Severe Weather - March 25-28 - Mid/Deep South/OH Riv Valley

[RL3AO]

SPC has tagged the area.



DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0353 AM CDT MON MAR 23 2009

VALID 261200Z - 311200Z

...DISCUSSION...

LATEST MEDIUM-RANGE GUIDANCE REMAINS IN RELATIVELY GOOD AGREEMENT IN
THE EVOLUTION OF THE LARGE-SCALE PATTERN THROUGH MUCH OF THE
EXTENDED PERIOD. ADDITIONALLY...THESE DATA HAVE STARTED TO SHOW
SOME IMPROVEMENT IN RUN-TO-RUN CONSISTENCY...PARTICULARLY THROUGH
ABOUT D5 /FRI MAR 27TH/ OR D6 /SAT MAR 28TH/.

THE PRIMARY FEATURE OF INTEREST IS INTENSE MID/UPPER-LEVEL LOW WHICH
IS FORECAST TO EVOLVE OVER THE CNTRL/SRN ROCKIES ON D4 /THU MAR
26TH/. THIS FEATURE IS EXPECTED TO THEN SHIFT EWD THROUGH THE
CNTRL/SRN PLAINS ON D5...BEFORE LIFTING NEWD INTO THE UPPER MIDWEST
BY D6. AS THIS OCCURS...A SECONDARY IMPULSE WILL ROTATE EWD THROUGH
THE LOWER MS VALLEY TOWARD THE MID ATLANTIC COAST BY THE END OF D7
/SUN MAR 29TH/.

MEANINGFUL MODEL DIFFERENCES STILL EXIST IN THE PHASE AND
MATURATION/EVOLUTION OF THIS SYNOPTIC SYSTEM. AS A RESULT...THE
OVERALL SEVERE WEATHER THREAT AND MORE SPECIFIC LOCATIONS THAT MAY
BE IMPACTED STILL REMAIN SOMEWHAT UNCERTAIN. DESPITE THESE
ISSUES...IT DOES APPEAR THAT INGREDIENTS WILL BE COMING TOGETHER BY
D5 OVER PARTS OF THE SRN PLAINS INTO LOWER MS VALLEY SUCH THAT A
MORE WIDESPREAD SEVERE WEATHER EVENT IS BECOMING INCREASINGLY
POSSIBLE. CONSIDERABLE AIR MASS MODIFICATION OVER THE GULF OF
MEXICO SHOULD SUPPORT DEWPOINTS IN THE 60S WITHIN SYSTEM WARM
SECTOR. THIS MOISTURE COMBINED WITH STEEP LAPSE RATES WILL RESULT
IN THE POTENTIAL FOR MODERATE INSTABILITY WITHIN A STRONGLY SHEARED
AND FORCED ENVIRONMENT.

IT APPEARS THIS SEVERE WEATHER POTENTIAL WILL SHIFT EWD INTO THE
CNTRL/ERN GULF STATES AND TN VALLEY ON D6 AS THE STRONG UPPER TROUGH
AND ASSOCIATED COLD FRONT SWEEP EWD ACROSS THE REGION.

..MEAD.. 03/23/2009

[KWT]

Models do seem to be suggestive of another outbreak developing, esp if the gulf moisture can remian in place further south. Seems like a lot of events have set-up quite far east this year so far?

[Meso]

I'm liking the look of the GFS for Texas on Thursday... The instability is insane, 3500+ CAPE, and -12 Lifted Index.. With dew points into the upper 60s.

Though I think it may be a case of the GFS being on crack.

CAPE




Lifted Index




Dew Points

[KWT]

Sounds like a proper Spring tornado chasing type set-up, though I do wonder how strong the cap would be in that sort of situation?

[CrazyC83]

Might want to change the dates as it appears to be starting on March 25.

[JonathanBelles]

Would this be able to slide into Florida or poof out in GA?

[RL3AO]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0332 AM CDT TUE MAR 24 2009

VALID 271200Z - 011200Z

...DISCUSSION...

