SPC AC 262038
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0338 PM CDT SUN JUL 26 2009
VALID 262000Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NERN CONUS TO VA...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MS DELTA...W-CENTRAL
GULF COASTAL REGION...
CORRECTED FOR GEN TSTM ARROW
--- UPDATES ---
...MS DELTA...W-CENTRAL GULF COASTAL REGION...
SPATIAL EXTENT OF SVR POTENTIAL CONTINUES TO COMPRESS COASTWARD AS
REMNANTS OF EARLIER MULTICELLULAR COMPLEXES CONTINUE TO MOVE SWD
ACROSS CENTRAL/WRN MS...NRN LA AND E TX. ADDITIONAL DEVELOPMENT
ALONG OR JUST BEHIND LEADING OUTFLOW EDGES SHOULD REINFORCE
ASSOCIATED COLD POOL...WHILE WIDELY SCATTERED CONVECTION NOW
DEVELOPING IN WEAKLY CAPPED AIR MASS AHEAD OF BOUNDARY MAY COALESCE
INTO MORE ORGANIZED MULTICELLULAR CLUSTERS WITH DAMAGING GUSTS
POSSIBLE. BOUNDARY COLLISIONS BETWEEN SWD PROPAGATING OUTFLOWS AND
SEA BREEZE ALSO MAY YIELD SHORT-TERM ERUPTION OF TSTMS AS WELL IN
ENVIRONMENT CHARACTERIZED BY SFC DEW POINTS 70S F...SUPPORTING
ANTECEDENT MLCAPE 1500-2500 J/KG.
...NERN CONUS TO VA...
MINOR ADJUSTMENTS MADE TO REFLECT CURRENT AND NOWCAST
CONVECTIVE/DESTABILIZATION TRENDS...AS DIURNAL CONVECTION CONTINUES
TO INTENSIFY AND INCREASE IN COVERAGE IN SEVERAL BKN BANDS AND SMALL
CLUSTERS AHEAD OF FRONT. MAIN THREAT REMAINS DAMAGING DOWNDRAFT
GUSTS...THOUGH LARGE HAIL AND A TORNADO OR TWO ARE POSSIBLE FROM ANY
SUSTAINED/DISCRETE SUPERCELLS ESPECIALLY OVER ERN MID-ATLANTIC
REGION AND SRN NEW ENGLAND. REF MCD 1680...WWS 625-626 AND
SUBSEQUENT MESOSCALE DISCUSSIONS FOR NEAR-TERM GUIDANCE.
..EDWARDS.. 07/26/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT SUN JUL 26 2009/
...SYNOPSIS...
UPPER LOW CENTERED OVER THE NRN GREAT LAKES WILL LIFT NEWD INTO
ONTARIO/WRN QUEBEC AS A SERIES OF IMPULSES ROTATE THROUGH THE TROUGH
AND AID IN CONVECTION. ONE SUCH WAVE/MCV WAS MOVING NEWD THROUGH
NERN PA AND ANOTHER WAS SHIFTING ENEWD ACROSS THE OH VALLEY TOWARD
THE NERN STATES. ERN WA UPR LOW IS FORECAST TO BEGIN MOVING SEWD AS
HEIGHTS BUILD IN BRITISH COLUMBIA. AT THE SFC...REMNANT COLD
FRONT...ROUGHLY DEFINED BY DEWPOINT DISCONTINUITY IN THE NERN
STATES...STRETCHED FROM ERN NY/PA SWWD INTO NRN VA...THEN WSWWD
THROUGH THE LOWER OH/TN VALLEYS AND INTO SRN OK/WRN TX.
...NRN NY AND VT...
INITIAL POTENTIAL FOR STRONGER CONVECTION ACROSS THE NERN STATES
WILL BE OVER NRN NY AND VT AS MCV APPROACHES FROM THE SW. WEAK
CAPPING INVERSION...MODEST INSTABILITY AND 30-40 KT DEEP LAYER SHEAR
WILL BE SUFFICIENT FOR SEVERE STORMS AND EVEN A SUPERCELL OR TWO
THROUGH THE AFTERNOON HOURS.
...SRN NY/SRN NEW ENGLAND SWD INTO VA...
