Heavy Rain in Virginia, May 18, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON
300 PM EDT FRI MAY 18 2001

KLWX RADAR SHOWING SOME LIGHT SHOWER ACTIVITY MOVING INTO WESTERN
SECTIONS OF FA. SOME SUBSTANTIAL RAINFALL COMPLEX OVER EASTERN
INDIANA AND WESTERN OHIO. SOME BREAKS IN THE LOW OVERCAST OVER THE
PAST COUPLE OF HOURS HAVE ALLOWED TEMPS TO JUMP UP INTO THE MID 60S
MOST AREAS.

WARM FRONT TO THE SOUTH OF US CURRENTLY IS EXPECTED TO MOVE
NORTHWARD OVERNIGHT PER 00Z ETA/AVN. BOTH MODELS PICK UP THE SURFACE
LOW OVER THE OHIO VALLEY AT 18Z AND MOVE IT ALONG THE FRONT
OVERNIGHT. PRETTY STRONG JET DYNAMICS LEADING TO GOOD UVV FIELDS ON
BOTH ETA AND AVN OVERNIGHT. CONVECTION ACROSS THE MIDWEST SHOULD
MAKE ITS WAY INTO THE AREA BY LATE EVENING.. WITH BOTH MODELS
KEEPING SOME LIFT AND MOISTURE OVER THE AREA INTO THE MORNING HOURS
TOMORROW. WILL GO CAT POPS ALL AREAS TONIGHT... AND CONTINUE MENTION
OF THUNDER SINCE THE AMOUNT OF LIFT MOVING OVER THE AREA TONIGHT
SHOULD RESULT IN SOME ELEVATED CONVECTION.  PW VALUES APPROACH 1.5
INCHES ALL AREAS TONIGHT.. AND PLAN TO MENTION SOME RAIN HEAVY AT
TIMES FOR THE NORTHERN 2/3 OF FA... WHERE LIFT FROM JET AND
CONVERGENCE ALONG SURFACE FEATURES SHOULD BE MAXIMIZED.

WARM FRONT SLIDES TO THE SOUTH BY MID AFTERNOON TOMORROW.. AND
REMAINS THE FOCUS FOR PRECIP AS MODELS IN GENERAL AGREEMENT THAT
SOME CONVECTION WILL FORM OVER SW VA TOWARD LATE AFTERNOON. PLAN TO
END PRECIP IN THE NORTHERN 2/3 OF THE FA BY MIDDAY... BUT KEEP
MENTION OF PRECIP FOR CHO/SHD AREA THROUGH THE AFTERNOON. FORECAST
SOUNDINGS SOME SOME MODERATE INSTABILITY IF ENOUGH SUN APPEARS TO
PUSH TEMPS UP TO GUIDANCE VALUES. NOT A REAL SEVERE THREAT ON THE
SOUNDINGS.. BUT WEAK MID LEVEL WINDS AND HIGH PW VALUES MAY RESULT
IN SOME HEAVY RAINFALL AT TIMES FOR CHO AREA TOMORROW.

FLASH FLOOD THREAT APPEARS MINIMAL AT TIMES... AS FFG VALUES THIS
MORNING ARE ALL OVER 2.0 INCHES FOR 1 HOUR AND 3.5 INCHES FOR 6
HOURS. BASIN AVERAGE QPF VALUES SHOULD ALL BE AROUND AN INCH OR SO.

MODELS AGREE IN TRYING TO PUSH THE FRONT FAR ENOUGH SOUTH OF THE
AREA BY SUNDAY MORNING THAT PRECIP SHOULD NOT BE A PROBLEM. CLOUD
FORECAST UNCERTAIN AS SFC FLOW SHOULD REMAIN NELY... WHICH IS NOT
FAVORABLE FOR SCOURING OUT LOW LEVEL MOISTURE.

RETURN FLOW SETTING UP BY MONDAY... WHICH MAY PUT US BACK INTO A
MARINE AMS. HAVE ADDED CHANCE OF SHOWERS FOR MONDAY..BUT IT MAY END
UP MORE OF A LIGHT RAIN AND DRIZZLE. NEXT SYNOPTIC SYSTEM AFFECTS US
TUESDAY...BRINGING A PRETTY GOOD CHANCE OF SHOWERS AND THUNDERSTORMS.

TEMPS NEXT COUPLE OF DAYS HIGHLY RELIANT ON CLOUD COVER... BUT AM
CONFIDENT IN THE WAY MOS GUIDANCE PRODUCTS ARE HANDLING CLOUD COVER.

DCA   61  76  61  78 /  90  90  10  10
BWI   59  75  57  77 /  90  90  10  10
MRB   59  76  56  78 / 100  80  10  10
IAD   59  76  55  78 / 100  80  10  10
CHO   62  79  58  80 /  80  90  20  10
HGR   57  74  55  77 / 100  80  10  10
NHK   61  77  59  77 /  90  90  10  10

.LWX...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.

MARGRAF!