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Severe Weather Threat... feb 24th-25


janetjanet998

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Of interest

The last image is 0-1km

Images from www.wright-weather.com used with permission

Looks like the hi-res WRF-NMM, so it must be. I didn't know it was available in 1 hr chunks from NCEP.

Beau gets those maps from Wright-Weather.com, a pay service. And for unrelated but nostalgic reasons, a few of ours former home with respect to weather forums back in the early 2000's.

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I think Jackson, TN is an okay target point - somewhere from that center point to 35-40 miles either side seems to be a good bet for tornadoes. Instability prob won't be known until nowcast time - within 6-12 hours of event. Tough call for KY/TN border.

Yeah it's not like Jackson ever gets hit :)

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I know this is Tennessee-centric, but I think it worth posting here anyway. OK, this is my first call--I may make another. The dark red indicates highest risk for severe, the light red indicates a heightened likelihood of severe, and the orange indicates a conditional risk for severe:

23qxc93.png

Discussion

I am using the WRF-NMM, the SREF, and forecast products by the NWS as guidance for my forecast.

Guidance indicates a surface low forming in Oklahoma and deepening as it moves northeast toward southeast Missouri during the day on Thursday. There will be warm air advection across the risk area tomorrow, bringing in ample moisture. There will be a mid-level jet streak near 100 kt and a low-level jet stream over 60 kt, creating strong deep layer shear. There will be a shortwave to the west that will be bring cooler air into the upper atmosphere, helping to destabilize it. Low level winds will back ahead of the storms, creating heightened low-level helicity. There will be ongoing precipitation across the area during the morning and early afternoon, but it will affect the northern and eastern areas most. The WRF-NMM shows multiple rounds of thunderstorms forming across Arkansas and the Mid-South during the day tomorrow. The SREF shows heightened SIGTOR tomorrow >= 2, with the SIGTOR's as high as 2 inching into extreme southwest Tennessee and extreme northwest Mississippi during the early evening.

Because of this, the threat is highest during the afternoon in central and southern Arkansas where the daytime heating will be maximized. A lesser threat fingers east into the Memphis metro, with the condition that if there are gaps in the clouds, one or more of the multiple rounds of thunderstorms might be severe. Finally, the system should be weakening as it moves east, but if there are breaks in the cloud cover and storms can form, then those areas would have problems, too.

Any comments or criticisms welcome.

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One area that might sneak up on people early on is back in OK. Storms will probably initiate early at around 18z or so in eastern OK near the intensifying surface low. This is also in a region of very steep lapse rates associated with the cold pool aloft, resulting in a local maximum of CAPE. Low-level helicity should be very high with the backing of the surface winds and intensifying low-level jet. These will probably be more mini-supercellular in structure given the intense shear.

It'll be interesting to see how much clearing there'll be over much of the warm sector tomorrow. The forecasted RH fields in the mid-levels from the NAM, GFS, and RUC (especially) suggest some clearing most likely in the southeastern half of AR, northern MS, and perhaps into SW TN. The 00z 4km WRF run keeps these areas pretty clean through 22z as well.

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One area that might sneak up on people early on is back in OK. Storms will probably initiate early at around 18z or so in eastern OK near the intensifying surface low. This is also in a region of very steep lapse rates associated with the cold pool aloft, resulting in a local maximum of CAPE. Low-level helicity should be very high with the backing of the surface winds and intensifying low-level jet. These will probably be more mini-supercellular in structure given the intense shear.

yeah I was watching that as well, the warm sector is expanded farther north on both the GFS/NAM 00z runs across OK when compared to the 18z run.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1145 PM CST WED FEB 23 2011

VALID 241200Z - 251200Z

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

WRN

TN...SMALL PART OF SERN MO...NRN MS...

...THERE IS A SLGT RISK OF SVR TSTMS ERN PARTS OF THE SRN PLAINS TO

THE LWR OH VLY...LWR MS VLY...MID-SOUTH...