LATEST MEDIUM-RANGE GUIDANCE REMAINS RELATIVELY CONSISTENT /IN BOTH
INTER-MODEL COMPARISON AND INTRA-MODEL RUN-TO-RUN TENDENCIES/ IN THE
EVOLUTION OF THE LARGE-SCALE PATTERN THROUGH D5 /SAT MAR 28TH/.
THROUGH THIS TIME FRAME...A POWERFUL MID/UPPER-LEVEL LOW WILL
TRANSLATE EWD THROUGH THE CNTRL/SRN PLAINS ON D4 /FRI MAR 27TH/
BEFORE LIFTING RAPIDLY NEWD INTO THE GREAT LAKES REGION ON D5. IN
THE LOW LEVELS...SURFACE LOW OVER THE SRN PLAINS WILL DEVELOP NEWD
THROUGH THE MID MS VALLEY...AND EVENTUALLY MORE NWD INTO THE GREAT
LAKES. MEANWHILE...TRAILING STRONG COLD FRONT WILL SURGE EWD
THROUGH THE SRN PLAINS...LOWER MS VALLEY...EVENTUALLY REACHING THE
MID/SERN ATLANTIC COAST BY LATE D5 OR D6 /SUN MAR 29TH/.

ON D4...A MOIST AND UNSTABLE AIR MASS IS EXPECTED TO SPREAD NWD/NEWD
ACROSS THE LOWER MS VALLEY IN ADVANCE OF EWD-MOVING COLD FRONT.
THIS INSTABILITY WILL COMBINE WITH STRENGTHENING WIND FIELDS AND
INCREASED FORCING FOR ASCENT TO FOSTER WIDESPREAD TSTMS ACROSS THE
REGION FRI AND FRI NIGHT. SOME MODEL GUIDANCE SUGGESTS THAT A
FAIRLY LARGE AREA OF MODERATE INSTABILITY WILL DEVELOP WITHIN SYSTEM
WARM SECTOR. SHOULD THIS OCCUR...THE POTENTIAL WILL EXIST FOR A
FAIRLY SIGNIFICANT SEVERE WEATHER EPISODE...INCLUDING THE THREAT FOR
STRONG TORNADOES.

THE THREAT FOR SEVERE STORMS WILL CONTINUE INTO D5 OVER PORTIONS OF
THE CNTRL AND ERN GULF STATES EWD TO THE SERN ATLANTIC COAST. GIVEN
THAT THE PRIMARY SURFACE LOW AND STRONGEST DYNAMIC FORCING WILL
REMAIN DISPLACED WELL TO THE N OF THE REGION...THERE IS SOME
QUESTION AS TO HOW WIDESPREAD THESE SEVERE STORMS WILL BE.
THEREFORE...NO AREA WILL BE DELIMITED ATTM.

BEYOND D5...MODEL SOLUTIONS BEGIN TO DIVERGE...LEAVING THE REMAINING
PORTION OF THE EXTENDED PERIOD QUITE UNCERTAIN.

..MEAD.. 03/24/2009

[KWT]

Seems to me this is almost a reboot of the current severe set-up with the gulf moisture retreating further south before slowly being forced back northwards inbto Texas and LA.

[Ed Mahmoud]

San Antonio Slammer?

[KWT]

What is that for Ed?
Not bad to get a 30% at day 2 though, does look like a southern states set-up with all the gulf moisture further south then recently.

[RL3AO]

10%H tornado risk for today.

[Bunkertor]

Might want to change the dates as it appears to be starting on March 25.

