Oklahoma Severe Weather Discussion - May 2013

[venture]

Slight Risk in the state next 3 days. Here are the SPC outlooks...

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT TUE MAY 07 2013

VALID 071300Z - 081200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN AND EVE ACROSS PARTS
OF THE CENTRAL HIGH PLAINS...

...SYNOPSIS...
STRENGTHENING OF A SUBTROPICAL JET STREAK IS ALREADY EVIDENT IN
SATELLITE LOOPS OVER THE LOWER LATITUDE EASTERN PACIFIC. AND IT
APPEARS THAT A CONTINUED PHASING OF THIS FEATURE WITH AN IMPULSE IN
THE SOUTHERN BRANCH OF A SPLIT MID-LATITUDE PACIFIC JET WILL
CONTRIBUTE TO FURTHER INTENSIFICATION OF MID/UPPER FLOW EAST
NORTHEASTWARD ACROSS BAJA INTO THE NORTHERN MEXICAN PLATEAU LATER
TODAY AND TONIGHT. THIS IS EXPECTED TO CONTRIBUTE TO THE EASTWARD
ACCELERATION OF A CLOSED LOW ACROSS THE SOUTHERN SIERRA NEVADA INTO
THE FOUR CORNERS REGION BY 12Z WEDNESDAY. AS THIS OCCURS...A CLOSED
LOW NEAR THE SOUTHERN APPALACHIANS SHOULD BECOME MORE PROGRESSIVE AS
WELL...GRADUALLY ACCELERATING NORTHEASTWARD INTO THE MID ATLANTIC
COAST STATES.

IN THE WAKE OF THE SOUTHEASTERN CLOSED LOW...MOISTURE RETURN FROM
THE GULF OF MEXICO APPEARS LIKELY TO REMAIN RATHER MODEST...AND
GENERALLY CONFINED TO THE RIO GRANDE VALLEY...PERHAPS NORTHWARD INTO
PARTS OF THE TEXAS SOUTH PLAINS BY LATE TONIGHT. BUT...LOW-LEVEL
WARMING...AND SOME MOISTENING ASSOCIATED WITH
EVAPOTRANSPIRATION...BENEATH STEEPENING MID-LEVEL LAPSE RATES...WILL
CONTRIBUTE TO DESTABILIZATION AND INCREASING POTENTIAL FOR
THUNDERSTORM ACTIVITY ACROSS THE PLAINS TODAY. MEANWHILE...DESPITE
SOME STABILIZATION OF MID-LEVEL LAPSE RATES ACROSS MUCH OF THE
INTERMOUNTAIN WEST COMPARED TO PRIOR DAYS...A GRADUAL MOISTENING OF
LOWER/MID-LEVELS IS EXPECTED TO COMPENSATE...CONTRIBUTING TO ENOUGH
INSTABILITY WITH SURFACE HEATING FOR SCATTERED THUNDERSTORMS...AIDED
BY OROGRAPHIC AND SYNOPTIC FORCING FOR UPWARD VERTICAL MOTION.
SCATTERED THUNDERSTORM ACTIVITY WILL ALSO PERSIST IN ASSOCIATION
WITH THE EASTERN UPPER LOW. ALTHOUGH MOST STORMS PROBABLY WILL
REMAIN RELATIVELY WEAK IN NATURE...THE RISK FOR SEVERE STORMS MAY
NOT BE NEGLIGIBLE...PARTICULARLY ACROSS PARTS OF THE SOUTH CENTRAL
HIGH PLAINS.

...S CNTRL HIGH PLAINS...
ONGOING WEAK THUNDERSTORM ACTIVITY IS EXPECTED TO SPREAD NORTHEAST
OF THE REGION DURING THE DAY...IN ASSOCIATION WITH A WEAK SHORT WAVE
IMPULSE EMERGING FROM THE INTERMOUNTAIN WEST. THIS FEATURE IS
EXPECTED TO EVENTUALLY TURN EASTWARD TOWARD THE MID MISSOURI
VALLEY...AROUND THE SOUTHERN PERIPHERY OF A QUASI-STATIONARY WEAK
MID-LEVEL CYCLONIC CIRCULATION OVER THE DAKOTAS...WHILE SHORT WAVE
RIDGING BUILDS FROM THE SOUTHERN INTO CENTRAL ROCKIES...AHEAD OF THE
UPSTREAM CLOSED LOW.

