SWODY2
SPC AC 181725
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM CDT WED MAY 18 2011
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE CENTRAL
AND SOUTHERN PLAINS...
...CENTRAL/SRN PLAINS...
THE 12Z NAM/GFS ARE SIMILAR IN THE EVOLUTION OF THE WRN U.S. UPPER
TROUGH...WITH THE LEADING EDGE OF A 70-80 KT JET MAX EJECTING NWD
ALONG THE ERN SIDE OF THE TROUGH FROM NERN NM INTO SD. THIS RESULTS
IN THE BROAD UPPER TROUGH TO REMAIN NEARLY STATIONARY THROUGH THE
PERIOD. HOWEVER...WITHIN THIS LARGER SCALE TROUGH...A CLOSED LOW
MOVES FROM WRN CO INTO ERN WY...WHILE AN IMPRESSIVE SHORTWAVE TROUGH
SHIFTS RAPIDLY EWD FROM SRN CA INTO NRN NM...AMPLIFYING THE SRN BASE
OF PARENT TROUGH.
ELEVATED THUNDERSTORMS...ASSOCIATED WITH THE NM UPPER JET MAX AND
CONSEQUENT STRENGTHENING LOW LEVEL JET...ARE LIKELY TO BE ONGOING AT
THE START OF THE PERIOD ACROSS PORTIONS OF KS/NEB. WHILE THESE
STORMS MAY PRODUCE MARGINALLY SEVERE HAIL IN THE MORNING...THEY
SHOULD SHIFT EWD INTO THE LOWER MISSOURI RIVER VALLEY AND WEAKEN.
THEREAFTER...SURFACE FEATURES ACROSS THE REGION THURSDAY WILL BE
SIMILAR TO TODAY. HOWEVER...A WARM FRONT...CURRENTLY LOCATED IN
OK...IS FORECAST TO STRETCH E-W NEAR I-70 IN KS BY LATE THU
AFTERNOON...AS SURFACE LOW MIGRATES NWD FROM THE TX PANHANDLE INTO
WRN KS. AT THE SAME TIME...THE SURFACE DRYLINE IS ONCE AGAIN
EXPECTED TO STRETCH ACROSS WRN OK INTO W CENTRAL TX...AND EXTEND NWD
TO THE WARM FRONT IN WRN KS. THE WARM FRONT AND DRYLINE SHOULD
PROVIDE THE PRIMARY FOCUS FOR CONVECTION SINCE LARGE SCALE DYNAMICAL
LIFTING WILL BE WEAK. DIURNAL HEATING AND DEWPOINTS WELL INTO THE
60S WILL RESULT IN A MODERATELY UNSTABLE AIR MASS. INCREASING WINDS
ALOFT WILL STRENGTHEN THE DEEP LAYER SHEAR TO NEAR 50 KT...SO THE
INSTABILITY AND SHEAR WILL BE SUPPORTIVE OF SUPERCELLS. ALTHOUGH THE
AIR MASS IS LIKELY TO REMAIN MOSTLY CAPPED ACROSS THE WARM
SECTOR...STRONG BOUNDARY LAYER HEATING NEAR AND WEST OF THE DRYLINE
SHOULD AID IN SURFACE PARCELS REACHING THEIR CONVECTIVE
TEMPERATURE...WITH AT LEAST ISOLATED THUNDERSTORMS FORMING AFTER
21Z. FORECAST SOUNDINGS INDICATE THAT ANY STORMS THAT DEVELOP WOULD
POSE A THREAT FOR VERY LARGE HAIL AND WIND DAMAGE. ALSO...JUST EAST
OF THE DRYLINE AND ESPECIALLY NEAR THE WARM FRONT IN KS...THE
COMBINATION OF THE MOIST BOUNDARY LAYER AND 1 KM SHEAR BETWEEN 20-30
KT MAY SUPPORT A FEW TORNADOES. SINCE STORMS WILL BE
THERMODYNAMICALLY DRIVEN...THEY ARE EXPECTED TO WEAKEN AROUND MID
EVENING.
DRYLINE WILL MOVE WWD OVERNIGHT. AS LARGE SCALE FORCING SPREADS IN
FROM THE WEST...STORMS MAY DEVELOP AFTER 06Z NEAR THE LOW LEVEL
CONVERGENCE FROM NEAR SPS TO SJT. THE UPDRAFT ROOTS ARE LIKELY TO BE
ELEVATED...THOUGH SHEAR AND INSTABILITY WOULD SUPPORT LARGE HAIL AND
POSSIBLE WIND DAMAGE.
...MID ATLANTIC...
SLOW MOVING UPPER LOW WILL BE SHUNTED EWD FROM THE FAR ERN OH VALLEY
INTO NJ BY EARLY FRI MORNING. THIS FEATURE IS ONCE AGAIN EXPECTED TO
INITIATE STRONG AFTERNOON CONVECTION ALONG THE ERN PERIPHERY OF THE
UPPER LOW. INSTABILITY IS NOT FORECAST TO BE PARTICULARLY
STRONG...AROUND 500 J/KG...THOUGH THE COLD AIR ALOFT AND 30-40 KT
DEEP LAYER SHEAR SHOULD SUPPORT A FEW STORMS WITH HAIL OR GUSTY
WINDS. PORTIONS OF THE REGION MAY BE UPGRADED TO A SLIGHT RISK ON
THE DAY 1 OUTLOOK...ONCE AREAS WHERE GREATER HEATING/INSTABILITY CAN
BE IDENTIFIED.
..IMY.. 05/18/2011
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