Oklahoma Severe Weather Discussion - April 2011

[venture]

Quick update on today and tomorrow.

Today looks to be what we see right now. Isolated areas of showers/storms and cool weather. Some will produce severe criteria hail mainly in South Central and Northeast Oklahoma. Activity will quickly move east by this evening and should have a relatively dry night. GFS does indicate some chance for precip overnight into early tomorrow, so we'll have to see.

As far as Friday, NAM has dramatically shifted west to within 20 miles of the GFS solution now (unlike yesterday where they were 75-100 miles apart). Activity initiation in Oklahoma will be tricky still. NAM tends to keep it mostly to the east and Northeast until early evening. GFS has a few chances in SW OK by early afternoon. They both come together showing a line of convection forming right over the I-44 corridor by early evening 5-7PM time frame. Evaluating the forecast soundings for KOKC for the 36 hr time frame (00Z Friday/7PM Thurs) from the NAM, GFS, and UKMET...indications are for a high end slight risk (which is what SPC has us in now) with just a hair shy of being upgraded to a moderate risk.

Things that are still not perfect for storms. Relative humidity is forecast to be fairly low upstairs, but this shouldn't be an issue. Instability is really going to depend on where things setup. If things shift west just 20-30 miles that will mean a lot for the Metro area. CAP strength is forecast to be fairly strong, but not unbreakable at all. This could put a lid on convection until the front gets closer. Most shear values look good for rotating storms, but not all the measurements are in line.

Tomorrow still appears to be a day to watch however and don't be shocked if things get upgraded to a moderate risk by SPC some where in the state.

[FritterGirl]

I just want a bit of rain.... :-/

[venture]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 175
NWS STORM PREDICTION CENTER NORMAN OK
235 PM CDT THU APR 21 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

WESTERN ARKANSAS
SOUTHEAST KANSAS
SOUTHWEST MISSOURI
EASTERN OKLAHOMA

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 235 PM UNTIL
1000 PM CDT.

SCATTERED LARGE HAIL
ISOLATED HAIL TO 2.0 INCHES IN DIAMETER POSSIBLE
ISOLATED TORNADOES

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 80
STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES SOUTH
SOUTHEAST OF POTEAU OKLAHOMA TO 65 MILES NORTH NORTHEAST OF
JOPLIN MISSOURI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...ELEVATED TSTMS ARE INCREASING IN COVERAGE AND INTENSITY
THIS AFTERNOON ALONG A SSWLY LLJ WHICH HAS STRENGTHENING TO 30-40
KT. THIS LLJ WILL CONTINUE TO DEVELOP NEWD TOWARD THE MID MS VALLEY
BY EVENING IN ADVANCE OF A MIDLEVEL VORTICITY MAXIMUM TRANSLATING
ENEWD ACROSS THE CNTRL AND SRN PLAINS. THE INCREASING MOISTURE ATOP
A STABLE BOUNDARY LAYER AND BELOW MIDLEVEL LAPSE RATES OF 7-8 C/KM
IS YIELDING A MODERATELY UNSTABLE ENVIRONMENT WITH MUCAPE VALUES OF
1500-2500 J/KG. WHEN COUPLED WITH EFFECTIVE BULK SHEAR OF 35-45
KT...SETUP WILL SUPPORT THE DEVELOPMENT OF SUPERCELLS CAPABLE OF
LARGE HAIL.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 25035.

[Achilleslastand]

So the rain they predicted we would get today missed us again here in central okla?

[Easy180]

High and Dry. High and Dry

[PennyQuilts]

$#@^%(*&@%!&&%$#&!!!

[Dustin]

^ditto!

[venture]

Looks like yesterdays 18Z and 00Z GFS model run handled today's precip the best. Bulk of the precip is in the east, everything else was expected to be widely scattered so not everyone was going to get some. We haven't seen much materialize yet to the west so that part of the forecast hasn't worked out all that well. Rainfall rates not all that great, and any rainfall around the Metro area today has been mainly sprinkles or a light shower that hasn't done much.

[venture]

Before everyone gets all depressed. :-P Afternoon discussion from Norman...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
340 PM CDT THU APR 21 2011

.DISCUSSION...
ALTHOUGH I HATE TO POSSIBLY JINX US... BUT IT APPEARS THAT A MORE ACTIVE PERIOD THAN WE HAVE SEEN IN A WHILE COULD EVOLVE OVER THE NEXT SEVERAL DAYS.