IN THE WAKE OF THIS INITIAL CONVECTION...STRONG SURFACE HEATING IS
EXPECTED TO CONTRIBUTE TO AN AXIS OF WEAK TO MODERATE
DESTABILIZATION FROM THE TEXAS SOUTH PLAINS THROUGH THE TEXAS/
OKLAHOMA PANHANDLE REGION INTO WESTERN KANSAS. WHILE SURFACE DEW
POINTS MAY NOT BE MUCH HIGHER THAN THE UPPER 40S TO NEAR 50F AT PEAK
LATE AFTERNOON HEATING/MIXING...THIS STILL MAY BE SUFFICIENT FOR
CAPE OF 500-1000+ J/KG...AND SCATTERED STORM DEVELOPMENT.

MODELS SUGGEST A BELT OF 30-40 KT WESTERLY MID-LEVEL FLOW WILL
OVERSPREAD THE INSTABILITY AXIS ACROSS THE PANHANDLE REGION INTO
WESTERN KANSAS...WHERE A MODEST SOUTHERLY 850 MB JET WILL CONTRIBUTE
TO SUFFICIENT VERTICAL SHEAR FOR SUPERCELL STRUCTURES. WITH
THERMODYNAMIC PROFILES CHARACTERIZED BY A DEEPLY MIXED BOUNDARY
LAYER WITH SIZABLE TEMPERATURE/DEW POINT SPREADS...LARGE HAIL AND
DAMAGING WIND GUSTS APPEAR THE PRIMARY SEVERE THREATS WITH
STORMS...WHICH SHOULD PERSIST INTO EARLY EVENING.

ADDITIONAL STORM DEVELOPMENT IS POSSIBLE LATER THIS EVENING INTO THE
OVERNIGHT HOURS...ACROSS THE CENTRAL PLAINS TOWARD THE MIDDLE
MISSOURI VALLEY...SUPPORTED BY FORCING ASSOCIATED WITH ENHANCED WARM
ADVECTION ON THE NOSE OF A STRENGTHENING LOW-LEVEL JET. WEAK
INSTABILITY PROBABLY WILL LIMIT SEVERE POTENTIAL WITH THIS
ACTIVITY...BUT EVAPORATIVE COOLING ASSOCIATED WITH SIZABLE SUB-CLOUD
TEMPERATURE-DEW POINT SPREADS COULD CONTRIBUTE TO DOWNWARD MIXING OF
HIGHER MOMENTUM AIR TO THE SURFACE...AND A FEW STRONG SURFACE GUSTS.

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT TUE MAY 07 2013

VALID 081200Z - 091200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS W-CENTRAL TX AND WRN
OK...MUCH OF KS TO MO RIVER AREA...

...SYNOPSIS...
SPLIT-FLOW PATTERN IN MID-UPPER LEVELS WILL PERSIST THROUGH
PERIOD...SUCH THAT NRN STREAM REMAINS OVER CANADA WITH CORE OF
SUBTROPICAL JET ACROSS NRN MEX AND S TX. HOWEVER...BROAD NATURE OF
SRN JET WILL YIELD FAVORABLY STG 250-500 MB WINDS ACROSS SRN HIGH
PLAINS...IN CONJUNCTION WITH HEIGHT-GRADIENT ENHANCEMENTS RELATED TO
WRN CLOSED LOW. THAT CYCLONE -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER MRY AREA -- IS FCST TO MOVE EWD TO UT/AZ BORDER REGION
BY START OF PERIOD. THEREAFTER...ASSOCIATED 500-MB CIRCULATION
CENTER AND VORTICITY MAX SHOULD SHIFT ENEWD ACROSS SRN CO AND WEAKEN
BY 9/12Z...WITH SHORTWAVE TROUGH EXTENDING WSWWD TO SECONDARY
PERTURBATION OVER CENTRAL/SRN CA.

