Feb 22nd-24th Severe Thread

[andyhb]

Large 30% area with sig-hatched across much of the Deep South for Thursday Evening/Overnight:

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0230 AM CST TUE FEB 21 2012

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM SRN AND ERN TX INTO A

PORTION OF THE SERN STATES...

...SYNOPSIS...

MODELS HAVE CONVERGED TO SIMILAR SOLUTIONS WITH REGARD TO EVOLUTION

OF SYNOPTIC PATTERN. BROAD UPPER TROUGH WILL REMAIN DOMINANT...AND

THIS FEATURE IS FORECAST TO AMPLIFY OVER THE MS VALLEY AS A STRONG

UPPER JET DROPS SEWD THROUGH THE INTERMOUNTAIN WEST...REACHING THE

SRN PLAINS TOWARD THE END OF THE PERIOD. MEANWHILE...SWLY LLJ WILL

STRENGTHEN OVER THE SERN STATES AND OH VALLEY IN ASSOCIATION WITH

THE AMPLIFYING NRN STREAM TROUGH. ECMWF HAS TRENDED TOWARD A SLOWER

EJECTION OF SRN STREAM UPPER LOW THAT WILL CUTOFF OVER NRN MEXICO

AND IS NOW SIMILAR TO THE GFS WITH THE NAM STILL BEING THE SLOWEST

MODEL. THE UPPER LOW WILL LIKELY REACH SRN TX LATER THURSDAY NIGHT.

AT THE SURFACE PRIMARY CYCLONE IS FORECAST TO CONSOLIDATE OVER THE

OH VALLEY OR GREAT LAKES WHILE A TRAILING COLD FRONT ADVANCES SEWD

THROUGH THE SRN PLAINS...LOWER MS VALLEY AND INTO WRN PORTIONS OF

THE SERN STATES.

...SERN STATES...

POTENTIAL FOR SIGNIFICANT SEVERE WEATHER WILL EXIST THURSDAY EVENING

AND OVERNIGHT.

STRENGTHENING SWLY BOUNDARY LAYER WINDS WILL CONTRIBUTE TO NEWD

TRANSPORT OF MODIFYING GULF AIR WITH DEWPOINTS FROM THE UPPER 60S

OVER SRN AND ERN TX INTO THE GULF COASTAL STATES TO NEAR 50 OVER SRN

PORTIONS OF THE OH VALLEY. GREATEST INSTABILITY WILL LIKELY DEVELOP

OVER THE LOWER MS VALLEY REGION JUST AHEAD OF THE FRONT WHERE PLUME

OF STEEPER LAPSE RATES WILL ADVECT EWD AND OVERTAKE THE WRN EDGE OF

THE MOIST AXIS. MLCAPE IN THIS REGION COULD RANGE FROM 1000-1500

J/KG. HOWEVER...THE RETURNING LOW LEVEL MOISTURE MIGHT CONTRIBUTE TO

THE DEVELOPMENT OF CLOUDS OVER A PORTION OF THIS REGION...AND THE

ATMOSPHERE WILL LIKELY REMAIN CAPPED TO SURFACE BASED CONVECTION

MUCH OF THE DAY. MODEL CONSENSUS IS THAT STORMS WILL DEVELOP BY

EARLY EVENING IN ZONE OF HEIGHT FALLS AND INCREASING FRONTAL

CONVERGENCE ASSOCIATED WITH THE AMPLIFYING WAVE AND STRENGTHENING

LLJ. ACTIVITY WILL EXIST WITHIN A STRONG KINEMATIC ENVIRONMENT AS

LLJ INCREASES TO IN EXCESS OF 50 KT WITH STRONG DEEP LAYER WINDS AND

VERTICAL SHEAR. THIS ENVIRONMENT WILL SUPPORT ORGANIZED STORMS

INCLUDING SUPERCELLS AND BOWING STRUCTURES WITH UPSCALE GROWTH

LIKELY OVERNIGHT. LARGE HAIL...DAMAGING WIND AND A FEW TORNADOES

WILL BE POSSIBLE AS STORMS DEVELOP EWD.

...OH VALLEY...

MOISTURE AND INSTABILITY WILL BE MORE LIMITED WITH NWD EXTENT INTO

THE OH VALLEY WITH MUCAPE AOB 500 J/KG LIKELY. FORCING WITHIN

FRONTAL ZONE WILL PROMOTE A LOW TOPPED LINE OF CONVECTION EMBEDDED

WITHIN STRONG VERTICAL SHEAR DURING THE AFTERNOON AND EVENING.

DESPITE THE LIMITED INSTABILITY SOME THREAT WILL EXIST FOR ISOLATED

DAMAGING WIND. LOW SEVERE PROBABILITIES HAVE BEEN INTRODUCED...BUT

AREA MAY NEED TO BE INCLUDED IN A SLIGHT RISK IN LATER OUTLOOKS.

...TX...

A FEW STORMS WILL PROBABLY DEVELOP ALONG SWRN EXTENSION OF THE FRONT

INTO ERN AND SRN TX WHERE STEEP LAPSE RATES AND A MOIST BOUNDARY

LAYER WILL PROMOTE MODERATE INSTABILITY. HOWEVER...THE ATMOSPHERE IN

THIS REGION WILL BE MORE CAPPED AND COVERAGE OF STORMS...ESPECIALLY

ACROSS SRN TX WILL BE MODULATED BY TIMING OF SRN STREAM WAVE. ANY

STORMS THAT DEVELOP WILL BE CAPABLE OF MAINLY ISOLATED DAMAGING WIND

AND HAIL.

