FXUS61 KPBZ 230048 AAB
AFDPBZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
748 PM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE WILL BRING COLD AND DRY CONDITIONS THROUGH THURSDAY.
A LOW PRESSURE SYSTEM WILL BRING A WINTRY MIX LATE THURSDAY
NIGHT AND FRIDAY.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
MADE CHANGES TO OVERNIGHT CLOUD COVER AS LOW CLOUD CONTINUE TO
SHIFT TOWARD THE SOUTHWEST. TEMPERATURES WILL BE ABOUT 5 DEGREES
BELOW NORMAL.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
HIGH PRESSURE IS EXPECTED TO REMAIN IN CONTROL OF THE WEATHER FOR
THE DISTRICT WEDNESDAY NIGHT AND THURSDAY BEFORE A POTENT SURFACE
LOW DEVELOPS IN THE PLAINS. MODELS HAVE BEEN TRENDING SOMEWHAT
SLOWER AND COLDER WITH THIS SYSTEM. IT NOW APPEARS THAT
PRECIPITATION SHOULD NOT ARRIVE UNTIL LATE THURSDAY NIGHT IN THE
WESTERN FORECAST AREA...AND AROUND DAYBREAK CHRISTMAS IN THE EAST.
SURFACE TEMPERATURES WILL BE SLOW TO WARM...AND WARM ADVECTION
AROUND 850 MB IS EXPECTED BEFORE TEMPERATURES WARM AT THE SURFACE.
EXCEPT FOR THE SOUTHERNMOST COUNTIES IN THE FORECAST AREA...MOST
LOCATIONS COULD START WITH A MIX OF RAIN AND FREEZING RAIN BEFORE
CHANGING OVER TO ALL RAIN BY FRIDAY AFTERNOON. AREAS NORTH AND EAST
OF PITTSBURGH WOULD HAVE THE GREATEST THREAT OF RECEIVING
ACCUMULATING FREEZING RAIN. HAVE ALSO INCREASED POPS TO CATEGORICAL.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
ON CHRISTMAS NIGHT STRONG CLOSED LOW OVER WESTERN LAKES WILL ALLOW
A SECONDARY LOW CENTER TO DEVELOP INLAND OF THE DELMARVA PENINSULA
WITH MOISTURE LOOKING TO BE THROWN BACK ACROSS EASTERN 2/3RD OF THE
CWA FRIDAY NIGHT INTO EARLY SATURDAY. HPC PROGS NOT TOO FAR OFF
00Z ECMWF AND 12Z GFS WITH THIS DEVELOPMENT. LOOKS TO BE A VERY
COMPLICATED SCENARIO SO FOR NOW BUMPED UP POPS TO LIKELY WITH A
MIX OF PRECIPITATION FRIDAY NIGHT TRANSITIONING TO ALL SNOW
EARLY SATURDAY MORNING... WITH SNOW DIMINISHING IN THE AFTERNOON
AS SURFACE LOW HEADS TO NEW ENGLAND. SUNDAY AND MONDAY CLOSED LOW
SLOWLY SLIDES EAST ACROSS UPPER OHIO VALLEY WITH BELOW NORMAL
TEMPERATURES AND SNOW SHOWERS. COLD SURFACE HIGH SHOULD ALLOW A
DRY DAY TUESDAY.
&&
.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
BLEND OF RECENT SATELLITE AND SURFACE DATA SHOW MVFR STRATOCUMULUS
SLOWLY ERODING FROM NORTH TO SOUTH ACROSS THE UPPER OHIO VALLEY THIS
EVENING. RECENT NAM MODEL PROFILES AND GFS LAMP OUTPUT CONFIRM
THAT THIS TREND WILL CONTINUE OVERNIGHT. SO EXPECT THE MVFR
STRATOCUMULUS TO DISSIPATE TO VFR CONDITIONS BY 06Z NEAR KPIT AND
KLBE...BUT IT MAY NOT DISSIPATE TO VFR NEAR KZZV AND KMGW UNTIL
12Z-15Z. CONDITIONS SHOULD REMAIN VFR ACROSS THE UPPER OHIO VALLEY
THROUGH DAYTIME THURSDAY.
SURFACE WINDS WILL BE LESS THAN 4 KTS OVERNIGHT AND MAINLY FROM
THE NORTH. WINDS COULD BECOME MORE NORTHEASTERLY NEAR 6 KTS
DAYTIME WEDNESDAY.
RECENT SREF MODEL OUTPUT CONTINUES TO SHOW A STRONG MIDWEST LOW
PRESSURE SYSTEM SPINNING A FRONTAL BAND OF IFR PRECIPITATION
THROUGH THE UPPER OHIO VALLEY THURSDAY NIGHT INTO DAYTIME FRIDAY.
THERE COULD ALSO BE A PERIOD OF FREEZING RAIN AND SURFACE ICING
PROBLEMS AT THE START. THE ENSUING COLD UPPER LOW CENTER COULD
FOLLOW WITH MVFR SNOW SHOWERS ACROSS THE UPPER OHIO VALLEY FRIDAY
NIGHT INTO SUNDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.
&&
$$