MEANWHILE...SMALLER/WEAKER VORTEX NOW OVER SD SHOULD EVOLVE INTO
POSITIVELY-TILTED/OPEN-WAVE TROUGH AND MOVE EWD ACROSS IA/MN BORDER
REGION TOWARD UPPER MS VALLEY. LARGE CYCLONE NOW MEANDERING
ERRATICALLY OVER SRN APPALACHIANS SHOULD WEAKEN AND MOVE GENERALLY
NEWD ACROSS MID-ATLC REGION DAY-2...BUT STILL CONTRIBUTE TO
POTENTIAL FOR ISOLATED TO WIDELY SCATTERED TSTMS IN POCKETS OVER
BROAD AREA OF MID-ATLC...CENTRAL APPALACHIANS REGION...TIDEWATER AND
PIEDMONT.

AT SFC...LEE CYCLONE IS FCST TO DEEPEN THROUGH FIRST HALF OF PERIOD
INVOF SRN PORTIONS KS/CO BORDER. BY LATE AFTN...SHARPENING DRYLINE
SHOULD EXTEND SSEWD ACROSS ERN PORTIONS TX PANHANDLE THEN SWD OVER
S-CENTRAL TX INTO NRN COAHUILA. DRYLINE MAY RETREAT SLIGHTLY DURING
EVENING...BUT NOT BEYOND LEE TROUGH POSITION OVER TX PANHANDLE AND
PERMIAN BASIN REGIONS. SFC TROUGH AND FRONTOGENETIC ZONE SHOULD ARC
FROM LOW NNEWD OVER WRN KS THEN ENEWD ACROSS NRN KS TO SERN NEB/NWRN
MO AREA. THIS BOUNDARY MAY UNDERGO SUBSTANTIAL MODULATION BY
CONVECTIVE PRECIP THROUGH PERIOD...AND ITS SPECIFIC
LOCATION/STRENGTH REMAINS RATHER UNCERTAIN.

...DRYLINE REGIME...SW KS TO SW TX...
TSTMS ARE EXPECTED TO DEVELOP INVOF DRYLINE DURING AFTN...MOVING
SLOWLY EWD TO NEWD WITH GREATEST THREAT BEING LARGE/DAMAGING
HAIL...SVR GUSTS ALSO LIKELY IN LATER STAGES. TORNADO POTENTIAL
APPEARS MUCH LESS THAN WIND/HAIL AND VERY CONDITIONAL ON STORM-SCALE
PROCESSES. AMBIENT MOISTURE IS GOING TO BE LESS THAN PROGGED BY
MOST MODELS...MAINTAINING HIGH DIURNAL LCL HEIGHTS. NMM-B MEMBERS
OF SREF CONTINUE THEIR TREND OF RELATIVELY SUBDUED MOISTURE FIELDS
OVERALL...AND DEPICTIONS OF SWATH OF DEEP MIXING OVER PORTIONS
CENTRAL/N TX DURING AFTN. THIS SCENARIO RESULTS IN SFC DEW POINTS
MAINLY 50S F...PERHAPS WITH SMALL POCKETS OF LOW 60S...WITHIN AROUND
75-100 NM E OF DRYLINE...AND APPEARS MOST REASONABLE GIVEN CURRENT
IMMATURE STATE OF UPSTREAM AIR MASS MODIFICATION BEHIND COLD
ERN-CONUS GYRE.

EML WILL IMPART VERY STEEP MIDLEVEL LAPSE RATES...BUT ALSO SHOULD
YIELD ENOUGH BASAL CINH TO RESTRICT CONVECTIVE COVERAGE INVOF
DRYLINE TO ISOLATED OR WIDELY SCATTERED. FCST SOUNDINGS...MODIFIED
FOR MORE REASONABLE/MUTED RETURN-FLOW MOISTURE SCENARIO...STILL
SUGGEST 1500-2000 J/KG MLCAPE DURING 21Z-03Z TIME FRAME. INCREASE
IN DEEP SHEAR WITH SWD EXTENT WILL OVERLIE GREATER SFC HEATING...BUT
WITH MORE UNCERTAINTY REGARDING TSTM COVERAGE AND DURATION.
ALTHOUGH CONVECTIVE COVERAGE MAY NOT BE THAT DENSE DIURNALLY...ANY
TSTMS THAT DO DEVELOP FROM PORTIONS W-CENTRAL/SW TX NWD OVER WRN OK
ARE LIKELY TO ASSUME SUPERCELL CHARACTERISTICS AT LEAST IN TRANSIENT
FASHION...PRODUCING SUBSTANTIAL HAIL. COVERAGE OF MOST
DRYLINE-INITIATED TSTMS SHOULD LESSEN BY AROUND 06Z.