..DIAL.. 02/21/2012

[andyhb]

Day 4 as well:

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0309 AM CST TUE FEB 21 2012

VALID 241200Z - 291200Z

...DISCUSSION...

/DAY 4/

A THREAT FOR SIGNIFICANT SEVERE STORMS WILL LIKELY PERSIST OVER ERN

PORTIONS OF THE SERN STATES FROM NRN FL...GA INTO THE CAROLINAS AND

THE DELMARVA REGION IN ASSOCIATION WITH AMPLIFYING UPPER TROUGH AND

ATTENDANT STRENGTHENING KINEMATIC FIELDS WITHIN MOIST WARM SECTOR.

[andyhb]

Tremendous LLJ on the 00z Euro at 96 hrs (shift it back westward across the Carolinas at 90 hrs and peak heating and that looks damn ugly):

[metalicwx366]

NWS Jacksonvile......

.LONG TERM...FRIDAY THROUGH MONDAY

FRIDAY IS BEGINNING TO SHAPE UP AS A NASTY DAY AS A STRONG COLD

FRONT PUSHES THROUGH. TIGHT GRADIENT AHEAD OF THE FRONT WILL

RESULT IN WINDY CONDITIONS WITH GUSTS OVER 40 MPH. TEMPERATURES

WILL PUSH INTO THE 80S AHEAD OF THE COLD FRONT (POSSIBLY MID TO

UPPER 80S OVER SOUTHEAST PORTIONS OF THE AREA). A STRONG LOW LEVEL

JET (50 KTS AT 850 MB) WILL ACCOMPANY THIS SYSTEM. ALSO OF

CONCERN IS THAT THE AREA WILL BE WITHIN THE RIGHT ENTRANCE REGION

OF THE UPPER LEVEL JET AXIS. STRONG TO SEVERE STORMS WILL BE A

CONCERN IF THIS SOLUTION HOLDS AND THE FRONT COMES THROUGH DURING

THE DAY. EVEN WITHOUT SEVERE STORMS...DANGEROUS WIND GUSTS WILL BE

POSSIBLE EVEN OUTSIDE OF CONVECTION. LOCAL INTERESTS SHOULD

CONTINUE TO MONITOR THIS DEVELOPING SITUATION.

[downeastnc]

Some snippets from MHXand ILM overnight disco........ sounds like the timing and conditions could be prime for a rough afternoon gonna be interesting to see how the models evolve the threat..

MHX

HOWEVER...THE BEST DYNAMICS LOOKS TO BE

FRIDAY AFTERNOON/EVENING AHEAD OF THE FRONT WITH AN IMPRESSIVE LOW

LEVEL JET SIGNATURE. THE 00Z EURO WITH AROUND A 90 KT 850MB JET

ALONG THE COASTAL PLAIN...AND THE GFS NOT FAR OFF AROUND 80KTS

OFFSHORE. THIS ALONG WITH PLENTY OF SFC BASED LIFT...PWATS AOA

1.5"...AND UPPER LEVEL FORCING WILL INCREASE THE CHANCE FOR AMPLE

AMOUNT OF FORCING. HAVE PLACED MUCH OF THE CWA IN ISO THUNDER WITH

MARGINAL CAPE VALUES THIS FAR OUT.

ILM

HAVE BEEN

EXAMINING CONVECTIVE POTENTIAL BASED OFF PREVIOUS DISCUSSION...AND

TEND TO AGREE THAT IT IS STILL A BIT EARLY TO MENTION THUNDER IN THE

FORECAST DUE TO CONTINUING TIMING ISSUES AND UNCERTAINTY...BUT WILL

DISCUSS HERE THE POTENTIAL.

STRONG LOW LEVEL CONVERGENCE AHEAD OF THIS BOUNDARY IN A WARM AND

RATHER HUMID AIRMASS WILL SUPPORT DEEP LIFT OF PARCELS. THIS OCCURS

IN CONJUNCTION WITH A MODELED 60 KT LLJ MOVING OVERHEAD...AND THE

CAROLINAS ENTERING THE RIGHT ENTRANCE PORTION OF A 130KT 300MB JET

STREAK. ADDITIONALLY...FORECAST SOUNDINGS DEPICT THAT SURFACE BASED

INSTABILITY WILL BE PRESENT...AND MID-LEVEL LAPSE RATES WILL

APPROACH 7C/KM. HOWEVER...THE COMBINATION OF SOME TIMING ISSUES

(IE...WILL IT SLOW TO A NOCTURNAL EVENT)...BEST MOISTURE BEING WELL

AHEAD OF THE FRONT...AND BEST UPPER SUPPORT MISSING TO THE

NORTH...PROMPTS ONLY HIGH CHANCE OF CONVECTIVE SHOWERS AS THE POP/WX

FOR NOW. IF THUNDER BECOMES MORE LIKELY...THE PRESENCE OF THE STRONG

LLJ WOULD PROMOTE THE POTENTIAL FOR DAMAGING WINDS...BUT IT IS FAR

TOO EARLY TO ADDRESS THIS IN ANY FORECAST.

[audioguy3107]

FFC still unimpressed as usual:

GFS SHOWS AROUND 200 SURFACE BASED CAPE NOSING UP INTO THE ATLANTA AREA JUST AHEAD OF THE FRONT ON FRIDAY. THIS COUPLED WITH A 50KT LOW LEVEL JET AND MODERATE UPPER SHORT-WAVE SUPPORT HAS WARRANTED

ADDING A SLIGHT CHANCE OF THUNDERSTORMS TO THE ZONES ON FRIDAY.

