000
FXUS61 KPBZ 102321
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
621 PM EST WED MAR 10 2010

.SYNOPSIS...
A WARM FRONT WILL MOVE NORTH OF THE REGION TONIGHT. A LOW
PRESSURE SYSTEM MOVING OUT OF THE PLAINS WILL THEN BRING A BETTER
CHANCE OF WIDESPREAD PRECIPITATION TO THE AREA THURSDAY NIGHT
THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH THURSDAY/...
LIGHT SCATTERED SHOWERS THIS EVENING WITH WARM FRONT WILL WORK
NORTHEAST ACROSS THE REGION EARLY TONIGHT WITH MAINLY CLOUDY
SKIES.

OVERNIGHT TEMPERATURES WILL CONTINUE TO REMAIN WELL ABOVE NORMAL
AS STRONG WARM AIR ADVECTION PUSHES +6 TO +8C TEMPS OVER THE
REGION. THE REGION SHOULD REMAIN DRY THROUGH THE MORNING HOURS
THURSDAY AS 500MB LOW CLOSES OFF AND ROTATES THE NEXT SHORTWAVE
NORTHWARD...BRINGING A CHANCE OF SHOWERS RAIN BACK INTO THE
FORECAST BY AFTERNOON. TEMPERATURES WILL REMAIN WELL ABOVE NORMAL.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
UPPER LEVEL LOW STRENGTHENS ACROSS THE CENTRAL PLAINS THURSDAY
NIGHT AND LEAD SHORTWAVE WILL ROTATE ACROSS UPPER OHIO VALLEY INTO
EARLY FRIDAY MORNING BRINGING A ROUND OF SHOWERS. CLOUDS AND A
BIT OF SUN POSSIBLE FRIDAY AFTERNOON IN BETWEEN SHORTWAVES WITH
SHOWERS CHANCE SLOWLY INCREASING BY LATE DAY AS MAIN SLUG OF
MOISTURE HEADS NORTHEAST WITH UPPER LOW BECOMING NEGATIVE TILT ON
SATURDAY. LEFT A CHANCE FOR THUNDERSTORMS FRIDAY AFTERNOON BUT
MODELS HAVE BEEN TRENDING DOWN CHANCES FOR THUNDER BASED ON
FORECAST SOUNDINGS. WIDESPREAD SHOWERS SATURDAY WITH POSSIBLE
HEAVY RAIN. WITH SNOW MELT FROM RIDGES AND SNOW COVERED OR
SATURATED GROUND ELSEWHERE FLOOD WATCH ISSUED FROM THURSDAY NIGHT
THROUGH THE WEEKEND. TEMPERATURES WILL BE QUITE MILD THURSDAY INTO
FRIDAY BEFORE COOLING BUT REMAINING ABOVE NORMAL SATURDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
THE 12Z OPERATIONAL GFS HAS SHOWN MORE AGREEMENT WITH THE ECMWF WITH
THE POSITIONING OF THE UPPER LEVEL LOW AND ITS ASSOCIATED SURFACE
LOW SATURDAY NIGHT INTO SUNDAY. THE ECMWF/HPC SOLUTION INDICATES
CYCLOGENESIS OFF THE CAROLINA COAST SATURDAY...WITH THE LOW MOVING
NORTHWEST INTO EASTERN PA BY 12Z SUN. THESE SOLUTIONS LEAN TOWARD
LIKELY POPS WITH MORE WIDESPREAD RAINFALL SATURDAY NIGHT BEGINNING
TO DECREASE IN COVERAGE ON SUNDAY. HPC FORECAST ALONG WITH A
GFS/ECMWF BLEND SUPPORT AN ADDITIONAL INCH OF RAINFALL ACROSS THE
AREA WITH LOCALLY HIGHER AMOUNTS.

THE UPPER LEVEL LOW WILL ADVECT EAST OF THE AREA INTO THE
MID-ATLANTIC SUNDAY NIGHT INTO MONDAY...WITH BEST ASCENT SHIFTING
EAST OF THE AREA. MODEL SOUNDINGS SUPPORT A MIX OF RAIN AND SNOW
SHOWERS FOR THE RIDGES OF GARRETT AND TUCKER COUNTIES EARLY MONDAY
MORNING. A DEEP LAYER OF MOISTURE ON THE BACK SIDE OF THE SYSTEM
WILL CONTINUE TO ALLOW FOR THE CHANCE OF RAIN SHOWERS TO CONTINUE
INTO EARLY TUESDAY. HIGH PRESSURE WILL BUILD IN FROM THE
NORTHWEST...WITH A DRY FORECAST FOR TUESDAY AND WEDNESDAY.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...

