2/20-21/13 Southern Plains-Dixie Alley Severe Threat

[thunderman]

The area of low pressure that we are all watching for winter weather possibilities next towards next weekend, looks as if it may have quite the significant severe weather side as well on Thursday. The area of interest will be from east Texas into Dixie Alley.

As we saw with the last event on Sunday, there looks to be a small area of sufficient moisture return along and ahead of the front across LA, MS, AL, southern AR, and east TX. This area of better moisture/theta-e looks to also be co-located with 50+ knts of mid/upper level shear with surface winds containing an easterly component … yielding large and open hodographs. It still remains to be seen how much forcing we get into this area. If storms can manage to stay semi-discrete and surface based then we could be looking at another round of tornadoes … with strong to violent tornadoes in the cards.

Definitely need to keep an eye on this.

[Ed Lizard]

Just looking at AccuWx PPV (and have looked at GFS products), lots of wind energy, apparently 'meh' lapse rates and temps struggling to reach 70.  Euro CAPE near or below 500 J/Kg in the South.  Maybe that would be enough with the wind...

 

I didn't have time to capture 12Z GFS, I tried to catch a sounding just ahead of the precip/windshift in Alabama last night.  At least 12Z Euro forecast sounding isn't saturated to 150 mb like this.  I will say, 55 knots around 900 mb, I'd guess heavy rain could produce severe gusts.  Hoping 17 dropsondes in Pacific this after noon make 0Z guidance.

 

 

 

And this is as good as it gets on 18Z GFS.  Seems 70-90 knots of 0-500 mb shear goes unutilized, except I've seen people before say GFS underestimated instability, especially this far out.

 

[andyhb]

That's also at 06z in the morning, Ed.

 

Even so, with the GFS soundings saturated up to 150 mb (which is nonsense), of course the instability outputs are going to take a hit.

 

The 12z Euro actually showed almost 1500 J/kg, nudging into MS on Thursday afternoon/evening, upon looking at Wundermaps.

[Stebo]

A few things, that sounding you posted ED is unrealistically moist. I don't buy for a second that the sounding is going to be moist to 150mb. Plus the map is for 06z, the risk area is back to the West and would me centered around 00z.

[Disc]

150hrs, but still pretty darn impressive.

 

 

[Ed Lizard]

A few things, that sounding you posted ED is unrealistically moist. I don't buy for a second that the sounding is going to be moist to 150mb. Plus the map is for 06z, the risk area is back to the West and would me centered around 00z.

 

I looped that Twister data CAPE, and that really was the best it got.  Looking at new GFS soundings, Friday 0Z (Thursday evening) surface temps in Northern Alabama and Tennesee near/below 15C despite Southerly winds.  BNA in the 40sF.  Even South Alabama looks cool (MOB, DHN).

 

Didn't say I believe in a saturated profile to 150 mb.  Or that GFS surface temps would be correct.

 

On Euro, not sure why AccuPx and Wundermaps are different, unless one is surface or mixed layer, and the other is most unstable.  AccuWx PPV maps leave something to be desired in the labeling.

 

I should figure out the Wundermaps, looks like 3 hour time steps on Euro...

[andyhb]

DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0354 AM CST SAT FEB 16 2013
  
   VALID 191200Z - 241200Z
  
   ...DISCUSSION...
   THE LATEST MEDIUM RANGE MODELS AND MODEL ENSEMBLES REMAIN FAIRLY
   CONSISTENT WITH RUNS OVER THE PAST SEVERAL DAYS...PARTICULARLY WITH
   REGARD TO A STRONG SHORT WAVE IMPULSE THAT APPEARS LIKELY TO DIG
   INTO THE CALIFORNIA COAST EARLY NEXT WEEK.  A DEEP MID-LEVEL CLOSED
   LOW MAY EVOLVE AS THE IMPULSE MIGRATES INLAND...BUT IT IS EXPECTED
   TO REMAIN PROGRESSIVE...AS ANOTHER IMPULSE EMERGES FROM THE STRONG
   UPSTREAM MID-LATITUDE PACIFIC JET...AND APPROACHES THE PACIFIC
   NORTHWEST COAST BY MID WEEK.  
  
