FXUS61 KPBZ 030234
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
934 PM EST WED DEC 2 2009
.SYNOPSIS...
STRONG LOW PRESSURE OVER KENTUCKY WILL MOVE ACROSS THE OHIO VALLEY
TONIGHT AND THURSDAY...BRINGING GUSTY WINDS AND OCCASIONAL
SHOWERS. COLDER AIR WILL BRING CLOUDS AND SCATTERED SNOW SHOWERS
INTO LATE WEEK.
&&
.NEAR TERM /THROUGH THURSDAY/...
DRY SLOT IS CURRENTLY MAKING ITS WAY ACROSS THE REGION...WHICH IS
BRINGING A BREAK IN SHOWERS FOR MOST LOCATIONS. HOWEVER...THE DRY
SLOT IS PARTIALLY FILLING IN...AND ANOTHER LINE OF SHOWERS IS
EXPECTED WITH THE PASSAGE OF THE COLD FRONT ITSELF. WITH THE COLD
FRONT STILL EXTENDING SOUTH FROM KENTUCKY SOUTH INTO GEORGIA...AND
LOW PRESSURE EXPECTED TO PASS ACROSS OHIO...THE FRONT IS NOT
EXPECTED TO MOVE THROUGH UNTIL AFTER MIDNIGHT. AS THE COLD FRONT
ARRIVES...MOST LOCATIONS SHOULD SEE ANOTHER COUPLE OF HOURS
OF RAIN...WITH INCREASING WIND SPEEDS BEHIND THE FRONT. AN
ISOLATED THUNDERSTORM COULD NOT EVEN BE RULED OUT. THE ENTIRE
FORECAST AREA COULD SEE GUSTS UP TO 40 MPH WITH STRONG WINDS ALOFT
ABLE TO MIX DOWN TO THE SURFACE WITH THE FRONTAL PASSAGE.
TEMPERATURES SHOULD RISE A FEW DEGREES TONIGHT WITH WARM ADVECTION
AHEAD OF THE FRONT.
ADDITIONAL EVENING UPDATE MADE TO ADD SEVERAL PENNSYLVANIA RIDGE
COUNTIES TO WIND ADVISORY...AND KEEP ADVISORY GOING THROUGH THE
OVERNIGHT HOURS. SEVERAL REPORTS OF TREES DOWN HAVE BEEN REPORTED
IN THE LAST HOUR IN COUNTIES ALONG THE RIDGES...AND WITH WINDS
ALREADY AROUND 40 MPH AHEAD OF THE LINE OF SHOWERS THAT IS
ANTICIPATED TO MOVE THROUGH...FEEL THAT THIS ADDITIONAL FORCING
SHOULD BRING MANY COUNTIES ABOVE ADVISORY THRESHOLD.
WHILE BULK OF DEEP MOISTURE WILL BE EXITING EARLY THURSDAY STILL
THINK ENOUGH FOR LIKELY POPS EARLY BECOMING CHANCE LATE. CHANGE
OVER TO SNOW LOOKS TO HOLD OFF UNTIL THURSDAY NIGHT WITH
TEMPERATURES FAIRLY STEADY THURSDAY.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
COLD ADVECTION AND UPSLOPE WILL BRING SCATTERED SNOW SHOWERS INTO
FRIDAY MAINLY NORTH AND ALONG I-80 AND ACROSS THE RIDGES. STORM
SYSTEM WILL MOVE DEVELOPING OFFSHORE OF THE CAROLINAS FRIDAY NIGHT
INTO SATURDAY AND MODELS ARE TRYING TO THROW MOISTURE BACK INTO
THE SOUTHEAST RIDGES FOR SATURDAY. WILL KEEP CHANCE POPS IN THE
SOUTHERN RIDGES FOR ALL SNOW AS THICKNESS WOULD SUPPORT. AS OF NOW
BEST QPF LOOKS TO STAY EAST SO NOTHING SIGNIFICANT EXPECTED BUT
THIS WILL NEED TO BE MONITORED. OTHERWISE LIGHT LAKE EFFECT
ACCUMULATIONS IN THE USUAL LOCATIONS. TEMPERATURES NOT FAR FROM
MAV MOS.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
COLDER WEATHER WILL CONTINUE FOR THE FIRST HALF OF NEXT WEEK AS
BROAD BROAD MID/UPPER TROUGH IS PROJECTED OVER CANADA AND THE
NORTHERN U.S. THIS PROGRESSIVE PATTERN WILL FEATURE RAPIDLY MOVING
DISTURBANCES OVER THE UPPER OHIO VALLEY WITH DRY AIR AND SURFACE
HIGH PRESSURE LIMITING SIGNIFICANT PRECIPITATION CHANCES. BEST
OPPORTUNITY TO EXPERIENCE SOME SNOW SHOWERS DURING THE PERIOD
LOOKS TO BE OVER AREAS NORTH OF PITTSBURGH DUE TO THE COLD FLOW
ACROSS THE GREAT LAKES.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
BASED TAF FORECASTS ON BLEND OF RECENT SURFACE AND RADAR
DATA...INCLUDING VERTICAL RADAR WIND PROFILES...AND NAM MODEL OUTPUT
AND ITS PROFILES.
