FXUS61 KPBZ 250000
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
700 PM EST THU DEC 24 2009

.SYNOPSIS...
HIGH PRESSURE WILL PROVIDE DRY WEATHER FOR THE REGION TONIGHT.
HOWEVER...HOLIDAY CHANGES ARE FORTHCOMING AS MOISTURE WILL
OVERSPREAD THE REGION WITH THE ADVANCE OF LOW PRESSURE TOWARD THE
GREAT LAKES. FREEZING RAIN AND RAIN ARE EXPECTED FOR CHRISTMAS AND
COLD AIR IN THE WAKE OF THE SYSTEMS COLD FRONT WILL BRING THE
CHANCE OF SNOW SHOWERS FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
STRONG LOW PRESSURE IS PROJECTED TO MOVE UP THE MISSISSIPPI VALLEY
ON FRIDAY AND SPREAD A FAIRLY DEEP MOISTURE SWATH OVER THE UPPER
OHIO REGION. PRECIP PROBABILITIES HAVE BEEN CONSISTENT, SO GRADUAL
ESCALATION TREND TO CATEGORICAL NUMBERS ON FRIDAY HAS BEEN
CONTINUED WITH SOME ADJUSTMENTS TO TIMING. QPF AMOUNTS ARE PROGGED
UNDER AN INCH WITH BROAD MID LEVEL DRY SLOT EXPECTED TO SWEEP
ACROSS THE AREA DURING THE AFTERNOON...AND OHRFC EXPECTS LIQUID TO
BE ABSORBED INTO THE SNOW PACK...THUS NO FLOOD WATCH AND A RATHER
CONSERVATIVE RIVER FORECAST.

MAIN PROBLEM WILL BE TIMING AND PRECIP TYPE UNDER STRONG WARM
ADVECTION REGIME. FREEZING RAIN IS A GOOD BET FOR MOST OF THE
REGION AND FORECAST HAS BEEN UPDATED WITH SURFACE TEMPERATURES
ADJUSTED DOWN FOR THE NEAR TERM GIVEN FORECAST OF WET BULB
TEMPERATURES AFTER DAYBREAK ON FRIDAY. GFS HINTS AT WET BULBING
ALOFT AS WELL AND SOME AREAS MAY EXPERIENCE A BRIEF PERIOD OF SLEET
OR SNOW, BUT WILL STAY WITH THE MORE SIGNIFICANT WEATHER TYPE
TODAY...AND THAT FORECAST SUPPORTS A WINTER WEATHER ADVISORY FOR
WESTERN PA ZONES AS WELL AS GARRETT, PRESTON AND TUCKER COUNTIES.
FREEZING RAIN IS STILL EXPECTED TO CHANGE TO ALL RAIN AS THE DAY
PROGRESSES.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
WITH COLDER AIR PROJECTED TO SWEEP IN BEHIND THE SYSTEM, PRECIP
WILL GRADUALLY CHANGE OVER TO SNOW SHOWERS FRIDAY NIGHT INTO
SATURDAY...POTENTIAL FOR WHICH WILL CONTINUE THROUGH SUNDAY AS THE
MID/UPPER LOW CONTINUES TO DIG SLOWLY EASTWARD.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
UPPER LEVEL LOW OVER THE LOWER GREAT LAKES WILL MOVE INTO NEW 
ENGLAND BY TUESDAY. PERSISTANT 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 /00Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL CONTINUE TO PREVAIL ACROSS THE TERMINALS THIS
EVENING AS HIGH PRESSURE MOVES NORTHEAST OF THE AREA. A POTENT LOW
PRESSURE SYSTEM WILL LIFT NORTHWARD ACROSS THE MISSOURI VALLEY
OVERNIGHT...BRINGING LOW-LEVEL WIND SHEAR TO THE TERMINALS BY THE
EARLY MORNING. LOW-LEVEL MOISTURE RELATED TO THE SYSTEM WILL BRING
PRECIPITATION TO THE AREA AROUND 12Z FRIDAY.

SURFACE TEMPS NEAR FREEZING AT THE ONSET OF PRECIPITATION AND WARM
AIR ALOFT MAY ALLOW FOR A PERIOD OF FREEZING RAIN ACROSS THE
TERMINALS WITH THE ONSET OF PRECIPITATION FRIDAY MORNING. TEMPO
GROUPS ARE FORECAST FOR FREEZING RAIN STARTING AT 11Z AT KZZV
...13Z-14Z AT KPIT/KAGC/KBVI/KHLG AND 15Z- 16Z AT KFKL/KDUJ/KLBE.
PRECIPITATION WILL TURN OVER TO RAIN BY LATE MORNING EVERYWHERE
EXCEPT KDUJ/KFKL...WHERE -FZRA COULD PREVAIL FOR TWO TO THREE
HOURS BEFORE CHANGING OVER TO RAIN AROUND 20Z.

RAIN WILL CONTINUE TO PREVAIL MOSTLY ACROSS THE TERMINALS ON
FRIDAY AND FRIDAY NIGHT...WITH CEILINGS BECOMING MVFR WITH
MARGINAL IFR CONDITIONS POSSIBLE. SOUTHEASTERLY WINDS OF AROUND 15
KTS GUSTING TO 20-25 KTS FRIDAY EVENING WITH LOW-LEVEL WIND SHEAR
CONTINUING. BY SATURDAY MORNING...RAIN WILL TURN TO SNOW SHOWERS
WITH WIND SHEAR ALOFT DECREASING AND SURFACE WINDS BECOMING
LIGHTER...SHIFTING TO SOUTHWESTERLY.

MVFR/IFR RESTRICTIONS WITH SCATTERED SNOW SHOWERS ARE EXPECTED TO
PERSIST SATURDAY INTO EARLY NEXT WEEK AS THE UPPER LEVEL LOW
SLOWLY MOVES ACROSS THE GREAT LAKES INTO NEW ENGLAND.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY FROM 6 AM TO 4 PM EST FRIDAY FOR 
     MDZ001.
OH...NONE.
PA...WINTER WEATHER ADVISORY FROM 6 AM TO 4 PM EST FRIDAY FOR 
     PAZ008-009-015-016-023.
     WINTER WEATHER ADVISORY FROM 6 AM TO NOON EST FRIDAY FOR 
     PAZ007-013-014-020>022-030-032.
WV...WINTER WEATHER ADVISORY FROM 6 AM TO 4 PM EST FRIDAY FOR 
     WVZ041.
     WINTER WEATHER ADVISORY FROM 6 AM TO NOON EST FRIDAY FOR 
     WVZ023.

&&

$$