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Severe Weather Threat... feb 24th-25


janetjanet998

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Yeah no doubt the Super Tuesday Outbreak was much bigger than the outbreak the day that EF4 hit Lone Grove. Although I thought the Lone Grove tornado may have been possibly stronger before it hit the town. I could be wrong but I thought they were indicating like 180-200kts of gate to gate shear which is possibly EF5 intensity and a very explosive environment over a small area(78temp, 64dew, and 2000-3000J/kg). The Lone Grove had a smaller explosive environment over parts of central south Oklahoma vs most of Dixie Alley. Yeah a few ingreidents could make a big difference.

The closest radar to the storm was in Norman and the lowest tilt hit the storm at about 6,800 feet. You were not looking at the tornado, but at the mesocyclone. There is no basis in determining tornado intensity from a radar beam at 6,800 feet. If you're going to TESSA on March 13 be sure to see the 11:30 AM presentation by Jason Dunn on the operations of radar. Its very good!

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GFS/NAM slowly (operative word: slowly) coming in line with last night's 0Z Euro on trough timing/placement... knock on wood. ECM still faster however, and I think this is the more accurate solution. Considering the progressive nature of this system this is not too surprising and I believe the primary severe wx axis will rest over the MS River (as opposed to areas further west in wrn AR or ern OK) (though I could be wrong).

For some reason NAM kills moisture below 850mb which reduces SBCAPE to near nil. Do not believe this solution (as the other models show a relatively deep moist layer), however veering of low-level flow warrants watching of future runs for continuation of this trend. Meanwhile the GFS is 5C cooler than the NAM at the surface. Still lots up in the air....

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DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1255 AM CST WED FEB 23 2011

VALID 241200Z - 251200Z

..THERE IS A MDT RISK OF SVR TSTMS OVER CNTRL AND ERN AR

NRN MS...AND WRN TN...

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN OK AND NERN TX EWD

INTO THE TN AND LOWER OH VALLEYS...

..SYNOPSIS

A POTENT UPPER LOW...NOW OFF THE WRN COAST OF BAJA CA...WILL BE

PICKED UP BY THE SRN STREAM JET AND WILL EMERGE INTO SRN HIGH PLAINS

BY THU MORNING. AT THE SURFACE...LOW PRESSURE WILL DEEPEN AS IT

MOVES FROM NWRN TX/WRN OK EWD INTO NRN AR BY 00Z...AND CONTINUING

NEWD ALONG THE OH RIVER OVERNIGHT AND INTO FRI MORNING. INCREASING

SLY FLOW AHEAD OF THE LOW WILL AID IN MOISTURE TRANSPORT ACROSS THE

WARM SECTOR WHICH WILL BE BOUNDED ON THE N END BY A WARM FRONT

EXTENDING EWD FROM THE LOW...ROUGHLY ALONG THE 39.50 DEGREE PARALLEL

AT 00Z.

..ERN OK/NERN TX EWD ACROSS AR AND INTO KY AND TN

THUNDERSTORMS ARE EXPECTED TO BE ONGOING ACROSS NWRN TX INTO SRN OK

THU MORNING NEAR THE SURFACE LOW AND NEAR THE DEVELOPING

DRYLINE/COLD FRONT SURGE. THESE STORMS WILL BE CAPABLE OF HAIL...AND

PERHAPS GUSTY WINDS. OTHER STORMS WILL EXTEND FROM KS EWD INTO THE

OH VALLEY WHERE A SWLY LOW LEVEL JET WILL ENHANCE LIFT ALONG AND

NEAR THE WARM FRONT.

THUNDERSTORMS SHOULD INTENSIFY DURING THE DAY FROM N TX INTO ERN OK

BY MID AFTERNOON...WITH A CONTINUED HAIL AND INCREASING SEVERE WIND

THREAT. VEERING LOW LEVEL WINDS MAY TEMPER THE INITIAL THREAT OF

TORNADOES. THE MOST DANGEROUS STORMS ARE EXPECTED DURING THE LATE

AFTERNOON INTO THE EVENING...FIRST ACROSS AR THEN SPREADING NEWD

ACROSS NRN MS AND WRN TN. HERE...850 MB FLOW IN EXCESS OF 60 KT IS

EXPECTED IN ASSOCIATION WITH THE DEEPENING LOW...WITH ENHANCED LOW

LEVEL HODOGRAPH CURVATURE ALONG THE RESIDUAL WARM FRONT.

