SWODY1
SPC AC 050555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1155 PM CST MON FEB 04 2008
VALID 051200Z - 061200Z
..THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF AR...FAR NERN
TX...NRN LA...CNTRL AND NRN MS...WRN TN...SERN MO...SRN IL AND FAR
SWRN IND...
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN LOW PLAINS AND
LOWER MS VALLEY NEWD INTO THE OH VALLEY...
..SYNOPSIS...
STRONG...UPPER TROUGH CURRENTLY EVOLVING OVER THE FOUR CORNERS
REGION WILL LIFT NEWD TODAY ACROSS THE SRN PLAINS INTO MID MS VALLEY
AS MID AND UPPER-LEVEL JET STREAKS INTENSIFY IN THE DOWNSTREAM
POSITION FROM THE ARKLATEX INTO LOWER OH VALLEY. IN THE LOW
LEVELS...SURFACE LOW ALONG THE RED RIVER OVER S-CNTRL OK/N-CNTRL TX
IS FORECAST TO DEEPEN SLIGHTLY WHILE DEVELOPING NEWD TO N-CNTRL AR
BY 06/00Z AND INTO SRN OH BY THE END OF THE PERIOD. ATTENDANT DRY
LINE INITIALLY FROM THE LOW SWD INTO CNTRL TX IS EXPECTED TO EVOLVE
INTO A PACIFIC COLD FRONT WHILE PROGRESSING EWD THROUGH THE
ARKLATEX. MEANWHILE...A STRONGER COLD FRONT WILL SURGE SEWD FROM
CNTRL OK AND WRN TX...EVENTUALLY OVERTAKING PACIFIC COLD FRONT NEAR
THE MS RIVER TONIGHT.
..SRN LOW PLAINS AND LOWER MS VALLEY NEWD INTO THE OH VALLEY...
05/00Z OBSERVED SOUNDINGS FROM THE TX COAST INTO LOWER MS VALLEY
INDICATED THE PRESENCE OF A RELATIVELY STRONG CAP ATOP MODEST
BOUNDARY LAYER MOISTURE WITH MEAN MIXING RATIOS OF 10-13 G/KG.
A BROAD...SWLY LLJ ESTABLISHED FROM THE NWRN GULF OF MEXICO INTO THE
LOWER GREAT LAKES WILL UNDERGO CONSIDERABLE STRENGTHENING
TODAY...SUPPORTING A FURTHER INCREASE IN BOUNDARY LAYER MOISTURE
CONTENT. SURFACE DEWPOINTS IN THE LOW TO MID 60S WILL BE COMMON
ACROSS THE MID SOUTH WITH UPPER 60S TO AROUND 70 F ALONG THE GULF
COAST. THIS MOISTURE COUPLED WITH MIDLEVEL LAPSE RATES OF 7-7.5
C/KM SHOULD SUPPORT A MODERATELY UNSTABLE AIR MASS /MLCAPES OF
AROUND 1000 J PER KG/ BY AFTERNOON FROM SERN OK AND ERN TX EWD/NEWD
ACROSS AR...LA AND MS. INSTABILITY WILL TEND TO DECREASE WITH NEWD
EXTENT ACROSS THE OH VALLEY.
TSTMS ARE EXPECTED TO BE ONGOING AT THE ONSET OF THE PERIOD ALONG
FRONT FROM OH/IND/IL SWWD INTO SRN MO...WITH ONGOING OR DEVELOPING
STORMS OVER PARTS OF CNTRL/ERN OK INTO N-CNTRL/CNTRL TX. LATEST
SHORT TERM MODEL GUIDANCE SUGGESTS THAT THE MOST INTENSE STORMS WILL
LIKELY OCCUR FROM VICINITY OF SURFACE LOW SWD ALONG PACIFIC COLD
FRONT AS STRONG...DEEP LAYER FORCING FOR ASCENT OVERSPREADS
DESTABILIZING WARM SECTOR.
SOME UNCERTAINTIES IN THIS CONVECTIVE EVOLUTION REVOLVE AROUND: 1)
WHETHER STORMS WILL REMAIN CONFINED TO ALONG THE FRONT AND 2)
PRIMARY CONVECTIVE MODE. ETAKF SOUNDINGS WHICH APPEAR TO BETTER
RESOLVE THE OBSERVED CAP TEND TO LIMIT STORMS TO ALONG THE FRONT.
ONE POTENTIAL CAVEAT IS A RATHER WELL-DEFINED SHORT WAVE TROUGH
EMBEDDED IN SUB-TROPICAL MOISTURE PLUME NEAR THE LOWER RIO GRANDE
VALLEY AS OF 05/0530Z. THIS SYSTEM WILL PRECEED THE PRIMARY UPPER
TROUGH...AND IT IS POSSIBLE THAT FORCING FOR ASCENT ASSOCIATED WITH
THIS FEATURE COULD INITIATE MORE DISCRETE STORMS DOWNSTREAM FROM THE
MAIN CONVECTIVE DEVELOPMENT ANTICIPATED ALONG THE FRONT.
FORECAST SOUNDINGS INDICATE THAT THE MODERATE RISK AREA WARM SECTOR
WILL BE STRONGLY SHEARED WITH EFFECTIVE SRH VALUES OF 250-350 M2/S2
AND EFFECTIVE BULK SHEARS OF 50-60 KT. ANY MORE DISCRETE STORMS
THAT CAN DEVELOP WILL BE CAPABLE OF POTENTIALLY STRONG AND
LONG-TRACK TORNADOES. LARGE HAIL WILL ALSO BE POSSIBLE...AS WILL
CORRIDORS OF DAMAGING WINDS. THE WIND THREAT MAY TEND TO INCREASE
TONIGHT OVER THE LOWER OH AND LOWER MS VALLEYS AND POINTS E AS
STORMS GROW UPSCALE INTO A QUASI-LINEAR MCS. HIGH RESOLUTION MODEL
DATA SETS SUGGEST THAT THE CHARACTER OF THIS MCS COULD BE
SHORT...BROKEN LINES OF SUPERCELLS AND/OR BOWS WITH A CONTINUED
THREAT OF STRONG TORNADOES.
UNCERTAINTIES IN THE CONVECTIVE EVOLUTION GIVEN THE
ABOVEMENTIONED...LEAD SHORT WAVE TROUGH AND PRIMARY CONVECTIVE MODE
ARE GREAT ENOUGH SUCH THAT A CATEGORICAL MODERATE RISK WILL BE
MAINTAINED. AN UPGRADE TO HIGH RISK MAY BECOME NECESSARY ONCE
THESE DETAILS BECOME MORE CLEAR.
.MEAD.. 02/05/2008
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