Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 241954
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
354 PM EDT TUE MAR 24 2015

.SYNOPSIS...
HIGH PRESSURE EXTENDING OVER THE NORTHEAST AND MID ATLANTIC STATES
WILL GRADUALLY MOVE OFFSHORE BY EARLY WEDNESDAY. A WARM FRONT IS
THEN FORECAST TO LIFT NORTH THROUGH THE REGION WEDNESDAY NIGHT,
FOLLOWED BY A STRONG COLD FRONT CROSSING THE MID ATLANTIC THURSDAY
EVENING. A SECONDARY COLD FRONT SHOULD THEN PASS THROUGH THE REGION
LATE FRIDAY. HIGH PRESSURE IS EXPECTED TO FOLLOW OVER THE WEEKEND,
WITH ANOTHER COLD FRONT REACHING THE AREA MONDAY.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE SYNOPTIC SETUP IS COMPRISED OF A TROUGH IN THE NORTHEAST AND
INTO THE MID ATLANTIC. AT THE SURFACE, HIGH PRESSURE CENTERED NEAR
THE EASTERN GREAT LAKES EXTENDS DOWN INTO THE MID ATLANTIC. THIS IS
ALLOWING FOR LIGHT WINDS AND WILL DOMINATE OUR WEATHER THROUGH
TONIGHT. THE LINGERING OVERCAST THIS AFTERNOON COMBINED WITH A LACK
OF MIXING HAS KEPT TEMPERATURES ACROSS MUCH OF THE AREA IN THE 30S.
HOWEVER WHERE THINNING AND CLEARING IS TAKING PLACE THIS AFTERNOON,
THE TEMPERATURES ARE RESPONDING AND GETTING INTO THE 40S.

A SHORT WAVE WITH ITS VORTICITY BECOMING MORE CHANNELIZED IS
FORECAST TO CLEAR OUR AREA THROUGH EARLY THIS EVENING. THIS IS
ASSOCIATED WITH THE EXTENSION OF A SHORT WAVE TROUGH AXIS THAT WILL
ALSO SHIFT TO OUR EAST EARLY THIS EVENING. THE MOISTURE ASSOCIATED
WITH THIS FEATURE COMBINED WITH A SUBSIDENCE INVERSION AND A NEARBY
THERMAL GRADIENT ALOFT, HAS ALLOWED THE CLOUD DECK TO HANG ON LONGER
FOR MUCH OF THE CWA. THERE IS DRYING THOUGH WORKING SOUTHWARD THIS
AFTERNOON, WHICH WILL ERODE THE CLOUD DECK SOUTHWARD BENEATH THE
SUBSIDENCE INVERSION. AS A RESULT, THE CLOUDS ARE EXPECTED TO THIN
AND CLEAR FROM NORTH TO SOUTH THROUGH EARLY THIS EVENING.

AS THE AFOREMENTIONED SURFACE HIGH BEGINS TO SHIFT EASTWARD THROUGH
THE NIGHT, A LIGHT SOUTHEASTERLY FLOW WILL START TO DEVELOP. THIS
WILL ALLOW THE SURFACE DEW POINTS TO START CREEPING UPWARD, HOWEVER
A COLD NIGHT IS EXPECTED WITH LIGHT WINDS AND ANY LINGERING CLOUDS
DISSIPATING. AS FOR THE LOW TEMPERATURES, WE USED MOSTLY A NAM/GFS
MOS BLEND.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
HIGH PRESSURE AT THE SURFACE WILL BE SHIFTING TO OUR EAST DURING THE
MORNING AS A SHORT WAVE RIDGE MOVES ACROSS. AS THIS OCCURS, AN UPPER-
LEVEL TROUGH WILL AMPLIFY SOME FROM THE MIDWEST TO THE OHIO VALLEY
AND EVEN TAKE ON A NEGATIVE TILT. THE FLOW ALOFT WILL BACK AND ALLOW
FOR WAA TO INCREASE ACROSS THE REGION, ESPECIALLY FROM THE EASTERN
GREAT LAKES DOWN THE OHIO VALLEY. IT IS IN THESE AREAS WHERE THE
STRONGEST LOW-LEVEL JET IS FORECAST TO MOVE THROUGH DURING THE
COURSE OF THE DAY.