   IN ASSOCIATION WITH THE LEAD SYSTEM...WHICH STILL APPEARS LIKELY TO
   LIFT EAST NORTHEAST OF THE SOUTHERN ROCKIES THROUGH THE CENTRAL
   PLAINS/MID MISSOURI VALLEY REGION LATE WEDNESDAY NIGHT THROUGH EARLY
   THURSDAY EVENING...SIGNIFICANT SURFACE CYCLOGENESIS APPEARS LIKELY
   ACROSS THE CENTRAL PLAINS.  THIS MAY BE ACCOMPANIED BY INCREASING
   CONVECTIVE POTENTIAL...INCLUDING AT LEAST SOME RISK FOR SEVERE
   STORMS...ACROSS PARTS OF THE CENTRAL AND SOUTHERN PLAINS LATE
   WEDNESDAY/WEDNESDAY NIGHT.  HOWEVER...IT STILL APPEARS MOST PROBABLE
   THAT SEVERE WEATHER POTENTIAL WITH THIS SYSTEM WILL BECOME MAXIMIZED
   ON THURSDAY...AS DAYTIME HEATING CONTRIBUTES TO
   DESTABILIZATION...AND RETURN FLOW CONTINUES OFF AN INCREASINGLY
   MOIST BOUNDARY LAYER OVER THE GULF OF MEXICO.
  
   AS THIS MOISTURE OVERRUNS A RESIDUAL COOL/STABLE BOUNDARY LAYER
   LINGERING OVER PARTS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST
   ...THE MOIST/UNSTABLE WARM SECTOR BOUNDARY LAYER MAY NOT BECOME
   PARTICULARLY BROAD.  BUT IT IS EXPECTED TO BECOME SIZABLE ENOUGH TO
   SUPPORT A SIGNIFICANT RISK FOR SEVERE STORMS...AT LEAST ON THE
   SOUTHERN FRINGE ON THE MORE STRONGLY DIFLUENT HIGH-LEVEL FLOW... AND
   MID-LEVEL HEIGHT FALLS...ACROSS THE LOWER MISSISSIPPI VALLEY
   THURSDAY AFTERNOON AND EVENING.  THIS MAY INCLUDE THE RISK FOR
   SUPERCELLS WITH A FEW TORNADOES.
  
   ..KERR.. 02/16/2013

[andyhb]

DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0347 AM CST SUN FEB 17 2013
  
   VALID 201200Z - 251200Z
  
   ...DISCUSSION...
   THE LATEST MEDIUM RANGE FORECAST GUIDANCE MAINTAINS GENERAL TRENDS
   OF THE PAST SEVERAL DAYS CONCERNING A MAJOR UPPER TROUGH AND
   ASSOCIATED STRONG JET STREAK THAT APPEAR LIKELY TO EMERGE FROM THE
   SOUTHWESTERN U.S. BY THE MIDDLE OF THE COMING WORK WEEK.  THE TROUGH
   AXIS STILL APPEARS LIKELY TO TAKE ON A NEGATIVE TILT AS IT
   PROGRESSES ACROSS THE SOUTHERN ROCKIES INTO THE CENTRAL AND SOUTHERN
   PLAINS BY 12Z THURSDAY...BEFORE LIFTING NORTHEASTWARD AND
   DEAMPLIFYING ACROSS THE UPPER MIDWEST ON FRIDAY.  PRIMARY SURFACE
   CYCLOGENESIS IS EXPECTED ACROSS EASTERN COLORADO INTO WESTERN
   KANSAS...BUT MODELS INDICATE SECONDARY WAVE DEVELOPMENT FROM PARTS
   OF NORTHWEST INTO EASTERN TEXAS WEDNESDAY NIGHT.  THIS MAY
   EVENTUALLY BECOME THE FOCUS FOR AN EVOLVING SQUALL LINE...AND
   INCREASING SEVERE WEATHER POTENTIAL...AS FORCING ENCOUNTERS BETTER
   MOISTURE RETURN OFF THE GULF OF MEXICO.  HIGHEST SEVERE
   PROBABILITIES STILL APPEAR TO EXIST ON THURSDAY...AS THE WAVE AND
   ASSOCIATED SQUALL LINE DEVELOP EASTWARD ALONG A WARM FRONT ACROSS
   THE LOWER MISSISSIPPI VALLEY.  SURFACE DEW POINTS IN THE WARM SECTOR
   OF THE WAVE MAY REACH THE MID 60S ACROSS PARTS OF SOUTHEAST TEXAS
   INTO SOUTHERN LOUISIANA AND MISSISSIPPI.  ASSOCIATED BOUNDARY LAYER
   DESTABILIZATION ON THE SOUTHERN PERIPHERY OF THE DIFLUENT HIGH LEVEL
   FLOW AND MID-LEVEL HEIGHT FALLS COULD BECOME SUPPORTIVE OF DISCRETE
   SUPERCELLS NEAR/AHEAD OF THE SQUALL LINE... WITH A RISK FOR
   TORNADOES...IN ADDITION TO DAMAGING WIND GUSTS.
  