...while BHM ramping up their wording:

...MODERATE DEGREE OF INSTABILITY TO SUPPORT THUNDERSTORMS AS A SURFACE COLD FRONT APPROACHES AND MOVES THROUGH THE AREA THURSDAY NIGHT. WIND AND BULK SHEAR CHARTS ALSO SUGGEST AN INCREASING

THREAT OF SEVERE STORMS...INCLUDING TORNADOES. THE SPC DAY 3 OUTLOOK LAYS OUT THE PARTICULARS RATHER WELL. AND WHILE THERE ARE STILL MANY TIMING AND POSITIONING DETAILS TO BE WORKED OUT...I THINK IT IS PRUDENT TO KICK OUR HWO WORDING AND THREATS UP A NOTCH.

[kanc2001]

early thoughts are the cold (relatively speaking) marine layer for us near the beach will stabilze the atmosphere to below severe levels.

[RevDodd]

The folks in Raleigh are taking a cautious approach, citing low CAPE vales:

"MODELS SHOW ANOTHER SOUTHERN STREAM UPPER LEVEL TROUGH/LOW DIGGING INTO THE SOUTHWESTERN UNITED STATES AND NORTHERN MEXICO TUESDAY INTO WEDNESDAY AND EVENTUALLY EJECTING EASTWARD AND AFFECTING CENTRAL NORTH CAROLINA THURSDAY INTO FRIDAY. DURING THE SAME TIME FRAME...A NORTHERN STREAM TROUGH WILL AMPLIFY AS IT MOVES INTO THE CENTRAL UNITED STATES...PROMOTING SURFACE CYCLOGENESIS ACROSS THE TENNESSEE AND OHIO VALLEY. THE ASSOCIATED SURFACE COLD FRONT IS FORECAST TO MOVE THROUGH CENTRAL NORTH CAROLINA FRIDAY AFTERNOON AND EVENING.

ALL OF THIS WILL RESULT IN PRECIPITATION CHANCES INCREASING LATE THURSDAY...WITH THE BEST TIME FRAME FOR SHOWERS COINCIDING WITH THE FRONTAL PASSAGE DURING THE DAY ON FRIDAY. AHEAD OF THE FRONT...STRONG SOUTHWESTERLY SURFACE FLOW WILL PUSH TEMPERATURES INTO THE UPPER 60S TO LOWER 70S ACROSS AREA ON BOTH THURSDAY AND FRIDAY. ALSO...MOISTURE WILL POOL AHEAD OF THE APPROACHING FRONT...WITH MAXIMUM PRECIPITABLE WATER VALUES FORECAST TO RANGE BETWEEN ONE AND ONE AND A HALF INCHES. THIS SHOULD RESULT IN SOME WEAK INSTABILITY OVER EASTERN NORTH CAROLINA...ALTHOUGH CURRENT FORECAST SOUNDINGS SHOW VERY MARGINAL CAPE VALUES. NEVERTHELESS...WILL MAINTAIN THE MENTION OF A SLIGHT CHANCE OF THUNDER ACROSS THE COASTAL PLAIN...ESPECIALLY SINCE THE FRONTAL PASSAGE IS EXPECTED TO OCCUR DURING A FAVORABLE TIME OF DAY.

[audioguy3107]

The forecast high on Thursday for this area is around 71 degrees....definitely warmer than the last several of our winter threats. I'm at work and haven't taken a look at any of the models to see whether a CAD could squash any instability or not. With highs in the lower 70's I would think instability should be a little higher.

[jrips27]

Impressive outlook from the SPC. I can't remember the last time I was in a 30% hatched area at Day 3.

Spann's thinking: http://www.alabamawx.com/?p=57212

I thought this was interesting...

"IMPORTANT NOTE: I have stated that I will no longer say “this is event is NOTHING like April 27″. I can say that about every severe weather threat on my watch for the rest of my life, most likely. I think the people of Alabama clearly understand this now. There won’t be any more April 27 type events for a long time, but there will be many tornado threats every year, and we have to pay attention to all of them. It just takes one tornado for that event to become one families “April 27″.

[Shawn]

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE COLUMBIA SC

207 PM EST TUE FEB 21 2012

THEN THE RAIN

CHANCES SHOULD BEGIN TO INCREASE THURSDAY NIGHT IN ADVANCE OF THE

NEXT SYSTEM. MODELS STARTING TO COME INTO BETTER AGREEMENT FOR THE

SYSTEM LATE THURSDAY INTO FRIDAY...ALTHOUGH THERE IS STILL SOME

TIMING AND STRENGTH DETAILS. WILL CONTINUE TO GO WITH CHANCE POPS

FOR THE END OF THE WEEK. EXPECTING MAINLY SHOWERS WITH THIS

SYSTEM...ALTHOUGH CAN NOT RULE OUT A LITTLE THUNDERSTORM ACTIVITY

ALONG THE FRONT.

Does anyone know where to find the STP (significant tornado) maps etc that Spann used in that video?

Nevermind, they're located at http://www.wxcaster.com/weather.php3

[NavarreDon]

GSP is starting to look at Thurs. in the short term:

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...