TORNADOES...A FEW POSSIBLY STRONG...AND PARTICULARLY DAMAGING WINDS

WILL BE POSSIBLE MAINLY BETWEEN 00Z-06Z.

A CRITICAL COMPONENT TO THE SEVERE THREAT WILL BE THE PLACEMENT OF

THE WARM FRONT THROUGHOUT THE DAY...AS IT WILL DETERMINE THE TRACK

OF THE SURFACE LOW. CURRENTLY...THE MORE NRN ECMWF SOLUTION IS

PREFERRED...BUT A SWD SHIFT IN FUTURE MODEL GUIDANCE COULD RESULT IN

A COMPRESSION OF THE NRN EDGE OF THE SEVERE PROBABILITIES IN

SUBSEQUENT OUTLOOKS.

..JEWELL.. 02/23/2011

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I'm surprised SPC went with the MDT

On Day 2... in February :thumbsup:

45% hatched is a bold call, but it could verify with the severe winds. Won't expect them to go higher with it, though.

06z NAM soundings showing 50 kt SW winds around 900mb... easy mix down to the SFC with those boomers rolling through.

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I'll start really considering my target after the 12Z run start rolling in and I can get a hold of some higher resolution data (4 km WRF, HRRR) to see what they're showing, but my gut is telling me I may end up just south and east of Little Rock tomorrow afternoon. Any chase is gonna be a one hit wonder, as there is no way to follow the storms with those kinds of motions in Arkansas.

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I'll start really considering my target after the 12Z run start rolling in and I can get a hold of some higher resolution data (4 km WRF, HRRR) to see what they're showing, but my gut is telling me I may end up just south and east of Little Rock tomorrow afternoon. Any chase is gonna be a one hit wonder, as there is no way to follow the storms with those kinds of motions in Arkansas.

Sounds like the best place to me (especially being on the eastern side). Unfortunately you'll be battling plenty of cloud cover in addition to the terrain. Good luck!

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MEM...I think they will get above 70

also they talk about a pre-frontal trough where veered SW winds hit SSE winds

also another line of storms could form west of that too

WIND FIELDS ARE PROGGED TO INTENSIFY ALONG AND SOUTH OF THE FRONT

IN THE WARM SECTOR...WITH NORTHEAST MISSISSIPPI HAVING THE BEST

CHANCE TO MIX ENOUGH OUT TO SEE SOME SUN THURSDAY AFTERNOON.

INSTABILITY AMOUNTS BETWEEN 400 AND 1000 J/KG SEEM LIKELY IN THE

WARM SECTOR AS TEMPERATURES CLIMB TO NEAR 70 AND DEWPOINTS IN THE

LOW TO MID 60S. THE 0-6KM BULK SHEAR CONTINUES TO BE IMPRESSIVE

WITH WIDESPREAD AMOUNTS OF 60-80 KTS. WITH NO ANTICIPATED CIN AND

VERY LOW LCLS THE ENTIRE WARM SECTOR MAY JUST BEGIN LIGHTING UP

BY NOON THURSDAY...AND CONTINUING LATE INTO THE EVENING AHEAD OF

THE COLD FRONT. BELIEVE THE BEST TIMING FOR ROTATING STORMS WILL

BE IN THE EARLY EVENING ALONG A PREFRONTAL TROUGH WHICH IS

FORECASTED TO BE JUST WEST OF THE MISSISSIPPI RIVER BY 26/02Z.

THIS TIMING IS ALSO COINCIDENTAL WITH A 50+ LLJ IN THE

MISSISSIPPI DELTA. DISCRETE SUPERCELLS WILL HAVE THEIR BEST

ENVIRONMENT DURING THIS TIME LEADING TO TORNADO FORMATION. IT

SHOULD ASLO BE MENTIONED THAT STORM SPEEDS APPEAR TO BE 50+ KNOTS

MAKING IT MORE DIFFICULT TO GET ACCURATE RADAR SAMPLING FOR

WARNINGS. SPOTTER REPORTS WILL BE MUCH MORE CRITICAL IN THE

WARNING PROCESS.

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NE Arkansas seems to be favored near dusk, with activity spreading into Tennesee and Northern Mississippi in the evening.