ELEVATED CONVECTION TO THE NORTH OF THE WARM FRONT...CURRENTLY LOCATED ACROSS NORTHERN TX... WILL LIKELY CONT TO PUSH OFF EAST OF THE AREA THIS AFTN. HOWEVER AS FRONT CONT TO LIFT NORTHWARD LATE TODAY AND THIS EVENING... COULD SEE A FEW MORE SFC-BASED STORMS AFFECT FAR SOUTHERN OK. THESE STORMS WILL HAVE THE POTENTIAL TO BE SEVERE.

SFC FRONT WILL CONT TO PULL BACK NORTHWARD OVERNIGHT RESULTING IN IMPROVING MOISTURE PROFILE... RESULTING IN MORE NUMEROUS SHOWERS AND THUNDERSTORMS. STILL QUITE A BIT OF ELEVATED INSTABILITY... SO SEVERE STORMS NOT OUT OF THE QUESTION... WITH BEST CHANCES ACROSS NORTHERN OK TONIGHT CLOSER TO LIFT ASSOCIATED WITH STRONGER WAA.

STRONGER MID-LEVEL STORM SYSTEM WILL MAKE ITS WAY EAST ACROSS THE CENTRAL AND NORTHERN PLAINS ON FRI... WHICH WILL PUSH COLD FRONT BACK SOUTH THROUGH NORTHERN OK. MEANWHILE... A DRYLINE WILL TAKE SHAPE NEAR THE WESTERN OK BORDER EARLY IN THE DAY AND WILL MAKE A RUN EAST TOWARD I-44 CORRIDOR DURING THE AFTN. EXPECT CONVECTION TO FIRE ALONG COLD FRONT/DRYLINE DURING AFTN HOURS TOMORROW. BEST ESTIMATE OF THESE BOUNDARIES LOCATIONS WOULD RUN NORTHEAST TO SOUTHWEST ALONG THE I-44 CORRIDOR. INSTABILITY AND WIND PROFILES WILL SUPPORT SEVERE STORMS FRI AFTN AND EVENING.

ALTHOUGH MODELS CONT TO SHOW MAIN SYNOPTIC BOUNDARY REMAINING NEAR I-44 THROUGH THE NIGHT INTO THE DAY ON SATURDAY... UNKNOWN DETAILS OF MESOSCALE BOUNDARIES WILL LIKELY PLAY A SIGNIFICANT ROLE ON WHERE LINES OF CONVECTION DEVELOP SAT NIGHT AND SUNDAY.

ANOTHER UPPER LEVEL STORM WILL MOVE OUT OF SOUTHERN ROCKIES INTO THE SOUTHERN PLAINS ON SUN. AS THIS OCCURS MAIN SFC BOUNDARY WILL LIFT BACK TO THE NORTH AND COULD SEE ANOTHER... MORE BROAD AREA OF SHOWERS/TSTMS SUN AFTN AND SUN NIGHT AS STORM SYSTEM MOVES EAST ACROSS THE AREA. IT APPEARS THAT THIS STORM SYSTEM MAY BE A BIT FASTER THAN HAS BEEN ADVERTISED... WHICH WILL RESULT IN STORM
DEVELOPMENT MONDAY AFTN EAST OF CENTRAL OKLAHOMA.

ANOTHER WAVE DROPS SE THROUGH THE ROCKIES ON TUE PROVIDING ANOTHER ROUND OF PRECIP.

[Thunder]

$#@^%(*&@%!&&%$#&!!!

Breathe. We're here for you.

[SkyWestOKC]

Venture, how's the weather looking to affect flights into OKC tomorrow? Obviously a tough call, but I will be flying in (or scheduled to) when these storms start to gain some steam (around 4-5pm). Will the line quickly move off to the east or does it look to be slow moving?

[venture]

Working on the forecast for tomorrow now. Cluster of strong storms now moving into SW OK and will be moving generally North to Northeast. Hail main threats. HRRR has a good handle on things showing this convection. It doesn't appear it will get north of I-40 and die out in the next few hours.

