SWODY1
SPC AC 132000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT TUE JUL 13 2010
VALID 132000Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHERN
PLAINS/UPPER MIDWEST...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS CAROLINAS/VA AND
SOUTHEAST STATES...
...NORTHERN PLAINS/UPPER MIDWEST...
FEW CHANGES TO PRIOR DAY 1 OUTLOOK...PLEASE CONSULT PREVIOUS
DISCUSSION AND LATEST WATCHES/MESOSCALE DISCUSSIONS. SURFACE BASED
SEVERE THREAT INCLUDING LARGE HAIL/ISOLATED TORNADOES IS STILL
EXPECTED TO INCREASE ESPECIALLY ACROSS THE EASTERN DAKOTAS TO
WESTERN MN THROUGH EARLY EVENING. A SPECIAL 18Z OBSERVED RAOB FROM
BISMARCK ND SAMPLED RELATIVELY STEEP LAPSE RATES WITH STRONG
WESTERLY FLOW /50-70 KT/ AROUND 5-6 KM AND ABOVE...WITH STRONGER
SOUTHERLY LOW LEVEL FLOW /25-30 KT/ AROUND 1-2 KM NOTED IN THE
AFTERNOON WSR-88D VWP DATA FROM GRAND FORKS/ABERDEEN. IN ALL...THIS
DEVELOPMENT WILL LIKELY GRADUALLY GROW UPSCALE INTO A SEVERE MCS
THIS EVENING/TONIGHT WITH A DAMAGING WIND THREAT INCREASING.
...SOUTHEAST STATES AND CAROLINAS/VA...
MINOR ADJUSTMENTS MADE TO OUTLOOK PROBABILITIES...BUT PRIOR FORECAST
REASONING LARGELY REMAINS UNCHANGED. IN THE WAKE OF A SMALL
MCS/LINEAR CLUSTER OVER NORTHEAST AL...ANY ADDITIONAL DEVELOPMENT IS
EXPECTED TO REMAIN ISOLATED ACROSS THE REMAINDER OF AL/MS OWING TO
MODEST NEAR-SURFACE CONVERGENCE AND RISING HEIGHTS ALOFT.
..GUYER.. 07/13/2010
.PREV DISCUSSION... /ISSUED 1128 AM CDT TUE JUL 13 2010/
...NRN PLAINS INTO UPPER MS VALLEY...
MORNING WATER VAPOR IMAGERY AND 12Z UPPER-AIR ANALYSIS INDICATE THE
PRESENCE OF AN INTENSE UPPER LOW OVER WRN CANADA INTO NWRN CONUS
WITH THE CENTER OF THE CIRCULATION REFORMING EWD ACROSS SRN PARTS OF
ALBERTA/SASKATCHEWAN. A SIGNIFICANT SHORT WAVE TROUGH HAS ROTATED
AROUND THIS FEATURE AND IS CURRENTLY LIFTING NEWD THROUGH THE UPPER
MS VALLEY AND SRN MANITOBA...WITH SOME INDICATION OF THE NEXT
UPSTREAM VORTICITY MAXIMUM CURRENTLY TRANSLATING EWD THROUGH
WRN/CNTRL MT. AT THE SURFACE...LOW PRESSURE OVER CNTRL SD IS
FORECAST TO REMAIN QUASI-STATIONARY OR PERHAPS REFORM WWD OWING TO
APPROACH OF NEXT MIDLEVEL IMPULSE. ASSOCIATED DEEPER WIND
SHIFT/FRONT IS EXPECTED TO PROGRESS SLOWLY EWD THROUGH THE DAKOTAS
TODAY...PROVIDING THE FOCUS FOR SEVERE TSTM DEVELOPMENT THIS
AFTERNOON.
SUSTAINED SLY LOW-LEVEL FLOW AHEAD OF SURFACE LOW AND ASSOCIATED
FRONT WILL SUPPORT THE NWD FLUX OF AN INCREASINGLY MOIST AIR MASS
THROUGH THE REGION TODAY WITH DEWPOINTS RISING THROUGH THE 60S F.
WHEN COUPLED WITH DAYTIME HEATING AND STEEP LAPSE
RATES...ENVIRONMENT IS EXPECTED TO BECOME MODERATE TO STRONGLY
UNSTABLE BY AFTERNOON WITH MLCAPE VALUES OF 2000-3000 J/KG. IN
ADDITION...THE EWD PROGRESSION OF 50-60 KT MIDLEVEL JET STREAK
ACROSS THE NRN PLAINS ALONG WITH A 30-35 KT LLJ WILL RESULT IN
INCREASINGLY STRONG SHEAR THROUGH THE DAY WITH DEEP-LAYER SHEAR OF
40-50 KT AND 0-1 KM SRH OF 100-200 M2/S2. AS SUCH...THE ENVIRONMENT
ACROSS THE ERN DAKOTAS INTO WRN MN IS EXPECTED TO BECOME QUITE
FAVORABLE FOR SUPERCELLS CAPABLE OF LARGE HAIL AND TORNADOES LATER
THIS AFTERNOON INTO TONIGHT.
LATEST MODEL GUIDANCE SUGGESTS THAT SURFACE-BASED STORMS WILL BECOME
INCREASINGLY LIKELY BY MID/LATE AFTERNOON ALONG FRONT OVER CNTRL/ERN
ND WITH ACTIVITY GRADUALLY BUILDING SWD INTO AT LEAST NERN SD AND
EVENTUALLY MOVING AND/OR DEVELOPING EWD INTO PARTS OF NWRN AND
W-CNTRL MN. STORMS WILL LIKELY GROW UPSCALE INTO AN MCS TONIGHT
WITH A CONTINUED THREAT FOR MAINLY HAIL AND DAMAGING WIND GUSTS
PERSISTING OVER THE ERN DAKOTAS INTO MN.