A WEAK WARM FRONTAL BOUNDARY WILL LINGER ACROSS THE REGION
TONIGHT. PREVAILING VFR CONDITIONS ARE EXPECTED TONIGHT.
HOWEVER...MOISTURE ASSOCIATED WITH THIS BOUNDARY COULD LEAD TO A
PERIOD OF MVFR...ESPECIALLY FROM ZZV NORTH TO FKL/DUJ.

VFR CONDITIONS WILL PREVAIL ACROSS THE TERMINALS ON THURSDAY. THE
WARM FRONTAL BOUNDARY WILL REMAIN ACROSS THE AREA...WITH A WAVE
OF UPPER LEVEL ENERGY PUSHING ACROSS THE TERMINALS THURSDAY NIGHT.
THIS WILL ALLOW FOR SCATTERED SHOWERS INTO FRIDAY MORNING...AND
THE POTENTIAL FOR REDUCED CONDITIONS.

WITH A WARM...MOIST AIR MASS ADVECTING NORTHWARD INTO THE
AREA...SHOWERS AND THUNDERSTORMS COULD DEVELOP FRIDAY AFTERNOON. A
BROAD AREA OF LOW PRESSURE WILL SLOWLY MOVE ACROSS THE TERMINALS
OVER THE WEEKEND...WITH RAIN...POSSIBLY HEAVY AT TIMES ON
SATURDAY...AND REDUCED CEILINGS AND VISIBILITIES POSSIBLE THROUGH
MONDAY.

&&

.HYDROLOGY...
THE POTENTIAL FOR FLOODING ACROSS THE UPPER OHIO VALLEY WILL
CONTINUE THROUGH THE WEEKEND. SMALL STREAMS...ESPECIALLY IN THE
MOUNTAINS OF WEST VIRGINIA...WESTERN MARYLAND...AND SOUTHWESTERN
PENNSYLVANIA ARE ALREADY RUNNING CLOSE TO BANKFULL AS WARM
TEMPERATURES AND MOIST DEW POINTS INDUCE SUBSTANTIAL RUNOFF FROM THE
MELTING OF THE DEEP SNOW PACK. AS OF WEDNESDAY MORNING...THE WATER
CONTENT OF THE SNOW PACK ACROSS THE MOUNTAINS WAS GENERALLY 5 INCHES
WITH LOCALLY 10 INCHES NEAR THE RIDGE TOPS. ELSEWHERE THE WATER
CONTENT OF THE MELTING SNOW PACK WAS 1 TO 3 INCHES. RECENT GEFS
MODEL OUTPUT SUGGESTS THE SNOW MELT CAN REDUCE THE WATER CONTENT OF
THE SNOW PACK BY 3 OR 4 INCHES BY FRIDAY.

MODEL OUTPUT ALSO INDICATES THAT MORE SUBSTANTIAL RAINFALL MAY MOVE
ACROSS THE UPPER OHIO VALLEY FRIDAY THROUGH SUNDAY...WHICH COULD ADD
SIGNIFICANT RUNOFF INTO STREAMS AND RIVERS AS SOILS ARE ALREADY
SATURATED. THE LARGER RIVERS WILL LIKELY EXPERIENCE SIGNIFICANT
RISES DURING THE WEEKEND DEPENDING ON HOW MUCH RAIN FALLS.
RIVERS CLOSE TO THE MOUNTAINS...SUCH AS THE CHEAT AND YOUGHIOGHENY
SHOULD BE AFFECTED FIRST...WHICH THEN COULD RAISE THE POTENTIAL FOR
FLOODING ALONG THE MONONGAHELA AND UPPER OHIO RIVERS.

THE ALLEGHENY...BEAVER AND MUSKINGUM RIVERS MAY ALSO HAVE A RAISED
POTENTIAL FOR FLOODING THIS WEEKEND...DEPENDING ON THE AMOUNT AND
AREAL EXTENT OF THE RAINFALL.

THE POTENTIAL FOR HEAVIER RAIN IS ASSOCIATED WITH THE SLOW EASTWARD
MOVEMENT OF A STRONG LOW PRESSURE SYSTEM FROM THE MIDWEST.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...FLOOD WATCH FROM THURSDAY EVENING THROUGH SUNDAY EVENING FOR
     MDZ001.
OH...FLOOD WATCH FROM THURSDAY EVENING THROUGH SUNDAY EVENING FOR
     OHZ039>041-048>050-057>059-068-069.
PA...FLOOD WATCH FROM THURSDAY EVENING THROUGH SUNDAY EVENING FOR
     PAZ007>009-013>016-020>023-029>032.
WV...FLOOD WATCH FROM THURSDAY EVENING THROUGH SUNDAY EVENING FOR
     WVZ001>004-012-021>023-041.

&&

$$

NWS PBZ Office Area Forecast Discussion