FXUS61 KPBZ 071918
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
218 PM EST MON DEC 7 2009
.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM WILL MOVE EAST OF THE REGION THIS
EVENING...WITH HIGH PRESSURE BUILDING IN OVERNIGHT. A DEVELOPING
LOW PRESSURE SYSTEM WILL THEN INTENSIFY AND MOVE NORTH INTO THE
WESTERN GREAT LAKES REGION LATE TUESDAY. A WINTRY MIX OF
PRECIPITATION WILL BE POSSIBLE WITH THIS SYSTEM TUESDAY
NIGHT...WITH PRIMARILY RAIN WEDNESDAY.
&&
.NEAR TERM /THROUGH TUESDAY/...
MOST OF THE LIFT AND MOISTURE ASSOCIATED WITH A WEAK LOW PRESSURE
SYSTEM THAT HAS BEEN GENERATING LIGHT SNOW SHOWERS OVER THE AREA...WILL
MOVE EAST OF THE REGION AROUND MIDNIGHT. SURFACE HIGH PRESSURE
WILL BUILD IN OVERNIGHT...BUT AMPLE CLOUD COVER IS STILL EXPECTED
WITH LOW CLOUD QUICKLY REPLACED BY HIGH CLOUDS.
CURRENTLY TIMING THE ONSET OF THE PRECIP...ASSOCIATED WITH THE
DEVELOPING LOW...INTO THE CWA AFTER 18Z. SO INITIAL ONSET OF PRECIP
COULD BE RAIN...THEN BACK TO SNOW AROUND SUNSET.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
FAIRLY COMPLEX WEATHER PERIOD EXPECTED. CURRENT FORECAST TRACK
TAKES INTENSIFYING LOW INTO WESTERN GREAT LAKES BY WEDNESDAY
MORNING. THE PRIMARY CONCERN IS FOR THE TUESDAY NIGHT
TIMEFRAME...WHERE ENOUGH COOLING IS EXPECTED TO HAPPEN TUESDAY
EVENING AT THE SURFACE...WHILE STRONG WAA PUSHES IN ALOFT. THIS
SCENARIO WOULD LEAD TO SLEET/FREEZING RAIN. RIGHT NOW...SOUNDING
PROFILES WOULD SUGGEST THE BEST CHANCE FOR ANY PROLONGED ICING
WOULD BE IN THE EASTERN RIDGES...WHERE COLDER AIR CAN BECOME
TRAPPED IN THE VALLEYS. WITH ANTICIPATED QPF FORECAST THERE IS THE POTENTIAL
FOR A HALF INCH OF ICE OVER THE SOUTHERN MOUNTAINS...WITH LESSER
AMOUNTS IN PA RIDGES. THEREFORE...GOING WITH A WINTER STORM WATCH
TO HIGHLIGHT THIS POTENTIAL OVER THE EASTERN AND SOUTHERN RIDGES.
A STRONG PUSH OF WAA WEDNESDAY MORNING SHOULD TURN THE ENTIRE CWA
OVER TO RAIN. EXPECT BREEZY WINDS TUESDAY NIGHT INTO WEDNESDAY IN
THE WAA. THE GUSTY WINDS COULD PROVIDE ADDITIONAL HAZARDS TO TREES
AND POWER LINES IN AREAS THAT RECEIVE ICE.
AFTER THE COLD FRONT SWEEPS THROUGH...THE PRECIP SHOULD QUICKLY
CHANGE OVER TO SNOW WEDNESDAY EVENING. HIGHER WIND GUSTS UP TO
AROUND 40 MPH WILL BE POSSIBLE IN THE TIGHT PRESSURE GRADIENT
FOLLOWING THIS FRONT. LATER FORECAST CYCLES WILL ASSESS POTENTIAL
FOR WIND HEADLINES IN THE WEDNESDAY AFTERNOON THROUGH THURSDAY
TIMEFRAME. AS FOR SNOWFALL BEHIND THE FRONT...ACCUMS SHOULD BE
FAIRLY LIGHT AS MOST MOISTURE FOR PRECIP IN THE WARM SECTOR.
HOWEVER...WRAP AROUND MOISTURE AND LAKE ENHANCEMENT WILL KEEP SNOW
SHOWERS GOING INTO THURSDAY.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
RESIDUAL LAKE ENHANCED/UPSLOPE SNOW SHOWERS AND WINDS WILL
GRADUALLY DIMINISH THURSDAY NIGHT/FRIDAY AS LOW PRESSURE EXITS TO
THE NORTHEAST. AFTER MAINLY DRY CONDITIONS FRIDAY NIGHT INTO
SATURDAY...GFS/ECMWF IN GENERAL AGREEMENT WITH TROUGHINESS/CHANCES
OF SNOW SHOWERS FOR THE LAST HALF OF THE WEEKEND INTO MONDAY. BELOW
NORMAL TEMPERATURES WILL PERSIST THROUGH THE LONG TERM.
&&
.AVIATION /19Z MONDAY THROUGH SATURDAY/...
VFR IS GENERALLY EXPECTED FOR THE NEXT 24 HOURS...WITH ISOLATED MVFR
IN -SHSN ACROSS THE I-80 CORRIDOR THIS AFTN...WITH PATCHY MVFR CIGS
FURTHER SOUTH. S/SW WINDS 4-7 KT THIS AFTN WILL BECOME LIGHT
WESTERLY TNGT.
LOW PRESSURE WILL APPROACH THE REGION FROM THE SOUTHWEST
TUESDAY...CROSSING THE AREA MIDWEEK. FOR PORTS FROM PIT SOUTH
THINK PRECIP WILL MAINLY BE RAIN...WITH PERHAPS SOME PATCHES OF
SLEET/FREEZING RAIN AT ONSET TUESDAY EVENING. FOR PORTS NORTH AND
EAST OF PIT/AGC...ENOUGH COLD AIR WILL BE IN PLACE FOR PRECIP TO
BEGIN AS SNOW TUESDAY EVENING...CHANGING TO SLEET/FREEZING RAIN
OVERNIGHT...CHANGING TO ALL RAIN BY WEDNESDAY AFTN. AT THIS
TIME...PORT DUJ LOOKS TO HAVE THE GREATEST CHANCE AT PROLONGED
FREEZING/FROZEN PRECIP. MVFR/AREAS OF IFR WILL PREVAIL TUESDAY
NIGHT/WEDNESDAY. WINDS WILL INCREASE WEDNESDAY IN ADVANCE OF THE
COLD FRONT WITH SUSTAINED WINDS 15-20 KT WITH GUSTS TO 30 KT.
AFTER THE FRONTAL PASSAGE WEDNESDAY NIGHT...PRECIP WILL CHANGE
TO SNOW AREA WIDE...WITH AREAS OF IFR THROUGH THURSDAY. WINDS WILL
INCREASE FURTHER IN THE WAKE OF THE FRONT...WITH NW WINDS OF AROUND
20 KT WITH GUST TO 35 KT WEDNESDAY NIGHT/EARLY THURSDAY. PRECIP
AND WINDS WILL GRADUALLY DIMINISH THURSDAY NIGHT/FRIDAY AS THE
LOW EJECTS TO THE NORTHEAST. MVFR TO LOW END VFR CLOUDS WILL
PERSIST INTO THE WEEKEND.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING FOR MDZ001.
OH...NONE.
PA...WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
MORNING FOR PAZ016-023-030-032.
WV...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING FOR WVZ023-041.
&&
$$
NWS/LS