NAMCN_CE2011022312F036.gif

NAM forecast sounding in NE Arkansas (Stutgart) not super unstable verbatim, but it looks like small errors in temperature would be big, but the low level shear is impressive.

post-138-0-62711300-1298475347.gif

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SWODY2 update looks similar, interesting note on forecast low instabilities/moisture in discussion. Moderate risk looks to have expanded slightly to include or come close to TXK.

snip

GIVEN MID

60S TO NEAR 70F DEW POINTS CURRENTLY PRESENT FROM THE WESTERN GULF

INTO SOUTHERN TEXAS...CURRENT MODEL PROGS MAY BE A BIT LOW ON

BOUNDARY LAYER MOISTURE RETURN INTO THE LOWER MISSISSIPPI VALLEY AND

OZARK PLATEAU BY LATE THURSDAY AFTERNOON AND EVENING.

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Reviewing the 12Z NAM and GFS - they both look incredible when it comes to shear, backing winds as sfc and strong winds aloft. Plenty of moisture now showing up at the edge of the Gulf.

BUT....forecast skew-t plots for LIT and BNA show very little instability during this time. Looks to be a High Shear / Low CAPE setup.

IF...CAPE were to increase then this will be a potentially more severe event.

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Reviewing the 12Z NAM and GFS - they both look incredible when it comes to shear, backing winds as sfc and strong winds aloft. Plenty of moisture now showing up at the edge of the Gulf.

BUT....forecast skew-t plots for LIT and BNA show very little instability during this time. Looks to be a High Shear / Low CAPE setup.

IF...CAPE were to increase then this will be a potentially more severe event.

Instability WILL be higher along and just south of the warm front. November 29, 2010 is a good example. Models had around 750 J/kg of SBCAPE but the Lake Charles sounding around 12-1 PM had over 2,500 J/Kg. There will be a pocket of higher values not being shown on the models. I'll definitely be out chasing tomorrow, most likely along US-82 in Arkansas based off current data.

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SWODY2 update looks similar, interesting note on forecast low instabilities/moisture in discussion. Moderate risk looks to have expanded slightly to include or come close to TXK.

snip

Models are probably underplaying the temp/moisture advection of the strong LL jet... wouldn't be surprised if instability came in both greater and further north than NAM/GFS shows (though NAM usually handles it better).

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Looks like it has a secondary area of convection firing along the 'dryline' in East Texas plus a few cells near the surface low in Oklahoma. :popcorn:

Seen and approved of thumbsupsmileyanim.gif

Incidentally, also shows storms firing along the cold front in N.OK/S.KS this evening, which is supported by OUN's WRF, HRRR, and RUC. May not be severe, but ahhhh... It's almost spring.

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Instability WILL be higher along and just south of the warm front. November 29, 2010 is a good example. Models had around 750 J/kg of SBCAPE but the Lake Charles sounding around 12-1 PM had over 2,500 J/Kg. There will be a pocket of higher values not being shown on the models. I'll definitely be out chasing tomorrow, most likely along US-82 in Arkansas based off current data.

You are most likely correct on the situation. I can't imagine with that strong of a LLJ and the juice that is forming along the Gulf, that instability will not be around. Might not be around LIT, but where they do get sun - it could get really nasty!

Best of luck to you David as you go chasing. It sounds like the NWS is going to need you guys out there in droves to help with the reports!

Be safe everyone!

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NAM_221_2011022318_F30_WSPD_925_MB.png

This is hot off the 18Z run for tomorrow evening. I may have missed it in previous runs, but the NAM is now backing the 925 MB winds more southerly across most of the warm sector, and particularly across Arkansas where my interest is highest. If this is correct, then I would not be at all surprised to see significant tornadoes tomorrow. Hodographs off the 18Z run also look more ominous. Keep in mind this is for 6 PM tomorrow. Convection should have been underway for several hours by this point.

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This is hot off the 18Z run for tomorrow evening. I may have missed it in previous runs, but the NAM is now backing the 925 MB winds more southerly across most of the warm sector, and particularly across Arkansas where my interest is highest. If this is correct, then I would not be at all surprised to see significant tornadoes tomorrow. Hodographs off the 18Z run also look more ominous. Keep in mind this is for 6 PM tomorrow. Convection should have been underway for several hours by this point.

Yeah guidance has clearly trended more amped with this storm as the wave off the coast is clearly stronger than projected and more inline with what previous intense runs suggested from the Euro/UK.