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT TUE MAY 07 2013

VALID 091200Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS LOWER MI TO ERN MO...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS OK AND CENTRAL/NRN
TX...

...SYNOPSIS...
SPLIT-FLOW PATTERN FCST TO CONTINUE IN MID-UPPER LEVELS.
WELL-DEFINED CYCLONE NOW OVER SERN CONUS SHOULD WEAKEN AND EJECT
NEWD OVER MID-ATLC REGION THROUGH DAY-2. AS HEIGHTS FALL ACROSS ERN
CANADA...THIS SYSTEM SHOULD DEAMPLIFY FURTHER DAY-3...MOVING NEWD
ACROSS COASTAL MID-ATLC AND NEW ENGLAND...CONTRIBUTING TO GEN
THUNDER POTENTIAL OVER PORTIONS OF THOSE REGIONS. MID-UPPER LEVEL
CYCLONE NOW CENTERED OVER CENTRAL CA COASTAL AREAS SHOULD MOVE EWD
ACROSS 4-CORNERS REGION THROUGH DAY-2...AND PROGS ARE REASONABLY
CONSISTENT WITH THAT MUCH OF ITS EVOLUTION.

HOWEVER...RIGHT AROUND START OF DAY-3...09/12Z...STRONG DIFFERENCES
APPEAR IN OPERATIONAL AND SREF GUIDANCE REGARDING THIS SYSTEM AND
ITS INTERACTION WITH UPSTREAM SHORTWAVE TROUGH OVER CA. WEAKENING
IS EXPECTED EITHER WAY. HOWEVER...WHETHER OR NOT THIS PERTURBATION
CONTINUES MOVING EWD OVER CENTRAL PLAINS...AS PROGGED BY
NAM/ECMWF...OR RETROGRADES BACK INTO PERIPHERAL VORTICITY FIELD OF
CA TROUGH AS FCST BY SPECTRAL AND MOST SREF MEMBERS...WILL DEPEND ON
AMPLITUDE OF LATTER PERTURBATION. DESPITE THESE DIFFERENCES...BASIC
PATTERN OF POSITIVELY TILTED TROUGHING FROM CENTRAL PLAINS TO CA IS
CONSISTENT...AS IS PRESENCE OF ENHANCED MID-UPPER LEVEL FLOW ACROSS
NRN MEX. NRN RIM OF SUBTROPICAL JET SHOULD LIE OVER CENTRAL/S TX BY
10/00Z.

SMALL/CUT-OFF/MID-UPPER LEVEL CYCLONE NOW OVER SD IS EXPECTED TO
WEAKEN AND SHIFT EWD ACROSS UPPER MS VALLEY AND LOWER MI AS
OPEN-WAVE TROUGH. ASSOCIATED SFC LOW SHOULD FORM ALONG NERN SEGMENT
OF FRONTAL ZONE EARLY IN PERIOD...OVER MO/IA...THEN MOVE ACROSS IL
TOWARD SRN LOWER MI THROUGH REMAINDER PERIOD. TRAILING COLD FRONT
SHOULD MOVE SEWD TO SERN KS...WRN OK AND ERN NM BY 10/00Z. THIS
BOUNDARY SHOULD INTERSECT DRYLINE OVER W-CENTRAL/SWRN OK OR ADJACENT
NW TX...WITH DRYLINE SSWWD ACROSS W-CENTRAL TX TO COAHUILA.

...SRN PLAINS TO UPPER GREAT LAKES/OH VALLEY...
BROAD SWATH FROM SW TX TO OH VALLEY REGION WILL MOISTEN SUFFICIENTLY
BY THIS TIME TO SUPPORT DIURNAL TSTMS ALONG AND S OF FRONTAL
ZONE...AND E OF DRYLINE...WITH SFC DEW POINTS COMMONLY IN 60S F.
THOSE BOUNDARIES...AS WELL AS OUTFLOW/DIFFERENTIAL-HEATING
BOUNDARIES PRODUCED BY PRIOR OVERNIGHT/MORNING CONVECTION...SHOULD
FOCUS RELATIVE CONCENTRATIONS OF CONVECTION AND AT LEAST MRGL SVR
POTENTIAL DAY-3. AFOREMENTIONED UNCERTAINTIES IN PATTERN ALOFT WILL
AFFECT GEOMETRY OF LOW-MIDDLE LEVEL WINDS AND RELATED
FAVORABILITY--OR NOT--OF DEEP SHEAR...ESPECIALLY N OF CENTRAL/SRN TX
SUBTROPICAL JET. ACCORDINGLY...KINEMATIC PROFILES VARY
SUBSTANTIALLY IN FCST SOUNDINGS IN MANY GIVEN SPOTS...FROM MODEL TO
MODEL.