...CNTRL/ERN GULF COAST STATES...
LINEAR CONVECTIVE SYSTEM WHICH EVOLVED EARLY THIS MORNING OVER AR IS
PROGRESSING ESEWD THROUGH NERN MS/NWRN AL AT AROUND 35 KT. THIS MCS
IS LOCATED ALONG THE SRN FRINGE OF STRONGER LARGE-SCALE FORCING
ASSOCIATED WITH AMPLIFYING MIDLEVEL TROUGH WHICH WILL PROGRESS EWD
THROUGH THE OH/TN VALLEYS AND NRN GULF COAST STATES TODAY. DESPITE
POOR MIDLEVEL LAPSE RATES OBSERVED BY 12Z SOUNDINGS...AMBIENT INFLOW
AIR MASS IS EXPECTED TO EXPERIENCE STRONG DIABATIC HEATING. WHEN
COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE 70S F...ENVIRONMENT
WILL BECOME MODERATE TO STRONGLY UNSTABLE BY AFTERNOON WITH MLCAPE
APPROACHING 2000-3000 J/KG.
EARLIER VWP DATA FROM MEMPHIS SAMPLED A BELT OF SEASONABLY STRONG
/I.E. 40-50 KT/ MIDLEVEL FLOW FOR THAT LATITUDE WHICH WILL LIKELY
TRANSLATE EWD IN TANDEM WITH THE SHORT WAVE TROUGH. RESULTANT WIND
PROFILES WILL EXHIBIT DEEP WLY FLOW WITH SUFFICIENT VERTICAL SHEAR
TO MAINTAIN AN ORGANIZED MCS ACROSS THE REGION WITH THE PRIMARY
THREAT BEING DAMAGING WIND GUSTS.
...VA INTO THE CAROLINAS...
12Z MESOSCALE MODEL GUIDANCE SUGGESTS THAT WEAK LOW PRESSURE IS
LIKELY TO CONSOLIDATE ACROSS THE PIEDMONT OF THE CAROLINAS TODAY IN
ADVANCE OF MIDLEVEL TROUGH APPROACHING THE REGION FROM THE WEST.
MORNING VISIBLE SATELLITE DATA INDICATE THE PRESENCE OF LOW
CLOUDINESS ACROSS THE REGION WHICH SHOULD TEND TO DIMINISH WITH
DEEPER PBL MIXING. BOUNDARY LAYER REMAINS VERY MOIST WITH DEWPOINTS
IN THE 70S F...AND WHEN COUPLED WITH INCREASED DIABATIC
HEATING...EXPECT ENVIRONMENT TO BECOME MODERATELY UNSTABLE WITH
MLCAPE OF 1000-2000 J/KG.
SUSTAINED CONVERGENCE INVOF SURFACE LOW AND DEVELOPING LEE
TROUGH...IN CONCERT WITH INCREASED HEIGHT FALLS/DYNAMIC FORCING
ATTENDANT TO MIDLEVEL TROUGH ARE EXPECTED TO PROMOTE AN INCREASE IN
STORM COVERAGE AND INTENSITY THROUGH THE DIURNAL HEATING CYCLE.
STEADILY STRENGTHENING WLY FLOW AHEAD OF THE MIDLEVEL TROUGH MAY
SUPPORT THE DEVELOPMENT OF MULTICELL CLUSTERS OR ORGANIZED TSTM
BANDS WITH THE THREAT FOR DAMAGING WIND GUSTS.
...NJ INTO THE LOWER HUDSON VALLEY /NYC AREA/ AND SWRN NEW
ENGLAND...
A WELL-DEFINED MCV IS TRANSLATING NNEWD ALONG THE DE RIVER VALLEY
WITH A BAND OF STRONG TSTMS PERSISTING ALONG THE ERN/SERN PERIPHERY
OF THE CIRCULATION. FAIRLY WIDESPREAD CLOUDS WILL TEND TO LIMIT THE
DEGREE OF HEATING AND RESULTANT DESTABILIZATION TODAY ALONG SYSTEM
TRACK. HOWEVER...THE PRESENCE OF A VERY MOIST BOUNDARY LAYER /I.E.
DEWPOINTS IN THE 70S F/ WILL CONTRIBUTE TO POCKETS OF MODERATE
INSTABILITY. MOREOVER...ISALLOBARIC RESPONSE TO THIS SYSTEM IS
RESULTING IN A CORRIDOR OF BACKED LOW-LEVEL FLOW WHICH VEERS TO SWLY
IN THE MIDLEVEL...WITH A FAVORABLY SHAPED HODOGRAPH FOR STORM
ROTATION. IN FACT...SOME ROTATIONAL SIGNATURES HAVE BEEN OBSERVED
IN HIGH-RESOLUTION RADAR DATA...SUGGESTING AT LEAST A LOW THREAT FOR
A BRIEF TORNADO AND/OR STRONG WIND GUST. CURRENTLY...IT APPEARS
THAT THIS THREAT WILL REMAIN TOO BRIEF/MARGINAL TO WARRANT INCLUSION
OF HIGHER TORNADO PROBABILITIES AND A CATEGORICAL SLIGHT RISK AREA.
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