AS OF 230 PM TUESDAY...A WARM AND MOIST AIR MASS WILL DEVELOP OVER

THE REGION DURING THE MID WEEK. WEDNESDAY EVENING...A SHORT WAVE IS

EXPECTED TO RIPPLE WITHIN A LONGWAVE TROF AXIS ACROSS THE SOUTHERN

APPALACHIAN REGION DURING THE EARLY EVENING HOURS. GUSTY SOUTHWEST

WINDS ARE FORECAST TO BRING RISING DEWPOINTS ACROSS THE FORECAST

AREA...GENERALLY RANGING IN THE MID TO UPPER 40S. AN AREA OF

TSRA/SHRA IS EXPECTED TO DEVELOP DURING THE AFTERNOON UPSTREAM OF

THE REGION...STEERING FLOW WILL TRANSPORT THE CONVECTION NORTHEAST

ACROSS GEORGIA AND THE WESTERN CAROLINAS. DURING THE EVENING

HOURS...FORECAST SOUNDINGS INDICATE THAT CAPE VALUES WILL RANGE FROM

100 TO 400 J/KG ACROSS THE CWA. IN ADDITION...SWEAT VALUES WILL PEAK

BETWEEN 300-400 WITH EHI VALUES AROUND 1...THE CORE OF A H3 140 KT

JET WILL REMAIN ACROSS THE MIDLANDS AND COASTAL AREAS. GIVEN THE

BROAD FIELD OF WEAK INSTABILITY AND STRONG WIND FIELDS...IT IS

REASONABLE TO EXPECT ORGANIZED MCS TO SURVIVE INTO THE EVENING HOURS

ACROSS THE CWA. I WILL MAINTAIN CHC POPS ACROSS THE MTNS AND

FOOTHILLS...SCHC EAST OF I-85. THE POTENTIAL EXIST THAT ANY

ORGANIZED CONVECTION COULD PRODUCE DAMAGING WINDS DURING THE

EVENING...SUPPORTED BY SPC DY2 SLIGHT RISK AREA. I WILL HIGHLIGHT

THE RISK FOR DAMAGING TSRA WINDS IN THE HWO.

[downeastnc]

MHX says timing is going to crap looking more like a Friday night threat...

LARGE DETERMINISTIC MODEL SPREAD EXISTS FOR THE ARRIVAL OF A

STRONG COLD FRONT FRIDAY/FRIDAY NIGHT BUT MODEL CONSENSUS FAVORS A

SLOWER SOLUTION WITH THE FRONTAL PASSAGE SOMETIME FRI NIGHT. THE

LATER FRONTAL ARRIVAL SUGGESTS THE POSSIBILITY OF A THREAT OF

SEVERE WEATHER FRIDAY GIVEN THE INCREASING DIURNAL INSTABILITY

COUPLED WITH IMPRESSIVE JET STRUCTURE. LOTS OF TIME TO ADD DETAILS

AS CONFIDENCE INCREASES HEADING INTO FRIDAY BUT FOR NOW HAVE

EXPANDED ISO TSTMS TO INCLUDE THE ENTIRE CWA WHILE MAINTAINING

LIKELY POPS ON FRIDAY WITH DECREASING PCPN CHCS FRIDAY NIGHT.

[audioguy3107]

SPC has bumped up their day 2 outlook with a slight risk for parts of the SE so Wednesday could look a little stormy as well. Looks like another primarily high shear low CAPE situation.

[jrips27]

Any reason to expect a moderate risk in tonight's update? I really can't see it unless something changes on tonight's models.

[audioguy3107]

Any reason to expect a moderate risk in tonight's update? I really can't see it unless something changes on tonight's models.

I wouldnt think so, but of course if the models really ramped up the instability then it would be possible, but as of now I doubt it.

[Buckeye05]

Looks like this is gonna be a QLCS/derecho event.

[Thrasher Fan]

This is my nitch in the weather world and I'm late to the party. Bad job by me.

Here is the latest SPC outlook:

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1146 PM CST TUE FEB 21 2012

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR THE TN VALLEY AND SRN

APPALACHIANS...

...SYNOPSIS...

A BROAD UPPER TROUGH AND ASSOCIATED BELT OF 60+ KT MIDLEVEL WLYS

WILL RESIDE ACROSS THE CNTRL AND ERN CONUS TODAY. A SERIES OF

EMBEDDED IMPULSES WILL RESIDE WITHIN THE TROUGH...WITH ONE OF THESE

FEATURES EXITING THE GREAT LAKES REGION DURING THE AFTERNOON. A

POSITIVELY TILTED TROUGH AXIS EXTENDING SWWD FROM THE GREAT LAKES

DISTURBANCE WILL FRACTURE DURING THE DAY...WITH A SECOND IMPULSE

LOCATED EARLY THIS MORNING OVER THE SRN PLAINS MOVING QUICKLY EWD

ACROSS THE TN VALLEY DURING THE LATE MORNING AND EARLY AFTERNOON.

MEANWHILE...A SECOND UPPER DISTURBANCE WILL MOVE OUT OF THE CNTRL

PLAINS AND INTO THE SERN CONUS BY TONIGHT. IN THE LOW-LEVELS...SWLY

FLOW WILL STRENGTHEN DURING THE DAY FROM THE GULF COAST STATES NEWD

INTO THE MID-ATLANTIC REGION...WHICH WILL ASSIST IN MOISTURE

TRANSPORT INTO THE TN VALLEY AND SRN APPALACHIANS BY AFTERNOON.

...TN VALLEY AND SRN APPALACHIANS...