   ..KERR.. 02/17/2013

[Srain]

It looks like we will get some additional RECON from Hawaii from the G-IV.

 

WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1230 PM EST SUN 17 FEBRUARY 2013
SUBJECT: WINTER STORM PLAN OF THE DAY (WSPOD)
         VALID 18/1100Z TO 19/1100Z FEBRUARY 2013
         WSPOD NUMBER.....12-079

I.  ATLANTIC REQUIREMENTS
    1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
    2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

II. PACIFIC REQUIREMENTS
    1. FLIGHT ONE -- NOAA 49
       A. P52/ DROP 10 (22.3N 129.0W)/ 19/0000Z
       B. NOAA9 13WSC TRACK52
       C. 18/1930Z
       D. 19 DROPS AS PUBLISHED ON TRACK
       E. 41,000 TO 45,000 FT/ 19/0600Z

    2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE
       P53/ DROP 9 (15.5N 131.8W)/ 20/0000Z
 

[My Weather Today]

Someone needs to correct the title of this thread. It's says Jan 21st threat.

[Stebo]

Someone needs to correct the title of this thread. It's says Jan 21st threat.

Yeah it is for the 21st, the day 4 potential.

[Srain]

Added the 20th to account for the Day 3 Slight Risk for portions of Central/North Texas. There is some uncertainty on the evolution of the late Wednesday potential. The WSR missions that will fly tonight and tomorrow E of Hawaii should offer some stability via the short term meso guidance.

[Bryan Wood]

Yeah it is for the 21st, the day 4 potential.

 

But it is February unless we hit a Time Warp. The title says January.

 

As far as the discussion of a possible lack of CAPE, we've seen destructive tornadoes in Dixie Alley with 250-500 SBCAPE before...high shear and boundaries can be a big deal in cold season storms here. You won't see much in the way of destructive hail, but it's not unusual to see supercells dropping tornadoes with low CAPE.

[Stebo]

But it is February unless we hit a Time Warp. The title says January.

 

As far as the discussion of a possible lack of CAPE, we've seen destructive tornadoes in Dixie Alley with 250-500 SBCAPE before...high shear and boundaries can be a big deal in cold season storms here. You won't see much in the way of destructive hail, but it's not unusual to see supercells dropping tornadoes with low CAPE.

Ahh yeah good point, it is labelled with the wrong month. Lol

[Ed Lizard]

Early start in Northern Houston Suburbs.

[Srain]

E-mail update from Jeff:

 

Strong to severe thunderstorms have develop early this afternoon over Montgomery and San Jacinto Counties with tornado warnings ongoing on two separate cells. Activity appears associated with modest heating which has helped to break the mid level capping inversion and possible weak upper air disturbance noted on water vapor images over central TX. Expect activity will continue for the next few hours especially north of I-10 where capping is weakest, but will need to keep a close eye on cells over Fort Bend and NW Harris Counties as if they are able to break through the cap and utilize the strong lwo level shear in place they could become tornadic.

[Ed Lizard]

Several radar prompted tornado warnings in SW Arkansas, Lafayette county warned storm produced a funnel cloud near Lewisville.

[andyhb]

Nice line of four discrete supercells tornado warned in the Arklatex.

[Indystorm]

Those cells are impressive for what little dew points and CAPE we have in the area.  Helicity is quite substantial.  Does make me wonder what Thursday might hold if this system primes the pump.

[thunderman]

Sorry about the month error! haha

[andyhb]

Those cells are impressive for what little dew points and CAPE we have in the area.  Helicity is quite substantial.  Does make me wonder what Thursday might hold if this system primes the pump.

