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000
FXUS61 KPHI 121914
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
314 PM EDT SUN MAY 12 2013

.SYNOPSIS...
A SECONDARY BUT DRY COLD FRONT WILL CONTINUE TO SHIFT OFFSHORE
THIS AFTERNOON. HIGH PRESSURE OVER THE CENTRAL PORTION OF THE
NATION WILL BUILD EASTWARD THROUGH MIDWEEK. A STRONG WARM FRONT
WILL THEN CROSS THE REGION ON WEDNESDAY, FOLLOWED BY A COLD FRONT
MOVING THROUGH ON FRIDAY OR SATURDAY.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
AN 18Z SURFACE ANALYSIS PLACED LOW PRESSURE IN SOUTHEASTERN CANADA
WITH A TRAILING COLD FRONT FROM NORTHERN NEW ENGLAND TO OFF THE MID
ATLANTIC COAST. AN UPPER AIR ANALYSIS SHOWED A LARGE TROUGH FROM THE
CENTRAL PLAINS TO THE EAST COAST WITH THE CENTER OF IT JUST NORTH OF
LAKE HURON. A CYCLONICALLY CURVED 250 MB JET WAS FROM SOUTH-CENTRAL
CANADA TO THE UPPER OHIO VALLEY THEN UP ACROSS NEW ENGLAND.

WE WILL CONTINUE TO TRANSITION TO COLDER CONDITIONS AS A SECONDARY
BUT DRY COLD FRONT HAS NOW SHIFTED OFFSHORE. OUR SENSIBLE WEATHER
WILL BE DOMINATED BY LOW PRESSURE ACROSS SOUTHEASTERN CANADA. THIS
IS IN RESPONSE TO A LARGE AND ROBUST UPPER-LEVEL TROUGH THAT IS
AMPLIFYING INTO THE EAST. THE CAA WILL CONTINUE THROUGH TONIGHT AND
EVEN STRENGTHEN SOME. THE CYCLONIC FLOW COMBINED WITH THE CAA ALOFT
IS RESULTING IN STRATOCUMULUS MAINLY TO OUR WEST. SOME OF THIS MAY
TRY AND GET INTO THE NORTHWEST ZONES, WITH EVEN A FEW LIGHT SHOWERS
OR SPRINKLES. MOST OF THIS SHOULD BE CONFINED CLOSER TO THE GREAT
LAKES, HOWEVER WE MAY HAVE TO ADD IN SOME SPRINKLES ACROSS THE
POCONOS FOR A TIME THIS EVENING. OTHERWISE, A DRYING AIRMASS WITHIN
A CYCLONIC FLOW REGIME SHOULD KEEP MUCH OF THE AREA CLEAR/MOSTLY
CLEAR THROUGH THE NIGHT WITH SOMEWHAT MORE CLOUDS NEAR THE POCONOS.

THE GUSTY WINDS ARE ANTICIPATED TO REMAIN INTO THE EVENING, HOWEVER
THESE SHOULD THEN SUBSIDE THROUGH THE NIGHT. THE PRESSURE GRADIENT
IS FORECAST TO REMAIN TIGHTENED, WHICH TENDS TO KEEP SOME GRADIENT
WIND GOING. THIS ADDS A CONCERN REGARDING FROST FOR LATE TONIGHT.
THE AIRMASS IS DRYING AND AT LEAST SOME WIND IS ANTICIPATED TO
REMAIN THROUGH THE NIGHT, WITH PERHAPS THE MORE SHELTERED LOCATIONS
SEEING A MORE NOTED LESSENING OF THE WIND. THIS COMBINATION
TYPICALLY DOES NOT LEAD TO GOOD FROST FORMATION, THEREFORE WE SCALED
BACK THE MENTION TO PATCHY FROST. WE MAINTAINED THE FROST ADVISORY
AS IS THOUGH GIVEN FORECAST LOW TEMPERATURES DROPPING INTO THE LOW
AND MID 30S. JUST SOUTH AND EAST OF THE FROST ADVISORY, TEMPERATURES
WILL DROP INTO THE UPPER 30S HOWEVER HELD OFF ON EXPANDING THE FROST
ADVISORY AS TEMPERATURES MAY HOLD JUST ABOVE CRITICAL LEVELS.
DESPITE THE POTENTIAL FOR A LACK OF FROST, TEMPERATURES DROPPING
INTO THE LOW AND MID 30S CAN CAUSE ISSUES FOR SENSITIVE VEGETATION.

