SWODY2
SPC AC 251703
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1103 AM CST WED FEB 25 2009
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MIDWEST INTO
MID-SOUTH...
...SYNOPSIS...
LARGE-SCALE PATTERN WILL REMAIN PROGRESSIVE THROUGH THE DAY TWO
PERIOD WITH THE PRIMARY FEATURE OF INTEREST BEING LOW AMPLITUDE
SHORT WAVE TROUGH WHICH WILL TRANSLATE FROM THE NRN/CNTRL PLAINS
INTO THE OH VALLEY. THIS FEATURE WILL GRADUALLY PHASE WITH MORE
INTENSE HIGHER LATITUDE SHORT WAVE TROUGH ROTATING AROUND POLAR
VORTEX ANCHORED OVER HUDSON BAY. THIS EVOLUTION WILL RESULT IN THE
STRONGEST HEIGHT FALLS/DYNAMIC FORCING FOR ASCENT SPREADING EWD
THROUGH THE UPPER MIDWEST AND UPPER GREAT LAKES.
IN THE LOW LEVELS...PRIMARY SURFACE LOW IS FORECAST TO DEEPEN WHILE
DEVELOPING FROM THE CNTRL PLAINS ENEWD INTO THE LOWER MO VALLEY BY
THU AFTERNOON...AND SWRN ONTARIO BY FRI MORNING. AN ASSOCIATED WARM
FRONT WILL LIFT NWD THROUGH THE OH VALLEY INTO THE GREAT LAKES WHILE
TRAILING COLD FRONT STRENGTHENS WHILE PROGRESSING SEWD THROUGH THE
CNTRL PLAINS...MID MS VALLEY AND UPPER GREAT LAKES.
...MIDWEST INTO MID-SOUTH...
INTENSIFYING LLJ WILL SERVE TO ENHANCE THE NWD/NEWD FLUX OF AN
INCREASINGLY MOIST BOUNDARY LAYER WITH DEWPOINTS RISING INTO THE 50S
AHEAD OF SURFACE LOW AND ATTENDANT COLD FRONT OVER THE LOWER MO/MID
MS VALLEYS...TO LOWER 60S OVER THE ARKLATEX INTO LOWER MS VALLEY.
AN EML ORIGINATING OVER THE CNTRL ROCKIES WILL BE ADVECTED EWD ATOP
THE MOISTENING BOUNDARY LAYER...ESTABLISHING A CAP ACROSS SYSTEM
WARM SECTOR. WHILE MIDLEVEL LAPSE RATES WILL STEEPEN WITH THE
ARRIVAL OF THE EML...RATHER WARM TEMPERATURES CENTERED AROUND 700 MB
WILL LIMIT THE DEGREE OF CONVECTIVE INSTABILITY WITH MAXIMUM MLCAPE
VALUES LIKELY REMAINING BELOW 1000 J/KG.
CLUSTERS OF ELEVATED TSTMS WILL EITHER BE ONGOING OR FORM EARLY IN
THE PERIOD FROM THE MID MO VALLEY INTO PARTS OF IL/IND...DRIVEN
LARGELY BY LOW-LEVEL MOISTURE AND THERMAL ADVECTIONS NEAR AND N OF
SURFACE WARM FRONT. SOME OF THE MORE INTENSE STORMS WILL BE CAPABLE
OF MARGINALLY SEVERE HAIL GIVEN THE STEEPENING MIDLEVEL LAPSE RATES.
MORE ROBUST...SURFACE-BASED STORM DEVELOPMENT IS ANTICIPATED BY
MID-LATE AFTERNOON OVER MO AS LARGE-SCALE FORCING ASSOCIATED WITH
COUPLED UPPER-LEVEL JET STRUCTURE IS AUGMENTED BY MESOSCALE ASCENT
ALONG DEEPENING/STRENGTHENING SURFACE COLD FRONT.
ISALLOBARIC RESPONSE TO DEEPENING SURFACE LOW /I.E. LOCALLY BACKED
SURFACE WINDS/ IN CONJUNCTION WITH 45-55 KT WSWLY FLOW IN THE
MIDLEVELS WILL RESULT IN SUFFICIENT LOW AND DEEP-LAYER SHEAR FOR
ORGANIZED STORMS INCLUDING SUPERCELLS/BOWS. LARGE-SCALE PATTERN
EVOLUTION SUGGESTS A FAIRLY QUICK TRANSITION TO A LINEAR CONVECTIVE
SYSTEM WITH HAIL AND DAMAGING WINDS BEING THE PRIMARY SEVERE WEATHER
THREATS. STORMS SHOULD TEND TO WEAKEN THU NIGHT OVER THE OH VALLEY
AS SURFACE FRONT SHIFTS EWD INTO A PROGRESSIVELY DRIER BOUNDARY
LAYER. THE POTENTIAL FOR AT LEAST ISOLATED SEVERE STORMS WILL
CONTINUE OVERNIGHT OVER THE OZARK PLATEAU INTO LOWER MS VALLEY WHERE
DEWPOINTS IN THE 60S WILL MAINTAIN AT LEAST A MARGINALLY UNSTABLE
AIR MASS.
..MEAD.. 02/25/2009
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