000
FXUS61 KPHI 060904 AAC
AFDPHI
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
404 AM EST TUE JAN 6 2009
.SYNOPSIS...
HIGH PRESSURE WILL MOVE SLOWLY EAST AND OFFSHORE TONIGHT. AN ELONGATED
AREA OF LOW PRESSURE, FROM THE DELMARVA TO TEXAS, WILL CONSOLIDATE
OVER THE OHIO VALLEY LATE TONIGHT. PRECIPITATION WILL SPREAD INTO THE
REGION LATER TODAY WITH A WINTRY MIX FOR LATER TODAY INTO WEDNESDAY.
THE LOW PRESSURE WILL REMAIN OVER THE REGION INTO WEDNESDAY NIGHT THEN
MOVE OFF TOWARD NEW ENGLAND ON THURSDAY. HIGH PRESSURE WILL BUILD IN
FROM THE SOUTHWEST FRIDAY INTO THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
SWATH OF MOISTURE MOVING ACROSS OUR SOUTHERN ZONES THIS MORNING
WILL BE MOST LIGHT SNOW BUT AS IT FALLS THROUGH A SHALL WARM LAYER
COULD BECOME A PERIOD OF SLEET BUT NOT EXPECTING MUCH OF A PROBLEM
THROUGH THE MORNING RUSH HOUR. THE PRECIPITATION WILL BE
OVERSPREAD THE REMAINDER OF THE REGION AFTER 12Z BUT NOT EXPECTING
ANY PROBLEMS UNTIL AROUND THE 16-17Z PERIOD WHEN WE START TO SEE
ABOUT A TENTH OF MIXED PRECIP OVER THE REGION.
THE FIRST THING ONE NOTICES ARE THE DEW POINTS. BELOW ZERO IN NORTH
JERSEY AND ZERO IN THE POCONOS. THE SECOND THING ONE NOTICES IS THE
AMOUNT OF TIME IT IT GOING TO TAKE BEFORE THE PRECIPITATION ARRIVES
AND CULMINATES IN A WINTRY MESS ACROSS THE NORTHERN HALF OF THE CWA.
WINTER STORM WARNINGS HAVE BEEN ISSUED FOR FIVE NORTHWEST NEW JERSEY
COUNTIES AND NINE EASTERN PENNSYLVANIA COUNTIES. WINTER WX ADVISORY
FOR DELAWARE AND PA COUNTIES OF SOUTHEAST PA AND TWO NORTHEAST MARYLAND
AND SEVEN CENTRAL AND SOUTHWEST NJ COUNTIES. SINCE THERE WILL BE A
COMBINATION OF WX NOT GOING WITH ICE STORM FAR NORTH UNTIL MORE CLEAR
CUT LATER TODAY, BUT APPEARS THERE WILL BE ONE QUARTER TO POSSIBLY
ONE HALF INCH OF ICE BEFORE ENDING ON WEDNESDAY AND WILL WORD THE WARNINGS
APPROPRIATELY. SOUNDINGS SHOW THE ONSET OF ALL FREEZING RAIN COMING
AROUND 00Z WED AND CONTINUING FOR ABOUT 11-12 HOURS. THIS WILL HAVE
MAJOR CONSEQUENCES IN THE WARNING AREA WITH TREES AND POWER LINES
BEING COATED. HIGH TEMPERATES TODAY WILL RANGE FROM THE LOW TO
MID 30S NORTH AND IN THE UPPER 30S NEAR THE COAST. LOWS TONIGHT IN
THE 20S WARNING AREAS TO THE MID 30S EXTREME SOUTHERN ZONES.