[venture]

Here is the basic thinking I'm going with right now. NAM has snapped back to moving the front through OKC proper by early evening and has it just SE of the Metro area. GFS holds it back to just west of I-44, which is what I went with here. However, the severe probability are a blend of the two. Conditions ahead of the front will be very unstable. CAPE values are expected to be well north of 3000 j/kg. CIN values look pretty nonexistent by mid afternoon which would permit convection to begin developing by 4PM.

At this point it is looking like large hail is going to be the main threat, and thats why I went moderate. However, there will be some tornadoes in the state. Storm motions look pretty similar on most model runs with an almost due east movement of 25-30 mph. So these things won't really be moving all that fast. The main area that would have my interest though would be SW of the Metro area near the triple point intersection of the front and dryline. Instabilities are just forecast to be crazy high down there on all models and we could see a very significant storm pop up there. The CAP may come into play a bit tomorrow, especially further SW. The big thing in all of this is watching the speed of the cold front. If it blasts through here early then we end up with another eastern OK event. If it follows GFS of approaching OKC and stalling (and moving back north overnight)...storm chances will be decently high around here - for a change.

[venture]

MESOSCALE DISCUSSION 0512
NWS STORM PREDICTION CENTER NORMAN OK
1127 PM CDT THU APR 21 2011

AREAS AFFECTED...NRN OK INTO SRN AND ERN KS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 220427Z - 220700Z

STORMS ARE EXPECTED TO FORM ACROSS FAR NRN OK INTO SRN AND ERN KS
OVER THE NEXT SEVERAL HOURS...CONTINUING INTO FRIDAY MORNING. VERY
LARGE HAIL WILL BE POSSIBLE AND A WW MAY BE REQUIRED BY 07-08Z.

00Z SOUNDINGS FROM AROUND THE REGION INDICATE VERY STEEP MID TO
UPPER LEVEL LAPSE RATES AND STRONG INSTABILITY IN PLACE WITH AMPLE
DEEP LAYER SHEAR FOR STORM ORGANIZATION AHEAD OF AN UPPER TROUGH NOW
BEGINNING TO AFFECT THE CNTRL/SRN HIGH PLAINS. WITH A PERSISTENT
SWLY LOW LEVEL LET...MOISTURE AS SEEN ON 00Z OUN AND LMN SOUNDINGS
WILL CONTINUE TO STREAM NWD ACROSS OK AND INTO KS...AND EVENTUALLY
WRN MO.

AS THE MOIST AND UNSTABLE AIR MASS CONTINUES NWD...FORCING
ASSOCIATED WITH WARM ADVECTION AND THE LOW LEVEL JET SHOULD BREACH
THE CAPPING INVERSION JUST BELOW 700 MB...WITH AN ERUPTION OF STRONG
TO SEVERE CONVECTION POSSIBLE FROM FAR N CNTRL OK INTO MUCH OF ERN
KS AND MOVING INTO WRN MO BY MORNING. VERY LARGE HAIL WILL BE THE
PRIMARY THREAT WITH THESE STORMS.

[Thunder]

You said that there are storms coming in now, are the risks laid out applied to the storms happening now or for later on in the day?

[SkyWestOKC]

For once I am praying for a non-event. Any day except for tomorrow!

[venture]

You said that there are storms coming in now, are the risks laid out applied to the storms happening now or for later on in the day?

The storms in SW OK have dissipated as expected. My risk is for storms after noon tomorrow. The boundary positions are for early evening based on GFS.

[Thunder]

The storms in SW OK have dissipated as expected. My risk is for storms after noon tomorrow. The boundary positions are for early evening based on GFS.

Kool. Lets see if its gonna be cloudy all day or actually clear skies with total sunshine.

[venture]

SPC outlook is going with the faster solution of the NAM moving the front through quickly. Agreement that main threat is going to be very large hail with a minimal tornado threat. SPC slight risk runs roughly right along I-44 and to the south and east. This puts the southern and eastern sections of the OKC metro area (Lincoln/Pott/Cleveland/McClain counties) in the slight risk area. They do have a hatched area for large area over the slight risk area with 30% probabilities.

Like I said above, my outlook leans much more on the GFS than NAM. Reading the latest HPC model discussion they are going with a GFS/ECMWF blend for the forecast as the bulk of the models are similar with the NAM being an outliers going further south with the frontal boundary. So we will just have to see how it works out.

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1251 AM CDT FRI APR 22 2011

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS OH WWD TO MO THEN SWWD TO
PORTIONS CENTRAL TX....

