SPC AC 311249
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT THU JUL 31 2008
VALID 311300Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN MS RIVER VALLEY
ACROSS THE SRN GREAT LAKES REGION...
...THERE IS A SLGT RISK OF SVR TSTMS OVER MUCH OF THE CAROLINAS...
...UPPER MIDWEST...
LONG-LIVED BOW ECHO WITH HISTORY OF SIGNIFICANT DAMAGING WINDS EARLY
THURSDAY MORNING CONTINUES ALONG WELL-DEFINED SURFACE FRONT
EXTENDING FROM THE SRN GREAT LAKES INTO SERN MN AS OF 13Z. SOME
QUESTION ABOUT WHETHER OR NOT SYSTEM WILL SURVIVE STRONG CAPPING
THROUGH THE MID/LATE MORNING ACROSS THE UPPER MS RIVER VALLEY.
HOWEVER...CLEAR SKIES AND STEEP LAPSE RATES AHEAD OF THE
SYSTEM...ALONG WITH WELL-DEFINED MCV...SUGGEST SYSTEM MAY EITHER
CONTINUE SEVERE OR WEAKEN BRIEFLY BEFORE RE-INTENSIFYING LATER THIS
MORNING/EARLY THIS AFTERNOON DOWNSTREAM. IF SYSTEM DOES WEAKEN
CONSIDERABLY THIS MORNING...RELATED OUTFLOW/DIFFERENTIAL HEATING
ZONE WILL BLEND WITH SYNOPTIC WARM FRONT OVER NRN IA/SRN WI INTO NRN
IL. THIS SHOULD SERVE AS PRIMARY FOCUS FOR AFTERNOON/EVENING SVR
POTENTIAL INCLUDING SUPERCELL RISK.
BY AFTERNOON...VERY STG INSTABILITY SHOULD DEVELOP WITHIN AND S OF
WARM FRONTAL/DIFFERENTIAL HEATING ZONE...WITH STG SFC HEATING AND
FRONTAL CONVERGENCE TO YIELD WEAK CINH. SFC DEW POINTS IN THE UPPER
60S TO LOW 70S F WILL BE COMMON BY MID-LATE AFTERNOON BENEATH 7-8
DEG C/KM MIDLEVEL LAPSE RATES...CONTRIBUTING TO MLCAPES IN 3000-4000
J/KG RANGE. ALTHOUGH SFC WINDS ARE NOT FCST TO BE PARTICULARLY
STG...DIRECTIONAL SHEAR IS. RELATIVELY BACKED FLOW INVOF BOUNDARY
SHOULD YIELD LOOPED HODOGRAPHS...AS WELL AS ENHANCED STORM-RELATIVE
INFLOW IN NARROW CORRIDOR. DISCRETE SUPERCELLS WOULD HAVE POTENTIAL
FOR DAMAGING HAIL GIVEN THEIR INTERNAL FORCING AND LARGE AMBIENT
BUOYANCY. INSTABILITY GRADIENT WILL BE FAVORED CORRIDOR FOR MOTION
OF ANY SUBSEQUENT MCS...EXPANDED UPSCALE OR RE-INTENSIFIED FROM
EARLIER ACTIVITY. ASSOCIATED WIND THREAT MAY EXTEND ACROSS MUCH OF
THE SRN GREAT LAKES AND CENTRAL IND/IL GIVEN BROAD REGION OF
MODERATE NWLY FLOW ALOFT.
...SERN CONUS...
RELATIVE CONCENTRATION OF PULSE/MULTICELL EVENTS -- PRIMARILY
DAMAGING DOWNBURST WINDS -- MAY DEVELOP DURING AFTERNOON AS CINH
WEAKENS...NEAR AND E OF WEAK LEE-SIDE TROUGH. SCATTERED-NUMEROUS
TSTMS IN CLUSTERS ARE POSSIBLE. SFC DEW POINTS COMMONLY 70S F --
WITH SOME POCKETS MIXED INTO UPPER 60S -- COMBINED WITH STG DIABATIC
HEATING SHOULD BE SUFFICIENT TO OVERCOME WEAK LAPSE RATES ALOFT.
RESULT SHOULD BE MLCAPES 1500-2500 J/KG ATOP STEEP THERMAL LAPSE
RATES IN SUB CLOUD LAYER. FCST SOUNDINGS SUGGEST SHALLOW INVERTED-V
PROFILE CHARACTERISTIC OF WELL-MIXED ENVIRONMENTS AND SUPPORTING
DOWNDRAFT ACCELERATION. COLD POOL ORGANIZATION AND OUTFLOW
BOUNDARIES WILL STRONGLY INFLUENCE THREAT WITHIN OUTLOOK AREA.
...NERN CONUS...
WEAK CONVERGENCE INVOF FRONT/TROUGH...DIURNAL HEATING...AND
FAVORABLE MOISTURE SHOULD SUPPORT POTENTIAL FOR SCATTERED LATE
MORNING THROUGH LATE AFTERNOON TSTMS WITH RISK FOR STRONG/MARGINALLY
SEVERE WIND GUSTS AND/OR HAIL. SHEAR WILL REMAIN SUPPORTIVE OF WEAK
STORM-SCALE ORGANIZATION...ALTHOUGH VERY WEAK LOW-MID LEVEL LAPSE
RATES WILL LIMIT BOTH AVAILABLE INSTABILITY AND RESULTANT UPDRAFT
INTENSITIES.
...TN-TX...
FRONTAL ZONE WILL CONCENTRATE CONVECTIVE POTENTIAL DURING
AFTERNOON...AND MAY BE ENHANCED BY DIFFERENTIAL HEATING OVER TN/KY
AREA -- S OF LARGE/PERSISTENT AREA OF PRECIP AND CLOUDS PRESENTLY
UNDERWAY AND LIKELY TO PERSIST THROUGH MUCH OF REMAINDER OF MORNING.
LOCALIZED AREAS OF ENHANCED PULSE/MULTICELL POTENTIAL MAY DEVELOP
INVOF STRONGER BOUNDARIES OR THEIR INTERSECTIONS...HOWEVER
COMBINATION OF SUCH MESOSCALE UNCERTAINTIES AND WEAKNESS OF
DEEP-LAYER WIND FIELDS PRECLUDES CATEGORICAL OUTLOOK ATTM.
..EVANS/EDWARDS/SMITH.. 07/31/2008
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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