FXUS61 KPBZ 080510
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1210 AM EST TUE DEC 8 2009
.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM AND ITS LIGHT SNOW SHOWERS WILL EXIT
EAST BY MORNING. A LOW PRESSURE SYSTEM FROM CALIFORNIA WILL INTENSIFY
AND MOVE NORTH INTO THE WESTERN GREAT LAKES REGION LATE TUESDAY. A
WINTRY MIX OF PRECIPITATION WILL BE POSSIBLE NORTH AND EAST OF
PITTSBURGH WITH THIS SYSTEM TUESDAY NIGHT...WITH PRIMARILY RAIN
WEDNESDAY.
&&
.NEAR TERM /THROUGH TUESDAY/...
LIGHT SNOW SHOWERS FROM EXITING GREAT LAKES MAY CAUSE A THIN COAT
OF SNOW THAT CAN FREEZE INTO BLACK ICE. SO A SPECIAL WEATHER
SYSTEM WILL BE ISSUED TO REFLECT THAT OVERNIGHT HAZARD.
TUESDAY...THE SURFACE LOW ACROSS CALIFORNIA WILL STRENGTHEN AS IT
MOVES ACROSS THE ROCKIES INTO THE CENTRAL PLAINS. AN INITIAL SHORT
WAVE...CURRENTLY COLOCATED WITH PRECIP ACROSS LOUISIANA WILL LIFT
NEWD INTO THE TN VALLEY AND WILL BE AT THE DOORSTEP OF OUR AREA LATE
TUESDAY AFTERNOON. THIS WILL ALLOW FOR THE CHANCE FOR PRECIP TO
BEGIN TO START ACROSS THE AREA BY EARLY TUESDAY EVENING. PRECIPITATION
INITIALLY WILL BE A MIX OF RAIN AND SNOW AS IT ADVECTS INTO AREAS
NORTH OF PITTSBURGH...WITH A WINTRY MIX OF SNOW...SLEET...AND
FREEZING RAIN POSSIBLE ACROSS THE HIGHER ELEVATIONS. FOR
TEMPERATURES...HIGHS WILL BE IN THE MID TO UPPER 30S ACROSS MUCH
OF THE AREA...ALTHOUGH THE RIDGES WILL ONLY WARM INTO THE LOWER
30S.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
FAIRLY COMPLEX WEATHER PERIOD EXPECTED. CURRENT FORECAST TRACK
TAKES INTENSIFYING LOW FROM THE CENTRAL PLAINS INTO THE WESTERN
GREAT LAKES BY WEDNESDAY MORNING. THE PRIMARY CONCERN IS FOR THE
TUESDAY NIGHT TIMEFRAME...WHERE COOLING IS EXPECTED TUESDAY
EVENING AT THE SURFACE...WHILE STRONG WAA PUSHES IN ALOFT. TEMPS
AT THE SURFACE CONTINUE TO TREND WARMER ACROSS THE LOWER
ELEVATIONS...WHICH WOULD LIMIT FREEZING RAIN PRIMARILY TO THE
EASTERN RIDGES. FORECAST HAS BEEN ADJUSTED TO PRECIP STARTING AS A
RAIN/SNOW MIX JUST NORTH OF PITTSBURGH. MEANWHILE FOR AREAS SOUTH
AND WEST...PRECIP WILL REMAIN RAIN INTO WEDNESDAY MORNING.
FOR THE HIGHER ELEVATIONS OF THE EASTERN RIDGES AND ALONG AND
NORTH OF INTERSTATE 80...THIS SCENARIO WOULD LEAD TO SLEET/FREEZING
RAIN. RIGHT NOW...SOUNDING PROFILES ALSO 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 AND BREEZY WINDS THERE IS THE POTENTIAL FOR A HALF INCH
OF ICE OVER THE SOUTHERN MOUNTAINS...WITH LESSER AMOUNTS IN THE PA
RIDGES. THEREFORE...A WINTER STORM WATCH REMAINS 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 /06Z TUESDAY 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.
&&
$$