...SYNOPSIS...
IN MID-UPPER LEVELS...INITIALLY STRONGER SHORTWAVE TROUGH NOW MOVING
EWD OVER ID IS FCST TO WEAKEN...MOVE SLOWLY SEWD TO WY AND BECOME
STRONGLY POSITIVELY-TILTED. MEANWHILE...LEADING SHORTWAVE TROUGH --
NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER WRN WY...WILL BECOME
DOMINANT PERTURBATION...EVOLVING INTO CLOSED 500-MB LOW CENTERED
OVER NWRN SD BY 22/18Z. THIS FEATURE THEN SHOULD ACCELERATE ENEWD
TO LS BY END OF PERIOD...EITHER AS MRGL CLOSED CYCLONE OR STG
OPEN-WAVE TROUGH.

LEE-SIDE SFC CYCLONE -- INITIALLY ANALYZED OVER SERN CO -- IS
EXPECTED TO LIFT NEWD ALONG STRENGTHENING FRONTAL ZONE FROM SRN KS
TO WRN IL BY 23/00Z...EVOLVING INTO TRIPLE-POINT CYCLONE FOR
OCCLUDED SFC LOW OVER SD MORE CLOSELY ASSOCIATED WITH UPPER TROUGH.
THIS SHOULD BECOME DOMINANT CYCLONE...OCCLUDE...AND REACH SSM AREA
BY END OF PERIOD. MEANWHILE...COLD FRONT WILL SWEEP EWD ACROSS
MO/IL/OH BY 23/12Z...STALLING OVER SE OK AND NW TX AS SECONDARY/WEAK
LOW DEVELOPS INVOF SPS. ADVECTION AND MIXING SHOULD FORCE DRYLINE
EWD ACROSS W-CENTRAL/NW TX AND SWRN OK DURING DAY...REACHING FROM
CENTRAL OK SWWD ACROSS W-CENTRAL TX TO EXTREME NRN COAHUILA BY
23/00Z. COLD FRONT WILL OVERTAKE DRYLINE OVER CENTRAL/SWRN OK PRIOR
TO AFOREMENTIONED SFC LOW DEVELOPMENT...WHERE FRONT/DRYLINE TRIPLE
POINT SHOULD SET UP BY END OF PERIOD.

IN GENERAL...WARM FRONT SHOULD MOVE NEWD ACROSS SERN MO/SRN IL EARLY
IN PERIOD...INTO CENTRAL PORTIONS IL/INDIANA AND SWRN OH BY LATE
AFTERNOON. HOWEVER...EFFECTIVE BAROCLINIC ZONE MAY BECOME
WAVY/SEGMENTED DUE TO CONVECTIVE EFFECTS ALONG AND N OF IT.

...OH VALLEY AND ADJOINING STATES...
MULTIPLE ROUNDS OF TSTMS MAY AFFECT THIS AREA...BEGINNING WITH
CARRY-OVER CONVECTION FROM PRIOR PERIOD MOVING EWD ACROSS PORTIONS
IL/INDIANA/OH DURING DAY. THIS ACTIVITY LARGELY WILL OCCUR ALONG
AND N OF NEWD-MOVING WARM FRONT WITH ELEVATED EFFECTIVE INFLOW
PARCELS...AND MRGL HAIL THREAT. EITHER BACKBUILDING/TRAILING
PORTION OF THAT ACTIVITY...OR NEWER DEVELOPMENT OVER SERN KS/MO
BEHIND IT...SHOULD MOVE EWD INTO WARM SECTOR OVER OH VALLEY REGION.
FOREGOING/PRECONVECTIVE AIR MASS WILL DESTABILIZE INTO AFTERNOON
FROM COMBINATION OF DIABATIC HEATING AND BOUNDARY-LAYER THETAE
ADVECTION. WEAK MLCINH SHOULD YIELD EFFECTIVE SFC-BASED PARCELS BY
MIDDAY...WHILE LAPSE RATES INCREASE STRONGLY WITH SWWD EXTENT FROM
OH TO ERN MO. CORRESPONDINGLY...MLCAPE SHOULD RANGE FROM 1000 J/KG
NEAR ERN INDIANA/OH WARM-FRONTAL SEGMENT TO NEARLY 3000 J/KG OVER
SRN MO.

