SWODY2
SPC AC 010542
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1242 AM CDT TUE SEP 01 2009
VALID 021200Z - 031200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
STRONGER WESTERLIES STILL APPEAR LIKELY TO REMAIN GENERALLY WELL
NORTH OF THE CANADIAN/U.S. BORDER THROUGH THIS FORECAST PERIOD.
HOWEVER...A STRONG ZONAL POLAR JET STREAK NOSING ACROSS THE MID
LATITUDE PACIFIC IS PROGGED TO CONTRIBUTE TO THE NORTHEASTWARD
ACCELERATION OF A PREVIOUSLY CUT-OFF UPPER LOW ACROSS THE PACIFIC
NORTHWEST COAST BY LATE WEDNESDAY NIGHT/EARLY THURSDAY. AS THIS
OCCURS...DESTABILIZATION ASSOCIATED WITH MOISTURE ADVECTION ON
SOUTHERLY FLOW MAY SUPPORT SCATTERED THUNDERSTORMS ACROSS THE
NORTHERN GREAT BASIN DURING THE AFTERNOON AND EVENING HOURS. A BIT
LATER IN THE EVENING AND OVERNIGHT...MID-LEVEL COOLING AND
STRENGTHENING ONSHORE FLOW MAY BE ACCOMPANIED BY A FEW STORMS ALONG
THE WESTERN SLOPES OF THE CASCADES.
WHILE UPPER RIDGING WEAKENS ACROSS PARTS OF THE NORTHWEST...
DOWNSTREAM FLOW IS EXPECTED TO REMAIN BROADLY ANTICYCLONIC ACROSS
MUCH OF THE INTERMOUNTAIN WEST AND ROCKIES INTO THE PLAINS... WHILE
WEAK CYCLONIC FLOW LINGERS ACROSS MUCH OF THE MISSISSIPPI VALLEY
THROUGH THE ATLANTIC SEABOARD. A COUPLE OF SMALL MID-LEVEL
CIRCULATIONS DIGGING EAST OF THE RIDGE INTO THE TROUGH MAY BE
ACCOMPANIED BY SCATTERED THUNDERSTORMS ACROSS MUCH OF THE NORTHERN
AND CENTRAL PLAINS AND PARTS OF THE LOWER MISSISSIPPI VALLEY.
BUT...SEASONABLY HIGH MOISTURE CONTENT AIR CHARACTERIZED BY
PRECIPITABLE WATER IN EXCESS OF 2 INCHES IS ONCE AGAIN EXPECTED TO
BE CONFINED TO THE FLORIDA PENINSULA...ALONG WITH HIGHEST
THUNDERSTORM PROBABILITIES.
MEANWHILE...A SIGNIFICANT MOISTURE INCREASE OFF THE GULF OF
CALIFORNIA INTO THE SOUTHERN PLATEAU REMAINS POSSIBLE...AIDED BY
HURRICANE JIMENA. AND THIS WILL PROBABLY ALSO BE ACCOMPANIED BY AT
LEAST SCATTERED THUNDERSTORM ACTIVITY.
...CENTRAL PLAINS...
NORTHWESTERLY FLOW ALOFT STILL APPEARS LIKELY TO STRENGTHEN SOMEWHAT
IN A BROKEN BAND ACROSS THE REGION WEDNESDAY... CONTRIBUTING TO
MODESTLY STRONG DEEP LAYER SHEAR SUFFICIENT FOR SUPERCELLS...AT
LEAST IN POCKETS. WITH NO GULF RETURN FLOW DEVELOPING...MOISTURE
LEVELS REMAIN THE PRIMARY LIMITING FACTOR WITH REGARD TO SEVERE
POTENTIAL...GIVEN THE EXPECTED PRESENCE OF STEEP LAPSE RATES. SREF
GUIDANCE CONTINUES TO INDICATE THAT MIXED LAYER CAPE WILL MOST
LIKELY REMAIN BELOW 2000 J/KG.
WITHIN A BROADER LOW-LEVEL WARM ADVECTION REGIME ACROSS MUCH OF THE
CENTRAL PLAINS...VIGOROUS STORM DEVELOPMENT DURING THE AFTERNOON
HOURS SEEMS MOST PROBABLE FROM PARTS OF WEST CENTRAL/SOUTHWEST
NEBRASKA INTO PARTS OF NORTHWEST/NORTH CENTRAL KANSAS. THIS IS
WHERE FORCING ASSOCIATED WITH THE DIGGING MID-LEVEL CIRCULATION MAY
WEAKEN INHIBITION...ALLOWING FOR AT LEAST ONE OR TWO SEVERE STORMS
CAPABLE OF LARGE HAIL/DAMAGING WIND GUSTS. THIS ACTIVITY MAY NOT
LAST LONG INTO THE EVENING...BUT NEW STORM DEVELOPMENT COULD
SUBSEQUENTLY DEVELOP ON THE NOSE OF A NOCTURNALLY STRENGTHENING
LOW-LEVEL JET...FROM PARTS OF CENTRAL KANSAS INTO PARTS OF
CENTRAL/EASTERN OKLAHOMA...WHERE A WARM ELEVATED MIXED LAYER MAY
SUPPRESS DAYTIME CONVECTION. IF THIS OCCURS...STRONGER ACTIVITY
COULD ALSO BE ACCOMPANIED BY SOME HAIL AND POTENTIALLY DAMAGING WIND
GUSTS.
...SOUTHERN PLATEAU...
CONVECTIVE POTENTIAL FOR WEDNESDAY IS STILL UNCLEAR...BUT THE RISK
FOR STORMS IN THE PRESENCE OF A DEEPLY MIXED BOUNDARY LAYER WITH
SIZABLE TEMPERATURE/DEW POINT SPREADS AND WEAK TO MODERATE POTENTIAL
INSTABILITY SUPPORTS AT LEAST LOW SEVERE PROBABILITIES.
..KERR.. 09/01/2009
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