&&
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
THIS WILL BE A CLEANING UP PERIOD AS WE SEE THE WINTRY MIX END IN
THE WARNING AREA EXCEPT POSSIBLY HOLDING ON JUST A FEW HOURS
LONGER IN THE HIGHER ELEVATIONS THEN ALL RAIN PREVAILS BUT ONLY
BRIEFLY. AS PART OF THE LOW PRESSURE SYSTEM MOVES OFFSHORE WITH
COLD AIR FILTERING BACK IN BY 00Z WITH THE RAIN TURNING OVER TO
SNOW SHOWERS WITH A FRESH WESTERLY WIND. BEING PESSIMISTIC FOR THE
HIGHS AT THE MOUNTAIN TOPS ONLY REACHING 30 BUT ABOVE FREEZING
ELSEWHERE. WILL BE BACK IN AGAIN TONIGHT TO SEE HOW TO HANDLE THE
PRECIPITATION THERE FOR WEDNESDAY. TEMPERATURES RISE RATHER
QUICKLY DOWN THROUGH THE LEHIGH VALLEY(NEAR 40) TO THE LOWER 50S
SOUTHERN ZONES. LOWS FOR WEDNESDAY NIGHT WILL CAUSE SIGNIFICANT
PROBLEMS WITH THE PRECIPITATION FREEZING FROM THE DELAWARE VALLEY
NORTH WITH LOWS DOWN INTO THE LOWER 20S HIGHER ELEVATIONS. SO
FREEZING CONCERNS WILL NOT GO AWAY UNTIL THE NEXT DAY. MINUS 12C
AT 80H INTO OUR NORTHERN ZONES WILL BRING COLD CONDITIONS ACROSS
THE REGION.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
5-WAVE MODEL GUIDANCE HAS BEEN SHOWING A VERY ROBUST MID-LEVEL
LONGWAVE TROUGH SITTING OVER THE EASTERN THIRD OF THE COUNTRY FOR
SEVERAL DAYS NOW. BUILDING HEIGHTS IN THE PACIFIC WEST ONLY ENHANCE
THE TROUGHINESS MAKING FOR A VERY ACTIVE PERIOD.
SURFACE LOW PRESSURE THAT IS FORECASTED TO PROVIDE THE REGION WITH
SOME WINTRY PRECIPITATION DURING THE PREVIOUS DAYS WILL MOVE TO THE
NORTHEAST ON THURSDAY. THE MID-LEVEL TROUGH SWINGS THROUGH AND PULLS
A WEAK COLD FRONT THROUGH PLACING US IN A NORTHWEST FLOW REGIME.
AIRMASS CHANGE OCCURS BEHIND THE FRONT AND COLDER CANADIAN AIR
FILTERS IN THE REGION. A FEW LEFT OVER VORTICITY MAXIMUMS COMBINED
WITH REMNANT MOISTURE AND TEMPERATURES AT OR BELOW FREEZING, MAY
PRODUCE SOME SNOW SHOWERS ACROSS THE NORTH WITH A MIX OF RAIN/SNOW
ACROSS THE SOUTH.
HIGH PRESSURE BUILDS IN BRIEFLY ON FRIDAY BRINGING WITH IT AN
INITIAL NORTHWEST FLOW AND SOME MORE CAA. 1000-850MB HEIGHTS REALLY
REFLECT THE COLD AIR FILTERING DOWN AS 850MB TEMPERATURES DROP INTO
THE -15C RANGE. SURFACE PRESSURE GRADIENT TIGHTENS SO IT MAY BE A
PRETTY BREEZY AND COLD DAY.
AS A SHORTWAVE MID-LEVEL RIDGE AXIS TRIES TO BUILD IN ON SATURDAY,
IT BECOMES SUPPRESSED BY A MID-WEST LOW PRESSURE SYSTEM. THIS LOW
PRESSURE SYSTEM PUSHES A WEAK WARM FRONT THROUGH SATURDAY AFTERNOON.
FORECASTED ISENTROPIC FORCING IS MINIMAL AT MOST AHEAD OF THE COLD
FRONT ASSOCIATED WITH THE LOW PRESSURE SYSTEM. IT APPEARS THAT MOST
OF THE PRECIPITATION THAT FALLS WILL BE WITHIN THE COLD FRONT
CONVERGENCE ZONE. 850MB TEMPS SHOULD STAY ABOVE FREEZING IN OUR
SOUTHERN ZONES MAKING FOR A MOSTLY RAIN EVENT, BUT COLDER
TEMPERATURES TO THE NORTH WILL TAKE OUR NORTHERN ZONES ALL SNOW.
COLD FRONT FINALLY SWINGS THROUGH LATER ON SATURDAY NIGHT AS HIGH
PRESSURE ONCE AGAIN BUILDS INTO THE REGION. THERE COULD BE SOME
LINGERING MOISTURE LEFT OVER ON SUNDAY WHICH MAY PROVIDE SOME SNOW
AND RAIN SHOWERS ACROSS THE REGION. HIGH PRESSURE BUILDS BACK IN ON
MONDAY WITH VERY COLD TEMPERATURES AT 850MB TRANSLATING TO AT OR
BELOW FREEZING DAYTIME HIGHS.