SURFACE OBSERVATIONS EARLY THIS MORNING SHOW UPR 50S TO MID 60S

DEWPOINTS RESIDING OVER THE GULF COAST REGION. AS LOW-LEVEL SWLY

WINDS INCREASE DURING THE MORNING AND AFTERNOON...THIS MOISTURE WILL

RAPIDLY ADVANCE INTO THE TN VALLEY AND SRN APPALACHIANS WITH MID 50S

DEWPOINTS BECOMING COMMON ACROSS THE REGION. MEANWHILE A SHORTWAVE

IMPULSE WILL MOVE FROM THE SRN PLAINS INTO THE TN VALLEY BY LATE

MORNING/EARLY AFTERNOON. ASCENT ASSOCIATED WITH THIS FEATURE

COMBINED WITH DESTABILIZATION ABOVE AN INITIALLY STABLE NEAR SURFACE

AIRMASS WILL FAVOR ELEVATED THUNDERSTORM DEVELOPMENT OVER PORTIONS

OF ERN AR AND WRN TN/NRN MS.

AHEAD OF THESE STORMS...SURFACE TEMPERATURES WILL WARM INTO THE 60S

OVER MOST OF TN...NERN MS...NRN AL AND NRN GA...FAVORING THE

DEVELOPMENT OF SBCAPE VALUES NEAR 500 J/KG AS MOISTURE CONTINUES TO

ADVECT N-NEWD INTO THE REGION. AS THE WRN IMPULSE MOVES E ACROSS THE

AREA...THIS SHOULD LEAD TO AN INCREASING THREAT FOR SURFACE BASED

THUNDERSTORMS AS THE INITIAL ELEVATED STORM ACTIVITY NEAR THE W END

OF THE SLGT RISK ENCOUNTERS INCREASINGLY BUOYANT BOUNDARY LAYER

PARCELS OVER TN. IN ADDITION STORMS OF A MORE ISOLATED/DISCRETE

NATURE MAY DEVELOP S OF THE THUNDERSTORM ACTIVITY MOVING ACROSS

TN...PARTICULARLY AS A SECOND UPPER DISTURBANCE APPROACHES THE AREA

TOWARD LATE AFTERNOON/EVENING.

MODEL GUIDANCE INDICATES MIDLEVEL WLYS WILL INTENSIFY SLIGHTLY TO

60-90 KT DURING THE AFTERNOON IN RESPONSE TO SEVERAL UPPER IMPULSES

MOVING ACROSS THE ERN HALF OF THE NATION. AS THIS OCCURS...A

LOW-LEVEL SWLY JET WILL ALSO STRENGTHEN TO 40 KT. THIS WIND PROFILE

WILL FAVOR STRONG VERTICAL WIND SHEAR /I.E. 0-6 KM BULK WIND

DIFFERENCE NEAR 70 KT/ AND FAST EWD STORM MOTIONS IN EXCESS OF 40 KT

ACROSS THE WARM SECTOR. THE COMBINATION OF STRONG DEEP-LAYER WLY

FLOW...FAST MOVING STORMS...AND DIURNAL STEEPENING OF LOW-LEVEL

LAPSE RATES WILL SUPPORT A DAMAGING WIND THREAT ACROSS THE SLGT RISK

AREA. IN ADDITION...INCREASING WIND FIELDS TOWARD LATE AFTERNOON

WILL LEAD TO HODOGRAPH STRUCTURE BECOMING VERY FAVORABLE FOR

SUPERCELL THUNDERSTORMS...WITH EFFECTIVE SRH VALUES FORECAST TO

RANGE FROM 200-400 M2 S-2. THUS...LARGE HAIL AND A FEW TORNADOES

WILL ALSO BE POSSIBLE.

...GULF COAST REGION OF MS...AL AND THE FL PANHANDLE...

WEAK ASCENT AND A MOISTENING BOUNDARY LAYER WILL SPREAD INTO THE

GULF COAST REGION OF MS...AL AND THE FL PANHANDLE BY AFTERNOON. AS

SURFACE DEWPOINTS APPROACH THE MID 60S AND TEMPERATURES WARM INTO

THE UPR 60S TO LOW 70S...MLCAPE VALUES NEAR 500 J/KG WILL BE

POSSIBLE...AND WILL AID IN SHOWER DEVELOPMENT WITH EMBEDDED

THUNDERSTORMS. IN ADDITION...AS THE AFTERNOON PROGRESSES LOW-LEVEL

WIND PROFILES WILL GRADUALLY STRENGTHEN...WHICH WILL RESULT IN

SUFFICIENTLY STRONG VERTICAL WIND SHEAR FOR ROTATING UPDRAFTS THAT

MAY POSE A MARGINAL THREAT FOR DAMAGING WIND GUSTS OR A BRIEF

TORNADO.

[andyhb]

New Day 1 graphics:

[andyhb]

30% sig-hatched removed from Thursday's outlook, thermodynamics looking very questionable at this time:

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0102 AM CST WED FEB 22 2012

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN TX INTO A PORTION OF

THE SERN STATES AND SRN PORTIONS OF THE OH VALLEY...

...SYNOPSIS...

TREND HAS BEEN FOR NAM AND GFS TO CONVERGE TO SIMILAR SOLUTIONS

REGARDING EVOLUTION OF BOTH NRN AND SRN STREAMS...WITH THE ECMWF

STILL INDICATING AT LEAST MODEST DIFFERENCES. MODEL CONSENSUS IS

THAT A BROAD UPPER TROUGH WILL AMPLIFY OVER THE ERN STATES AS A

SHORTWAVE TROUGH DROPS SEWD FROM NRN ROCKY MOUNTAIN REGION INTO THE

MID MS VALLEY. HOWEVER...GFS AND NAM REMAIN MORE PROGRESSIVE WITH

NRN STREAM TROUGH THAN THE ECMWF. ECMWF HAS TRENDED TOWARD NAM AND

GFS REGARDING SRN STREAM CUTOFF LOW...AND ALL MODELS NOW INDICATE

THIS FEATURE WILL REMAIN OVER NRN MEXICO THIS PERIOD. SFC LOW

PRESSURE WILL CONSOLIDATE OVER THE OH VALLEY AND LIFT NEWD OVERNIGHT

WITHIN EXIT REGION OF UPPER JET THAT WILL STRENGTHEN ALONG BASE OF

UPPER TROUGH. THE TRAILING COLD FRONT WILL ADVANCE THROUGH A PORTION

OF THE SERN STATES AND TX.