AS FOR LOW TEMPERATURES, WE USED AN EVEN GFS/NAM MOS BLEND THEN MADE
SOME MINOR TWEAKS. THE HOURLY TEMPERATURES INCORPORATED SOME OF THE
LAMP/LAV GUIDANCE TO HELP TRY AND CAPTURE TRENDS, WITH TEMPERATURES
PERHAPS HOLDING UP A LITTLE MORE FOR AWHILE GIVEN THE WIND.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
OUR WEATHER WILL BE DOMINATED BY A LARGE UPPER-LEVEL TROUGH THAT IS
ACTUALLY FORECAST TO SHARPEN UP THROUGH THE DAY. THIS WILL RESULT IN
VERY COLD AIR ALOFT, AS A POCKET OF NEAR -30C AIR AT 500 MB ARRIVES
BY LATE IN THE AFTERNOON. THIS WILL TRANSLATE TO A RATHER CHILLY
DAY. DESPITE THE FORECAST SOUNDINGS LOOKING RATHER DRY UP THROUGH
THE COLUMN, THERE IS A FAIRLY SHALLOW MOIST LAYER BETWEEN ABOUT
5,000 AND 8,000 FEET. IT APPEARS THAT THE CONVECTIVE TEMPERATURES
WILL BE REACHED ACROSS MUCH OF THE AREA BY MIDDAY GIVEN THE RATHER
COLD AIR ALOFT. THIS SHOULD RESULT IN STRATOCUMULUS DEVELOPMENT,
HOWEVER THE QUESTION IS HOW EXTENSIVE DOES THIS BECOME. BASED ON THE
RATHER COLD AIR ALOFT IN CONJUNCTION WITH THE SHARPENING UPPER-LEVEL
TROUGH, A FAIR AMOUNT OF CLOUDS SHOULD DEVELOP OVER LAND. AS A
RESULT, WE INCREASED THE SKY COVER A DECENT AMOUNT.

A STRONG SHORT WAVE ROUNDING THE BASE OF THE SHARPENING UPPER-LEVEL
TROUGH MAY TRY AND PRODUCE SOME LIGHT SHOWERS OR SPRINKLES TOWARD
THE DELMARVA LATER IN THE AFTERNOON. GIVEN THE DRYNESS IN THE
FORECAST SOUNDINGS ESPECIALLY THE SUB-CLOUD LAYER, WE KEPT A DRY
FORECAST GOING ATTM /PERHAPS SOME SPRINKLES OR VIRGA/. THE EXCEPTION
IS WE CARRIED A CHC OF SPRINKLES ACROSS THE FAR NORTHWEST ZONES AS
DEVELOPING CLOUDINESS COULD PRODUCE SOME SPRINKLES OVER THE HIGHER
ELEVATIONS. HERE, THE DEPTH OF THE CLOUD LAYER SHOULD BE SHALLOW
ENOUGH SO ANYTHING THAT REACHES THIS FAR SOUTH AND EAST IS RATHER
LIGHT.

ONCE AGAIN, WE SHOULD HAVE A DECENT MIXED BOUNDARY LAYER WITH
SURFACE DEW POINTS DROPPING MOSTLY INTO THE 20S. WHILE THE PRESSURE
GRADIENT IS FORECAST TO RELAX SOME THROUGH THE AFTERNOON, ENOUGH
WIND WITHIN THE MIXED BOUNDARY LAYER SHOULD RESULT IN SOMEWHAT
BREEZY CONDITIONS FOR A TIME. IT DOES NOT APPEAR TO BE AS STRONG AS
TODAY /SUNDAY/ HOWEVER.

AS FOR TEMPERATURES, WE USED A NAM/GFS MOS BLEND THEN ADJUSTED DOWN
A LITTLE GIVEN THE CLOUDS THAT ARE ANTICIPATED TO DEVELOP THROUGH
THE DAY.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
**NEAR RECORD COLD AND FROST FREEZE POTENTIAL TUESDAY MORNING**

THE EXTENDD PD WILL START OUT WITH TWO MAIN WX FEATURES ON THE
MAP, A LARGE LOW OVER ERN CANADA AND A LARGE AREA OF HIGH PRESSURE
OVER THE LWR MS VLY WHICH WILL BUILD EWD. MONDAY NIGHT LOOKS TO
BE THE COLDEST NIGH A MAINLY CLEAR SKY AND FAIRLY LIGHT WIND, BUT
TEMPS WILL REBOUND BY TUE.

SO THE FIRST HALF OF THE WEEK LOOKS DRY. HOWEVER, THERE IS SOME
FROST POTENTIAL MONDAY MORNING, MAINLY N AND W, WITH THE LIMITING
FACTOR BEING IF THE WIND IS TOO STRONG. TUE MORNING LOOKS TO BE A
SLAM DUNK, ESPECIALLY N AND W AND PSBLY INTO THE NORMALLY COLDER
AREAS S AND E FOR FREEZE AND FROST.

THE HIGH MOVES OFF THE COAST BY WED AND LOW PRESSURE MOVES ACRS
ONTARIO. A WARM FRONT WILL MOVE ACRS THE REGION LATER WED AND
THERE COULD BE SOME RAIN INTO WED NIGHT WITH THIS FRONT.

LOW PRECIP CHCS LINGER THRU FRI AND INTO SAT UNTIL A CDFNT CROSSES
THE AREA.

TEMPS WILL START OFF ABOUT 10 TO 15 DEGREES BELOW NRML ON MON AND
RISE INTO THE 80S (ABOUT 10 DEGREES ABOVE NRML BY THU), SO ITS A
BIT OF A ROLLER COASTER RIDE.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

REST OF THIS AFTERNOON...VFR. SOME STRATOCUMULUS BASES AROUND 5,000
FEET ARE ANTICIPATED TO DISSIPATE INTO THE EVENING. WEST-NORTHWEST
WINDS 10-20 KNOTS WITH SOME GUSTS TO AROUND 25 KNOTS.