&&
.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
A COLD MESSY STORM WILL AFFECT OUR AREA THIS AFTERNOON, TONIGHT, AND
INTO WEDNESDAY. AIR TRAFFIC WILL BE STRONGLY NEGATIVELY AFFECTED,
WITH CEILINGS AND VISIBILITIES DETERIORATING TO IFR AND LOW IFR LATE
THIS AFTERNOON AND TONIGHT. FROZEN AND EVEN FREEZING PRECIPITATION
IS EXPECTED TO OCCUR AT KPHL AND IN THE KPHL METROPOLITAN AREA THIS
AFTERNOON AND INTO EARLY TONIGHT, BEFORE WARMING OCCURS AND CHANGES
THE PRECIPITATION TO PLAIN RAIN DURING THE EVENING. MODEL GUIDANCE
IN ESSENCE WAS COLDER ON THIS 00Z RUN; HOWEVER, THE NAM APPEARED TO
BE ANOMALOUSLY COLDER.
ON THE WEATHER MAP, LARGE LOW PRESSURE FROM THE TENNESSEE VALLEY TO
THE WESTERN GREAT LAKES EARLY THIS MORNING...WITH A WARM FRONT
EXTENDING TO THE CENTRAL MID ATLANTIC COAST...WILL ADVANCE INTO OUR
AREA TODAY. MID LEVEL CLOUDS BEFORE SUNRISE WILL LOWER TO MARGINAL
VFR BY MIDDAY. THERE COULD BE SCATTERED LIGHT SNOW OR RAIN EARLY
THIS MORNING OVER THE SOUTHERN TAF SITES (KBWI AND KDOV REPORTED
SOME EARLIER), AND EVEN OVER THE CENTRAL TAF SITE BY LATE MORNING.
BUT, THE LOWER LEVELS ARE VERY DRY, AND, EVEN IF ANY PRECIPITATION
OCCURS, IT SHOULD BE TOO LIGHT TO LOWER VISIBILITIES MUCH IF AT ALL
THIS MORNING.
THE WINDS WILL BACK TO NORTHEAST AND INCREASE SOMEWHAT TODAY,
ALLOWING COLDER LOW LEVEL AIR TO DROP SOUTHWARD INTO MUCH OF OUR
AREA. AS DEEPER-LAYERED MOISTURE ARRIVES, THIS WILL COMBINE TO
CREATE A WINTRY MIX ACROSS MOST OF THE TAF SITES TO START, WITH A
TRANSITION TO PLAIN RAIN FROM SOUTH TO NORTH DURING THIS AFTERNOON
FAR SOUTH, AND THIS EVENING CENTRAL, AS SLIGHTLY WARMER AIR TRIES TO
PUSH IN FROM THE EAST. THE EXCEPTIONS WILL BE KRDG AND KABE, WHERE
MORE FROZEN AND FREEZING PRECIPITATION IS EXPECTED TO OCCUR, AND A
WINTER STORM WARNING IS IN EFFECT FOR THE PUBLIC ZONES THERE.
OUTLOOK...
THE MAIN LOW CENTER WILL MOVE INTO THE OHIO VALLEY TONIGHT AND INTO
NEW ENGLAND WEDNESDAY. A WEAK SECONDARY LOW IS LIKELY TO FORM ALONG
THE MID ATLANTIC COAST LATE TONIGHT INTO WEDNESDAY, AND MOVE
NORTHEAST UP THE COAST AND EVENTUALLY TAKE OVER THE CIRCULATION FROM
THE INLAND CENTER, BUT NOT UNTIL WEDNESDAY NIGHT WHEN IT IS WELL TO
THE NORTHEAST OF OUR AREA. THE ASSOCIATED COLD FRONT WITH THIS
SYSTEM WILL CROSS OUR AREA LATE WEDNESDAY OR WEDNESDAY EVENING.
THE STEADY PRECIPITATION WILL BECOME SHOWERY LATER WEDNESDAY AS
COLDER AIR RETURNS. SCATTERED SNOW SHOWERS WILL BE POSSIBLE THURSDAY
AS AN UPPER-LEVEL DISTURBANCE MOVES ACROSS OUR AREA. HIGH PRESSURE
WILL BRING A RETURN TO FAIR WEATHER AND VFR CONDITIONS LATER
THURSDAY NIGHT INTO SATURDAY.
&&
.MARINE...
