SWODY2
SPC AC 180553
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1253 AM CDT FRI MAR 18 2011
VALID 191200Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE THAT THE LARGE-SCALE PATTERN WILL UNDERGO
AMPLIFICATION DURING THIS FORECAST PERIOD...WITH AN UPPER TROUGH
PROGGED TO DEEPEN ACROSS THE EASTERN PACIFIC INTO THE WESTERN
U.S...WHILE AN UPPER RIDGE BUILDS ALONG AN AXIS NEAR OR JUST EAST OF
THE MISSISSIPPI RIVER. WITHIN THE UPPER TROUGH...THE MORE PROMINENT
SHORT WAVE TROUGHS APPEAR LIKELY TO DIG OFF THE PACIFIC COAST...BUT
GUIDANCE DOES SUGGEST THAT A SIGNIFICANT IMPULSE WILL MIGRATE INLAND
ACROSS THE CENTRAL CALIFORNIA COAST BY EARLY SATURDAY...BEFORE
LIFTING THROUGH THE GREAT BASIN INTO THE NORTHERN ROCKIES BY
SATURDAY EVENING.
EAST OF THE ROCKIES...AS THE UPPER RIDGE BUILDS...THE CENTER OF A
LARGE COLD SURFACE RIDGE IS PROGGED TO RETREAT EASTWARD ACROSS THE
GREAT LAKES...WHILE A WEAKER HIGH CENTER DOES THE SAME ACROSS THE
NORTHEASTERN GULF OF MEXICO. MOISTURE RETURN FROM THE WESTERN GULF
OF MEXICO...CURRENTLY IN THE PROCESS OF BECOMING DISRUPTED...MAY NOT
COMMENCE AGAIN UNTIL SATURDAY NIGHT...WHEN IT PROBABLY WILL BE
DIRECTED TOWARD THE SOUTHERN HIGH PLAINS. HOWEVER...A RIBBON OF
HIGHER PRECIPITABLE WATER /IN EXCESS OF 1 INCH/...ASSOCIATED WITH
MOISTURE THAT HAS ALREADY ADVECTED INLAND...IS EXPECTED TO BECOME
FOCUSED ALONG A FRONTAL ZONE ON THE SOUTHERN PERIPHERY OF THE GREAT
LAKES HIGH CENTER. THIS APPEARS LIKELY TO EXTEND FROM SOUTHERN MID
ATLANTIC COASTAL AREAS INTO THE SOUTH CENTRAL HIGH PLAINS BY 12Z
SATURDAY...BEFORE CONTINUING SLOWLY SOUTHWARD THROUGH THE SOUTH
ATLANTIC COAST STATES...WHILE RETREATING NORTHWARD WITH THE FRONT
THROUGH THE LOWER MISSOURI/ MIDDLE MISSISSIPPI VALLEY.
...SOUTH CENTRAL PLAINS INTO MID MS VALLEY...
ASSOCIATED WITH THE EVOLVING PATTERN...AN INCREASINGLY DIVERGENT
UPPER FLOW FIELD COUPLED WITH STRENGTHENING LOW-LEVEL WARM ADVECTION
LIKELY WILL CONTRIBUTE TO FAVORABLE LARGE-SCALE FORCING FOR
CONVECTIVE DEVELOPMENT ACROSS PARTS OF THE SOUTH CENTRAL PLAINS BY
SATURDAY MORNING. THIS IS EXPECTED TO BE FOCUSED TO THE COOL SIDE
OF THE RETREATING FRONT...BUT MOISTENING ABOVE THE FRONTAL
INVERSION...BENEATH STEEP MID-LEVEL LAPSE RATES...PROBABLY WILL
YIELD MODEST CAPE. THIS MAY PROMOTE THE RISK FOR HAIL IN STRONGER
STORMS. WHILE SOME OF THIS COULD APPROACH OR BRIEFLY EXCEED SEVERE
CRITERIA...THE THREAT IS EXPECTED TO BE LIMITED BY SOMEWHAT WEAK
VERTICAL SHEAR. CONVECTION ACTIVITY IS EXPECTED TO GRADUALLY DEVELOP
NORTHWARD AND NORTHEASTWARD ACROSS PARTS OF THE CENTRAL PLAINS AND
MIDDLE MISSISSIPPI VALLEY THROUGH THE REMAINDER OF THE PERIOD.