 

A wildcard here might be that sfc wave/possible sub-synoptic low developing north of the ST Jet axis that the D4 mentions. That may temporarily offset the occluding of the primary sfc low in the Plains and lead to locally enhanced low level shear and moisture advection. Considering the diffluent upper/mid level flow in that area (LA/MS), that would be something to watch.

[Chicago Storm]

Those cells are impressive for what little dew points and CAPE we have in the area.  Helicity is quite substantial.

The environment today wasn't that bad...

 

[andyhb]

Well, the 00z Euro only trended a full state south with the primary surface low on Thursday at 72 hrs compared to last night. This has potentially significant implications as it allows the significant low level kinematics with the strong LLJ to remain firmly entrenched over the Lower MS Valley throughout the period.

[andyhb]

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0226 AM CST TUE FEB 19 2013

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS THURSDAY ACROSS PARTS OF
EASTERN TEXAS THRU THE LOWER MISSISSIPPI VALLEY...

...SYNOPSIS...
LARGE-SCALE UPPER TROUGHING FORECAST TO EVOLVE ACROSS MUCH OF THE
WESTERN AND CENTRAL U.S. THE NEXT COUPLE OF DAYS IS EXPECTED TO
PERSIST THROUGH THIS PERIOD AND BEYOND. THE MOST PROMINENT SHORT
WAVE TROUGH EMBEDDED WITHIN THIS REGIME APPEARS LIKELY TO BE IN THE
PROCESS OF LIFTING IN NEGATIVELY TILTED FASHION ACROSS THE CENTRAL
AND SOUTHERN HIGH PLAINS AT 12Z THURSDAY. MODELS SUGGEST THAT THIS
FEATURE WILL THEN CONTINUE PIVOTING AROUND AN ASSOCIATED DEEP
LOW/MID-LEVEL CYCLONE MIGRATING FROM THE CENTRAL PLAINS TOWARD THE
UPPER MIDWEST THROUGH EARLY FRIDAY. WHILE A STRONG MID/UPPER JET
ASSOCIATED WITH THIS FEATURE IS FORECAST IN A BROAD CYCLONIC BELT
ACROSS THE SOUTHERN PLAINS RED RIVER VALLEY/OZARK PLATEAU AND MIDDLE
MISSISSIPPI VALLEY...A STRONG SUBTROPICAL JET IS EXPECTED TO PERSIST
IN A BELT ACROSS THE LOWER RIO GRANDE VALLEY THROUGH THE GULF COAST
VICINITY. WHILE MID-LEVEL HEIGHTS MAY RISE ALONG AN AXIS NORTH OF
AN INCREASINGLY PROMINENT CARIBBEAN HIGH CENTER...GUIDANCE REMAINS
SUGGESTIVE THAT THERE WILL BE AT LEAST WEAK MID-LEVEL HEIGHT FALLS
ACROSS THE CENTRAL GULF COAST/LOWER MISSISSIPPI VALLEY REGION DURING
THE DAY THURSDAY.

IN MANY RESPECTS...THE FORECAST EVOLUTION OF THE LARGE-SCALE PATTERN
REMAINS SIMILAR TO SOME THAT HAVE BEEN ASSOCIATED WITH CONSIDERABLE
SEVERE WEATHER POTENTIAL. HOWEVER...AN EXPANSIVE SURFACE
RIDGE...WHICH APPEARS LIKELY TO DEVELOP SOUTHEASTWARD IN THE WAKE OF
THE LARGE UPPER TROUGH NOW SHIFTING EAST OF THE MISSISSIPPI
VALLEY...MAY MITIGATE THIS POTENTIAL. IT IS BECOMING MORE OBVIOUS
THAT A COOL/COLD AND STABLE SURFACE-BASED AIR MASS WILL BE
ENTRENCHED ACROSS MUCH OF THE EASTERN PLAINS AND MISSISSIPPI VALLEY
EARLY THURSDAY...AND IT MAY PROVE SLOW TO MODIFY. MOST MODELS
INDICATE THAT THE SUB 1000 MB SURFACE LOW OVER THE CENTRAL HIGH
PLAINS AT 12Z THURSDAY WILL WEAKEN CONSIDERABLY AS IT REDEVELOPS
NORTHEASTWARD THROUGH PARTS OF THE MIDDLE/LOWER MISSOURI VALLEY.
AND SECONDARY WAVE DEVELOPMENT ALONG A SURFACE FRONT ACROSS CENTRAL
TEXAS PROBABLY WILL REMAIN WEAK AND WEAKEN AS IT TRACKS EAST
NORTHEASTWARD ACROSS THE ARKLATEX AND LOWER MISSISSIPPI VALLEY.
STILL...MOISTENING AND DESTABILIZATION ABOVE THIS STABLE LAYER
SHOULD BECOME SUPPORTIVE OF CONSIDERABLE THUNDERSTORM ACTIVITY...AND
A WINDOW OF OPPORTUNITY STILL APPEARS TO EXIST FOR SEVERE BOUNDARY
LAYER BASED STORM DEVELOPMENT DURING THE DAY THURSDAY.