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Time to bring back one of my favorite tools from the last couple seasons.

While it is a small percentage, keep in mind that this factors in the probability of MLCAPE > 1000 (which this time of year we expect to be small). So with < 10% prob of MLCAPE reaching 1000, this sig. tor. ingredients is being dominated by shear and helicity. We know what a dangerous situation low CAPE, high shear scenarios can be.

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Time to bring back one of my favorite tools from the last couple seasons.

While it is a small percentage, keep in mind that this factors in the probability of MLCAPE > 1000 (which this time of year we expect to be small). So with < 10% prob of MLCAPE reaching 1000, this sig. tor. ingredients is being dominated by shear and helicity. We know what a dangerous situation low CAPE, high shear scenarios can be.

Yeah in this type of setup if its showing anything on that map we need to be concerned.

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE MEMPHIS TN

403 PM CST WED FEB 23 2011

.DISCUSSION...

...ROBUST SEVERE WEATHER EVENT ANTICIPATED THURSDAY AFTERNOON AND

EVENING...

ALL OF THE FOCUS FOR THIS FORECAST PERIOD IS FOCUSED UPON

POTENTIAL FOR SEVERE WEATHER AND FLASH FLOODING FROM LATER TONIGHT

THROUGH THURSDAY NIGHT. A POTENT MID LEVEL SHORTWAVE OBSERVED ON

WATER VAPOR IMAGERY OVER THE DESERT SOUTHWEST THIS AFTERNOON WILL

EJECT NORTHEASTWARD ACROSS THE SOUTHERN PLAINS THURSDAY AND INTO

THE MID MISSISSIPPI AND TENNESSEE VALLEY THURSDAY NIGHT. IN

RESPONSE TO THE APPROACHING UPPER LEVEL SHORTWAVE...SURFACE LOW

PRESSURE WILL ORGANIZE OVER OKLAHOMA THURSDAY MORNING. A WARM

FRONT EXTENDING EAST FROM THE SURFACE LOW INTO THE LOWER

MISSISSIPPI VALLEY WILL SURGE NORTHWARD LATE TONIGHT INTO THURSDAY

MORNING AND EVENTUALLY STALL ACROSS NORTHERN PORTIONS OF THE MID

SOUTH BY THURSDAY AFTERNOON. A LOW LEVEL JET WILL INTENSIFY LATER

TONIGHT AND WILL NOSE INTO THE WARM FRONTAL BOUNDARY LATE TONIGHT.

NUMEROUS SHOWERS AND THUNDERSTORMS WITH INCREASING ELEVATED

INSTABILITY ALONG AND NORTH OF THE FRONT WILL RESULT IN HEAVY

RAINFALL LATE TONIGHT. THIS THREAT FOR HEAVY RAIN WILL CONTINUE

ACROSS NORTHEAST ARKANSAS...THE MISSOURI BOOTHEEL...INTO NORTHWEST

TENNESSEE THROUGH EARLY FRIDAY MORNING AS THE FRONT STALLS ACROSS

THIS AREA. THE POTENTIAL WILL EXIST FOR TRAINING CONVECTION WITH A

BROAD AREA OF 2 TO 4 INCHES WITH ISOLATED HIGHER AMOUNTS. THE

FLASH FLOOD WATCH ACROSS AREAS NORTH OF INTERSTATE 40 WILL REMAIN

IN EFFECT FROM MIDNIGHT TONIGHT THROUGH 3 AM CST FRIDAY MORNING.