Crazy was right

...LA/MS/AL WED EVENING/NIGHT...
MODEL GUIDANCE IS IN GENERAL AGREEMENT THAT THE STRONGEST LOW LEVEL
JET AND ASSOCIATED VERTICAL SHEAR WILL BE OVER EASTERN LA AND MS
AFTER DARK. SIMILAR TO FARTHER WEST...UNCERTAINTY REMAINS AS TO HOW
FAR NORTH THE WARM FRONT WILL RETREAT. HOWEVER...IT DOES APPEAR
THAT AT LEAST A FEW SEVERE/SUPERCELL STORMS WILL BE POSSIBLE ALONG
THE BOUNDARY DURING THE EVENING. FORECAST SOUNDINGS FROM THE
NAM/NAMKF/GFS AND NMM4 MODELS ALL INDICATE A RISK OF STRONG
TORNADOES IF DISCRETE STRUCTURES CAN BE MAINTAINED. THIS AREA MAY
REQUIRE AN UPGRADE TO MODERATE RISK IN LATER UPDATES AS CONFIDENCE
IN PLACEMENT OF THE WARM FRONT INCREASES. MODELS ALSO SUGGEST THAT
STORMS WILL ORGANIZE INTO A SQUALL LINE AFTER MIDNIGHT WITH A
CONTINUED RISK OF DAMAGING WINDS AND TORNADOES.

[CrazyC83]

The Day 3 has some really strong wording:

SPC AC 250724

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0224 AM CDT WED MAR 25 2009

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN TX EWD INTO TN VALLEY
AND CNTRL GULF STATES...

...SYNOPSIS...

A SIGNIFICANT MIDLEVEL LOW IS FORECAST TO TRANSLATE EWD THROUGH THE
SRN PLAINS INTO THE LOWER MS VALLEY DURING THE DAY THREE PERIOD.
THIS SYSTEM WILL BE ACCOMPANIED BY A 100+ KT MIDLEVEL JET STREAK AND
INCREASING DIFFLUENT FLOW IN THE HIGH-LEVELS...BETWEEN CYCLONICLY
CURVED POLAR JET STREAK AND SUBTROPICAL JET SITUATED ALONG THE GULF
COAST. THE NET RESULT WILL BE INTENSE LARGE-SCALE FORCING FOR
ASCENT SPREADING EWD THROUGH OK/TX INTO THE LOWER MS VALLEY THROUGH
THE FORECAST PERIOD.

IN THE LOW LEVELS...LATEST GFS AND ECMWF DIFFER SLIGHTLY ON THE
TRACK AND INTENSITY OF ATTENDANT SURFACE LOW WITH THE GFS BEING THE
MOST PROGRESSIVE AND DEEPEST SOLUTION. BOTH MODELS HAVE INDICATED
FAIRLY GOOD RUN-TO-RUN CONSISTENCY WITH A BLEND OF THE TWO FOLLOWED
FOR THE SURFACE PATTERN. AS SUCH...IT APPEARS THE PRIMARY SURFACE
LOW WILL DEVELOP FROM N-CNTRL TX ENEWD THROUGH THE ARKLATEX BEFORE
MOVING MORE NNEWD TOWARD THE CONFLUENCE OF THE MS AND OH RIVERS.
TRAILING COLD FRONT WILL SHIFT EWD FROM ERN TX INTO THE LOWER MS
VALLEY WHILE ASSOCIATED WARM FRONT LIFTS NWD THROUGH THE TN VALLEY
TOWARD THE OH RIVER.

...ERN TX EWD INTO THE TN VALLEY AND CNTRL GULF STATES...

...POTENTIAL INCREASING FOR A SEVERE WEATHER OUTBREAK FRI AND FRI
NIGHT...

MODEL GUIDANCE CONTINUES TO INDICATE THAT A RATHER BROAD WARM SECTOR
WILL BECOME ESTABLISHED FRI FROM ERN TX EWD ACROSS THE GULF COAST
STATES WITH DEWPOINTS INCREASING THROUGH THE 60S TO PERHAPS AROUND
70 ALONG THE COAST. THIS MOISTURE WILL COMBINE WITH STEEP MIDLEVEL
LAPSE RATES...RESULTING IN A MODERATELY UNSTABLE AIR MASS BY
AFTERNOON.