...LOWER MISSISSIPPI VALLEY...
LATEST MODEL DATA...INCLUDING THE NAM/SREF AND ECMWF...DO INDICATE
RAPID BOUNDARY LAYER MOISTENING IS POSSIBLE BY MIDDAY THURSDAY
ACROSS AT LEAST MUCH OF LOUISIANA AND ADJACENT WEST
CENTRAL/SOUTHWESTERN MISSISSIPPI. IT APPEARS PROBABLE THAT
PRECIPITABLE WATER WILL INCREASE UP TO AROUND 1.5 INCHES ACROSS THIS
REGION...AS SURFACE DEW POINTS INCREASE INTO THE MID 60S. THIS IS
EXPECTED TO OCCUR BENEATH INITIALLY STEEP MID-LEVEL LAPSE RATES
/700-500 MB IN EXCESS OF 8 DEGREES C PER KM/...WHICH MAY YIELD MIXED
LAYER CAPE OF 500-1000 J/KG BY EARLY AFTERNOON. IT IS BECOMING MORE
UNCLEAR IF FORCING WILL MAINTAIN THE EASTWARD PROGRESSION OF A
POTENTIALLY EVOLVING CLUSTER OF STORMS ACROSS THE REGION. THE
ENVIRONMENT MAY BE MORE CONDUCIVE TO DISCRETE STORM DEVELOPMENT...IN
THE PRESENCE OF WIND PROFILES CHARACTERIZED BY STRONG DEEP LAYER
SHEAR...AND LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS. WHILE
UNCERTAINTY MAY BE INCREASING A BIT...IT DOES NOT APPEAR COMPLETELY
OUT OF THE QUESTION THAT PARAMETERS COULD COME IN PHASE TO SUPPORT
ONE OR TWO LONG LIVED SUPERCELLS CAPABLE OF PRODUCING STRONG
TORNADOES ACROSS PARTS OF CENTRAL/SOUTHERN LOUISIANA INTO
MISSISSIPPI.

..KERR.. 02/19/2013

[TropicalAnalystwx13]

Hodographs are large and looping...depending on the amount of instability that develops, we may be looking at a good possibility of significant to violent tornadoes across central Louisiana on Thursday afternoon. Thermodynamics are not that indifferent from last week's system that produced the EF4 Hattiesburg tornado.

 

[thunderman]

With the possibility of sufficient instability and the hodos being modeled, there seems to be a real possibility of long lived supercells with an inherent significant tornado risk ... should discrete convection get established.

East-central LA Thursday evening:

[thunderman]

SREF Significant Tor Ingredients
 

[TropicalAnalystwx13]

.DISCUSSION...

SFC HIGH PRESSURE NEARLY OVHD THIS AFTN...WITH SFC LOW DEEPENING

QUICKLY OVER PANHANDLES OVERNIGHT. DESPITE LIGHT EAST WINDS

OVER EAST TX...BECMG GUSTIER TOWARDS CENTRAL TX...DEWPOINTS LOWER

FURTHER WEST...WITH MAINLY UPPER TEENS TO LOWER 20S OVER CENTRAL TX.