TWO PRIMARY AREAS OF RELATIVE SVR CONCENTRATION MAY BE...
1. ALONG COLD FRONT FROM LOWER MI SWWD ACROSS IL...WHERE FRONTAL
FORCING AND FOREGOING DIABATIC HEATING SHOULD SUPPORT BAND OF
STG-SVR TSTMS WITH DAMAGING GUSTS AND HAIL NEAR SVR LIMITS POSSIBLE.
VEERED WARM SECTOR FLOW AND WINDS ALOFT CLOSE TO PARALLEL WITH
BOUNDARY INDICATE QUASI-LINEAR CONVECTION.

2. ALONG/AHEAD OF FRONT AND DRYLINE OVER PORTIONS TX/OK..WHERE STG
SFC HEATING AND 2000-3000 J/KG MLCAPE MAY BECOME JUXTAPOSED WITH
LOCALIZED ENHANCEMENTS TO LOW-LEVEL SHEAR NEAR BOUNDARIES. PROGGED
SFC FLOW IS WEAK...HOWEVER...LIMITING HODOGRAPH SIZE IN MOST AREAS.
CONVECTION MAY BE RATHER MESSY AND CLUSTERED OVER THIS REGION...BUT
WITH SVR HAIL/GUSTS POSSIBLE GIVEN STRENGTH OF BUOYANCY AND AT LEAST
MRGL DEEP-LAYER WIND PROFILES.

..EDWARDS.. 05/07/2013

[venture]

Okay so here is a bit more of a break down. Tornado threat next few days is low, but not zero. Tomorrow is probably the best chance to see any. Thursday looks like a garbled mess. Really quick today, best chance is NW OK for some hailers. Nothing major. Probably good storms for some photography if they stay isolated enough. So on to tomorrow; here is the setup:



The good ol' dryline will be dancing along the TX/OK border in the afternoon. High instability will be building throughout much of Western OK through the day. Central OK is going to be more on the line and Eastern should be relatively quiet. Storms will fire in the afternoon along the dryline, probably starting in SW OK where the better convergence is going to be. Storms will move NE at about 20-25 mph. There will be a bit of a cap early on, but is very breakable. The indices are there which would highlight a large hail event with the chance for a few tornadoes. The hail I think is set in stone. The tornado threat has a big mitigating factor...well actually two. LCL levels on the forecast soundings are up around 800mb, which is very high up in the air. Normally we need those down in into the 900s (think lower the number higher up in the air). The other big thing is the relatively poor shear conditions. Directional shear is there - no problem. Speed shear is rough. Surface winds of 20kts only start increase to 30kts at 500 mb. That's pretty pathetic. Now if we see any localized boundaries setup or storms take hard right turns, we could see a localized enhancement to the shear environment that could improve the tornado risk. That still doesn't make up for the high LCL heights. Still can't rule a tornado or two out, especially if models are off on the forecast a bit. Everything else is pretty much in line for tornadic development - both NAM and GFS agree on that.

On to Thursday...what a mess. Okay so on the map below, ignore the warm front. Its not really a warm front, I just needed something to highlight a boundary in that area - plus the warm front is aimed the wrong way. The take away is that there will be boundary in that area just north of I-44. Dryline will be out of far SW OK through North Texas. Expect fairly widespread storms on Thursday over central and eastern OK. Would expect the best chance of severe weather south of the boundary in the greater instability. If sun breaks out anywhere, probably most likely in SE OK, that will raise the severe risk quite a bit.