SRN RIM OF SUBSTANTIAL HEIGHT FALLS ASSOCIATED WITH NRN PLAINS/UPPER
MIDWEST SHORTWAVE TROUGH ARE EXPECTED TO REMAIN N OF UNDISTURBED
WARM SECTOR. HOWEVER...TIGHTENING HEIGHT GRADIENTS ALOFT...ALONG
WITH LOW-LEVEL MASS RESPONSE AND ISALLOBARIC FORCING...SHOULD RESULT
IN FAVORABLE LOWER-MIDDLE TROPOSPHERIC SHEAR FOR SVR. TORNADO
PROBABILITY ALONG/S OF WARM FRONT APPEARS SUFFICIENT BY ITSELF TO
WARRANT SLGT CATEGORICAL OUTLOOK...BUT ANYTHING BEYOND THAT WILL
DEPEND STRONGLY ON MOST PROBABLE CONVECTIVE MODE...WHICH APPEARS TOO
UNCERTAIN OR MIXED ATTM TO CONCENTRATE ANY CORRIDOR OF GREATER
THREAT. EXPECT FAVORABLY LARGE HODOGRAPHS...WITH 0-1 KM AGL SRH
COMMONLY 200-400 J/KG ALONG AND S OF WARM FRONT. DAMAGING WIND IS
LIKELY...AND THREAT FOR LARGE HAIL WILL INCREASE SWWD IN STEP WITH
HIGHER LAPSE RATES/BUOYANCY.

...OZARKS TO CENTRAL/SW TX...
TSTMS ARE EXPECTED TO DEVELOP INVOF COLD FRONT AND DRYLINE DURING
AFTERNOON...OFFERING VERY LARGE/DAMAGING HAIL AND SVR GUSTS.
TORNADO POTENTIAL IS CONDITIONAL ON STORM-SCALE PROCESSES...GIVEN
MORE DEEPLY MIXED SUBCLOUD LAYERS AND HIGHER LCL THAN FARTHER NE.
EXPECT 8-9 DEG C/KM 700-500 MB LAPSE RATES...STG SFC HEATING AND DEW
POINTS COMMONLY 60S F...YIELDING PRE-STORM MLCAPE 2500-3500 J/KG.
CONVECTIVE COVERAGE SHOULD BECOME MORE WIDELY SCATTERED TO ISOLATED
WITH SWWD EXTENT...BUT ALSO WITH DISCRETE TSTMS FOR LONGER PERIODS
OF TIME IN SUPPORT OF SUPERCELL POTENTIAL. ALTHOUGH LOW-LEVEL FLOW
AND HODOGRAPH SIZE SHOULD WEAKEN FROM SRN OK SWD...DEEP-LAYER SHEAR
STILL MAY FAVOR SUPERCELLS...WITH INCREASING POTENTIAL FOR STRONGLY
DEVIANT MOTIONS INTO CENTRAL TX.

THREAT S OF RED RIVER WILL BE MORE STRONGLY TIED TO DIURNAL HEATING
THAT FARTHER NE...AND AS SUCH...SHOULD WANE AFTER ABOUT 03Z.
CONVECTION OVER OH VALLEY AND OZARKS MAY PERSIST IN PROGRESSIVELY
MORE LINEAR FORM OVERNIGHT...WITH HAIL/TORNADO THREATS BECOMING MORE
MRGL AND WIND BECOMING DOMINANT SVR RISK.

[Thunder]

Stay away cold front! >_<

[venture]

Trend in the HRRR and RUC models seems to support cold front passage of OKC city limits between 11AM and 1PM. If this happens, it would setup something similar to last week of activity remaining in Eastern & South central Oklahoma.

[Thunder]

Trend in the HRRR and RUC models seems to support cold front passage of OKC city limits between 11AM and 1PM. If this happens, it would setup something similar to last week of activity remaining in Eastern & South central Oklahoma.

Please do not jinx our weather. :-(

[venture]

Decent look at the SPC's thinking for OUN's area...

[Bostonfan]

Probably won't rain a drop. Maybe forecasts should go out only 1-2 hours in advance.

[silvergrove]

Probably won't rain a drop. Maybe forecasts should go out only 1-2 hours in advance.

It is frustrating but it is still nice to know what we can expect (at least sometimes). :/