SWODY1
SPC AC 101256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT TUE MAY 10 2011
VALID 101300Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE OH VALLEY
TO CAROLINAS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE UPPER
MIDWEST...
...IND/OH TO CAROLINAS...
MORNING WATER VAPOR IMAGERY SHOWS SUBTLE VORTICITY MAXIMA CRESTING
MIDLEVEL RIDGE AXIS FROM THE UPPER MIDWEST INTO THE OZARKS WHICH ARE
LIKELY CONTRIBUTING TO ONGOING ELEVATED STORMS ACROSS THE GREAT
LAKES AND MID MS VALLEY. THESE FEATURES WILL BEGIN TO TURN MORE
SEWD TODAY AND ACCELERATE...REACHING THE SERN ATLANTIC COAST BY
11/12Z. AT THE SAME TIME...SURFACE WARM FRONT WILL CONTINUE TO
SLOWLY LIFT NEWD...LIKELY EXTENDING ALONG A LINE FROM NRN IND-SWRN
OH-WRN PARTS VA/NC-NRN SC BY LATE AFTERNOON. STEEP LOW TO MIDLEVEL
LAPSE RATES COUPLED WITH BOUNDARY LAYER DEW POINTS IN THE 60S WILL
YIELD A MODERATELY TO STRONGLY UNSTABLE AIR MASS TODAY W/SW OF WARM
FRONT WHERE MLCAPE VALUES WILL APPROACH 2000-3000+ J/KG.
FRONTAL UPLIFT COUPLED WITH SUSTAINED LOW-LEVEL WAA AND DCVA IN
ADVANCE OF MIDLEVEL IMPULSES MAY ALLOW SOME REMNANT OF ONGOING
ELEVATED STORMS TO TRANSITION TO SURFACE-BASED BY AFTERNOON ACROSS
PARTS OF IND/OH. ADDITIONAL IN SITU STORM FORMATION APPEARS LIKELY
ALONG THE WARM FRONT THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE.
FORECAST HODOGRAPHS EXHIBIT PRONOUNCED VEERING OF WINDS WITH HEIGHT
AND 40-50 KT OF DEEP NWLY SHEAR WHICH WILL BE SUPPORTIVE OF
SUPERCELLS WITH THE INITIAL STORM DEVELOPMENT. WITH TIME...ONE OR
MULTIPLE FORWARD-PROPAGATING MCSS ARE EXPECTED TO EVOLVE...PRODUCING
SWATHS OF DAMAGING WINDS AND HAIL.
...MN/WI...
SURFACE LOW OVER ERN SD IS FORECAST TO DEVELOP NWD OR NWWD TODAY IN
CONJUNCTION WITH STRONG VORTICITY MAXIMUM LIFTING NNEWD THROUGH THE
WRN DAKOTAS. AS THIS OCCURS...ASSOCIATED WARM FRONT WILL
CONCURRENTLY LIFT NWD...EXTENDING FROM THE RED RIVER VALLEY TO SRN
WI BY LATE AFTERNOON/EARLY EVENING. BOUNDARY LAYER DEWPOINTS IN THE
60S AND STEEP MIDLEVEL LAPSE RATES WILL CONTRIBUTE TO A STRONGLY
UNSTABLE AIR MASS S OF WARM FRONT TODAY WHERE MLCAPE VALUES WILL
INCREASE TO 2500-3500+ J/KG.
LATEST MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING THAT THE
STRONG HEIGHT FALLS/FORCING FOR ASCENT ATTENDANT TO ABOVE-MENTIONED
VORTICITY WILL REMAIN TO THE W OF THE REGION THROUGH THIS
EVENING...LEAVING SURFACE-BASED STORM INITIATION IN QUESTION DUE TO
THE STRENGTH OF THE CAP. THE MOST PROBABLE AREA OF STORM
DEVELOPMENT WILL BE NRN OR CNTRL MN LATE THIS AFTERNOON INTO EVENING
INVOF SURFACE FRONTAL OCCLUSION.
SHOULD STORMS DEVELOP...THE COMBINATION OF THE STRONG INSTABILITY
AND VERTICALLY VEERING WIND PROFILES WILL SUPPORT SUPERCELL
DEVELOPMENT WITH A RISK FOR VERY LARGE HAIL...DAMAGING WINDS AND A
FEW TORNADOES. SUBSEQUENT UPSCALE GROWTH TO A SEWD-MOVING MCS WOULD
BE POSSIBLE TONIGHT WITH A CONTINUED THREAT FOR HAIL AND DAMAGING
WINDS INTO PARTS OF WI.
...SRN PLAINS...
WELL-DEFINED VORTICITY MAXIMUM CURRENTLY MOVING INTO THE TX BIG BEND
REGION SHOULD CONTINUE NEWD TODAY WITHIN PREVAILING SWLY MIDLEVEL
FLOW REGIME. FORCING FOR ASCENT ASSOCIATED WITH THIS FEATURE HAS
FOSTERED WIDELY SCATTERED TSTMS THIS MORNING FROM THE TX LOW ROLLING
PLAINS TO NEAR DRT. 12Z SOUNDINGS FROM DRT AND FWD SUGGEST THAT
THIS ACTIVITY IS LIKELY ELEVATED ABOVE THE CAP AND ROOTED WITHIN A
STEEP LAPSE RATE ENVIRONMENT WITH 700-500 MB LAPSE RATES OF 9.0-9.5
C/KM. AS SUCH...ACTIVITY WILL BE CAPABLE OF ISOLATED OCCURRENCES OF
HAIL AS IT MOVES/DEVELOPS EWD/NEWD THIS MORNING.
BY AFTERNOON...CONSIDERABLE MODEL VARIABILITY AND INHERENT FORECAST
UNCERTAINTY EXISTS WITH RESPECT TO CONVECTIVE EVOLUTION. CURRENT
THINKING IS THAT CORRIDOR OF FORCING IN ADVANCE OF SHORT WAVE TROUGH
WILL CONTINUE TO FOSTER TSTM DEVELOPMENT TOWARD AND EVENTUALLY E OF
THE I-35 CORRIDOR AND SURFACE DRYLINE. GIVEN THE STRENGTHEN OF THE
CAP...IT IS UNCERTAIN WHETHER THESE STORMS WILL BECOME ROOTED IN THE
BOUNDARY LAYER OR REMAIN ELEVATED.
FARTHER W ALONG THE DRYLINE...AREA WILL REMAIN IN A ZONE OF
SUBSIDENCE IN THE WAKE OF SHORT WAVE TROUGH PASSAGE LATER TODAY.
MOREOVER...CONVERGENCE ALONG THE BOUNDARY WILL WEAKEN WITH TIME AS
LEE CYCLOGENESIS COMMENCES OVER SERN CO. THE NET RESULT IS A LOW
CONFIDENCE IN DIURNAL STORM FORMATION ALONG THE DRYLINE THIS
AFTERNOON INTO EVENING.
DUE TO THE HIGH UNCERTAINTY IN CONVECTIVE EVOLUTION AND WHERE THE
GREATEST SEVERE WEATHER THREAT WILL MATERIALIZE...THE CATEGORICAL
SLIGHT RISK HAS BEEN REMOVED.
..MEAD/GRAMS.. 05/10/2011
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