TSTMS SHOULD BE ONGOING FRI MORNING BOTH WITHIN WARM SECTOR AND N OF
WARM FRONT FROM THE OZARK PLATEAU EWD INTO THE LOWER MS VALLEY.
ADDITIONAL TSTMS WILL DEVELOP THROUGH THE DAY ALONG AND AHEAD OF
COLD FRONT AS A BAND OF STRONG ASCENT ASSOCIATED WITH UPPER SYSTEM
OVERSPREADS FRONTAL ZONE. ACTIVITY WILL LIKELY CONSOLIDATE ALONG
COLD FRONT FRI NIGHT AS IT BEGINS TO ACCELERATE EWD THROUGH THE
LOWER MS VALLEY.

UNCERTAINTY STILL EXISTS WITH REGARD TO THE DOMINANT CONVECTIVE
MODE...DEGREE OF CONVECTIVE INSTABILITY...AND WHETHER ANY WEAKER
IMPULSES WILL PRECEDE PRIMARY UPPER TROUGH...POTENTIALLY INFLUENCING
THE EVOLUTION OF THE CONVECTIVE EVENT. HOWEVER...SHOULD A WARM
SECTOR ENVIRONMENT SIMILAR TO THE 25/00Z GFS ACTUALLY DEVELOP /I.E.
MLCAPE OF 1500-2500 J PER KG AND 0-1 KM SHEAR OF 30-40 KT/...THE
POTENTIAL WILL EXIST FOR A SIGNIFICANT TORNADO EVENT FRI AND FRI
NIGHT.

A CATEGORICAL SLIGHT RISK WILL BE INTRODUCED ATTM DUE TO THE
ABOVE-MENTIONED UNCERTAINTIES. HOWEVER...SHOULD MODEL GUIDANCE
REMAIN CONSISTENT WITH THE CURRENTLY FORECAST
THERMODYNAMIC/KINEMATIC PARAMETERS...AN UPGRADE TO AT LEAST MODERATE
RISK WILL BE REQUIRED IN SUBSEQUENT OUTLOOKS.

..MEAD.. 03/25/2009

CLICK TO GET WUUS03 PTSDY3 PRODUCT

NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
CURRENT UTC TIME: 1133Z (7:33AM), RELOAD THIS PAGE TO UPDATE THE TIME

[KWT]

So there is a risk today but it seems like the main threat is indeed on Friday, as noted there is very strong wording for Friday it has to be said...

[Bunkertor]

Strong wording indeed, but Fri development will depend on what´s going on tomorrow...as ever.

[CrazyC83]

Today could be pretty big too though. They did hold back on an upgrade since there are questions regarding cloud cover.

[CrazyC83]

SPC AC 251229

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0729 AM CDT WED MAR 25 2009

VALID 251300Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM TX ACROSS THE LOWER MS
VALLEY AND CENTRAL GULF COAST REGION...

...SYNOPSIS...
MAJOR TROUGHING CONTINUES TO DEVELOP OVER THE CENTRAL PORTION OF
CONUS AS VIGOROUS S/WV AND JET MAX DIGS SEWD PAC NW TODAY.
DOWNSTREAM THE S/WV IMPULSE CURRENTLY SRN ROCKIES WILL INTERACT WITH
STRONG SUBTROPICAL JET ACROSS NRN MEX AS THEY BOTH SHIFT EWD ACROSS
SRN PLAINS INTO LOWER MS VALLEY THIS FORECAST PERIOD AND PROVIDE A
PRONOUNCED AREA OF UPPER DIFFLUENCE BY THIS EVENING. LOW LEVEL
RESPONSE WILL BE DEVELOPMENT OF A WAVE ON THE TRAILING FRONTAL ZONE
SERN TX THIS AFTERNOON. AN INCREASING SLY LOW LEVEL JET OF 30-40KT
DEVELOPS ERN TX BY THIS AFTERNOON INCREASING TO 50-60KT SHIFTING EWD
ACROSS GULF STATES OVERNIGHT AS THE SURFACE WAVE MOVES ENEWD ALONG
THE RETREATING WARM FRONT ACROSS THE NRN GULF STATES.

SEVERAL DAYS OF RETURN FLOW HAVE RESULTED IN THE AVAILABILITY OF A
VERY MOIST AIR MASS NOW IN PLACE TO S OF FRONTAL ZONE WITH DEWPOINTS
GENERALLY WELL INTO THE 60S AS FAR E AS CENTRAL GULF COAST.

