SWODY1
SPC AC 200102
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0802 PM CDT SUN AUG 19 2007
VALID 200100Z - 201200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NRN HIGH PLAINS/NRN
ROCKIES REGION...
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS VA...
..SYNOPSIS...
COMPLEXITY CHARACTERIZED MID/UPPER LEVEL PATTERN ACROSS CONUS.
STRONG/NEGATIVELY TILTED SHORTWAVE TROUGH -- EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER NRN ROCKIES -- IS FCST TO LIFT NEWD ACROSS MOST
OF MT AND SRN AB OVERNIGHT. DOWNSTREAM FROM THIS
PERTURBATION...SPLIT FLOW PATTERN WILL BECOME MORE PRONOUNCED WITH
STRONG UPPER DIFLUENCE SHIFTING EWD ACROSS NRN PLAINS TO UPPER MS
VALLEY. WEAK/EMBEDDED UPPER LEVEL PERTURBATIONS ARE EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER NERN MO/SERN IA...AND OVER MN/WRN IA.
SEPARATE MID/UPPER TROUGH -- ASSOCIATED WITH REMAINS OF TC ERIN --
SHOULD LIFT NEWD ACROSS MO...WHILE UPPER RIDGING PREVAILS TO ITS N
OVER NRN MN AND NWRN ONT. NRN STREAM FLOW CONVERGES AGAIN ACROSS ST
LAWRENCE VALLEY AND NERN CONUS IN ASSOCIATION WITH PRONOUNCED
TROUGHING FROM NRN GREENLAND SWD OVER CANADIAN MARITIMES. FARTHER
SW...WEAK TROUGH/CYCLONIC SHEAR ZONE WILL PERSIST BEHIND ERIN
TROUGH...SWWD ACROSS OK AND CENTRAL TX. THIS TROUGHING MAY BEGIN TO
PHASE LOOSELY WITH LARGE/PERSISTENT TUTT LOW MOVING WWD OVER WRN
GULF OF MEXICO...SPLITTING SRN CONUS RIDGING INTO SERN AND SERN
ANTICYCLONES.
AT SFC...WAVY/QUASISTATIONARY FRONTAL ZONE IS ANALYZED FROM
VA/TIDEWATER AREA WNWWD ACROSS WV...CENTRAL INDIANA TO LOW OVER SERN
SD/NWRN IA...SWWD ACROSS N-CENTRAL NEB THEN NWWD ACROSS SWRN SD AND
E-CENTRAL/N-CENTRAL MT. LEE-SIDE CYCLONE OVER N-CENTRAL MT IS FCST
TO CONSOLIDATE DURING NEXT FEW HOURS AND LIFT NEWD INTO SWRN
SASK...WHILE ASSOCIATED LOW LEVEL COLD FRONT SWEEPS EWD ACROSS
WRN/CENTRAL WY AND PORTIONS S-CENTRAL/SERN MT.
..NRN ROCKIES/NRN HIGH PLAINS...
SCATTERED TO WIDELY SCATTERED STG-SVR TSTMS SHOULD CONTINUE TO POSE
RISK OF DAMAGING WIND AND OCCASIONAL LARGE HAIL THROUGH AT LEAST
EARLY EVENING AS ACTIVITY MOVES ENEWD TO NEWD ACROSS REMAINDER MT
AND NRN WY. ACTIVITY IS OCCURRING WITHIN BROAD SWATH OF LARGE SCALE
ASCENT AND FAVORABLE DEEP-LAYER FLOW AHEAD OF SHORTWAVE TROUGH --
AND WILL MOVE OVER DEEP/WELL-MIXED BOUNDARY LAYER E OF MOUNTAINS
THAT WILL SUPPORT DAMAGING GUST POTENTIAL. REF WWS 617-618 AND
RELATED MESOSCALE DISCUSSION FOR NEAR-TERM GUIDANCE.
