FXUS61 KPBZ 251106
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
605 AM EST FRI DEC 25 2009

.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM, MOVING NORTHWARD THROUGH THE MIDWEST,
WILL PUSH FREEZING RAIN AND RAIN INTO THE AREA THIS CHRISTMAS DAY.
COLDER AIR WILL MOVE IN FOR THE WEEKEND. 

&&

.NEAR TERM /THROUGH TODAY/...
WATCHING TEMPS CLOSELY AND CONFIDENCE IN WIDESPREAD FREEZING RAIN
EVENT IS DWINDLING. TEMPERATURES CONTINUE TO RISE UNDER STRONG WAA
AROUND STACKED SYSTEM ROTATING NORTHWARD ACROSS THE MIDWEST. NOT
ONLY ARE SFC TEMPERATURES WARMING, BUT IT WILL TAKE A WHILE FOR
RAIN TO START REACHING THE GROUND AS LOW REMAINS WELL WEST OF THE
AREA AND ATMOSPHERE IS DRY.

DUE TO INITIAL GROUND COLDNESS AND SURFACE LAYER DRYNESS, EXPECT
TO SEE WET BULBING OCCURRING AT THE ONSET OF PRECIP, WHICH WILL
DROP TEMPS A FEW DEGREES. WILL LEAVE THE ADVISORY AS IS FOR THIS
MORNING, BUT THE EVENT MAY BE MORE LOCALIZED.

SECOND CONCERN IS SPEED OF WIND GUSTS IN DOWN SLOPE AREAS
IMMEDIATELY WEST OF THE APPALACHIAN MOUNTAIN RIDGES. HAVE ISSUED A
WIND ADVISORY FOR TODAY FOR THE HIGHEST RIDGES AS NOT ONLY IS THE
WINDS JUST ABOVE THE SFC SCREAMING, BUT THERE IS A STRONG
POSSIBILITY FOR THE PREVIOUSLY MENTIONED DOWN-SLOPING.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
JUDGING FROM RECENT SREF MODEL OUTPUT...EXPECT THE COLD FRONT TO
MOVE THROUGH TONIGHT. THE RESULTING COOL DOWN WILL CHANGE
PRECIPITATION TO ALL SNOW BY LATE SATURDAY NIGHT. THE PROBLEM WITH
PRECIP TONIGHT IS THE LACK OF MID AND UL MOISTURE WHICH WILL NOT
ALLOW FOR ICE TO DROP INTO THE LOWER LEVELS...THUS PREVENTING AN
ATMOSPHERE CONDUCIVE TO SNOW MAKING. HAVE PUT IN A MENTION OF
FREEZING DRIZZLE LATE TONIGHT. THIS WILL HAVE TO BE LOOKED AT
MORE CLOSELY ON A LATER PACKAGE. 

FORECASTED TEMPERATURES USING A BLEND OF RECENT SREF MODEL OUTPUT
AND GFS MOS.

WITH UL REMAINING WEST OF THE AREA THIS WEEKEND EXPECT A BREAK IN
PRECIP SATURDAY AND THROUGH THE FIRST HALF OF SUNDAY.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
UPPER LEVEL LOW OVER THE LOWER GREAT LAKES WILL MOVE INTO NEW 
ENGLAND BY TUESDAY. PERSISTENT LOW LEVEL NORTHWEST FLOW AND COLD AIR 
INSTABILITY WILL CONTINUE TO GENERATE SCATTERED SNOW SHOWERS THROUGH 
EARLY TUESDAY. 

SURFACE HIGH PRESSURE WILL BUILD INTO THE REGION LATE TUESDAY AND 
WEDNESDAY BRINGING DRY WEATHER. A LOW PRESSURE SYSTEM OVER THE 
SOUTHEASTERN STATES WILL BRING MOISTURE AND A CHANCE OF SNOW SHOWERS 
TO THE NORTHERN WEST VIRGINIA/WESTERN MARYLAND MOUNTAINS THURSDAY. 