SKIES HAVE GENERALLY BEEN SUNNY FROM VA INTO SRN NJ THIS MORNING AND
THIS HAS ALLOWED TEMPERATURES TO WARM INTO THE 80S. AS MCV SHIFTS
NEWD...CLOUDS ARE EXPECTED TO DECREASE ACROSS SRN NY/SRN NEW
ENGLAND. CONTINUED HEATING OF THE MOIST BOUNDARY LAYER...DEWPOINTS
AROUND 70...AND 6.5 C/KM MID LEVEL LAPSE RATES WILL YIELD MLCAPES
AROUND 2000 J/KG ALONG AND EAST OF FRONT/DEWPOINT DISCONTINUITY. THE
SEASONABLY STRONG SWLY MID-UPPER FLOW AND 30-40 KT OF EFFECTIVE
SHEAR WILL LIKELY RESULT IN WELL ORGANIZED AND SUSTAINED
STORMS...WITH SUPERCELLS AND BOWING SEGMENTS POSSIBLE.
UNIDIRECTIONAL WINDS ABOVE THE BOUNDARY LAYER SUGGEST DAMAGING WINDS
WILL BE THE PRIMARY THREAT. HAIL IS ALSO ANTICIPATED AND AN ISOLATED
TORNADO OR TWO IS POSSIBLE ACROSS SRN NY/SWRN NEW ENGLAND IF S/SELY
BOUNDARY LAYER WINDS CAN BE MAINTAINED THROUGH THE DAY.
...LOWER MS/TN VALLEYS...
ELEVATED THUNDERSTORMS ARE ONGOING FROM ERN TX EWD INTO MS. THESE
STORMS WERE LIKELY SUPPORTED BY THE LOW LEVEL JET...BUT HAVE
WEAKENED SOMEWHAT AS THE JET SPEEDS HAVE DECREASED. THOUGH SHEAR IS
WEAK...VERY MOIST ENVIRONMENT AND CONTINUED WARM ADVECTION BETWEEN
700-850 MB IS EXPECTED TO MAINTAIN STORMS ACROSS THE LOWER MS VALLEY
THROUGH THE AFTERNOON HOURS. PWAT/S NEARING 2 INCHES...LOW TO MID 70
DEWPOINTS AND 500 MB TEMPERATURES AROUND -10C WILL SUPPORT MLCAPES
TO 3000 J/KG...WHERE STRONG HEATING OCCURS. IF THE STORMS CAN
ORGANIZE AND FORM A COLD POOL...THE POTENTIAL FOR A SWD MOVING
MCS...WITH NWLY FLOW ALOFT...WOULD ENHANCED THE POTENTIAL FOR WIND
DAMAGE. ALTHOUGH A SEVERE STORM OR TWO ARE POSSIBLE ACROSS NRN
AL/NRN GA AND INTO ERN TN...THE SEVERE THREAT APPEARS LOWER THAN
ACROSS THE LOWER MS VALLEY DUE TO WEAKER CONVERGENCE AND MORE
CLOUDINESS AHEAD OF THE FRONT.
...CENTRL/SRN HIGH PLAINS...
ONCE MID/HIGH LEVEL CLOUDS THIN AND STRONGER HEATING COMMENCES...
SCATTERED STORMS ARE ONCE AGAIN EXPECTED TO INITIATE OVER THE
CO/NERN NM MOUNTAINS. THEREAFTER...THE NWLY FLOW ALOFT AND
INSTABILITY AXIS SHOULD CARRY THE STORMS SEWD INTO THE ADJACENT HIGH
PLAINS. WEAK WINDS BETWEEN 500-700 MB SHOULD RESULT IN STRONG
OUTFLOW/S AND THE POTENTIAL FOR A CLUSTER OR TWO TO ORGANIZE...WITH
STRONG WINDS AND PERHAPS SOME HAIL.
...NRN ROCKIES...
STORMS WILL ALSO REDEVELOP OVER THE NRN RCKYS THIS AFTN...THOUGH
STRONGER SHEAR ON THE SRN FRINGE OF THE UPPER LOW IS EXPECTED TO
REMAIN WEST OF THE STRONGER INSTABILITY. HOWEVER...BY LATE
AFTERNOON...A WELL MIXED BOUNDARY LAYER MAY SUPPORT A THREAT FOR
STRONG AND GUSTY WINDS WITH STRONGER STORMS.
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