...TN AND OH VALLEYS...

AXIS OF MODEST BOUNDARY LAYER MOISTURE WITH 50-55 F DEWPOINTS WILL

ADVECT THROUGH PRE-FRONTAL WARM SECTOR ACROSS TN AND KY DURING THE

DAY BENEATH 6.5-7 C/KM MID LEVEL LAPSE RATES. THIS WILL RESULT IN

SOME DESTABILIZATION AS THE BOUNDARY LAYER WARMS. HOWEVER...MUCAPE

SHOULD REMAIN AOB 500 J/KG OWING TO LIMITED LOW LEVEL MOISTURE. THE

STEEPER MID LEVEL LAPSE RATES WILL BE ASSOCIATED WITH A REMNANT EML

THAT WILL CAP THE WARM SECTOR. HOWEVER...AN INCREASE IN

FRONTOGENETIC FORCING AND DEEPER ASCENT ASSOCIATED WITH IMPULSE

MOVING THROUGH BASE OF AMPLIFYING TROUGH SHOULD CONTRIBUTE TO

THUNDERSTORM INITIATION FROM KY SWD INTO THE TN VALLEY BY LATE

AFTERNOON. THERMODYNAMIC PROFILES SUGGEST STORMS WILL BE LOWER

TOPPED...BUT ACTIVITY WILL BE EMBEDDED WITHIN STRONG LOW-MID LEVEL

JETS WITH EFFECTIVE SHEAR OF 50+ KT AND SIZEABLE 0-1 KM HODOGRAPHS.

THE MARGINAL THERMODYNAMIC ENVIRONMENT COULD POTENTIALLY SERVE AS A

LIMITING FACTOR...BUT SOME THREAT WILL EXIST FOR MAINLY ISOLATED

DAMAGING WIND...HAIL AND PERHAPS A TORNADO OR TWO THROUGH EARLY-MID

EVENING.

...SERN STATES...

HAVE SCALED BACK ON SEVERE PROBABILITIES DUE IN PART TO POTENTIAL

LIMITING FACTORS LIKELY TO BE IMPOSED BY EXPECTED THERMODYNAMIC

ENVIRONMENT. IT ALSO APPEARS THAT SRN STREAM CUTOFF UPPER LOW NOW

OVER CNTRL BAJA WILL NOT AFFECT THIS REGION LATE THURSDAY NIGHT AS

PREVIOUSLY ADVERTISED BY EARLIER ECMWF RUNS. THE 850 MB TRAJECTORIES

WILL REMAIN WLY UNTIL THURSDAY AFTERNOON WHEN FLOW WILL BEGIN TO

BACK SLIGHTLY IN RESPONSE TO AMPLIFYING TROUGH. THE WLY TRAJECTORIES

SHOULD LIMIT NWD EXTENT OF QUALITY MOISTURE JUST ABOVE THE

SURFACE...BUT RICHER BOUNDARY LAYER MOISTURE SHOULD ADVECT INTO SRN

HALF OF SERN STATES. WARMER AIR ALOFT AT BASE OF EWD ADVECTING EML

WILL CONTRIBUTE TO A CAP OVER MUCH OF THE WARM SECTOR. GIVEN DEEPER

FRONTAL FORCING WILL REMAIN FARTHER NORTH ACROSS TN AND OH

VALLEYS...CONFIDENCE IS NOT HIGH THAT STORMS WILL INITIATE IN THIS

AREA DURING THE AFTERNOON. THUNDERSTORM POTENTIAL MAY INCREASE LATER

THURSDAY NIGHT AS THE COLD FRONT ADVANCES SEWD AND INTERACTS WITH

RICHER MOISTURE RESIDING OVER CNTRL PORTIONS OVER THE SERN STATES.

STRONG VERTICAL SHEAR WILL SUPPORT A THREAT OF ORGANIZED STORMS.

GIVEN STRONG LINEAR FORCING...POTENTIAL EXISTS FOR STORMS TO GROW

UPSCALE...BUT EMBEDDED SUPERCELL AND BOWING STRUCTURES WILL BE

POSSIBLE.

...ERN AND SRN TX...

A FEW STORMS COULD STILL DEVELOP ALONG SWRN EXTENSION OF THE FRONT

INTO SERN AND SRN TX WHERE STEEP LAPSE RATES AND A MOIST BOUNDARY

LAYER WILL PROMOTE MODERATE INSTABILITY. HOWEVER...THE ATMOSPHERE IN

THIS REGION WILL BE MORE CAPPED...AND COVERAGE OF STORMS COULD BE

LIMITED. CURRENT INDICATIONS ARE THAT STORMS MAY INITIATE POST

FRONTAL OVERNIGHT WITHIN ZONE OF DEEPER LIFT. ANY STORMS THAT

DEVELOP WILL BE CAPABLE OF MAINLY ISOLATED HAIL AND GUSTY WINDS.