AS AREA OF STRONG LARGE-SCALE ASCENT ALOFT MOVES OVER INCREASINGLY
MOIST LOW LEVEL ENVIRONMENT OVER NERN WY...ERN MT AND PERHAPS WRN
DAKOTAS...ONE OR TWO CLUSTERS OF S-SVR TSTMS MAY PERSIST/DEVELOP
THROUGH LATE EVENING...E OF RELATIVELY DRY SFC PLUME. SUCH
CONVECTION MAY BE MOST CONCENTRATED/WELL-ORGANIZED INVOF 850 MB WARM
FRONT -- ORIENTED PARALLEL TO AND ABOUT 100-150 NM NE OF SFC
BOUNDARY -- FROM N-CENTRAL/NERN MT SEWD ACROSS WRN SD. THAT REGIME
WILL FEATURE CONVERGENT/30-40 KT SELY LLJ THAT WILL PROVIDE RICH LOW
LEVEL MOISTURE AND FAVORABLE STORM-RELATIVE INFLOW.
..VA...
PLUME OF ENHANCED MID-UPPER LEVEL FLOW CONTINUES TO CONTRIBUTE TO
FAVORABLE BULK SHEAR PROFILES ALONG AND JUST S OF FRONT THIS
EVENING...E.G. 50-60 KT EFFECTIVE SHEAR. LOW LEVEL SHEAR/VORTICITY
AND LIFT EACH WILL REMAIN ENHANCED ALONG FRONT AS WELL...IN
ENVIRONMENT OF RICH LOW LEVEL MOISTURE AND 1500-2000 J/KG
MLCAPE...CONTRIBUTING TO POTENTIAL FOR SVR TSTMS INCLUDING A FEW
SUPERCELLS. REF MESOSCALE DISCUSSION 1808 AND WW 619 FOR MORE
DETAILS. THREAT SHOULD DIMINISH AFTER ABOUT 05-06Z AS BOUNDARY LAYER
BUOYANCY IS REMOVED BY GRADUAL SFC/DIABATIC COOLING PROCESS.
..IA/SD BORDER REGION TO OH VALLEY AND OZARKS...
SCATTERED-NUMEROUS TSTMS SHOULD CONTINUE TO DEVELOP AND PERHAPS
BACKBUILD ACROSS IA...ASSOCIATED WITH HEAVY RAIN PRODUCING MCS.
MOISTURE IS VERY RICH OVER THAT AREA...AND EFFECTIVE LIFTED PARCELS
WILL REMAIN ROOTED AT SFC THROUGH MUCH OF THIS EVENING DUE TO
COMBINATION OF HIGH SFC THETAE AND LACK OF SBCINH. GIVEN WEAK
DEEP-LAYER SHEAR AND LACK OF SIGNIFICANT COLD-POOL POTENTIAL
EXPECTED...SVR POTENTIAL MAINLY CONSISTS OF LOCALIZED SMALL BOWS OR
WET MICROBURSTS...MOST OF WHICH WILL REMAIN BELOW 50 KT SVR CRITERIA
BUT WHICH STILL MAY TOPPLE TREES IN WET SOIL. A BRIEF/WEAK TORNADO
CANNOT BE RULED OUT IN STORM-SCALE INTERACTIONS OR MESOCYCLONIC
SPIN-UPS ALONG CONVECTION/BOUNDARY INTERACTIONS.
FARTHER S AND SE...NARROW PLUME OF MODERATE DEEP LAYER SHEAR WILL
SHIFT NEWD ACROSS IL/MO/NWRN AR...ATOP VERY RICH LOW LEVEL MOISTURE
AND E OF MIDLEVEL TROUGH ASSOCIATED WITH TC ERIN REMNANTS. REF SPC
MESOSCALE DISCUSSION 1807 FOR NEAR-TERM INFO ON ASSOCIATED
MRGL/SHORT-LIVED SVR THREAT.
.EDWARDS.. 08/20/2007
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