FXUS61 KPBZ 270006
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
706 PM EST THU NOV 26 2009
.SYNOPSIS...
IN THE WAKE OF A COLD FRONT...AN ARCTIC AIR MASS WILL BUILD INTO
THE AREA OVERNIGHT. WITH A COLD NORTHWESTERLY FLOW...THIS WILL
ALLOW FOR RAIN AND SNOW SHOWERS TONIGHT TURNING OVER TO ALL SNOW
SHOWERS ACROSS THE AREA BY FRIDAY. HIGH PRESSURE WILL BUILD IN ON
SATURDAY...WITH A DRY WEEKEND EXPECTED.
&&
.NEAR TERM /THROUGH FRIDAY/...
A CLOSED 500MB LOW IS LOCATED ACROSS SERN MICHIGAN WITH A TROF AXIS
EXTENDING SWD ACROSS THE OH VALLEY. THIS DEEP TROF IS THE DOMINANT
FEATURE ACROSS THE ERN HALF OF THE CONUS...WITH RIDGING ACROSS THE
WEST. AT THE SURFACE...A 1004 MB LOW IS ACROSS NORTH OF LAKE HURON WITH
A TROF EXTENDING SWWD INTO INDIANA. A FEW LIGHT RAIN SHOWERS HAVE
DEVELOPED ACROSS WRN PA...WITH AN AREA OF STRATOFORM PRECIP ACROSS
SWRN OHIO ADVECTING EWD TOWARD THE AREA.
TONIGHT...SFC TROF INTO WESTERN OHIO WILL ADVECT EWD ACROSS THE
REGION OVERNIGHT. THE DEEPEST MOISTURE ASSOCD WITH THE LOW WILL
REACH E-CNTRL OH BY 06Z. SHOWERS ASSOCD WITH THE TROF AXIS WILL
START AS RAIN SHOWERS THEN WILL QUICKLY TURN TO SNOW ACROSS THE
HIGHER ELEVATIONS...WITH SNOW SHOWERS ACROSS THE AREA BY THE PRE-
DAWN HOURS FRIDAY AS THICKNESSES DECREASE WITH CAA. SOME LIGHT
ACCUMULATION IS POSSIBLE ACROSS WRN PA WITH SNOW SHOWERS POSSIBLE
AT AN OPTIMAL TIME FOR ACCUMULATION BEFORE DAYBREAK. 1 TO 2 INCHES
ARE POSSIBLE ACROSS THE HIGHER ELEVATIONS OF THE EASTERN RIDGES. A
WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR GARRETT...TUCKER...AND
PRESTON COUNTIES WITH SNOW SHOWERS ONGOING THROUGH FRIDAY NIGHT.
THE 500MB TROF WILL BECOME MORE NEGATIVELY TILTED FRIDAY AS IT
ADVECTS OFF THE MID-ATLANTIC COAST...LEAVING THE AREA IN A NWRLY
FLOW IN ITS WAKE. WITH CAA THROUGHOUT THE DAY AND FCST 850 TEMPS
OF -6C TO -8C...THIS WILL BE FAVORABLE FOR SNOW SHOWERS FRIDAY
MORNING INTO THE EARLY AFTERNOON ACROSS THE AREA. FRIDAY WILL BE
NOTICEABLY COLDER AND BLUSTERY....WITH WINDS GUSTING TO 25 TO 30
MPH AND HIGHS ONLY WARMING INTO THE UPPER 30S ACROSS THE LOWLANDS
AND BARELY WARM UP TO FREEZING ACROSS THE HIGHER ELEVATIONS.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
WITH A MOISTURE FEED OFF A WARM...8C TO 10C...LAKE ERIE...THIS
WILL ALLOW FOR SOME LAKE EFFECT SNOW SHOWERS TO CONTINUE ACROSS
AREAS NORTH OF INTERSTATE 80 INTO FRIDAY EVENING...CUTTING OFF BY
SATURDAY MORNING AS RIDGING AND DRIER AIR BUILDS IN FROM THE WEST.
THIS PATTERN WILL ALSO BE FAVORABLE FOR SNOW SHOWERS ACROSS THE
EASTERN RIDGES. WITH THE WINTER WX ADVISORY CONTINUING FOR
GARRETT...TUCKER...AND PRESTON COUNTIES UNTIL 06Z SATURDAY...WITH
3 TO 5 INCHES OF TOTAL ACCUMULATION EXPECTED. WITH MORE OF A NRLY
COMPONENT TO THE FLOW OFF OF LAKE ERIE...THIS SHOULD LIMIT
ACCUMULATION ALONG AND NORTH OF INTERSTATE 80 TO 1 TO 2 INCHES.