TONIGHT...VFR. WEST-NORTHWEST WINDS GUSTING TO NEAR 20 KNOTS WILL
DIMINISH TO UNDER 10 KNOTS.

MONDAY...VFR, HOWEVER STRATOCUMULUS IS ANTICIPATED TO DEVELOP AND
TEND TO BECOME A CEILING STARTING AROUND MIDDAY. WEST-NORTHWEST
WINDS 10-15 KNOTS WITH GUSTS TO NEAR 20 KNOTS.

OUTLOOK...
TUESDAY...VFR. HIGH CONFIDENCE.

WEDNESDAY...VFR. HIGH CONFIDENCE. A SMALL CHANCE OF A SHOWER BY LATE
AFTERNOON, ESPECIALLY NORTHWEST.

WEDNESDAY NIGHT...LOWERING CEILINGS AND VISIBILITIES WITH SHOWERS
AND POSSIBLE THUNDERSTORMS ASSOCIATED WITH A WARM FRONT. SOUTH WIND.
MVFR AND IFR IS POSSIBLE. LOW TO MODERATE CONFIDENCE.

THURSDAY...CONTINUED POTENTIAL FOR LOWER CEILINGS WITH BOUNDARY IN
THE REGION AND PRECIPITATION ASSOCIATED WITH IT. LOW CONFIDENCE.

&&

.MARINE...
A SECONDARY BUT DRY COLD FRONT HAS SHIFTED TO OUR EAST AT MID
AFTERNOON. A CYCLONIC FLOW OF COLDER AIR WILL CONTINUE TO OVERSPREAD
THE AREA THROUGH MONDAY. THE GREATEST MIXING HAS BEEN AT THE COAST
AND INLAND WITH SOME GUSTS TO ABOUT 25 KNOTS AT TIMES. THE MIXING
HAS BEEN LESSENED OVER THE WATERS SINCE THE AIRMASS IS NOT ALL THAT
COLD YET. THE BOUNDARY LAYER WILL TURN COLDER TONIGHT AND THE
FORECAST SOUNDINGS SHOW DEEPENING MIXING. HOWEVER, IT IS NOT ALL
THAT CERTAIN THE WINDS WILL BE REMAIN HIGH ENOUGH TO WARRANT AN
ADVISORY. IT MAY BE A BIT BETTER NORTH THAN SOUTH, AND PERHAPS IN
LOWER DELAWARE BAY WITH PERHAPS SOME FUNNELING. THERE HAS BEEN SOME
UPTICK IN THE WINDS AT THE COASTAL OBSERVATIONS NEAR THE MOUTH OF
DELAWARE BAY, HOWEVER THIS MAY BE MORE LOCALIZED. THE OFFSHORE FLOW
SHOULD ALSO KEEP SEAS UNDER 5 FEET. BASED ON THE ABOVE, WE OPTED TO
CANCEL THE SMALL CRAFT ADVISORY FOR ALL THE ZONES. IT IS POSSIBLE
THIS MAY HAVE TO BE REISSUED ESPECIALLY FOR THE NORTHERN WATERS AS
FORECAST SOUNDINGS LOOKED A BIT BETTER THERE TONIGHT. IT DOES APPEAR
THAT ANY ELEVATED WINDS WILL BE LOWER DURING MONDAY AS THE BETTER
MIXING ONCE AGAIN IS FOCUSED MOSTLY ON LAND.

OUTLOOK...
A LARGE HIGH PRESSURE SYSTEM WILL SLOWLY MOVE TWD THE WATERS THRU
MIDWEEK. THEREFORE, NO FLAGS ARE ANTICIPATED MON NIGHT OR TUE. THEN,
A WARM FRONT WILL APPROACH AND SLY FLOW WILL INCREASE AND A WAA
SCA SITUATION LATE WED AFTN THROUGH THURSDAY MORNING IS PSBL.

&&

.CLIMATE...
RECORD LOWS THAT APPEAR VULNERABLE TO BE EQUALED OR EXCEEDED MONDAY
AND TUESDAY MORNING.

5/13 MONDAY
TTN  39 1939 AND 1907
RDG  36 1996 AND 1976

5/14 TUESDAY
MPO 29 1938
PHL 40 1996
RDG 33 1996
ILG 36 1996 1940 1939

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FROST ADVISORY FROM 3 AM TO 8 AM EDT MONDAY FOR PAZ054-055-
     060>062.
     FREEZE WATCH FROM LATE MONDAY NIGHT THROUGH TUESDAY MORNING
     FOR PAZ054-055.
NJ...FROST ADVISORY FROM 3 AM TO 8 AM EDT MONDAY FOR NJZ001-007.
     FREEZE WATCH FROM LATE MONDAY NIGHT THROUGH TUESDAY MORNING
     FOR NJZ001.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GORSE/NIERENBERG
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...NIERENBERG
AVIATION...GORSE/NIERENBERG
MARINE...GORSE/NIERENBERG
CLIMATE...DRAG