Looking at the forecast soundings, storms should be mainly east or any variation with a main eastward component. Wind profiles are very linear so tornado threat is exceptionally low. The setup is really just that of a grunge filled mess of showers and storms. Main and high winds the main threats with the strong storms. Instability will be moderate to high so the hail could get pretty large in any storms with well developed mesocyclones and sustained updrafts.

[kelroy55]

Once again our local weather folks don't agree on much... chances for rain:

............ Wed Thur Fri Sat

25.......... 0 40 40 30
5............ 30 60 20 20
9............ 40 60 30 0
4............ 50 70 30 20

[venture]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 147
NWS STORM PREDICTION CENTER NORMAN OK
555 PM CDT TUE MAY 7 2013

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
SOUTHWEST KANSAS
NORTHWEST OKLAHOMA

* EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 555 PM UNTIL
1100 PM CDT.

* PRIMARY THREATS INCLUDE...
SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO 2
INCHES IN DIAMETER POSSIBLE
SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES EAST AND WEST OF A LINE FROM 80 MILES NORTH
NORTHEAST OF GARDEN CITY KANSAS TO 55 MILES SOUTHWEST OF ALVA
OKLAHOMA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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...SCATTERED THUNDERSTORMS ARE INCREASING ACROSS SOUTHWEST
KS AND NORTHWEST OK. THESE STORMS ARE FORMING ALONG AN INSTABILITY
AXIS WHERE SUFFICIENT MLCAPE AND STEEP LAPSE RATES WILL PROMOTE HAIL
POTENTIAL IN THE STRONGEST STORMS. THE LOW LEVEL JET WILL ALSO
STRENGTHEN THIS EVENING...HELPING TO MAINTAIN/ORGANIZE THE
CONVECTION DESPITE WEAKENING INSTABILITY AFTER DARK.

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 450. MEAN STORM
MOTION VECTOR 26025.

[Anonymous.]

Nice and steamy this morning, with AM convection moving out and sun draping the W half of OK - instability for this evening will be high.

[venture]

Slight risk today covers all of Central and Western OK. Main risk very large hail. HRRR has storm initiation around 2PM this afternoon along the dryline out west at the OK/TX border. Storm motion today will be slightly north of due east. Tornado threat looks low, but not zero. Damaging wind threat could definitely go up as things start to collapse.

By 2PM today CAPE values over much of Central and SW OK will be north of 3000 j/kg. So these things will probably just explode once they get going. NAM isn't in total agreement with HRRR. It keeps the highest instability over NC OK and SC KS and maintains decent CIN along/south of I-44 and I-40.

By 5PM this is what the radar could look like if HRRR is right...

[venture]

Chat room will be rolling today and tomorrow: Live Chat | Weather Spotlight

[Tydude]

Area forecast discussion
national weather service norman ok
1036 am cdt wed may 8 2013

.discussion...
Most of the earlier convection has either dissipated or moved east
of our forecast area. A few showers...perhaps isolated
thunderstorms...do still remain possible...however...especially
along the red river where an mcv is drifting east.

Short-term models show convection redeveloping this
afternoon...possibly as early as 2 pm...in far western oklahoma.
There is some indication of storms elsewhere...but the strongest
storms should be in the current slight risk area...at least
initially. All the convection is likely to move in a generally
eastward direction...with the usual caveats for supercell splits
and mergers...so much of the region will probably see some
rain/storms by late this evening.

An outflow boundary now across northern oklahoma should begin to
move north late this morning...and may be into kansas before
storms redevelop...especially along the texas/oklahoma border
area.

Made a couple of minor adjustments to hourly wind forecasts...due
to the outflow boundary...but no other changes are planned for
this morning.

&&

[venture]

Outflow boundary from last night's activity pretty apparent right now on Visible imagery. A lot of CU going up in the vicinity of it from the southern Metro area up into NW OK. That will be a focus for storms today and then along the dryline out west. HRRR still calls for initiation around 2PM today along the dryline. Then initiates activity on the outflow boundary by 5PM. Not seeing much out along the dryline right now, some CU starting to develop. There is one area of elevated returns in Lipscomb County that could be the first storm going up.

[venture]

Storm initiation has begun on schedule in Lipscomb County TX and Ellis County OK.

[venture]

[venture]

Watch Soon...



