Thursday, May 7, 2009

MESO: Mesoscale Discussion 0747

ACUS11 KWNS 072243
SWOMCD
SPC MCD 072242
ILZ000-MOZ000-IAZ000-KSZ000-NEZ000-080045-

MESOSCALE DISCUSSION 0747
NWS STORM PREDICTION CENTER NORMAN OK
0542 PM CDT THU MAY 07 2009

AREAS AFFECTED...NERN KS...SRN IA...NRN MO...WRN IL

CONCERNING...TORNADO WATCH 258...

VALID 072242Z - 080045Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 258 CONTINUES.

LATEST SURFACE OBSERVATIONS INDICATE DEWPOINTS ACROSS MUCH OF THE
TORNADO WATCH ARE IN THE 50S F RESULTING IN SURFACE T/TD SPREADS OF
20-30 F. ALTHOUGH MID 60S F DEWPOINTS EXIST IN THE MOIST AXIS FROM
JUST SW OF TOP KS SWD...LOW LEVEL FLOW AND MOISTURE TRANSPORT REMAIN
MODEST WITH MEAN 2KM FLOW OF 15-20 KT.

STORMS SHOULD CONTINUE TO REDEVELOP ACROSS THE WARM FRONT ZONE FROM
SRN IA INTO NRN MO AS THE SWLY FEED OF UNSTABLE AIR PERSISTS. MOST
MODELS INDICATE THAT SOME STRENGTHENING OF THE LOW LEVEL JET WILL
OCCUR INTO THE 20-25 KT RANGE. THIS MAY INCREASE LOW LEVEL
SHEAR...BUT LOW LEVEL WINDS WILL ALSO VEER GRADUALLY WITH TIME GIVEN
RELATIVELY ZONAL FLOW ALOFT. THE END RESULT SHOULD BE TRAINING
ECHOES GRADUALLY SHIFTING SEWD AND POSSIBLY GROWING UPSCALE INTO AN
MCS. IF THIS OCCURS...THE PRIMARY THREATS WILL BE WIND AND HAIL.

A TORNADO THREAT MAY INCREASE LATER THIS EVENING AS LOW LEVEL
MOISTURE AND SHEAR INCREASE. MUCH WILL DEPEND ON STORM MODE BY THAT
TIME...AS CURRENT BOUNDARY LAYER CONDITIONS ACROSS THE TORNADO WATCH
FAVOR STRONG OUTFLOW PRODUCTION. IF MID 60S F DEWPOINTS CAN ADVECT
NEWD INTO THE SWRN PORTION OF THE STORM GENERATION ZONE NEAR THE
DRYLINE/WARM FRONT INTERSECTION...THERE COULD BE A TORNADO THREAT.
THIS WOULD MOST LIKELY OCCUR OVER FAR NERN KS AND NWRN MO.

..JEWELL.. 05/07/2009

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...ILX...LSX...DVN...DMX...EAX...OAX...TOP...

LAT...LON 39499034 39079132 39189224 39399357 39469424 39029477
38829573 39249630 39349620 39829585 40329581 40909561
41149496 41249346 41129289 40629177 40189069 39499034

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