THIS SHOWED THE STRONG NORTHEASTWARD MOVING LOW PRESSURE CENTER
PASSING THROUGH CENTRAL OHIO OVERNIGHT. ASSOCIATED DRY SLOT
SOUTHEAST OF THE CENTER HAS SPREAD THROUGHOUT THE UPPER OHIO
VALLEY...PROVIDING MOST TAF SITES WITH VFR EXPECT MVFR WITHIN THE
I-80 CORRIDOR. COLD FRONTAL BAND OF SHOWERS MOVING EASTWARD
THROUGH THE UPPER OHIO VALLEY CAN LOWER CONDITIONS TO MVFR WEST TO
EAST AFTER 04Z.
MAIN AVIATION CONCERN WILL CONTINUE TO BE THE STRONG WINDS JUST
ABOVE THE SURFACE. THE WINDS AT 2 KFT AGL ARE FROM THE SOUTHEAST
NEAR 50 KTS...AND ARE RESULTING IN MANY PILOT REPORTS OF LOW LEVEL
WIND SHEAR THIS EVENING. SURFACE WINDS HAVE BEGUN TO SWITCH INTO
THE SOUTHEAST AT 15 KTS WITH GUSTS TO 30 KTS GENERALLY...AND NEAR
40 KTS JUST WEST OF THE APPALACHIAN MOUNTAINS DUE TO DOWNSLOPING
EFFECTS.
ONCE THE LOW PRESSURE CENTER PASSES NORTH OF CLEVELAND...SURFACE
WINDS WILL BECOME SOUTHWEST WITH THE COLD FRONTAL PASSAGE THAT WILL
BREAK THE SURFACE INVERSION AND END THE LOW LEVEL WIND SHEAR...BUT
LIKEWISE ALLOW THE FASTER WINDS ALOFT EASIER ACCESS TO THE SURFACE. HENCE
SURFACE WIND GUSTS 07Z-15Z MAY REACH 35-40 KTS. SURFACE WINDS
THURSDAY AFTERNOON WILL BE GENERALLY WESTERLY 15-30 KTS...AND THEN
DECREASE TO NEAR 10 KTS THURSDAY NIGHT.
FORECASTED STRATOCUMULUS CEILINGS LATE TONIGHT INTO DAYTIME FRIDAY
TO BE MAINLY IN THE MVFR RANGE. VISIBILITY WILL BE MAINLY VFR...BUT
SCATTERED SNOW SHOWERS NORTH OF THE KPIT-KPHD CORRIDOR MAY CAUSE
BRIEF IFR PERIODS THURSDAY NIGHT.
A COLD UPPER TROUGH PASSING SLOWLY EASTWARD THROUGH THE GREAT LAKES
AND UPPER OHIO VALLEY THIS WEEKEND MAY MAINTAIN MVFR-VFR
STRATOCUMULUS ACROSS THE UPPER OHIO VALLEY SATURDAY INTO SUNDAY.
HIGH PRESSURE COMING EASTWARD IN ITS WAKE SHOULD FULLY RESTORE VFR
LATE SUNDAY INTO MONDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WIND ADVISORY UNTIL 10 AM EST THURSDAY FOR MDZ001.
OH...NONE.
PA...WIND ADVISORY UNTIL 10 AM EST THURSDAY FOR PAZ016-023-030-032.
WV...WIND ADVISORY UNTIL 10 AM EST THURSDAY FOR WVZ023-041.
&&
$$
