FXUS61 KPBZ 271538
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1038 AM EST FRI NOV 27 2009
.SYNOPSIS...
AN INTENSIFYING EAST COAST STORM WILL BRING BRISK NORTHWEST WINDS
ACROSS THE FORECAST AREA TODAY ALONG WITH SOME LAKE EFFECT SNOW
SHOWERS. HIGH PRESSURE WILL BUILD IN ON SATURDAY...WITH A DRY
WEEKEND EXPECTED.
&&
.NEAR TERM /THROUGH TONIGHT/...
15Z RUC 500MB ANALYSIS INDICATES AN UPPER LEVEL LOW CENTERED NEAR
LAKE ONTARIO WITH A NEGATIVELY TILTED TROF AXIS EXTENDING SEWD
INTO THE MID-ATLANTIC. AT THE SURFACE...A 992 MB SFC LOW IS MOVING
NORTHEASTWARD OFF THE COAST OF NEW ENGLAND WITH A 1025MB HIGH
CENTERED NEAR THE WESTERN GULF COAST. AN 850MB NWRLY FLOW OFF OF
LAKE ERIE ALONG WITH TEMPS ALOFT OF -6C AND CAA HAS ALLOWED FOR
WIDESPREAD RAIN AND SNOW SHOWERS ACROSS WRN PA...N-CNTRL WV...AND
WRN MD. ACROSS THE HIGHER ELEVATIONS OF THE EASTERN
RIDGES...ACCUMULATING SNOWFALL CONTINUES...WITH 2-4 INCHES
REPORTED THUS FAR.
THIS AFTERNOON AND TONIGHT...AS THE SFC LOW CONTINUES TO MOVE
NORTHEAST OF THE AREA...A NWRLY FLOW WILL CONTINUE OFF OF LAKE
ERIE...ALLOWING FOR RAIN AND SNOW SHOWERS TO BECOME ALL SNOW
SHOWERS ACROSS THE AREA. THIS AFTERNOON...THE FOCUS OF THE LAKE
EFFECT SNOW WILL SHIFT INTO THE AREA ALONG AND NORTH OF
INTERSTATE 80 WHICH HAS SEEN LITTLE PRECIP THIS MORNING.
OTHERWISE...SNOW SHOWERS WILL CONTINUE INTO TONIGHT ACROSS THE
AREA AND THE NORTHWEST FLOW WILL BEGIN TO WEAKEN. SOME LIGHT
ACCUMULATIONS ARE POSSIBLE ACROSS THE LOWLANDS...ESPECIALLY AFTER
SUNSET...WITH ONGOING ACCUMULATIONS ACROSS THE HIGHER ELVATIONS. HIGH
PRESSURE BUILDING INTO THE DISTRICT TOWARD DAYBREAK WILL ONLY
ALLOW FOR SOME LINGERING FLURRIES WITH SNOW SHOWER ACTIVITY
DIMINISHING ACROSS THE HIGHER ELEVATIONS. HIGHS TODAY WILL BE
SLIGHTLY BELOW NORMAL WITH LOWS TONIGHT RANGING FROM THE UPPER 20S
IN THE LOWLANDS AND LOWER TO MID 20S IN THE HIGHER ELEVATIONS.
A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE
GARRETT...TUCKER...AND PRESTON COUNTIES THROUGH 1 AM. WITH THE
AFTN PACKAGE...WILL LOOK INTO POSSIBLY EXPANDING THIS INTO SAT
MORNING. RECENT NAM12 INDICATES LAKE EFFECT KICKING IN THIS
AFTERNOON. RIGHT NOW...1 TO 2 INCHES ARE FCST ALONG AND NORTH OF
I-80...WILL NEED TO CONTINUE TO MONITOR THIS FOR A POSSIBLE
ADVISORY IF UPSTREAM RADAR TRENDS CONTINUE TO INCREASE.
&&
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
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 WARM ADVECTION
WILL ALLOW FOR TEMPS TO RECOVER TO NORMAL VALUES FOR HIGHS.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
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 /15Z FRIDAY THROUGH TUESDAY/...
EXPECT MVFR CEILINGS TO PREDOMINATE THROUGH THE TAF PERIOD AS COLDER
AIR PUSHES INTO THE UPPER OHIO VALLEY BEHIND A COLD FRONT.
VISIBILITIES WILL LOWER TO MVFR AT TIMES IN SNOW SHOWERS...WITH IFR
RESTRICTIONS IN HEAVIER SNOW SHOWERS ACROSS NORTHWEST PA AND NEAR
THE APPALACHIAN MOUNTAINS.
SURFACE WINDS WILL BE SOUTHWEST NEAR 10 KT...THEN BECOME WEST TO
NORTHWEST AT 15 KT WITH GUSTS TO 25 KT LATER THIS MORNING.
EXPECT COVERAGE OF SNOW SHOWERS TO DECREASE BY LATE TONIGHT AS
CAPPING INVERSION LOWERS. MAINLY VFR CONDITIONS SHOULD PREVAIL UNDER
A SURFACE RIDGE SATURDAY AND EARLY SUNDAY.
NEXT POTENTIAL FOR SUB VFR CONDITIONS ACROSS THE UPPER OHIO VALLEY
WILL BE SUNDAY NIGHT AND MONDAY IN SHOWERS WITH APPROACHING LOW
PRESSURE SYSTEM.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 1 AM EST SATURDAY FOR MDZ001.
OH...NONE.
PA...NONE.
WV...WINTER WEATHER ADVISORY UNTIL 1 AM EST SATURDAY FOR WVZ023-041.
&&
$$
