SWODY1
SPC AC 031939
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0239 PM CDT FRI JUL 03 2009
VALID 032000Z - 041200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL HIGH
PLAINS...CNTRL PLAINS AND MID-MO VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF CNTRL AND ERN
MT...
THE GREATEST CHANGE TO THE 20Z OUTLOOK IS TO TAKE THE SLIGHT RISK
OUT OF FLORIDA. ALTHOUGH MODERATE INSTABILITY IS IN PLACE IN
FL...STORM COVERAGE IS LESS THAN EXPECTED. IN ADDITION...VERY WEAK
VERTICAL SHEAR PROFILES SHOULD KEEP ANY SEVERE THREAT MARGINAL THIS
AFTERNOON. ANOTHER CHANGE TO THE OUTLOOK IS TO ADD PARTS OF WRN AND
NRN NEB INTO THE SLIGHT RISK AREA WHERE MODERATE INSTABILITY IS
ALREADY IN PLACE ACCORDING TO THE RUC. MODEL FORECASTS DEVELOP
SCATTERED THUNDERSTORMS IN THE NEB PANHANDLE WHERE WSR-88D VWPS
SUGGEST VERTICAL SHEAR PROFILES ARE ADEQUATE FOR SEVERE STORMS WITH
HAIL THE MOST LIKELY THREAT. ANOTHER CHANGE TO THE OUTLOOK IS TO
MAKE THE SLIGHT RISK IN ERN MONTANA SMALLER AND CO-LOCATED WITH A
POCKET OF MODERATE INSTABILITY ANALYZED BY THE RUC.
LASTLY...ADJUSTED THE 5 PERCENT PROBABILITIES TO BETTER AGREE WITH
CURRENT CONVECTIVE DEVELOPMENT...MESOSCALE FEATURES AND SHORT-TERM
MODEL FORECASTS.
..BROYLES.. 07/03/2009
.PREV DISCUSSION... /ISSUED 1141 AM CDT FRI JUL 03 2009/
...CENTRAL PLAINS...
WEAK/ELEVATED TSTMS FROM SRN NEB TO KS/MO BORDER AREA APPEAR THE
RESULT OF WEAK MID LEVEL DISTURBANCE AND MARGINAL ISENTROPIC LIFT ON
THE NOSE OF PLAINS LLJ EARLY TODAY. AS THIS LEADING DISTURBANCE
CRESTS THE UPPER RIDGE...A SERIES OF STRONGER SHORT WAVE IMPULSES
ARE FORECAST TO DEVELOP EAST AND FLATTEN THE NRN PERIPHERY OF HOT
SUB-TROPICAL ANTICYCLONE ACROSS THE SRN PLAINS. LEE/THERMAL LOW...
CURRENTLY NEAR CO/KS BORDER...WILL MAKE SLOW EWD PROGRESS INTO KS
THIS AFTERNOON. LIFT AND LOW LEVEL CONVERGENCE ARE LIKELY TO BE
ENHANCED NEAR THIS LOW BY THE APPROACH OF MID LEVEL SHORT WAVES NOW
OVER WY/CO AND NM PER WV IMAGERY. DESPITE WARM TEMPS ALOFT...INTENSE
SURFACE HEATING ALONG AND SOUTH OF DIFFERENTIAL HEATING/WARM FRONTAL
BOUNDARY SETTING UP NEAR KS/NEB BORDER WILL CONTRIBUTE TO SCATTERED
SURFACE BASED TSTM INITIATION NEAR THE LOW AND WARM FRONT LATER
TODAY. ADDITIONAL STORMS ARE LIKELY DEVELOP AND INCREASE ACROSS THE
HIGHER TERRAIN OF NM/CO/WY AND SPREAD EAST WITH THE APPROACHING
SHORT WAVE DISTURBANCES AND HEATING OF THE DAY.
ACROSS KS/NEB AND POINTS EAST...SLY/SELY LOW LEVEL FLOW WILL VEER
AND INCREASE WITH HEIGHT RESULTING IN DEEP-LAYER EFFECTIVE SHEAR ON
THE ORDER OF 40-50KT. THIS SHOULD PROVE SUFFICIENT FOR SUPERCELLS
NEAR THE LOW AND WARM FRONT FROM LATE AFTERNOON INTO THE EVENING.
ALONG WITH LARGE HAIL AND DAMAGING WINDS...A TORNADO OR TWO CANNOT
BE COMPLETELY RULED OUT WITH ANY DISCRETE AND PERSISTENT SUPERCELL
TRACKING NEAR THESE SURFACE FEATURES.