MESOSCALE DISCUSSION 0603
NWS STORM PREDICTION CENTER NORMAN OK
0219 PM CDT WED MAY 08 2013

AREAS AFFECTED...WRN OK...NWRN TX...SWRN KS

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 081919Z - 082015Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP
ACROSS MUCH OF WRN OK OVER THE NEXT 3-4 HOURS. LARGE HAIL AND
DAMAGING WINDS ARE PRIMARY SEVERE THREATS.

DISCUSSION...BOUNDARY LAYER MOISTURE IS QUICKLY ADVANCING NWD ACROSS
THE SRN PLAINS WITH THE LEADING EDGE OF HIGHER QUALITY DEW
POINTS...CHARACTERIZED BY 60F...NOW NORTH OF I-40 OVER OK. VIS
SATELLITE IMAGERY SUPPORTS THIS WITH CONSIDERABLE AMOUNT OF BOUNDARY
LAYER CU DEEPENING ACROSS SWRN OK WITHIN CONFLUENT MOISTENING FLOW.
DESPITE VEILED HIGH CLOUDS THAT ARE SPREADING ACROSS THIS
REGION...LOW LEVEL LAPSE RATES HAVE STEEPENING SUFFICIENTLY FOR
ISOLATED TSTM DEVELOPMENT OVER ELLIS COUNTY IN NW OK. FURTHER
WEAKENING OF CAP AND GRADUAL MOISTENING/DESTABILIZING WARM SECTOR
SHOULD CONTRIBUTE TO AN ENVIRONMENT FAVORABLE FOR ADDITIONAL TSTM
DEVELOPMENT INTO THE EVENING HOURS. LARGE HAIL AND DAMAGING WINDS
MAY ACCOMPANY ANY SUPERCELLS THAT EVOLVE OFF THE DRYLINE...OR ALONG
WEAK NW-SE ORIENTED CONFLUENCE ZONE THAT CURRENTLY EXTENDS FROM SFC
LOW OVER THE OK PANHANDLE...SEWD INTO NRN GRADY COUNTY.

..DARROW/CORFIDI.. 05/08/2013

[Jesseda]

So do you think the metro will see anything today? Just asking because my daughter has ball games from 7pm to 9:30 pm

[venture]

So do you think the metro will see anything today? Just asking because my daughter has ball games from 7pm to 9:30 pm

Yes. Anytime after 5PM seems most likely. Watching a lot of CU get congested in Grady County right now which could be a sign of storms forming there along the boundary laying overhead near us.

[Anonymous.]

Just keep an eye on radar trends, the cells/complexes of storms could split and redevelop several times as they progress east. They could easily part like a red-sea as they approach the metro, or an isolated cell could dump golfballs on us again.

[venture]

Everything is about to go. This is a 1.5 degree image from the Vance AFB radar, so its looking pretty high up.

[venture]

Since things are going to probably get more active pretty quickly I'll be watch the chat room for the rest of the afternoon now. Just copy/paste the address in my sig.

[kelroy55]

Since things are going to probably get more active pretty quickly I'll be watch the chat room for the rest of the afternoon now. Just copy/paste the address in my sig.

Thanks again for all the hard work.

[venture]

Cell in Western Canadian County is starting to come down, but a couple smaller new cells popping up around it. Cap is still holding things back, but should start to give way soon.

[venture]

• Message from SPC just popped up on our workstations alerting us to the watch coordination call. #okwx http://pbs.twimg.com/media/BJxMf5FCMAAXVVv.jpg
  
  

[venture]

• Prelim counties in watch. Six WFO's on coordination call with SPC right now. #okwx http://pbs.twimg.com/media/BJxNSWyCQAAH0bj.jpg
  
  

[venture]

Watch is officially out now...


OKLAHOMA COUNTIES INCLUDED ARE ALFALFA BEAVER BECKHAM BLAINE CADDO CANADIAN COMANCHE COTTON CUSTER DEWEY ELLIS GARFIELD GRADY GRANT GREER HARMON HARPER JACKSON JEFFERSON KAY KINGFISHER KIOWA LOGAN MAJOR NOBLE OKLAHOMA ROGER MILLS STEPHENS TILLMAN WA****A WOODS WOODWARD

WW 149 SEVERE TSTM KS OK TX 082020Z - 090400Z
AXIS..75 STATUTE MILES EAST AND WEST OF LINE..
100SSE CDS/CHILDRESS TX/ - 20NNE RSL/RUSSELL KS/ ..AVIATION COORDS.. 65NM E/W /39NNE ABI - 51WNW SLN/ HAIL SURFACE AND ALOFT..3 INCHES. WIND GUSTS..60 KNOTS.
MAX TOPS TO 500. MEAN STORM MOTION VECTOR 25025.

