SWODY2
SPC AC 171726
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT THU MAY 17 2007
VALID 181200Z - 191200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
NRN EXTENT OF UPPER RIDGE IN THE WEST IS EXPECTED TO SHIFT E TOWARD
THE NRN PLAINS AS A PACIFIC TROUGH MOVES INTO THE NWRN STATES AND
BRITISH COLUMBIA. IN THE EAST...MID/UPPER LEVEL TROUGH TRACKING
SEWD THROUGH THE OH VALLEY DURING DAY 1 IS FORECAST TO EVOLVE INTO A
CLOSED LOW AS IT MOVES SLOWLY EWD ACROSS THE CENTRAL
APPALACHIANS/MID ATLANTIC STATES ON FRIDAY.
IN THE LOW LEVELS...SURFACE HIGH CENTERED OVER THE UPPER MS VALLEY
THIS MORNING IS EXPECTED TO SHIFT SEWD INTO THE OH VALLEY AND MID
SOUTH. THIS SHOULD ALLOW MOISTURE TO ADVECT NWD FROM THE SRN HIGH
PLAINS ALONG WRN PERIPHERY OF SURFACE RIDGE INTO THE NRN PLAINS AS
SURFACE FLOW BECOMES MORE SLY WITHIN THIS CORRIDOR. MEANWHILE...A
COLD FRONT...INITIALLY EXTENDING FROM HUDSON BAY SWWD THROUGH SRN
MANITOBA/SASKATCHEWAN TO CENTRAL MT IS EXPECTED TO ADVANCE SLOWLY
SEWD REACHING THE ND/CANADIAN BORDER TO THE MT/WY BORDER BY 19/00Z.
..NRN PLAINS...
A LEAD SHORT WAVE TROUGH IN THE WEST...CURRENTLY MOVING NEWD ACROSS
WRN WA/BRITISH COLUMBIA...IS EXPECTED TO TOP THE RIDGE OVER SRN
CANADA ON FRIDAY WITH THE SRN EXTENT GLANCING THE NRN PLAINS.
UNCERTAINTIES WITH RESPECT TO QUALITY OF MOISTURE RETURN INTO THE
NRN PLAINS ON FRIDAY...STRENGTH OF CAP UNDER RIDGE...AND TIMING OF
COLD FRONT MOVING INTO FAR NRN ND BY EARLY FRIDAY EVENING CONTINUE
TO PRECLUDE INTRODUCTION OF HIGHER SEVERE PROBABILITIES.
STRONGEST INSTABILITY /MLCAPE 1000-1500 J/KG/ SHOULD DEVELOP OVER
PARTS OF THE ERN DAKOTAS INTO NWRN MN AS PLUME OF STEEP MID LEVEL
LAPSE RATES EXTEND EWD ATOP AXIS OF MOISTURE RETURN. STRONG SURFACE
HEATING MAY ALLOW A FEW TSTMS TO DEVELOP ACROSS FAR NERN ND WITH THE
APPROACH OF THE COLD FRONT...AND SSWWD ALONG THE DRY LINE INTO SRN
ND TO WRN NEB JUST AFTER PEAK HEATING. HOWEVER...AT THIS TIME...A
RATHER STRONG CAP IS EXPECTED TO INHIBIT DIURNAL TSTM INITIATION.
GREATER LIKELIHOOD FOR TSTM DEVELOPMENT AND AN ISOLATED SEVERE
THREAT SHOULD DEVELOP FRIDAY EVENING AS THE COLD FRONT PROGRESSES S
TOWARD SD AND CENTRAL MN TO LAKE SUPERIOR. INCREASING WAA ALONG LLJ
WILL LIKELY MAINTAIN DESTABILIZATION WITH SUFFICIENT ELEVATED CAPE
SUPPORTING A FEW SEVERE TSTMS FROM THE DAKOTAS INTO NRN/ CENTRAL MN
FRIDAY NIGHT.
..SWRN/SRN MT...
ALTHOUGH MOISTURE IS EXPECTED TO REMAIN SOMEWHAT LIMITED INTO
SWRN/SRN MT IN THE VICINITY OF THE COLD FRONT...STEEP LAPSE
RATES...SURFACE HEATING AND CONTINUED STREAM OF MID LEVEL MOISTURE
SPREADING NEWD WILL SUPPORT AT LEAST WEAK INSTABILITY FOR TSTMS.
N/NELY POST-FRONTAL UPSLOPE FLOW INTO THE HIGHER TERRAIN OF SWRN/
SRN MT WILL AID IN THIS TSTM DEVELOPMENT AND ALSO CONTRIBUTE TO
STRONGER DEEP LAYER SHEAR GIVEN INCREASING SWLY MID LEVEL FLOW.
ALTHOUGH WEAK INSTABILITY WILL TEND TO LIMIT THE SEVERE WEATHER
THREAT...STRONGER SHEAR...STEEP LAPSE RATES AND HIGH BASED STORMS
SUGGEST THE POTENTIAL FOR BOTH LOCALLY STRONG WIND GUSTS AND
ISOLATED HAIL.
..SRN ROCKIES TO MEXICAN BORDER...
MODELS SUGGEST WEAK MID LEVEL IMPULSE SHOULD TRANSLATE EWD WITHIN
MEAN RIDGE AXIS ON FRIDAY. ASCENT WITH ANY OF THESE FEATURES AND
A MODERATELY UNSTABLE AIR MASS SHOULD ALLOW TSTMS TO DEVELOP AGAIN
ON DAY2 FROM THE SRN ROCKIES SWD TO THE MEXICAN BORDER. A FEW TSTMS
MAY PRODUCE LOCALLY STRONG WINDS AND/OR ISOLATED HAIL APPROACHING
SEVERE LEVELS. HOWEVER...OVERALL WEAK WLY MID LEVEL WINDS NORTH OF
THE U.S./ MEXICO BORDER SHOULD LIMIT POTENTIAL FOR STORM
ORGANIZATION. GREATEST POTENTIAL FOR STORM ORGANIZATION MAY BE OVER
FAR SW TX... BUT CONFIDENCE REMAINS LOW AT THIS TIME.
..FL...
A COLD FRONT MOVING SWD THROUGH CENTRAL AND SRN FL ON FRIDAY WILL BE
THE FOCUS OF TSTM DEVELOPMENT...WITH TSTMS ALSO FORMING ALONG
SEA/LAKE BREEZES IN SRN FL. ALTHOUGH MODELS SUGGEST STRONGER DEEP
LAYER SHEAR ACROSS THE FL PENINSULA THAT WOULD SUPPORT ORGANIZED
STORMS...INSTABILITY MAY REMAIN TOO MARGINAL TO RESULT IN HIGHER
SEVERE PROBABILITIES. IF STRONGER INSTABILITY IS EXPECTED IN LATER
OUTLOOKS...THEN A CATEGORICAL RISK MAY THEN BE REQUIRED.
.PETERS.. 05/17/2007
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