MESO: Mesoscale Discussion 0669

ACUS11 KWNS 201521
SWOMCD
SPC MCD 201520
VAZ000-201745-

MESOSCALE DISCUSSION 0669
NWS STORM PREDICTION CENTER NORMAN OK
1020 AM CDT SUN APR 20 2008

AREAS AFFECTED...PARTS OF ERN VA

CONCERNING...HEAVY RAINFALL

VALID 201520Z - 201745Z

SEVERAL HOURS OF MDT-HEAVY RAINFALL CAN BE EXPECTED ACROSS MUCH OF
ERN VA. THE HEAVIEST TSTMS /HOURLY RATES 1-1.5 IN/ WILL LIKELY BE
CONFINED TO A 20 MILE CORRIDOR JUST WEST OF THE I-95 EXTENDING FROM
NEAR EMPORIA NWD TO JUST NW OF RICHMOND. ISOLD DMGG WIND GUSTS AND
PERHAPS A BRIEF TORNADO MAY ALSO OCCUR...PRIMARILY SOUTH OF
RICHMOND.

BACK EDGE OF THE BROAD WARM CONVEYOR ALONG ERN PERIPHERY OF THE SLOW
MOVING UPR LOW HAS REGENERATED WITH TSTM INTENSITY INCREASING
ALONG/W OF I-95. MESOANALYSIS PLACES A NARROW TONGUE OF 57-63F DEW
POINTS JUST EAST OF AN OCCLUDED FRONT WITH STRONGEST MOISTURE
CONVERGENCE ALONG THE NC/VA BORDER S OF EMPORIA COINCIDENT WITH A
WEAK MESOLOW. THIS LOW SHOULD MOVE SLOWLY NWD TOWARD RICHMOND
THROUGH MID-AFTN WITH THE FRONT MOVING VERY LITTLE. PERSISTENT
MOISTURE CONVERGENCE INVOF THIS FRONT/LOW WILL MAINTAIN THE THREAT
FOR TRAINING TSTMS WITH HEAVY RAINFALL FOR SEVERAL HOURS.

ADDITIONALLY...ENHANCED ESELY FLOW ALONG THE ERN QUADRANT OF THE
MESOLOW WILL BOOST LOW-LVL HELICITY AND GIVEN LOW LCL/S AND 30-35
KTS OF EFFECTIVE SHEAR...ISOLD TSTMS MAY ORGANIZE SUFFICIENTLY TO
PRODUCE BRIEF DMGG WIND GUSTS OR PERHAPS A TORNADO. ATTM...A WW IS
NOT ANTICIPATED WITH HEAVY RAINFALL BEING THE PRIMARY THREAT THROUGH
EARLY AFTN.

MORE TSTMS WILL DEVELOP FARTHER W/SW THIS AFTN AS THE COLD UPR LOW
MIGRATES SLOWLY EWD. THESE STORMS MAY BE MORE ROBUST WHERE STRONGER
INSTABILITY DEVELOPS IN CONCERT WITH STEEPER MID-LVL LAPSE RATES.

..RACY.. 04/20/2008

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

ATTN...WFO...AKQ...

36617771 37457763 37927768 37957747 37767735 37367730
36947727 36747732

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