chance for any severe thunderstorms will be western Oklahoma.

Upper system moves into the state on Saturday with stronger wind fields approaching the state and a dryline in the eastern Texas panhandle. The closed low/trof has a neutral tilt to it, so not sure how favorable conditions will be for significant severe weather. However, given good wind fields and moisture, CAPE values are in the 2000 J/Kg range and will be sufficient for severe thunderstorms. Saturday may be another case of widespread showers and thunderstorms ahead of the main system, thereby limiting the severe weather threat.

Numbers looks good and didn’t have to make many changes. EC seems a little cool tomorrow and Tuesday, so went with NWS Norman.

Verification:

OKC Temps 05/04 – 05/10

My Numbers: low 80s, lows 80s, upper 70s, upper 70s, upper 70s, low 80s and low 80s.
NWS Numbers: 80F, upper 70s, mid 70s, upper 70s, upper 70s, upper 70s and upper 70s.
Actual: 81F, 74F, 76F, 77F, 74F, 74F and 80F.

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