..DIAL.. 02/22/2012

[NrnILStormChaser]

I am not seeing a major event shaping up here for Thursday. Meager instability, strong unidirectional wind fields, lack of boundary layer moisture, dry air at h85, capping inversion and weak convergence. It is easy to see why the SPC backed off on a bold 30% hatched. As things evolve I can see areas closer to the Gulf lighting up into a linear mess. If storms are able to develop and sustain themselves.... strong winds aloft would promote damaging winds as downdrafts bring those 50-60 kt winds just above the surface down. 2% tor, 15% wind, 5% hail if I had to make an outlook right now

[NavarreDon]

GSP afd for today:

.NEAR TERM /THROUGH TONIGHT/...

AS OF DAYBREAK...A FINGER OF LOW CLOUDINESS WAS DEVELOPING FROM NE

GEORGIA INTO THE UPSTATE...GENERALLY S OF I-85. THE CLOUDS WILL

CONTINUE TO BUILD EAST FOR ANOTHER HOUR OR SO BEFORE THE WARMING

BOUNDARY LAYER LIFTS AND SCATTERS THEM. WE SHOULD GET A WARMER START

THAN THE LAST SEVERAL DAYS...SO THIS WILL HAVE TO BE WATCHED FOR HOW

IT AFFECTS THE HIGH TEMP LATER THIS MORNING.

FOR TODAY AND TONIGHT...WE WILL REMAIN NEAR THE BOTTOM OF A BROAD

LONG WAVE TROF WITH FAST-MOVING FLOW ALOFT...THAT WILL QUICKLY

TRANSPORT A WEAK SHORT WAVE ACROSS THE PLAINS AND EVENTUALLY

OVERHEAD THIS EVENING. AT THE SAME TIME...JET DYNAMICS ARE SOMEWHAT

FAVORABLE WITH ONE JET STREAK MOVING OFF THE CAROLINA COAST AND

ANOTHER DIVING THROUGH THE TROF TO OUR WEST. THIS WILL SET THE STAGE

FOR A FAVORABLE ENVIRONMENT FOR CONVECTION LATER IN THE DAY AS THE

GULF MOISTURE PLUME ADVECTS HIGHER DEWPT AIR AHEAD OF THE

APPROACHING UPPER WAVE. PRECIP CHANCES WILL BE RAMPED UP FROM THE

WEST IN THE AFTERNOON...TO THE CHANCE RANGE OVER THE MTNS AND NE

GEORGIA IN RESPONSE...AND THEN CARRIED OUT OVER THE FOOTHILLS AND

PIEDMONT IN THE EVENING AS THE WAVE PASSES. THE MAIN CONCERN IS OUR

SEVERE WEATHER POTENTIAL. MID LEVEL FLOW WILL INCREASE LATE IN THE

DAY WITH THE SHORT WAVE...WHILE A 40 KT LOW LEVEL JET DEVELOPS FROM

THE SW. THIS SHOULD SET UP A FAVORABLE SHEAR PROFILE. FCST

HODOGRAPHS ARE VERY VERY INTERESTING WITH THE NAM INDICATING STORM

RELATIVE HELICITY IN THE 300 TO 500 M2/S2 RANGE IN THE AFTERNOON AND

EVENING. IF WE COULD PLOP A MOIST UPDRAFT INTO THAT ENVIRONMENT IT

WOULD MOST CERTAINLY ROTATE. THE PROBLEM IS THE MODELS LACK MUCH IN

THE WAY OF SURFACE BASED INSTABILITY...WITH CAPE GENERALLY AROUND

500 J/KG IN THE MORE UNSTABLE NAM. THE THOUGHT THAT SPRINGS TO MIND

IS...WE HAVE DONE MORE WITH LESS. THINK THE SLIGHT RISK FROM SPC

LOOKS A-OK AND WE WILL HAVE TO BE ON THE LOOKOUT FOR MINI-SUPERCELLS

IF THIS COMES TO PASS AS EXPECTED...OR AT LEAST SOME WIND DAMAGE

PRODUCING MULTICELLS. IS IT SPRINGTIME ALREADY? THE CONVECTIVE

ACTIVITY SHOULD WIND DOWN IN THE LATE EVENING WITH THE LOSS OF

INSTABILITY AND WEAKENING SHEAR. TEMPS WILL REMAIN MILD OVERNIGHT

WITH NO REAL FRONTAL PASSAGE.

[NavarreDon]

And GSP for Thur.:

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...

AS OF 230 AM WEDNESDAY...AHEAD OF APPROACHING COLD FRONT...A

FAIR...BREEZY AND WARM DAY REMAINS ON TAP FOR THURSDAY. NEAR RECORD

WARMTH IS EXPECTED AS FTHL/PIEDMONT MAX TEMPS CLIMB THRU THE LOWER

70S. WITHIN THE STRONG DEEP SHEAR...AS THE COLD FRONT ADVANCES SE

THURSDAY NIGHT...TSTM ACTIVITY SHOULD INCREASE IN ACTIVITY ACRS THE

TENN VLY...AND IT REMAINS TO BE SEEN JUST HOW STOUT ANY POTENTIAL

DEEP CONVECTIVE LINE REMAINS AS IT MOVES TOWARD THE NC MTNS AND AWAY

FROM THE BETTER FRONTAL BAND FORCING. IN ADDITION...AS THE FRONT

INTERACTS WITH THE RICHER MOISTURE BUBBLING UP FROM THE SW...

