SWODY1
SPC AC 281619
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1119 AM CDT THU MAY 28 2009
VALID 281630Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE LOWER OH/TN VALLEYS
SWD INTO AL/GA...
...THERE IS A SLGT RISK OF SVR TSTMS IN SWRN TX...
...SYNOPSIS...
THE MAIN FEATURE OF CONVECTIVE SIGNIFICANCE THIS AFTERNOON/EVENING
WILL BE A MID LEVEL TROUGH SHIFTING SLOWLY EWD ACROSS THE OH/TN
VALLEYS SWD INTO THE GULF COASTAL STATES. MORNING WV IMAGERY SHOWED
SHORTWAVE TROUGHS EMBEDDED WITHIN THIS TROUGH OVER KY AND NRN AR/MO.
A HIGH LEVEL SPEED MAX AT 80-100 KT WAS LOCATED ON THE SOUTH SIDE OF
THE AR/MO SYSTEM...STRETCHING FROM CENTRAL OK INTO WRN TN. AT THE
SURFACE...WEAK SURFACE LOW WAS LOCATED IN FAR SRN IL...WITH A COLD
FRONT EXTENDING NEWD FROM THE LOW INTO NWRN OH...AND SWD ACROSS FAR
NWRN AL/ERN MS.
...CENTRAL APPALACHIANS SWWD INTO AL/GA...
SUNSHINE THROUGH SCT-BROKEN CLOUDS HAS WARMED TEMPERATURES INTO THE
MID/UPPER 70S FROM AL NEWD INTO SRN KY. AS READINGS WARM INTO THE
80S...MID/UPPER 60S DEWPOINTS WILL CONTRIBUTE TO MLCAPE VALUES NEAR
2000 J/KG. THOUGH WINDS THROUGH THE LOWER HALF OF THE TROPOSPHERE
ARE GENERALLY WLY...STRENGTHENING WINDS ALOFT... ESPECIALLY BETWEEN
400 AND 200 MB...ARE EXPECTED TO PROVIDE SUFFICIENT DEEP LAYER SHEAR
FOR ORGANIZED STRONG/SEVERE LINE SEGMENTS DURING THE AFTERNOON/EARLY
EVENING HOURS. THE DEGREE OF INSTABILITY AND UNDIRECTIONAL WLY WINDS
COMBINED WITH MID LEVEL DRYING...AS INDICATED ON 12Z LIT/JAN/SHV
SOUNDINGS...SHOULD FAVOR WIND DAMAGE WITH LINE SEGMENTS.
HOWEVER...500 MB TEMPERATURES AROUND -10C AND 500-700 MB LAPSE RATES
AT 7C/KM MAY ALSO SUPPORT HAIL.
FARTHER NEWD ACROSS OH AND WRN PA/NY...MORE PERSISTENT CLOUDS WILL
LIMIT INSTABILITY COMPARED TO AREAS FARTHER SOUTH. HOWEVER...
FORCING ASSOCIATED WITH UPPER TROUGH AND TEMPERATURES/DEWPOINTS IN
THE 70S/60S MAY YIELD A FEW STORMS WITH SEVERE HAIL AND STRONG
WINDS. FARTHER E ACROSS THE MID/SRN ATLANTIC STATES...ISOLATED
STRONG STORMS ARE ALSO POSSIBLE...BUT WEAKER SHEAR SHOULD RESULT IN
LESS ORGANIZED/PERSISTENT STORMS THAN IN THE SLIGHT RISK AREA.
...SWRN TX AND THE RIO GRANDE VALLEY...
LINGERING LOW-LEVEL MOISTURE N OF STALLED FRONT IN MEXICO...PLUS
COMBINATION OF WEAK ASCENT ASSOCIATED WITH SRN JET STREAM AND
DAYTIME HEATING SHOULD SUPPORT THUNDERSTORM DEVELOPMENT ACROSS SWRN
TX BY LATE AFTERNOON. VEERING WIND PROFILES IN THE LOWER 3 KM AND
MLCAPE VALUES OF 1000-2000 J/KG WOULD SUPPORT A FEW STORMS WITH HAIL
AND STRONG OUTFLOW WINDS.
...FL...
STORMS HAVE ALREADY DEVELOPED OVER THE WRN COAST OF THE PENINSULA
AND THE WLY WINDS ALOFT WILL CARRY THESE STORMS TOWARD THE EAST
COAST. THOUGH DEEP LAYER SHEAR IS WEAK...MLCAPES AOA 2000 J/KG WILL
SUPPORT SHORT LIVED WIND/HAIL EVENTS.
...ORE/NERN CA...
DAYTIME HEATING AND LINGERING MID LEVEL MOISTURE AROUND THE NWRN
PERIPHERY OF THE MID LEVEL RIDGE IN NV ARE EXPECTED TO SUPPORT
WIDELY SCATTERED THUNDERSTORM DEVELOPMENT OVER THE HIGHER TERRAIN OF
SRN ORE AND NERN CA LATE TODAY. DESPITE WEAK INSTABILITY...MID LEVEL
LAPSE RATES IN EXCESS OF 8 C/KM...AND INVERTED-V SOUNDINGS SHOULD
YIELD STORMS WITH STRONG GUSTY WINDS.
..IMY/GRAMS.. 05/28/2009
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