Special Weather Statement, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
334 AM EDT WED APR 20 2011

.SYNOPSIS...
A STRONG COLD FRONT WILL MOVE THROUGH THE AREA THIS MORNING. THIS
FRONT WILL BRING MORE SHOWERS AND STORMS TODAY. HIGH PRESSURE
WILL PROVIDE DRY AND COOL CONDITIONS TONIGHT THROUGH THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
UPDATED TO INCLUDE SVR WATCH 164.

RECENT RADAR DATA, USED IN CONJUNCTION WITH LATEST MODEL RUNS,
SHOWS THE LINE OF STRONG TO SEVERE THUNDERSTORMS OVER W OHIO,
CONTINUING TO WEAKEN AS IT MOVES EASTWARD INTO MORE STABLE AIR.
EXPECT THE LINE TO MOVE THROUGH THE AREA THIS MORNING, AHEAD OF
COLD FRONT WHICH WILL MOVE INTO C PA BY 18Z. LATEST DAY1 OUTLOOK
FROM SPC, MOVES THE SLIGHT RISK FOR SEVERE TO THE EAST OF THE
REGION. ALL THE DATA AND RECENT EVENTS, POINT TO A NON SEVERE
EVENT AFTER WATCH ENDS.

ACTIVITY WILL WIND DOWN VERY QUICKLY AFTER THE FRONT MOVES
EASTWARD AND WOULD EXPECT JUST SHOWERS BEHIND THE FRONT.

FORECASTED TEMPERATURES USING BLEND OF GFS MOS AND 21Z SREF VALUES.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
RECENT SREF MODEL OUTPUT CONTINUES TO SHOW HIGH PRESSURE COMING
EAST FROM THE DAKOTAS TO PROVIDE DRY CONDITIONS WITH SEASONABLY COOL
TEMPERATURES ACROSS THE UPPER OHIO VALLEY TONIGHT AND THURSDAY.

MODEL SOLUTIONS VARY WITH THE THU NIGHT AND FRIDAY FORECAST.
ANOTHER WARM FRONT WILL MOVE NORTHWARD THROUGH THE UPPER OHIO
VALLEY BY THE END OF THE WORK WEEK. MODELS ARE INDICATING THAT A
WAVE WILL MOVE ALONG THE NORTHERN FLANK OF THE FRONT LATE THURSDAY
NIGHT AND FRIDAY MORNING. THE DIFFERENCES ARRIVE WITH THE POSITION
OF THE FRONT FRIDAY, AND THE LOCATION OF THE WAVE. NAM KEEPS
EVERYTHING FURTHER SOUTH ON FRIDAY, INCLUDE THE UNSTABLE AIR. THE
GFS KEEPS THE AREA STABLE, BUT MOVES THE FRONT FURTHER NORTH. FOR
NOW WILL GO WITH A COMPROMISE AND KEEP THE HIGHER POPS ACROSS THE
SOUTH ON FRIDAY.

FORECASTED TEMPERATURES USING MAINLY GFS MOS.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
MODELS SHOWING SIMILAR OUTPUT FRIDAY NIGHT, WITH ANOTHER WAVE
MOVING NORTHWARD ALONG SFC BOUNDARY. FRIDAY NIGHT APPEARS TO BE A
BETTER TIME FOR MORE WIDESPREAD RAIN, WITH THE UNSTABLE AIR
REMAINING SOUTH OF THE REGION.

COLD FRONT ASSOCIATED WITH NEXT SYSTEM WILL MOVE ACROSS THE AREA
LATE SAT AND THEN STALL BY SAT NIGHT. THIS STALLED FRONT WILL KEEP
IN THE RISK FOR ACTIVITY THROUGH SUNDAY AND INTO MONDAY.

MODELS ARE IN DECENT AGREEMENT PUSHING FRONT NORTHWARD ON MONDAY
AND ALLOWING THE REGION TO ENTER THE WARM SECTOR BY TUESDAY.

AT THIS POINT, NOT A LOT OF CONFIDENCE IN THE LONG TERM FORECAST
AS MODELS GETTING A HANDLE ON A STATIONARY FRONT THAT FAR OUT,
GENERALLY RUN INTO PROBLEMS WITH THE DETAILS.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
LOW PRESSURE OVER OHIO WILL SWEEP A COLD FRONT ACROSS THE REGION
TODAY WITH FROPA LATE MORNING AT ZZV TO EARLY AFTERNOON ACROSS THE
EASTERN TERMINALS. GENERAL VFR AHEAD OF FRONT WITH INVERSION IN
PLACE AND LOW LEVEL JET OF 50KTS AT 2K FT HAVE ADDED LLWS UNTIL
FRONT APPROACHES TO MIX ATMOSPHERE. WITH INVERSION AND WEAK
INSTABILITY HAVE KEPT CB IN TERMINALS BUT EXPECTING ONLY MVFR WITH
FROPA IN SHOWERS AND ISOLATED THUNDERSTORMS. WITH FRONT AND BEHIND
STRONG PRESSURE GRADIENT WILL BRING WEST WINDS GUSTING TO NEAR 30KTS
INTO EARLY EVENING BEFORE DIMINISHING. SURFACE HIGH ACROSS WESTERN
GREAT LAKES WILL THEN SHIFT EAST WITH VFR CONDITIONS INTO THURSDAY
NIGHT.

A WARM FRONT WILL APPROACH FROM THE SOUTHWEST ON FRIDAY AND RETURN
THE CHANCE OF SHOWERS AND THUNDERSTORMS WITH RESTRICTIONS. LOW
PRESSURE MOVING ACROSS THE OHIO VALLEY WILL BRING POSSIBLE
RESTRICTIONS SATURDAY WITH A FRONT STALLING ACROSS REGION FOR SUNDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

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