...SOUTHEAST...
DAYTIME HEATING MAY YIELD MODERATE CAPE ALONG AND SOUTH OF THE
FRONTAL ZONE ACROSS PARTS OF THE SOUTHEAST STATES BY LATE SATURDAY
AFTERNOON. MID/UPPER FORCING FOR UPWARD VERTICAL MOTION AND
VERTICAL SHEAR WILL PROBABLY BE WEAK...BUT INHIBITION MAY WEAKEN
ENOUGH WITH AT LEAST SOME MID-LEVEL COOLING TO ALLOW THE DEVELOPMENT
OF SCATTERED THUNDERSTORM...PARTICULARLY FROM PARTS OF NORTHERN
ALABAMA INTO THE SAVANNAH VALLEY. GUSTY WINDS AND SOME HAIL WILL BE
POSSIBLE...BUT THIS IS MOSTLY EXPECTED TO REMAIN BELOW SEVERE
LIMITS...AND SHOULD DIMINISH BY EARLY EVENING.
...PECOS VALLEY INTO TX SOUTH PLAINS...
STRONG HEATING ALONG A WEAK SURFACE TROUGH MAY BECOME A FOCUS FOR
SUBSTANTIVE BOUNDARY LAYER DESTABILIZATION...AND INHIBITION MAY
WEAKEN ENOUGH FOR STORM DEVELOPMENT LATE SATURDAY AFTERNOON AND
EVENING. SHEAR ALONG THE WEST EDGE OF A DEVELOPING SOUTHERLY
LOW-LEVEL JET...BENEATH MODEST AND BROADLY CYCLONIC WESTERLY
MID-LEVEL FLOW PROBABLY WILL BE SUFFICIENT FOR SUPERCELLS...HOWEVER
MID/UPPER FORCING FOR UPWARD VERTICAL MOTION IS UNCLEAR AND SEEMS
LIKELY TO REMAIN WEAK. SO POTENTIAL FOR MUCH BEYOND A COUPLE OF
ISOLATED STORMS REMAINS UNCLEAR...AND 5 PERCENT SEVERE PROBABILITIES
HAVE BEEN MAINTAINED.
...PACIFIC COAST INTO NORTHERN HIGH PLAINS...
THUNDERSTORM PROBABILITIES APPEAR GENERALLY NEAR THE MINIMUM
THRESHOLD FOR A /GENERAL THUNDER/ OUTLOOK ACROSS MUCH OF THE REGION.
HOWEVER...A MID-LEVEL THERMAL TROUGH MAY ENHANCE DESTABILIZATION
AND CONTRIBUTE TO THE RISK FOR THUNDERSTORMS ACROSS PARTS OF THE
SACRAMENTO AND SAN JOAQUIN VALLEYS SATURDAY. SCATTERED
THUNDERSTORMS ALSO APPEAR POSSIBLE FROM THE SALT LAKE AREA THROUGH
THE UPPER SNAKE RIVER VALLEY...WHERE STRONGER MID-LEVEL HEIGHT FALLS
ARE EXPECTED COINCIDENT WITH PEAK AFTERNOON HEATING.
FINALLY...SUFFICIENT DESTABILIZATION MAY ALSO OCCUR WITH STRONG
HEATING ACROSS THE NORTHERN HIGH PLAINS...TO SUPPORT WIDELY
SCATTERED STORMS BY EARLY EVENING...PERHAPS AIDED BY FORCING
DOWNSTREAM OF THE IMPULSE LIFTING NORTHEAST OF THE GREAT BASIN.
..KERR.. 03/18/2011
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