..SYNOPSIS

FORMIDABLE MID-LEVEL SHORTWAVE TROUGH CURRENTLY OVER THE DESERT SW

IS EXPECTED TO EJECT ENE ACROSS THE CNTRL/SRN PLAINS THIS AFTERNOON

AND ACROSS THE LOWER/MID-MS VLY BY TONIGHT. IN THE LOWER LEVELS...A

LOW OVER WCNTRL OK EARLY THIS MORNING WILL INTENSIFY AND MIGRATE

INTO SRN MO BY LATE AFTERNOON AND TO THE MID-OH VLY BY 12Z/25. TO

THE E OF THE LOW...A WARM FRONT WILL ADVANCE NWD TO ALONG THE MO/AR

BORDER BY LATE MORNING AND THE OH VLY LATER IN THE DAY. A

PRE-FRONTAL TROUGH WILL MOVE EWD FROM E TX/OK EARLY IN THE DAY TO

THE MID-SOUTH AND TN VLY BY TONIGHT.

..ERN OK/TX EWD INTO THE MID-SOUTH/TN VLY

STRONG SLY LOW-LEVEL FLOW IN ADVANCE OF THE APPROACHING MID-LEVEL

WAVE WILL TRANSPORT LOWER AND MIDDLE 60S SFC DEW POINTS AS FAR N AS

ERN OK...NRN AR AND WRN TN/KY AHEAD OF THE ADVANCING PRE-FRONTAL

TROUGH TODAY. THIS WILL CONTRIBUTE TO SUFFICIENT INSTABILITY TO

SUPPORT A WIDESPREAD TSTM THREAT AS 90-120 METER MID-LEVEL HEIGHT

FALLS SPREAD ENE TODAY AND TONIGHT ACROSS THE SRN PLAINS TO THE

MID-SOUTH/TN VLY.

TSTMS WILL INCREASE IN THE PRE-DAWN HOURS OVER PORTIONS OF WRN

OK/NWRN TX NEAR THE SFC LOW AND DRYLINE/TROUGH AS THE LARGE-SCALE

ASCENT/STEEP MID-LEVEL LAPSE RATES BEGIN TO IMPACT WRN PERIPHERY OF

MOIST PLUME. THE STORMS WILL LIKELY PRODUCE HAIL DURING THE MORNING

HOURS OVER CNTRL OK AND NCNTRL TX OWING TO FAVORABLE MID-LEVEL LAPSE

RATE ENVIRONMENT.

THE MORNING STORMS WILL LIKELY INTENSIFY WITH ADDITIONAL SFC-BASED

ACTIVITY SPROUTING DURING THE LATE MORNING/AFTERNOON FROM NERN TX

INTO WRN/CNTRL AR ALONG THE PRE-FRONTAL TROUGH. THESE STORMS WILL

PROBABLY OFFER THE BEST OPPORTUNITY FOR HIGHER-IMPACT SEVERE THREATS

AS THEY MATURE OVER NRN LA...CNTRL/ERN AR...NWRN MS AND WRN TN

DURING THE LATE AFTERNOON-MID-EVENING HOURS. SSWLY 850 MB FLOW IN

EXCESS OF 55 KTS BENEATH INCREASING SWLY MID-LEVEL FLOW WILL BOOST

OVERALL DEEP-LAYER SHEAR FOR SUPERCELLS. DISCRETE STORMS THAT

DEVELOP CLOSE TO THE WARM FRONT...LIKELY IN CNTRL/NERN AR AND WRN

TN...WILL BE EMBEDDED IN 200-300 M2/S2 0-1KM SRH AND WILL OFFER THE

GREATEST OPPORTUNITY FOR STRONG TORNADOES.