DISCRETE STORMS MAY FORM ACRS AL/GA. INSTABILITY ACRS THE WESTERN

CAROLINAS WILL REMAIN ON THE WEAK SIDE AND AGAIN...JUST NOW FAR NE

ROBUST TSTMS EXTEND FROM THIS ACTIVITY REMAINS A QUESTION. AT ANY

RATE...WILL CONTINUE TO TALK UP THREAT OF SVR STORMS IN THE HWO.

[nrgjeff]

Agree 110%.

I am not seeing a major event shaping up here for Thursday. Meager instability, strong unidirectional wind fields, lack of boundary layer moisture, dry air at h85, capping inversion and weak convergence. It is easy to see why the SPC backed off on a bold 30% hatched. As things evolve I can see areas closer to the Gulf lighting up into a linear mess. If storms are able to develop and sustain themselves.... strong winds aloft would promote damaging winds as downdrafts bring those 50-60 kt winds just above the surface down. 2% tor, 15% wind, 5% hail if I had to make an outlook right now

I'm not sure what they were seeing even back at Day 3. Most of those problems listed above, from uniderectional winds to just-in-time or meager moisture, are symptoms of a terribly positively tilted trough. Euro has a southern piece of energy hanging back, and less positively tilted for the Carolinas Friday; however, the short-term guidance pushes everything along in sloppy positive tilt fashion. I'll be relaxing with my thoughts at home, enjoying this super mild weather, every day after work.

[tornadotony]

I am not seeing a major event shaping up here for Thursday. Meager instability, strong unidirectional wind fields, lack of boundary layer moisture, dry air at h85, capping inversion and weak convergence. It is easy to see why the SPC backed off on a bold 30% hatched. As things evolve I can see areas closer to the Gulf lighting up into a linear mess. If storms are able to develop and sustain themselves.... strong winds aloft would promote damaging winds as downdrafts bring those 50-60 kt winds just above the surface down. 2% tor, 15% wind, 5% hail if I had to make an outlook right now

Couldn't agree more. In fact, I think today has a slightly bigger threat than tomorrow does. Instability will still be rather meager today, but flow will be slightly unidirectional and moisture will be less meager, at least in a relative sense, due to less mixing.

[audioguy3107]

Some pockets of positive CAPE showing up now around the upstate of SC and NE Ga. Sun is breaking through now and temps are on the rise. We'll see what that may bring later this afternoon.

[Cheeznado]

The WSI RPM and HRRR not very impressed with storms for the ATL area- I suspect any severe will stay north of here, at least until 3Z or so.

[Thrasher Fan]

Even the paid pros are having trouble with this situation. Guess they are playing it safe and going with a Meso discussion.

MESOSCALE DISCUSSION 0141

NWS STORM PREDICTION CENTER NORMAN OK

0213 PM CST WED FEB 22 2012

AREAS AFFECTED...PARTS OF NRN MS...THE NRN HALF OF AL...PARTS OF SRN

TN...NWRN GA...FAR WRN NC

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 222013Z - 222215Z

CORRECTED TO CHANGE NS TO MS IN THE AREAS AFFECTED HEADLINE

CONTINUED AIRMASS DESTABILIZATION SUGGESTS INCREASING POTENTIAL FOR

SEVERE STORMS THIS AFTERNOON. WW WILL BE POSSIBLE IN THE NEXT 1-2

HOURS.

LATEST VISIBLE SATELLITE IMAGERY PAIRED WITH SURFACE AND OBJECTIVE

ANALYSES REVEAL A CLEARLY DESTABILIZING BOUNDARY LAYER...BENEATH

WHAT HAS BEEN A PERSISTENT CAPPING INVERSION. AS THE BOUNDARY LAYER

CONTINUES TO WARM/SLOWLY MOISTEN...THE EWD SPREAD OF COOLER

AIR/STEEPER LAPSE RATES ALOFT ASSOCIATED WITH THE WEAK UPPER TROUGH

NOW PROGRESSING ACROSS THE MID MS VALLEY WILL RESULT IN ADDITIONAL

DESTABILIZATION OVER THE NEXT FEW HOURS.

WHILE A LOW-LEVEL FOCUS FOR STORM DEVELOPMENT REMAINS DIFFICULT TO

DISCERN -- AND THUS LOCATION OF A CONCENTRATED THREAT AREA REMAINS

UNCERTAIN...INCREASINGLY STRONG/VEERING FLOW WITH HEIGHT IS

PROVIDING A KINEMATIC ENVIRONMENT SUPPORTIVE OF ORGANIZED/ROTATING

STORMS. THIS -- AND THE INCREASINGLY FAVORABLE THERMODYNAMICS --

SUGGEST THAT ANY STORMS WHICH CAN DEVELOP WILL LIKELY

ORGANIZE/INTENSIFY...WITH DAMAGING WINDS AND HAIL POSSIBLE ALONG

WITH SOME ISOLATED TORNADO POTENTIAL.

ATTM...CU FIELD APPEARS MOST ROBUST ACROSS NERN MS AND EWD ACROSS

NRN AL AND INTO THE SRN APPALACHIANS. WITH THIS AREA ON THE NRN

FRINGE OF THE BETTER THERMODYNAMIC ENVIRONMENT AND NEAR THE SRN

BOUNDARY OF STRONGER UPPER FORCING ASSOCIATED WITH THE PROGRESSING

WAVE...THIS AREA APPEARS ATTM TO BE THE MOST LIKELY INITIATION ZONE

FOR INITIAL CONVECTION.

[tornadotony]

[Buckeye05]

Nastiest looking storms are in Florida right now lol.