FURTHER SOUTH...INCLUDING EAST ARKANSAS...SOUTHWEST TENNESSEE...AND

NORTH MISSISSIPPI...WILL LIKELY BECOME ENTRENCHED WITHIN A

WARM/MOIST SECTOR AHEAD OF THE APPROACHING SHORTWAVE AND SURFACE

LOW. THIS WARM SECTOR WILL BE CHARACTERIZED BY TEMPERTURES INTO

THE LOW TO MID 70S AND DEWPOINTS INTO THE LOW AND MID 60S. AS THE

SHORTWAVE EJECTS ACROSS THE SOUTHERN PLAINS...THE SURFACE LOW WILL

DEEPEN AS IT MOVES NORTHEAST FROM OKLAHOMA INTO SOUTHEAST MISSOURI

BY THURSDAY EVENING. THE SHORTWAVE WILL BECOME INCREASINGLY

NEGATIVELY TILTED AS IT APPROACHES THE MID SOUTH THURSDAY

AFTERNOON. AS A COLDER AIRMASS ALOFT OVERSPREADS THE LOW LEVEL

WARM/MOIST SECTOR EXPECT INSTABILITY TO INCREASE APPRECIABLY WITH

SBCAPE BETWEEN 500-1000J/KG DEVELOPING. IN ADDITION...A POWERFUL

MID LEVEL JET STREAK APPROACHING 100KT AND AN ASSOCIATED LOW LEVEL

JET EXCEEDING 60 KNOTS WILL OVERSPREAD THE MID SOUTH BY THURSDAY

AFTERNOON. THIS SHOULD ENHANCE DEEP LAYER WIND SHEAR OVER THE AREA

THAT WILL CONTINUE THROUGH THURSDAY EVENING. ALSO...LOW LEVEL

WINDS SHOULD BACK AHEAD OF THE APPROACHING SURFACE LOW

PRESSURE...WITH 0-1KM STORM RELATIVE HELICITIES IN EXCESS OF

400M2/S2. THIS COMBINATION OF INCREASING INSTABILITY...STRONG DEEP

LAYER SHEAR...AND STRONG LOW LEVEL HELICITY WILL SUPPORT THE DEVELOPMENT

OF SUPERCELL STORM STRUCTURES AS WELL AS SHORT LINE SEGMENTS AS

THE PRIMARY STORM MODES. THESE STORMS WILL BE CAPABLE OF ALL

SEVERE POTENTIALS AS WELL AS HEAVY RAIN AND FLASH FLOODING.

RAINFALL AMOUNTS BETWEEN 1 AND 3 INCHES FALLING IN SHORT DURATION

WILL BE POSSIBLE WITH THE STRONGEST CONVECTION. A FLASH FLOOD

WATCH HAS BEEN ISSUED FOR AREAS ALONG AND SOUTH OF INTERSTATE 40

FROM NOON THURSDAY THROUGH 3 AM CST FRIDAY MORNING.

AS ANY RESIDUAL CAPPING ACROSS THE WARM SECTOR ERODES BY THURSDAY

AFTERNOON...EXPECT DISCRETE SUPERCELL THUNDERSTORMS TO DEVELOP WITHIN THE

WARM SECTOR ACROSS WESTERN PORTIONS OF THE AREA BY MID AFTERNOON.

THESE INITIAL STORMS WILL HAVE A THREAT OF TORNADOES...A FEW WHICH

COULD BE STRONG...DAMAGING WINDS...LARGE HAIL...AND HEAVY

RAINFALL. THESE DISCRETE STORMS WILL MOVE EAST OF THE MISSISSIPPI

RIVER BY EVENING FOLLOWED BY A BROKEN LINE OF SEVERE STORMS WITH

EMBEDDED SUPERCELLS. THE THREAT FOR ISOLATED TORNADOES...DAMAGING

WINDS...LARGE HAIL...AND HEAVY RAIN WILL CONTINUE. ALL SEVERE

WEATHER AND HEAVY RAINFALL WILL EXIT TO THE EAST OF THE REGION

EARLY FRIDAY MORNING WITH SURFACE HIGH PRESSURE BUILDING OVER THE

MID SOUTH FOR FRIDAY THROUGH SATURDAY. A PACIFIC ORIGIN AIRMASS

CAN BE EXPECTED WITH NEAR SEASONAL TEMPERATURES.

ANOTHER STRONG STORM SYSTEM WILL EFFECT THE FORECAST AREA SATURDAY

NIGHT THROUGH MONDAY MORNING WITH ADDITIONAL POTENTIAL FOR HEAVY

RAIN AND SEVERE WEATHER DURING THIS PERIOD. STAY TUNED TO LATER

FORECASTS FOR ADDITIONAL INFORMATION REGARDING THIS SEVERE

WEATHER/FLASH FLOODING POTENTIAL.

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Also 850 winds - NAM pumps 850 winds quite high tomorrow night

Nice images showing the potential, especially along and just southeast of the low track. Looks like a pretty classic scenario that if something touches down it will be EF2+ with those wind fields. Pick your model, they are all showing between 30 and 50 knots of 0-1km shear centered around the Bootheel.

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