LARGE LOW PRESSURE FROM THE TENNESSEE VALLEY TO THE WESTERN GREAT
LAKES EARLY THIS MORNING...WITH A WARM FRONT EXTENDING TO THE
CENTRAL MID ATLANTIC COAST...WILL ADVANCE INTO OUR AREA TODAY. AS
THIS SYSTEM TAKES SHAPE AND GETS CLOSER TODAY, THE PRESSURE GRADIENT
WILL TIGHTEN UP BETWEEN THE LOW AND HIGH PRESSURE TO THE EAST-
NORTHEAST. THE LOW-LEVEL FLOW FROM THE NORTHEAST WILL INCREASE THIS
AFTERNOON AND TONIGHT. BASED ON 00Z MODEL FORECAST SOUNDINGS, THE
BEGINNING TIME OF THE PREVIOUSLY-ISSUED SMALL CRAFT ADVISORY LOOKS
GOOD, STARTING FIRST IN THE SOUTHERN WATERS, AND THEN LATER OVER THE
NORTHERN WATERS AND DELAWARE BAY. THE LOW-LEVEL FLOW SHOULD BE
STRONG ENOUGH TO PRODUCE SOME 25 KNOTS WINDS IN DELAWARE BAY AS
WELL, ALTHOUGH IT MAY BE MORE MARGINAL IN THE UPPER BAY. FOR NOW, WE
WILL KEEP THE ADVISORY FOR THE BAY AS NORTHEAST TO EAST WINDS
SOMETIMES GUST A BIT HIGHER THAN THE MODELS INDICATE.
THE WARM FRONT (WITH PROBABLY A SECONDARY LOW) MOVING INTO THE AREA
LATE TONIGHT AND EARLY WEDNESDAY MAY KEEP THE GRADIENT FROM BECOMING
TIGHT ENOUGH FOR GALE CONDITIONS; LOCATIONS SOUTH OF THE WARM FRONT,
WHERE THE LOW LEVEL WARM SECTOR FLOW WILL INCREASE, MAY BE AN AREA
WHERE WINDS WILL NEAR GALE GUST LEVELS; STABILITY CONSIDERATIONS
WILL HOPEFULLY KEEP THE BEST WINDS JUST OFF THE SURFACE.
THEN, THE POST-COLD FRONTAL REGIME WEDNESDAY NIGHT AND ESPECIALLY
THURSDAY COULD SEE GALE GUSTS AS DOWNWARD MOMENTUM FLUX INCREASES.
AT THIS TIME, THERE IS ENOUGH UNCERTAINTY BETWEEN THE WEAKER NAM 925
HPA WINDS OF 35 KNOTS AND THE SLIGHTLY STRONGER GFS WINDS OF 40
KNOTS TO JUST KEEP THE SMALL CRAFT ADVISORY GOING WEDNESDAY NIGHT,
INSTEAD OF INSTITUTING A GALE WATCH. HOWEVER, THERE COULD BE GUSTS
TO 35 KNOTS, ESPECIALLY THURSDAY, AND THIS WILL HAVE TO BE ASSESSED
BY LATER FORECASTERS. FOR NOW, THE SMALL CRAFT ADVISORY WILL BE
STRETCHED THROUGH WEDNESDAY NIGHT (OUR FOURTH PERIOD), AND A FEW
GUSTS TO 35 KNOTS WILL BE MENTIONED WEDNESDAY NIGHT.
AS HIGH PRESSURE GRADUALLY BUILDS IN LATER FRIDAY, THE WINDS ARE
EXPECTED TO DIMINISH. THIS AREA OF HIGH PRESSURE WILL MOVE ACROSS
OUR AREA SATURDAY, HOWEVER A DEVELOPING WARM FRONT MAY APPROACH FROM
THE SOUTHWEST.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 10 AM EST
WEDNESDAY FOR PAZ054-055-061-062.
WINTER STORM WARNING FROM NOON TODAY TO 8 AM EST WEDNESDAY FOR
PAZ060-067>069.
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 6 PM EST
THIS AFTERNOON FOR PAZ070-071.
NJ...WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 10 AM EST
WEDNESDAY FOR NJZ001-007-008.
WINTER STORM WARNING FROM NOON TODAY TO 8 AM EST WEDNESDAY FOR
NJZ009-010.
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 6 PM EST
THIS AFTERNOON FOR NJZ012-015>019.
DE...WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 6 PM EST
THIS AFTERNOON FOR DEZ001.
MD...WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 6 PM EST
THIS AFTERNOON FOR MDZ008.
MARINE...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 6 AM EST
THURSDAY FOR ANZ430-431-450>452.
SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 6 AM EST
THURSDAY FOR ANZ453>455.
&&
$$
SYNOPSIS...EBERWINE
NEAR TERM...EBERWINE
SHORT TERM...EBERWINE
LONG TERM...EBERWINE
AVIATION.../
MARINE.../
(CORRECTED FOR STORM COORD MESSAGE)
