SWODY2
SPC AC 310619
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0119 AM CDT WED AUG 31 2011
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM NERN CO NEWD ACROSS THE
ERN DAKOTAS TO NRN MN/NWRN WI...
...SYNOPSIS...
A SERIES OF SHORTWAVE TROUGHS WILL PIVOT THROUGH LARGER SCALE
TROUGHING ACROSS THE INTERIOR NW THIS PERIOD AND MOVE FROM THE NRN
ROCKIES INTO SCNTRL CANADA. THESE SYSTEMS WILL ACT TO TEMPER THE
UPPER RIDGE AXIS ACROSS THE PLAINS AND MIDWEST AND SET THE STAGE FOR
A GRADUAL PATTERN CHANGE WITH THE CNTRL U.S. EXPANSIVE SUBTROPICAL
RIDGE EVENTUALLY BEING SUPPRESSED SWD.
A LEADING SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW WILL LIFT INTO
SRN CANADA DURING THE DY1 PERIOD...THROUGH EARLY THURSDAY MORNING.
THE COLD FRONT TRAILING FROM THE LOW IN CANADA IS FORECAST TO BE
SITUATED FROM NRN MN SWWD TO WY BY THURSDAY AFTERNOON WITH A
THERMAL/PRE-FRONTAL TROUGH LEADING THE FRONT...FROM ERN CO ACROSS
NEB TO MN. A STRONGER AND MORE AMPLIFIED TRAILING SHORTWAVE WILL
THEN DEVELOP EAST ACROSS THE NRN PLAINS THROUGH LATE THURSDAY NIGHT
WITH SUBSEQUENT 500MB HEIGHT FALLS AIDING LIFT AND TSTM DEVELOPMENT
ACROSS AND OVER THE ADVANCING COLD FRONT FROM WY/CO TO THE CNTRL/NRN
PLAINS...AND INTO THE UPPER MS VALLEY BY EARLY FRIDAY.
A WEAK SHORTWAVE TROUGH CRESTING THE RIDGE AXIS ACROSS THE GREAT
LAKES...COUPLED WITH PERSISTENT LOW LEVEL WARM ADVECTION...WILL
PROMOTE SCATTERED STORMS ACROSS THE ERN LAKES...PA AND NY.
NHC INDICATES A LOW PROBABILITY OF TC DEVELOPMENT IN THE GULF
THROUGH THE PERIOD AS AN UPPER LEVEL WAVE SPREADS NWWD...ON THE SRN
FLANK OF THE SUBTROPICAL RIDGE.
...MN SWWD TO CNTRL HIGH PLAINS...
MCS ASSOCIATED WITH LEADING FRONTAL WAVE AND WARM ADVECTION MAY BE
ONGOING EARLY IN THE PERIOD ALONG THE MN/CANADA BORDER AREA ON THE
EDGE OF A STRENGTHENING CAPPING INVERSION. VERY STRONG
DESTABILIZATION IS INDICATED IN THE WAKE OF THIS MCS...ALONG ITS
OUTFLOW BOUNDARY...ACROSS NRN MN DURING THE DAY. ENHANCED LIFT AND
DEEPENING FRONTAL CIRCULATION AIDED BY THE APPROACH OF THE NEXT
SHORTWAVE TROUGH ARE EXPECTED TO SUPPORT RENEWED TSTM DEVELOPMENT IN
NRN MN AS INHIBITION IS GRADUALLY OVERCOME LATER IN THE DAY.
DEEP-LAYER SHEAR WILL BE SUPPORTIVE OF SUPERCELLS IF STORMS CAN
INITIATE IN THIS AREA WITH VERY LARGE HAIL AND HIGH WINDS POSSIBLE.
ONE OR TWO STORM CLUSTERS MAY PERSIST AND SPREAD ACROSS THE
ARROWHEAD AND INTO WI THROUGH EARLY FRIDAY.
THE NEXT AREA OF CONCERN FOR SCATTERED SEVERE TSTMS WILL DEVELOP
ACROSS THE FRONT RANGE IN THE POST-FRONTAL UPSLOPE FLOW REGIME.
LARGE SCALE ASCENT WILL SPREAD ACROSS THESE AREAS COINCIDENT WITH
DIURNAL HEATING. DESPITE GENERALLY WEAKER INSTABILITY ACROSS THE
AREA...STRONG DIRECTIONAL SHEAR AND AN AXIS OF GREATER LOW LEVEL
MOISTENING AND ASCENT EXTENDING EAST INTO NEB/SD...SHOULD RESULT IN
A FEW STORM CLUSTERS EVOLVING THROUGH THE LATE EVENING. HAIL APPEARS
TO BE THE GREATEST THREAT WITH THIS DEVELOPING CONVECTION THAT
SHOULD CONTINUE TO PROPAGATE EAST ACROSS NEB/SD ATOP THE DEEPENING
FRONTAL SURGE WITH BOTH LAPSE RATES AND EFFECTIVE SHEAR MAINTAINING
A CHANCE FOR SEVERE HAIL.
...PA/NY...
MODEST DESTABILIZATION /MLCAPE 1000-1500 J PER KG/ IS INDICATED
ALONG A WEAK WARM FRONT FROM OH INTO PA/NY DURING THE AFTERNOON.
REGION WILL LIE BENEATH 20-30KT NWLY FLOW ALOFT AND THE PASSAGE OF A
LOW AMPLITUDE SHORTWAVE TROUGH MAY AID TSTM DEVELOPMENT. A FEW
STORMS MAY PERSIST AND GAIN MARGINAL SUPERCELL STRUCTURE GIVEN
FORECAST SHEAR/INSTABILITY PARAMETERS. HAIL AND LOCALLY STRONG WINDS
ARE POSSIBLE BUT GENERALLY MEAGER LARGE SCALE FORCING AND MARGINAL
CAPE/SHEAR PRECLUDE HIGHER SEVERE PROBABILITIES AT THIS TIME.
..CARBIN.. 08/31/2011
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