FORECAST STRENGTHENING OF THE LLJ TO AOA 50 KT AFTER DARK SUGGESTS
ANY CONGEALING TSTM CLUSTERS MAY CONTINUE TO BE SUPPORTED LATE INTO
THE NIGHT AND PERHAPS GROW UPSCALE INTO LINEAR MCS SPREADING EAST
ACROSS THE MO RIVER VALLEY AND INTO PARTS OF IA/MO BY EARLY SAT.
MORE ORGANIZED COLD POOL AND DEEP CONVECTION PREFERENTIALLY ALIGNED
WITH STRENGTHENING LOW THROUGH MID LEVEL FLOW COULD RESULT IN
SCATTERED DAMAGING WINDS ACROSS THESE AREAS THROUGH LATE TONIGHT.
...FL WWD ALONG IMMEDIATE GULF COAST...
EXPECT TSTMS TO CONTINUES TO DEVELOP AND INCREASE IN AREAL COVERAGE
INTO THIS AFTERNOON ALONG AND SOUTH OF QUASI-STATIONARY FRONTAL ZONE
OVER NRN FL. WHILE MID LEVEL FLOW ACROSS THE REGION WILL REMAIN
MARGINAL FOR GREATER STORM ORGANIZATION...LATEST OBJECTIVE DATA
INDICATES THAT INTENSE HEATING WAS RESULTING IN STRONG INCREASE IN
DCAPE VALUES FROM THE ERN PNHDL ACROSS NRN FL ATTM. GIVEN WEAK
INHIBITION AND ABUNDANT MOISTURE/INSTABILITY...EXPECT MARGINALLY
ORGANIZED/MULTICELL TSTMS WITH THE CAPABILITY OF DAMAGING WINDS AND
SOME HAIL TO PERSIST ACROSS MUCH OF FL WELL INTO THE AFTERNOON.
...MT...
WEAK MID LEVEL DISTURBANCE AND ASSOCIATED FRONTAL SURGE EAST OF THE
HIGH TERRAIN COMBINED WITH GREATER LOW LEVEL MOISTURE AND INCREASING
INSTABILITY SHOULD CONTRIBUTE TO INCREASINGLY STRONG TSTMS ACROSS
CNTRL/ERN MT TODAY. A FEW STOUT CELLS WERE ALREADY DEVELOPING OFF
THE HIGHER TERRAIN AND EXPECT THIS TREND TO CONTINUE. DEEP-LAYER
SHEAR ON THE ORDER OF 30-35KT SUGGESTS A FEW STORMS COULD ATTAIN
SUPERCELL CHARACTERISTIC WITH ATTENDANT THREATS OF LARGE HAIL AND
HIGH WINDS.
...NORTHEAST...
UNUSUALLY DEEP MEAN TROUGHING ACROSS NEW ENGLAND AND PARTS OF THE
NORTHEAST WILL BE REINFORCED THIS PERIOD AS ANOTHER STRONG IMPULSE
DIVES SEWD FROM ONTARIO AND PRODUCES ANOTHER ROUND OF WEAK HEIGHT
FALLS ACROSS NERN NY AND NRN NEW ENGLAND. LOW STATIC STABILITY AND
MARGINAL BACKGROUND ASCENT WITHIN THE TROUGH AXIS WILL AGAIN FAVOR A
DIURNAL INCREASE IN CONVECTION...ESPECIALLY ACROSS THOSE AREAS
RECEIVING GREATER SURFACE HEATING THROUGH EARLY AFTERNOON. LIMITED
CAPE AND MARGINAL CLOUD-BEARING SHEAR WITHIN THE SLACK FLOW IN THE
TROUGH AXIS SUGGEST THAT SEVERE STORM POTENTIAL SHOULD BE LOW.
HOWEVER...A FEW STORMS WILL BE CAPABLE OF HAIL/BRIEF STRONG/GUSTY
WIND FROM LATE AFTERNOON TO EARLY EVENING.
...SOUTHEAST ACROSS INTERMOUNTAIN WEST...
INTENSE SURFACE HEATING ON THE WRN PERIPHERY OF MONSOON MOISTURE
PLUME SHOULD SPUR WIDESPREAD TSTM DEVELOPMENT FROM AZ ACROSS UT AS
WELL AS THE ROCKIES AND INTO THE INTERIOR NW. MUCH OF THIS
CONVECTION WILL BE WEAKLY ORGANIZED DUE TO LIMITED FLOW/SHEAR AND
WILL BE TIED TO ELEVATED HEAT SOURCES/TERRAIN. ISOLATED STRONG TO
SEVERE WIND GUSTS AND PERHAPS A FEW MARGINAL SEVERE HAIL EVENTS
COULD OCCUR THROUGH THE LATE AFTERNOON.
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