SWODY2
SPC AC 201730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT SUN MAY 20 2007
VALID 211200Z - 221200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE NRN PLAINS
TO THE CENTRAL/SRN HIGH PLAINS...
..SYNOPSIS...
MID/UPPER LEVEL FLOW PATTERN IS EXPECTED TO BECOME MORE AMPLIFIED ON
MONDAY AS A TROUGH...NOW LOCATED ALONG THE BC/WA COAST...DIGS SEWD
FROM THE PACIFIC NW STATES INTO THE NRN/CENTRAL ROCKIES. FARTHER
S...A BROAD TROUGH WILL EVOLVE IN THE SUBTROPICAL WLYS WITH SEVERAL
WEAK IMPULSE TRANSLATING ENEWD FROM THE MEXICAN PLATEAU TO THE GULF
COAST STATES. AT THE SAME TIME... RIDGING IS PROGGED TO BEGIN
BUILDING ACROSS THE OHIO VALLEY/GREAT LAKES REGION...WHILE REMNANTS
OF CURRENT NORTHERN MID ATLANTIC CLOSED LOW LIFT NEWD OFF THE NRN
ATLANTIC COAST/CANADIAN MARITIMES.
AT THE SURFACE...A COLD FRONT ORIENTED NEARLY PARALLEL TO THE FLOW
ALOFT IS EXPECTED TO MOVE SLOWLY EWD ACROSS THE NRN PLAINS ON MONDAY
AND SHOULD EXTEND FROM NERN ND SWWD TO THE NEB PANHANDLE BY 22/00Z.
THE WRN EXTENT OF THIS FRONT WILL MOVE SEWD INTO CO...WHILE MODELS
INDICATE WEAK TROUGHING OVER WY. MEANWHILE...LEE TROUGHING ALONG
THE CENTRAL/SRN HIGH PLAINS WILL DEEPEN IN RESPONSE TO EVOLVING
UPPER FLOW PATTERN.
..PLAINS...
SURFACE RIDGE IS EXPECTED TO WEAKEN ACROSS THE GULF COAST/SERN
STATES ALLOWING LOW LEVEL ELY FLOW OVER THE WRN GULF BASIN TO BECOME
SELY ON MONDAY...WITH GULF MOISTURE /SURFACE DEWPOINTS INTO THE 60S/
RETURNING INLAND TO AT LEAST PARTS OF THE SRN/CENTRAL PLAINS.
SIMILAR SURFACE DEWPOINTS ARE EXPECTED ACROSS THE NRN PLAINS ALONG/E
OF COLD FRONT...BUT MUCH OF THIS MOISTURE SHOULD BE FROM
EVAPOTRANSPIRATION. DESPITE THE MOISTURE SOURCE...STEEP LAPSE RATES
EDGING EWD OVER THE PLAINS AND STRONG SURFACE HEATING WILL COMBINE
FOR MLCAPE VALUES AROUND 1500 J/KG ACROSS THE NRN PLAINS...AND
AROUND 2000 J/KG INTO THE SRN HIGH PLAINS.
30-40 KT SLY LLJ ACROSS THE PLAINS THROUGH MUCH OF EARLY DAY 2 IS
EXPECTED TO STRENGTHEN TO 40-50 KT MONDAY EVENING AND VEER SLIGHTLY
TO SSWLY. MODELS CONTINUE TO INDICATE STRONGER MID/UPPER LEVEL
WINDS WITH THE NRN STREAM TROUGH LAGGING THE INSTABILITY AXIS ACROSS
THE NRN PLAINS DURING DAY 2. HOWEVER...AT LEAST 30 KT OF SWLY MID
LEVEL WINDS ATOP AN INCREASING SLY LLJ INTO THE DAKOTAS/MN SUGGEST
SUFFICIENT DEEP LAYER SHEAR FOR MULTICELLS AND SOME SUPERCELLS.
PRIMARY SEVERE WEATHER THREATS ACROSS THE NRN PLAINS SHOULD BE HAIL
AND DAMAGING WINDS...BUT THE STRENGTHENING LLJ AND FLOW VEERING WITH
HEIGHT IN THE LOW LEVELS INDICATES A TORNADO POTENTIAL. MODELS
SUGGEST TSTMS/TSTM CLUSTERS MAY EVOLVE INTO A SQUALL LINE MOVING EWD
ACROSS NRN NEB/ERN DAKOTAS/NWRN MN MONDAY EVENING AND REACHING WEST
CENTRAL/SW MN BY 12Z TUESDAY.
FARTHER S...MODELS SHOW A WEAK MID LEVEL TROUGH MOVING EWD ACROSS
THE SRN/CENTRAL HIGH PLAINS. ASCENT WITH THIS FEATURE...INCREASING
CONVERGENCE ALONG THE DRY LINE/LEE TROUGH AND STRONG SURFACE HEATING
WILL LIKELY WEAKEN INHIBITION FOR SURFACE BASED TSTMS DEVELOPING
MONDAY AFTERNOON ACROSS THE SRN/CENTRAL HIGH PLAINS. DEEP LAYER
SHEAR VECTORS ARE EXPECTED TO BE MORE FAVORABLE FOR SUPERCELLS
ESPECIALLY ACROSS THE SRN HIGH PLAINS AND ALSO INTO PARTS OF ERN
CO/WRN KS...WHERE SSELY LOW LEVEL WINDS WILL BE LOCATED BENEATH
30-40 KT WLY MID LEVEL FLOW. THIS ACTIVITY SHOULD BE MORE DIURNAL
WITH THE OVERALL SEVERE THREAT IN THE SRN PART OF THE SLIGHT RISK
DIMINISHING BY MID-LATE MONDAY EVENING.
..WY...
LOW SEVERE PROBABILITIES ARE WARRANTED ACROSS WY WHERE MODELS
INDICATE STRONG DEEP LAYER SHEAR AND WEAK INSTABILITY WILL BE
SUPPORTIVE OF A FEW STRONG TO SEVERE STORMS WITH ISOLATED DAMAGING
WINDS AND HAIL THE MAIN THREATS.
.PETERS.. 05/20/2007
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