SWODY2
SPC AC 301729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SAT MAY 30 2009
VALID 311200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN PLAINS
AND NRN MS VALLEY...
...NRN PLAINS/UPPER MS VALLEY...
A WEST NORTHWEST FLOW PATTERN IS FORECAST ACROSS THE NRN STATES
SUNDAY. AT THE SFC...A COLD FRONT WILL MOVE SEWD ACROSS THE NRN
PLAINS AND SHOULD BE POSITIONED FROM NW MN SWWD ACROSS ERN SD INTO
WRN NEB BY 00Z. THUNDERSTORMS SHOULD DEVELOP BY LATE AFTERNOON ALONG
THE BOUNDARY AND MOVE SEWD ACROSS THE SLIGHT RISK AREA. MODEL
FORECASTS VARY ON HOW MUCH CONVECTION WILL DEVELOP. ATTM...AM
LEANING WITH THE NAMKF WHICH ORGANIZES A LINE OF STORMS BY EARLY
EVENING WITH A PERSISTENT MCS MOVING SEWD ACROSS SRN MN DURING THE
OVERNIGHT PERIOD.
NAMKF FORECAST SOUNDINGS ALONG THE BOUNDARY AT 00Z SHOW MLCAPE
VALUES FROM 1500 TO 2500 J/KG WITH MODERATE VERTICAL SHEAR ACROSS
THE ENTIRE SLIGHT RISK AREA. THIS SHOULD BE FAVORABLE FOR SEVERE
STORMS WITH THE GREATEST THREAT FOR LARGE HAIL ACROSS SD AND NRN NEB
WHERE MID-LEVEL LAPSE RATES ARE FORECAST TO BE STEEPEST. SUPERCELLS
MAY ALSO HAVE AN ISOLATED TORNADO THREAT. HOWEVER...WIND DAMAGE
COULD BE THE GREATEST SEVERE WEATHER THREAT IF A LINEAR MCS CAN
ORGANIZE AS THE NAMKF SUGGESTS ESPECIALLY AS THE LOW-LEVEL JET
INCREASES DURING THE EARLY EVENING.
...NRN NEW ENGLAND...
AN UPPER-LEVEL LOW IS FORECAST TO MOVE ACROSS QUEBEC SUNDAY AS A
COLD FRONT MOVES SEWD ACROSS NEW ENGLAND. THUNDERSTORMS SHOULD
DEVELOP ALONG THE BOUNDARY AS SFC TEMPS WARM WITH CONVECTION MOVING
ESEWD TOWARD THE COASTAL AREAS. FORECAST SOUNDINGS IN MAINE AT 21Z
SUNDAY SHOW STRONG VERTICAL SHEAR PROFILES /0-6 KM SHEAR VALUES IN
THE 60 TO 70 KT RANGE/ WITH ABOUT 30 KT OF FLOW AT 850 MB. THIS
ENVIRONMENT COULD BE SUPPORTIVE OF ISOLATED WIND DAMAGE DURING THE
AFTERNOON. HOWEVER...WEAK INSTABILITY SHOULD KEEP THE SEVERE THREAT
MARGINAL. THE FRONT IS FORECAST TO MOVE OFFSHORE BY LATE AFTERNOON
REDUCING THE SEVERE THREAT.
...ERN GULF COAST/SRN ATLANTIC SEABOARD...
RELATIVELY WEAK WEST NORTHWEST FLOW IS FORECAST ACROSS THE SERN
STATES. AT THE SFC...A MOIST AXIS SHOULD BE IN PLACE FROM SC WNWWD
ACROSS AL...NRN MS INTO NE AR. SFC HEATING AND LOW-LEVEL CONVERGENCE
ALONG PREEXISTING BOUNDARIES SHOULD RESULT IN SCATTERED THUNDERSTORM
INITIATION DURING THE LATE MORNING AND EARLY AFTERNOON. ALTHOUGH
VERTICAL SHEAR PROFILES WILL BE WEAK...A FEW MARGINALLY SEVERE PULSE
STORMS MAY DEVELOP WHERE STRONG INSTABILITY IS MAXIMIZED IN THE
AFTERNOON.
...WEST TX...
MODEL FORECASTS MOVE A WEAK UPPER-LEVEL TROUGH OVER WEST TX SUNDAY.
THUNDERSTORMS SHOULD DEVELOP NEAR AND SOUTH OF THE UPPER-LEVEL
TROUGH DURING THE AFTERNOON AS A CAP WEAKENS. THIS CONVECTION SHOULD
SPREAD SLOWLY EWD INTO AN AXIS OF INSTABILITY. FORECAST SOUNDINGS AT
00Z IN THE LUBBOCK AREA SHOW LOWER 50S F DEWPOINTS WITH ABOUT 20 KT
OF VERTICAL SHEAR AND MLCAPE VALUES OF 1000-1500 J/KG. THIS MAY BE
SUFFICIENT FOR A MARGINAL SEVERE THREAT WITH HAIL FAVORED DUE TO
STEEP MID-LEVEL LAPSE RATES.
...NRN CA/ORE...
AN UPPER-LEVEL RIDGE WILL REMAIN IN PLACE ACROSS THE WRN STATES
SUNDAY AS THUNDERSTORMS DEVELOP UNDER THE RIDGE DUE TO SFC HEATING.
A MOIST AXIS SHOULD BE IN PLACE ACROSS NRN CA AND WRN ORE WHERE THE
MODELS DEVELOP MODERATE INSTABILITY BY AFTERNOON. THIS ALONG WITH 25
TO 35 KT OF FLOW IN THE MID-LEVELS COULD BE SUFFICIENT FOR A
MARGINAL SEVERE THREAT DURING THE AFTERNOON.
..BROYLES.. 05/30/2009
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