FXUS61 KPBZ 241556
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1056 AM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE WILL PROVIDE DRY WEATHER FOR THE REGION THROUGH
TONIGHT. HOWEVER...MOISTURE WILL OVERSPREAD THE REGION AS LOW
PRESSURE ADVANCES TOWARD THE GREAT LAKES WITH THE POTENTIAL FOR
FREEZING RAIN AND RAIN LATE TONIGHT AND FRIDAY. COLD AIR ON THE
BACK SIDE OF THE LOW WILL THEN 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 SWATCH 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. THAT FORECAST SUPPORTS
ONGOING WINTER STORM WATCH FOR THE RIDGE ZONES WITH HEADLINE DECISION
COMING THIS AFTERNOON FOR WESTERN PENNSYULVANIA ZONES. FREEZING
RAIN IS STILL EXPECTED TO CHANGE TO ALL RAIN AS THE DAY
PROGRESSES.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
AS COLDER AIR SWEEPS IN BEHIND THE SYSTEM THE REMAINING PRECIP
WILL CHANGE OVER TO SNOW SHOWERS FRIDAY NIGHT INTO SATURDAY. AT
THIS TIME...LIMITED SUPPORT FOR MUCH MORE THAN SCATTERED SNOW
SHOWERS FORESEEN.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
CLOSED COLD UPPER LOW COULD CONTINUE TO INDUCE COLD AIR
INSTABILITY AND LAKE ENHANCED SNOW SHOWERS ACROSS THE UPPER OHIO
VALLEY SUNDAY INTO MONDAY NIGHT UNTIL IT EXITS TO NEW ENGLAND.
SURFACE HIGH SHOULD ALLOW FOR SOME DRYING WEDNESDAY. CLOUD COVER
WILL HOLD DAYTIME TEMPERATURES DOWN TO FEW DEGREES BELOW NORMAL
THROUGH THE EXTENDED PERIOD.
&&
.AVIATION /16Z THURSDAY THROUGH MONDAY/...
IFR STRATOCUMULUS OVER AREA NORTH OF PIT WILL BEGIN TO RETREAT
NORTH AS RIDGING AMPLIFIES ACROSS THE REGION THIS AFTERNOON.
EXPECT ANY RESTRICTIONS TO REMAIN NORTH OF A PIT TO LBE LINE.
VFR WILL PREVAIL FOR ALL OTHER AREAS. MID CLOUDS WILL INCREASE
THIS EVENING ACROSS OHIO...SPREADING ACROSS PA LATE
EVENING/OVERNIGHT AS LOW PRESSURE APPROACHES FROM THE SOUTHWEST.
IN ADDITION...WINDS ALOFT WILL INCREASE SIGNIFICANTLY...AND WITH
SURFACE WINDS AROUND 10 KT...WILL INCLUDE LOW LEVEL WIND SHEAR
LATE THURSDAY NIGHT FOR ALL PORTS.
LOW PRESSURE WILL ENTER THE UPPER OHIO VALLEY OVERNIGHT THURSDAY
NIGHT/CHRISTMAS DAY. INITIAL PRECIP WILL LIKELY BEGIN AT ZZV
BY 09Z CHRISTMAS DAY...PIT BY 11-13Z...AND FKL/DUJ 13-15Z.
THERMAL PROFILES SUGGEST PRECIP AT ZZV/HLG/MGW WILL REMAIN
LIQUID THROUGH THE DAYLIGHT HOURS CHRISTMAS DAY. FOR PIT/BVI
AGC/LBE...FREEZING PRECIP WILL BE BRIEF AT ONSET...WITH PERHAPS
1-2 HOURS DURATION BEFORE CHANGING TO RAIN. FOR FKL/DUJ...FREEZING
PRECIP WILL LIKELY LINGER A BIT LONGER...AS LATE AS 18Z OR SO.
MVFR RESTRICTIONS WILL PREVAIL IN THE PRECIP...WITH IFR PSBL IN
THE HEAVIER ACTIVITY. AS WINDS INCREASE AT THE SURFACE CHRISTMAS DAY
TO 15-20KT WITH GUSTS TO 25-30KT...LOW LEVEL WIND SHEAR WILL
DIMINISH.
MVFR/IFR RESTRICTIONS ARE EXPECTED TO PERSIST FOR THE WEEKEND INTO
MONDAY...AS SCATTERED RAIN AND SNOW SHOWERS CHANGE OVER TO ALL
SNOW BY SATURDAY NIGHT AS COLDER AIR MOVES IN BEHIND THE EXITING
SYSTEM.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR MDZ001.
OH...NONE.
PA...NONE.
WV...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR WVZ023-041.
&&
$$