SATURDAY...THE FLOW ALOFT WILL BECOME MORE WRLY AND MOISTURE WILL
ADVECT NE OF THE AREA...CUTTING OFF LINGERING SNOW SHOWERS AND
FLURRIES ACROSS THE HIGHER ELEVATIONS AND ALONG AND NORTH OF
INTERSTATE 80 BY NOON. HIGH PRESSURE WILL BUILD IN FROM THE
SOUTH...WITH CLOUD COVERAGE DECREASING FROM THE SOUTHWEST
THROUGHOUT THE DAY. INCREASING SUNSHINE AND WAA WILL ALLOW FOR
TEMPS TO RECOVER TO NORMAL VALUES FOR HIGHS.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
JUDGING FROM BLEND OF RECENT SREF GEFS AND ECMWF MODEL
OUTPUT...EXPECT THAT A WARM FRONT DEVELOPING AHEAD OF THE LOW
PRESSURE SYSTEM COMING FROM THE PACIFIC NORTHWEST MAY SPREAD SHOWERS
ACROSS THE UPPER OHIO VALLEY SUNDAY NIGHT. HOWEVER THE BULK OF
SHOWERS WILL OCCUR IN BANDS MONDAY...MONDAY NIGHT...AND POSSIBLY
TUESDAY MORNING...WITH THE PASSAGE OF THE COLD FRONT.
A SECOND LOW PRESSURE SYSTEM COMING MOVING THE GULF OF MEXICO TO NEW
ENGLAND LATE WEEK MAY SPREAD SHOWERS AS FAR WEST AS THE UPPER OHIO
VALLEY AS THE UPPER LOW WILL TRACK WEST OF THE APPALACHIAN
MOUNTAINS.
FORECASTED TEMPERATURES USING A BLEND OF HPC GUIDANCE AND GFS MOS.
EXPECT A COOL DOWN TO SLIGHTLY COOLER THAN NORMAL TEMPERATURES FOR
TUESDAY IN THE WAKE OF THE FIRST SYSTEM...THEN NEAR NORMAL
TEMPERATURES WEDNESDAY AND THURSDAY. PRECIPITATION TYPE WITH THE
SECOND SYSTEM MAY BE AN ISSUE AS SURFACE TEMPERATURES WILL BE WITHIN
A COUPLE DEGREES OF THE FREEZING POINT.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
BASED ON RECENT SURFACE DATA COUPLED WITH NAM MODEL PROFILES AND GFS
LAMP GUIDANCE...EXPECT CONDITIONS TO LOWER TO MVFR ACROSS THE UPPER
OHIO VALLEY WITH THE ONSET OF POST FRONTAL SNOW SHOWERS AFTER
04Z-06Z. CONDITIONS COULD LOWER AT TIMES TO IFR AT TIMES 09Z-15Z
WITH HEAVIER SNOW SHOWERS WITHIN THE I-80 CORRIDOR AND NEAR THE
APPALACHIAN MOUNTAINS.
SURFACE WINDS WILL BE FROM THE SOUTHWEST NEAR 10 KTS THROUGH LATE
TONIGHT...THEN BECOME WEST TO NORTHWEST BY FRIDAY MORNING AT SPEEDS
NEAR 15 KTS WITH GUSTS TO ABOUT 25 KTS.
AS VERTICAL MIXING BECOMES CAPPED BY A SUBSIDENCE INVERSION FRIDAY
AFTERNOON...EXPECT THE SNOW SHOWERS TO DECREASE AND HENCE
CONDITIONS CAN IMPROVE TO VFR BY FRIDAY NIGHT.
NEXT POTENTIAL FOR SUB VFR CONDITIONS ACROSS THE UPPER OHIO VALLEY
WILL BE MONDAY INTO TUESDAY WITH ONSET OF SHOWERS WITH LOW PRESSURE
SYSTEM COMING FROM THE PACIFIC NORTHWEST.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 1 AM EST
SATURDAY FOR MDZ001.
OH...NONE.
PA...NONE.
WV...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 1 AM EST
SATURDAY FOR WVZ023-041.
&&
$$