AS THE WAA OCCURS DURING THE DAY, WE ARE EXPECTING AN INCREASE IN
CLOUDS ACROSS THE ENTIRE AREA. THESE WILL LOWER AS THE FORECAST
SOUNDINGS INDICATE MID LEVEL MOISTURE INCREASING MORE QUICKLY AT
FIRST /ESPECIALLY WESTERN AREAS INITIALLY/ THEN THE LOWER LEVELS
GRADUALLY MOISTEN UP. AS THIS IS OCCURRING, AN INCOMING WARM FRONT
AND THE SOUTHEASTERN EXTENSION OF THE TROUGH GOING NEGATIVELY TILTED
SHOULD PRODUCE SOME SHOWERS OR A BAND OF SHOWERS FROM THE GREAT
LAKES REGION SOUTHEASTWARD. THE BEST FORCING HOWEVER APPEARS TO BE
MAINLY FOCUSED TO OUR NORTHWEST. AS A RESULT, WE ADJUSTED THE POPS
TO SHOW THE HIGHEST CHC ACROSS OUR WESTERN ZONES IN THE AFTERNOON.
THE FORECAST SOUNDINGS DO SUGGEST THAT AS THE MOISTENING IS
OCCURRING, SOME LOW-LEVEL DRY AIR MAY HANG ON. IT APPEARS THOUGH AS
THE AIRMASS MODIFIES AND BY THE TIME THE PRECIPITATION ARRIVES, IT
WILL BE MILD ENOUGH TO BE ALL RAIN. BASED ON THE QPF FORECAST AND
THE STRONGEST FORCING HANGING BACK TO OUR WEST, WENT WITH SHOWERY
WORDING.

AS FOR THE HIGH TEMPERATURES, MODERATION OF THE AIRMASS IS EXPECTED
AS WAA OCCURS. HOWEVER, THIS SHOULD BE TEMPERED SOME DUE TO
INCREASING CLOUDS AND A DEVELOPING ONSHORE FLOW AHEAD OF THE WARM
FRONT. OVERALL, WE USED A NAM/GFS MOS BLEND THEN MADE SOME TWEAKS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
AN ACTIVE PATTERN WITH A BRIEF WARM-UP WILL BE ONGOING AT THE START
OF THE LONG TERM, BEFORE ANOTHER MID/UPPER LEVEL TROUGH RETURNS
ALONG WITH CANADIAN HIGH PRESSURE FOR OVER THE WEEKEND. BY WEDNESDAY
NIGHT, WARM ADVECTION WILL BE TAKING HOLD ACROSS THE REGION AS A
SURFACE WARM FRONT CONTINUES TO LIFT NORTHWARD. WE HAVE MAINTAINED
HIGH CHANCE POPS THROUGH WEDNESDAY NIGHT, INCREASING POPS A LITTLE
INTO DAYBREAK THURSDAY. AS NOTED BY THE PREVIOUS SHIFT, WE HAVE ALSO
KEPT A MENTION OF DRIZZLE AND FOG THROUGH THE OVERNIGHT WEDNESDAY,
AS FORECAST SOUNDINGS SHOW SOME DRIER AIR ALOFT WITH VERY SATURATED
LOW LEVELS.

INTO THURSDAY, AN INCREASING SOUTHWEST FLOW WILL BE SETTING UP
ACROSS THE REGION AHEAD OF AN APPROACHING STRONG COLD FRONT.
SOUTHWEST WINDS MAY GUST TO AROUND 25 MPH INTO THURSDAY AFTERNOON
AHEAD OF THE ADVANCING FRONT AS TEMPERATURES WARM INTO THE 60S, WITH
SOME LOWER 70S POSSIBLE ACROSS SOUTHERN AREAS. INCREASING LOW LEVEL
MOISTURE WILL ALSO BE APPARENT ACROSS THE REGION AS DEWPOINTS ARE
FORECAST TO RISE INTO THE 50S. WITH THE APPROACHING COLD FRONT BY
LATE-DAY, WE INCREASE POPS TO LIKELY FOR THURSDAY AFTERNOON AND
EVENING AND MAINTAIN A CHANCE FOR TSTORMS AS CAPE VALUES ARE
FORECAST TO REACH UP TO A FEW HUNDRED J/KG. BRIEF DOWNPOURS AND A
FEW STRONGER WIND GUSTS ARE POSSIBLE WITH ANY DEVELOPING TSTORMS AS
PWAT VALUES ARE FORECAST TO RISE TO A LITTLE OVER AN INCH AND
FORECAST SOUNDINGS SHOW BULK SHEAR FROM 0-6 KM RANGING BETWEEN 40 TO
50 KT AS THE COLD FRONT NEARS THE REGION INTO THURSDAY EVENING.
OVERALL QPF AMOUNTS STILL LOOK TO RANGE MAINLY BETWEEN A QUARTER TO
THREE QUARTERS OF AN INCH. THROUGH THE REMAINDER OF THURSDAY
OVERNIGHT, WE STEP-DOWN POPS TO CHANCE FROM WEST TO EAST ACROSS THE
FORECAST AREA AS THE COLD FRONT PASSES OFFSHORE.