THEREFORE...DO NOT SEE REASON FOR DEWPOINTS TO INCREASE OVERNIGHT

AND RADIATION COOLING TO OCCUR AT LEAST THRU MIDNIGHT...WITH SLOW

ADVANCEMENT OF MID/UPPER LVL CLOUDS FROM WEST. SO HAVE LOWERED OVERNIGHT

TEMPS A FEW DEGREES...RANGING THRU THE 30S FOR THE MOST PART. AS

THESE HIGH BASED CLOUDS THICKEN...SOME LIGHT RAIN MAY OCCUR IN

ISENTROPIC LIFT ACROSS MAINLY EAST TX TOWARDS DAYBREAK...AND

EVAPORATIVE COOLING EFFECTS TO LIKELY OFFSET ANY WARMING FROM

THE ARRIVAL OF THE CLOUD BLANKET. NORTHERN SECTIONS SHOULD SEE

JUST ENOUGH WARM AIR NEAR SFC TO CONVERT ANY FRZN PCPN ALOFT TO

LIQUID RAIN WED MORNING AND DAYTIME. AFTER THIS INITIAL LIGHT

RAINFALL... SHOULD BE A BRIEF BREAK...BEFORE EMBEDDED CONVECTION

BEGINS TO SPREAD ACROSS AREA WED NIGHT...IN ADVANCE OF WARM FRONT.

LOW LVL SHEAR BECMG EXTREMELY STG WITH STG EASTERLY

COMPONENT...BENEATH A 50 TO 60 KT SSW LOW LVL JET...RESULTING FROM

INCREASING NEGATIVE TILTED TROUGH. QUESTION WILL BE HOW FAR NORTH

AND EAST WARM FRONT ADVANCES...BEFORE SFC FEATURES WRAP AROUND

ITSELF. THIS WILL DICTATE WHETHER WIDESPREAD HEAVY RAIN WITH

EMBEDDED CONVECTION...OR POSSIBLE SIGNIFICANT TORNADO OUTBREAK...DURING

THE DAY AND POSSIBLY INTO THE EVENING ON THURSDAY.

A SERIES OF SHORT WAVES WITH MEAN LONG WAVE TROUGHING TO CONTINUE

WESTERN CONUS TO KEEP COLD AIR OUT OF AREA. EXTENDED MODELS

DIFFER ON TIMING AND LOCATION OF THESE SHORT WAVES. HAVE SOME LOW

POPS IN EXTENDED./VII/.

[andyhb]

You might want to reference which WFO put out that forecast discussion, in this case, it is SHV (Shreveport).

[andyhb]

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1148 PM CST TUE FEB 19 2013

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS THURSDAY ACROSS PARTS OF
EASTERN TEXAS THRU THE LOWER MISSISSIPPI VALLEY...

...SYNOPSIS...
MUCH AS HAS BEEN FORECAST BY MODELS FOR THE BETTER PART OF THE LAST
WEEK...THE EVOLUTION OF A LARGE-SCALE UPPER TROUGH IS NOW WELL
UNDERWAY ACROSS THE PACIFIC COAST THROUGH THE ROCKIES...WITH A
STRONG SHORT WAVE IMPULSE DIGGING ACROSS CALIFORNIA...TOWARD THE
SOUTHERN INTERMOUNTAIN REGION. MODELS STILL INDICATE THAT THE
SMALLER SCALE TROUGH WILL TAKE ON AN INCREASING NEGATIVE TILT AS IT
PROGRESSES EAST OF THE SOUTHERN ROCKIES BY 12Z
THURSDAY...ACCOMPANIED BY A 100 KT 500 MB JET STREAK. THE IMPULSE
IS EXPECTED TO CONTINUE PIVOTING AROUND THE EASTERN PERIPHERY OF AN
ASSOCIATED DEEP LOWER/MID TROPOSPHERIC CYCLONE MIGRATING ACROSS THE
CENTRAL PLAINS...TOWARD THE UPPER MIDWEST...THROUGH THE REMAINDER OF
THIS PERIOD. THE SPEED MAXIMUM MAY WEAKEN...BUT STRONG CYCLONIC
MID/UPPER FLOW WILL PERSIST IN A BROAD BELT ACROSS THE SOUTHERN
PLAINS THROUGH THE MIDDLE MISSISSIPPI VALLEY...WHILE A BROADLY
ANTICYCLONIC SUBTROPICAL JET CURVES ACROSS THE LOWER RIO GRAND
VALLEY THROUGH THE GULF COAST VICINITY.