[venture]

• #OUN issues Severe Thunderstorm Warning for Custer, Dewey, Roger Mills [OK] till 4:00 PM CDT http://bit.ly/12eMvNQ?OUN
  by IEMBot OUN via twitter 3:21 PM

[Anonymous.]

Wow that is a huge watch box!

[venture]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 149
NWS STORM PREDICTION CENTER NORMAN OK
320 PM CDT WED MAY 8 2013

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
WESTERN AND CENTRAL KANSAS
WESTERN AND CENTRAL OKLAHOMA
WEST CENTRAL AND NORTHWEST TEXAS AND EASTERN PARTS OF THE TEXAS
PANHANDLE

* EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 320 PM
UNTIL 1100 PM CDT.

* PRIMARY THREATS INCLUDE...
NUMEROUS LARGE HAIL EVENTS EXPECTED WITH SEVERAL VERY LARGE HAIL
EVENTS TO 3 INCHES IN DIAMETER POSSIBLE
SEVERAL DAMAGING WIND GUSTS TO 70 MPH LIKELY
A FEW TORNADOES POSSIBLE

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 75
STATUTE MILES EAST AND WEST OF A LINE FROM 100 MILES SOUTH
SOUTHEAST OF CHILDRESS TEXAS TO 20 MILES NORTH NORTHEAST OF
RUSSELL KANSAS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 148...

DISCUSSION...SCTD SUSTAINED TSTMS/SUPERCELLS EXPECTED TO FORM ALONG
AND AHEAD OF DRY LINE/LEE TROUGH EXTENDING SSW FROM SW KS SFC LOW
INTO WRN TX. STRENGTH AND DISCRETE NATURE OF STORMS WILL BE AIDED BY
RELATIVELY MODEST LOW-LVL CONVERGENCE...PERSISTENT UPR
DIFFLUENCE...AND STEEP LOW TO MID-LVL LAPSE RATES...SUGGESTING A
RISK FOR BOTH LARGE HAIL AND LOCALLY DMGG WINDS. WHILE
TEMPERATURE-DEWPOINT SPREADS ARE SIZABLE IN WW ATTM...POTENTIAL WILL
EXIST FOR CORRIDORS WITH AN ENHANCED RISK FOR LOW-LVL
ROTATION/TORNADOES GIVEN EXPECTED STORM INTERACTIONS LATER THIS
EVE..AND AS BOUNDARY LAYER BEGINS TO COOL/SSWLY LLJ STRENGTHENS.
THUS...PARTS OF THE WW MAY REQUIRE POSSIBLE UPGRADE TO TORNADO WW
LATER THIS EVE.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 25025.

SEVERE THUNDERSTORM WATCH PROBABILITIES FOR WS 0149 NWS STORM PREDICTION CENTER NORMAN OK
0320 PM CDT WED MAY 08 2013

WS 0149
PROBABILITY TABLE:
PROB OF 2 OR MORE TORNADOES : 20%
PROB OF 1 OR MORE STRONG /F2-F5/ TORNADOES : 20%
PROB OF 10 OR MORE SEVERE WIND EVENTS : 60%
PROB OF 1 OR MORE WIND EVENTS >= 65 KNOTS : 20%
PROB OF 10 OR MORE SEVERE HAIL EVENTS : >95%
PROB OF 1 OR MORE HAIL EVENTS >= 2 INCHES : 50%
PROB OF 6 OR MORE COMBINED SEVERE HAIL/WIND EVENTS : >95%

&&
ATTRIBUTE TABLE:
MAX HAIL /INCHES/ : 3.0
MAX WIND GUSTS SURFACE /KNOTS/ : 60
MAX TOPS /X 100 FEET/ : 500
MEAN STORM MOTION VECTOR /DEGREES AND KNOTS/ : 25025
PARTICULARLY DANGEROUS SITUATION : NO