ACTIVITY SHOULD EVOLVE INTO A QLCS DURING THE MID-EVENING AND MOVE

QUICKLY ENE INTO THE TN VLY/DEEP SOUTH OVERNIGHT. THERE WILL REMAIN

A THREAT FOR DAMAGING WINDS/HAIL WELL INTO THE NIGHT...ESPECIALLY

OVER PARTS OF MIDDLE TN...MS AND WRN AL. GIVEN THAT THE STRONG

FORCING WILL EJECT NEWD TOWARD THE OH VLY...ISOLD DMGG WIND GUSTS

WILL BE POSSIBLE AS FAR N AS THE OH RVR AS WELL...THOUGH BETTER

INSTABILITY WILL BE FARTHER S.

..RACY/COHEN.. 02/24/2011

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Poor Jackson - have had friends down when they have been hit. Just the wrong place to live I guess. They have had it rough

Trying to juggle the flash flood threat with the storms - at least we wont be right in the middle of this outbreak

Now the Sunday event - could be a different beast.

Going to be a long six days.

I forget, what is it 3 F4s since 1999?

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Exciting day of work tomorrow :) here in Nashville!

I'll be right in the middle of downtown (our office), and if it goes through Jackson, it nearly always produces a few warnings in Nashville metro.

Seems like everything keeps moving a tad bit east with the updated forecasts, so it's not out of the realm that this becomes a significant event for Nashville.

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MESOSCALE DISCUSSION 0122

NWS STORM PREDICTION CENTER NORMAN OK

0307 AM CST THU FEB 24 2011

AREAS AFFECTED...NWRN TX THROUGH WRN AND N-CNTRL OK

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 240907Z - 241100Z

THREAT FOR MAINLY ISOLATED LARGE HAIL AND POSSIBLY ISOLATED STRONG

WIND GUSTS MAY INCREASE THROUGH EARLY MORNING FROM NWRN TX INTO WRN

AND N-CNTRL OK. ANY WW ISSUANCE REMAINS UNCERTAIN AT THIS TIME...BUT

WILL ULTIMATELY DEPEND ON CONVECTIVE TRENDS.

COLD FRONT EXTENDS FROM MID-MS VALLEY SWWD THROUGH CNTRL OK THEN WWD

AS A STATIONARY FRONT FROM WRN OK INTO THE TX PANHANDLE. UPPER

50S-LOW 60S BOUNDARY LAYER DEWPOINTS HAVE ADVECTED THROUGH

PRE-FRONTAL WARM SECTOR...WHILE STEEP LAPSE RATES ARE ADVECTING EWD

AND INTERCEPTING THE MOIST AXIS ACROSS SWRN OK AND NWRN TX RESULTING

IN RESERVOIR OF 1500 J/KG MUCAPE. STORMS ARE CURRENTLY DEVELOPING

WITHIN TWO DISTINCT REGIMES. THE FIRST IS ACROSS WRN TX WHERE

MID-LEVEL ASCENT ACCOMPANYING A NEWD EJECTING VORT MAX IS

INTERACTING WITH THE STEEP LAPSE RATE ENVIRONMENT...RESULTING IN

HIGH BASED STORMS NEAR LUBBOCK. THE OTHER IS OVER NRN OK INTO SRN KS

WHERE THETA-E ADVECTION AND ISENTROPIC ASCENT ALONG LLJ AXIS IS

CONTRIBUTING TO ELEVATED STORMS NORTH OF THE FRONT. WITH TIME...THE

DEEPER ASCENT WILL BEGIN TO INTERACT WITH THE MOISTER AND MORE

UNSTABLE THERMODYNAMIC ENVIRONMENT...WHICH COULD RESULT IN THE

DEVELOPMENT OF STRONGER STORMS FROM NWRN TX INTO WRN OK. STEEP MID

LEVEL LAPSE RATES...MODERATE MUCAPE AND SUFFICIENT EFFECTIVE SHEAR

FOR UPDRAFT ROTATION WILL PROMOTE A THREAT FOR ISOLATED LARGE HAIL

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