GUIDANCE CONTINUES TO INDICATE THAT A COLD/STABLE AIR MASS...
ASSOCIATED WITH AN ELONGATED SURFACE RIDGE EXTENDING ALONG AN AXIS
JUST EAST OF THE MISSISSIPPI VALLEY AT THE START OF PERIOD...WILL BE
SLOW TO MODIFY. AND AN INITIALLY DEEP /SUB 1000 MB/ SURFACE CYCLONE
ASSOCIATED WITH THE UPPER IMPULSE APPEARS LIKELY TO WEAKEN AS IT
MIGRATES NORTHEASTWARD OUT OF THE SOUTH CENTRAL PLAINS...TOWARD THE
GREAT LAKES REGION. MODELS HAVE TRENDED FARTHER SOUTH WITH THE
LOCATION OF INITIAL CYCLOGENESIS...ACROSS NORTHEAST NEW MEXICO INTO
THE PANHANDLE REGION...BUT THEY REMAIN SUGGESTIVE OF AT LEAST WEAK
SECONDARY WAVE DEVELOPMENT ALONG THE SURFACE FRONT ACROSS CENTRAL
TEXAS THROUGH THE ARKLATEX AND LOWER MISSISSIPPI VALLEY.

A 50-70 KT SOUTHERLY 850 MB JET APPEARS LIKELY TO EXTEND OFF THE
WESTERN GULF OF MEXICO THROUGH EASTERN PORTIONS OF THE SOUTHERN
PLAINS EARLY THURSDAY. THIS WILL CONTRIBUTE TO MOISTENING ABOVE THE
STABLE SURFACE-BASED LAYER...AND BENEATH STEEP LAPSE RATES...TO
SUPPORT SUFFICIENT DESTABILIZATION FOR THUNDERSTORM ACTIVITY...AS IT
SHIFTS EASTWARD...ACROSS AND EAST OF THE LOWER/MIDDLE MISSISSIPPI
VALLEY. THE EXTENT OF SUBSTANTIVE BOUNDARY LAYER MOISTENING REMAINS
SOMEWHAT OF A QUESTION...BUT ENOUGH INSTABILITY IS EXPECTED IN THE
PRESENCE OF STRONG SHEAR TO SUPPORT A RISK FOR SEVERE STORMS ACROSS
PARTS OF EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY.

...LOUISIANA AND ADJACENT SOUTHEAST TEXAS/ARKANSAS/MISSISSIPPI...
A MORE CERTAIN WINDOW OF OPPORTUNITY FOR THE JUXTAPOSITION OF
FAVORABLE LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION AND
BOUNDARY LAYER DESTABILIZATION APPEARS TO BE SHRINKING TO PORTIONS
OF CENTRAL AND SOUTHERN LOUISIANA DURING THE 21/18Z- 22/00Z TIME
FRAME. THIS IS WHERE GUIDANCE CONTINUES TO SUGGEST THAT A RAPID
INCREASE IN SURFACE DEW POINTS TO THE MID 60S IS POSSIBLE...PRIOR TO
WEAK MID-LEVEL HEIGHT FALLS AND STRONGER HIGH LEVEL DIFLUENCE
OVERSPREADING THE REGION. IT REMAINS UNCLEAR WHETHER LOW-LEVEL
FORCING WILL REMAIN SUPPORTIVE OF AN ORGANIZED CONVECTIVE
SYSTEM...BUT THE ENVIRONMENT SEEMS LIKELY TO BE CONDUCIVE TO AT
LEAST SCATTERED DISCRETE STORM FORMATION. WIND PROFILES
CHARACTERIZED BY STRONG DEEP LAYER SHEAR AND LARGE CLOCKWISE CURVED
LOW-LEVEL HODOGRAPHS WILL BE VERY FAVORABLE FOR SUPERCELLS.
TORNADIC POTENTIAL MAY BE ENHANCED AS STORMS TEND TO MOVE ACROSS OR
ALONG A ROUGHLY NORTHWEST/SOUTHEAST SURFACE WARM FRONTAL
ZONE...THOUGH THE EXTENT OF THIS POTENTIAL WILL DEPEND ON BOUNDARY
MODIFICATION TO THE COOL SIDE OF THE FRONT.

..KERR.. 02/20/2013