CLOUD COVER WILL HOLD DAYTIME TEMPERATURES DOWN TO FEW DEGREES BELOW 
NORMAL THROUGH THE EXTENDED PERIOD.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
A POTENT LOW PRESSURE SYSTEM WILL LIFT NORTHWARD ACROSS THE MISSOURI 
VALLEY...WITH AN OCCLUDED FRONT CROSSING THE AREA LATE TODAY AND 
TONIGHT. INITIAL PRECIP IS CROSSING EASTERN OHIO INTO FAR SOUTHWEST
PA...AND WILL CONTINUE TO WORK NORTH ACROSS THE REGION...WITH PRECIP 
JUST BEGINNING AT MGW/HLG/PIT/AGC...AND SHOULD BEGIN AT LBE/BVI IN 
THE NEXT HOUR OR SO...MOVING NORTH TO FKL/DUJ BY 15Z. PRECIP WILL BE 
LIQUID FROM A HLG/MGW LINE SOUTH AND WEST. FURTHER 
NORTH...TEMPERATURES ARE HOVERING AROUND FREEZING...AND WITH WET 
BULB EFFECTS...SOME BRIEF FZRA IS PSBL FOR BVI/PIT/AGC/LBE AT ONSET 
FOR AN HOUR OR TWO BEFORE CHANGING TO RAIN. FOR FKL/DUJ...COLDER AIR 
WILL HANG ON LONGER...SO WILL USE FZRA FOR 3-4 HOURS...CHANGING TO 
RAIN THIS AFTN. WINDS ALOFT WILL INCREASE TO 50-60KT AT 2000 FT...SO 
WILL USE LOW LEVEL WIND SHEAR FOR ALL PORTS THROUGH THIS EVENING. SE 
SURFACE WINDS OF 10-15 KT WILL PREVAIL FOR THE EARLY 
MORNING...INCREASING TO 15-20KT WITH GUSTS TO 30-35 KT THIS 
AFTN...WITH THE HIGHEST GUSTS AT LBE IN SOUTHEAST DOWNSLOPE FLOW. 
MVFR/AREAS OF IFR WILL PREVAIL WITH THE PRECIP TODAY INTO THIS 
EVENING...WITH LOWER CLOUDS PERSISTING THROUGH FRIDAY. WITH JUST 
MAINLY LOWER CLOUDS TNGT/EARLY SATURDAY...THINK MOST OF THE PRECIP 
WILL BE LIGHT SNOW SHOWERS AND DRIZZLE/FREEZING DRIZZLE OVERNIGHT.

FOR SATURDAY...THINK MOST AREAS WILL REMAIN DRY AS THE REGION WILL
BE IN THE DRY SLOT BETWEEN THE SURFACE FRONT TO THE EAST...AND
THE PARENT UPPER LOW ACROSS THE MIDWEST. HOWEVER...MAINLY MVFR
CIGS WILL REMAIN. FOR SUNDAY/MONDAY...THE UPPER LOW WILL EJECT
EAST ACROSS THE AREA...WITH SNOW SHOWERS/RESTRICTIONS. CONDITIONS
MAY IMPROVE TUESDAY AS THE LOW IS PROGGED TO EJECT EAST INTO
THE CANADIAN MARITIMES.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 4 PM EST 
     THIS AFTERNOON FOR MDZ001.
OH...WINTER WEATHER ADVISORY FROM 6 AM TO 10 AM EST THIS MORNING 
     FOR OHZ040-041-050.
PA...WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 4 PM EST 
     THIS AFTERNOON FOR PAZ008-009-015-016-023.
     WINTER WEATHER ADVISORY FROM 6 AM TO 10 AM EST THIS MORNING 
     FOR PAZ029-031.
     WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO NOON EST 
     TODAY FOR PAZ007-013-014-020>022-030-032.
WV...WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 4 PM EST 
     THIS AFTERNOON FOR WVZ041.
     WINTER WEATHER ADVISORY FROM 6 AM TO 10 AM EST THIS MORNING 
     FOR WVZ001>003.
     WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO NOON EST 
     TODAY FOR WVZ023.

&&

$$