...CENTRAL TX...
THUNDERSTORMS SHOULD BE DEVELOPING BY EARLY AFTERNOON CENTRAL TX AS
THE MOIST UNSTABLE AIR MASS RETURNING NWD IS LIFTED ACROSS THE
STALLED FRONTAL ZONE. THIS LEADS TO INITIALLY ELEVATED CONVECTION AS
LARGE SCALE ASCENT SPREADS EWD WITH APPROACHING SRN ROCKIES S/WV
TROUGH. WITH STEEP MID LEVEL LAPSE RATES AND MLCAPES UPWARDS TO
2000 J/KG...COUPLED WITH IN EXCESS OF 50-60KT OF CLOUD BEARING
SHEAR...SUPERCELL STORMS ACCOMPANIED BY VERY LARGE HAIL ARE LIKELY.

...EAST TX ACROSS LA AND MS...
BY LATE THIS AFTERNOON AND CERTAINLY THIS EVENING...CONDITIONS WILL
BECOME POTENTIALLY FAVORABLE FOR TORNADIC SUPERCELLS VICINITY AND
JUST TO S OF THE E/W WARM FRONT. MODEL SOUNDINGS ALL INDICATE THAT
HODOGRAPHS BECOME VERY FAVORABLE FOR TORNADOES AS SFC-1 KM SHEAR
INCREASES TO 30-40KT/DEEP LAYER SHEAR IN EXCESS OF 60KT AS
PRONOUNCED UPPER DIVERGENCE DEVELOPS IN RESPONSE TO THE FAVORABLE
JET STRUCTURE EVOLVING OVER LOWER MS VALLEY THIS EVENING.

THERE IS A CONCERN FOR POTENTIALLY LONG-LIVED SUPERCELLS ALONG WITH
POSSIBLE STRONG TORNADOES. ATTM WILL DEFER THE POSSIBLE UPGRADE TO
A MDT AS THERE CONTINUES TO BE A CONCERN HOW FAR N THE WARM FRONT
WILL BE ABLE TO RETURN GIVEN THE CLOUD COVER AND LACK OF STRONG
SURFACE CYCLOGENESIS PROGGED IN THE MODELS. NEVERTHELESS THE THREAT
OF SEVERE THUNDERSTORMS SHOULD SPREAD RAPIDLY EWD THRU THE EVENING
ACROSS THE LOWER MS VALLEY WITH NOT ONLY POSSIBLE TORNADIC
SUPERCELLS BUT ALSO EVOLVING INTO BOW ECHOES ENHANCING DAMAGING WIND
POTENTIAL.

,,,LA/MS AL WED EVENING/NIGHT...
STORMS WILL BECOME MORE OF A LINEAR MODE OVERNIGHT AND MOVE RAPIDLY
EWD ACROSS THE CENTRAL GULF STATES UNDER A FAVORABLY STRONG SHEAR
ENVIRONMENT. ALONG WITH WIND DAMAGE...EMBEDDED SUPERCELLS AND
ISOLATED TORNADOES WILL ACCOMPANY THE LINE EWD ACROSS MS/AL.

..HALES/SMITH.. 03/25/2009

CLICK TO GET WUUS01 PTSDY1 PRODUCT

NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
CURRENT UTC TIME: 1350Z (9:50AM), RELOAD THIS PAGE TO UPDATE THE TIME

[KWT]

Yep today does need to be watched as well, certainly could see some severe weather today it just depends on the cloud cover and whether it limits instablity.
I do think we could see a moderate risk from this as well later on in the day.

[CrazyC83]

Friday, on the other hand, could make today look like nothing. I expect a MDT on the first Day 2 tomorrow, and it could very well be a HIGH in the end. It could definitely be a major tornado outbreak.

[KWT]

Crazy, I think it could well end up on the cusp on a high risk though we've seen even them go bust nearly totally before, I remember one last year for example.