MODEL CONSENSUS THEN INDICATES A SECONDARY COLD PASSAGE LATE FRIDAY
TO FRIDAY NIGHT, WITH A LONGWAVE TROUGH ALSO MOVING IN ACROSS THE
EASTERN UNITED STATES. FRIDAY LOOKS TO BE A MAINLY CLOUDY DAY ACROSS
OUR REGION, WITH ISOLATED SHOWERS POSSIBLE, ESPECIALLY ACROSS
NORTHERN AREAS. OVER THE WEEKEND, DRY AND COOL CONDITIONS ARE
ANTICIPATED AS THE LONGWAVE TROUGH PASSES OVERHEAD AND SURFACE HIGH
PRESSURE BUILDS DOWN ACROSS THE AREA. THEREAFTER, A LOW PRESSURE
SYSTEM MOVING ACROSS SOUTHERN CANADA IS EXPECTED TO SEND A COLD
FRONT ACROSS OUR REGION MONDAY. ANY RAIN/SNOW SHOWERS AND PRECIP
AMTS LOOK TO BE LIGHT AT THIS TIME AND MAINLY ACROSS OUR NORTHERN
ZONES AS MOST OF THE FORCING WITH THIS SYSTEM IS EXPECTED TO BE TO
OUR NORTH. AS THAT SYSTEM PASSES OFFSHORE INTO MONDAY NIGHT, MORE
HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS THE REGION INTO
TUESDAY.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

REST OF THIS AFTERNOON...VFR CEILINGS /6000-10000 FEET/ WILL SCATTER
OUT FROM NORTH TO SOUTH INTO THE EVENING. THE WINDS WILL BE MAINLY
LIGHT AND VARIABLE.

TONIGHT...VFR WITH ANY LINGERING CLOUDS EARLY DISSIPATING SOUTHWARD.
LIGHT AND VARIABLE TO LOCALLY CALM WINDS.

WEDNESDAY...VFR WITH INCREASING CLOUDS. A DEVELOPING CEILING MAY
LOWER TO MVFR MAINLY LATE IN THE AFTERNOON ESPECIALLY NORTH AND WEST
OF KPHL. SOME SHOWERS SHOULD DEVELOP DURING THE AFTERNOON MOSTLY
WEST OF KPHL. THE CHANCE AS OF NOW IS LOW ENOUGH, AND THEREFORE A
MENTION WAS NOT INCLUDED IN THE TAFS AT KRDG AND KABE. SOUTHEASTERLY
WINDS GENERALLY 5-10 KNOTS.

OUTLOOK...
WEDNESDAY NIGHT INTO THURSDAY MORNING...IFR CONDITIONS WITH LOW
CLOUDS, FOG AND A CHANCE OF RAIN/DRIZZLE. LOW LEVEL WIND SHEAR IS
POSSIBLE ON THURSDAY MORNING TO MIDDAY DUE TO THE POSSIBLE PRESENCE
OF A LOW LEVEL SOUTHWESTERLY JET OVERHEAD.

THURSDAY AFTERNOON INTO THURSDAY NIGHT...MAINLY VFR WITH OCCASIONAL
MVFR AND IFR CONDITIONS IN SHOWERS AND SCATTERED THUNDERSTORMS.

FRIDAY...VFR CONDITIONS WITH NORTHWEST WINDS.

SATURDAY AND SUNDAY...VFR CONDITIONS.

&&

.MARINE...
HIGH PRESSURE EXTENDS ACROSS OUR AREA FROM THE EASTERN GREAT LAKES
INTO TONIGHT. THIS HIGH WILL THEN SHIFT OFF THE COASTS OF NEW
ENGLAND AND THE MID ATLANTIC WEDNESDAY MORNING, RESULTING IN A
SOUTHEASTERLY FLOW TO BECOME MORE ESTABLISHED. THE FLOW WILL
INCREASE SOME DURING THE COURSE OF WEDNESDAY, HOWEVER THE WINDS AND
AND SEAS ARE EXPECTED TO REMAIN WELL BELOW SMALL CRAFT ADVISORY
CRITERIA.

OUTLOOK...
WEDNESDAY NIGHT...SUB-ADVISORY CONDITIONS ARE EXPECTED.

THURSDAY AND FRIDAY...SCA CONDITIONS ARE EXPECTED TO DEVELOP DURING
THURSDAY MORNING AND LAST INTO EARLY FRIDAY WITH THE APPROACH AND
PASSAGE OF A COLD FRONT. WIND GUSTS WILL REACH INTO THE 25 TO 30
KNOT RANGE, WITH A WIND SHIFT FROM SOUTHWEST TO NORTHWEST OCCURRING
AS THE COLD FRONT PASSES OVER THE WATERS LATE THURSDAY NIGHT. IN
ADDITION, SEAS WILL STEADILY BUILD INTO THE 5 TO 8 FOOT RANGE FOR
THE COASTAL WATERS DURING THURSDAY AND THURSDAY NIGHT, BEFORE
SUBSIDING EARLY FRIDAY.

SATURDAY AND SUNDAY...MAINLY SUB-SCA CONDITIONS ARE EXPECTED. SOME
NORTHWEST WIND GUSTS AROUND 20 KNOTS PLUS ARE POSSIBLE FOR THE
COASTAL WATERS SATURDAY.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...KLINE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...KLINE
AVIATION...GORSE/IOVINO/KLINE
MARINE...GORSE/KLINE


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