Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 151351
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
951 AM EDT WED APR 15 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD ACROSS OUR REGION TODAY AND TONIGHT, THEN
SHIFT OFFSHORE THURSDAY INTO FRIDAY. A COLD FRONT WILL MOVE THROUGH
FRIDAY AS LOW PRESSURE DEVELOPS NEAR THE NORTH CAROLINA COAST, THEN
A SECONDARY COLD FRONT ARRIVES DURING SATURDAY. HIGH PRESSURE IS
SCHEDULED TO BRIEFLY BUILD IN FOR SUNDAY, THEN THE NEXT COLD FRONT
AND LOW PRESSURE SYSTEM MOVES IN FOR LATER MONDAY AND TUESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

9:30 AM UPDATE... HIGH PRESSURE WILL CONTINUE TO BUILD WITH
CONTINUED DRY AIR ADVECTION. THIS WILL RESULT IN ONLY SOME HIGH
CIRRUS THROUGH THE REMAINDER OF THE DAY ACROSS THE REGION.
SOUNDINGS OFF OF THE RAP AND HRRR INDICATE SOME WIND GUSTS AROUND
25 MPH WILL BE POSSIBLE FOR THE REMAINDER OF DAY AS WELL, SO
INCREASED WIND GUSTS A BIT WITH THIS UPDATE. TEMPERATURES AND
DEWPOINTS WERE ALSO ADJUSTED WITH THIS UPDATE. WITH THE DRY AIR
ADVECTION CONTINUED TO GO CLOSER TO THE MET BUT EVEN THAT IS
LIKELY A HIGH WITH THE DEWPOINTS, THESE WERE LOWERED SLIGHTLY
AGAIN. A RED FLAG WARNING HAS BEEN ISSUED FOR NORTHERN/CENTRAL NJ
ALONG WITH EASTERN PA FOR RH VALUES AROUND 20%, LOW FINE FUEL
MOISTURE AND NORTHERLY WIND GUSTS AROUND 25 MPH. PLEASE SEE FIRE
WEATHER SECTION OF AFD FOR MORE.


630 AM UPDATE...MAIN CHANGES WITH THIS UPDATE WERE FOR DEW POINT
TEMPERATURES. DEW POINTS HAVE FALLEN A BIT FASTER THAN EXPECTED
WITH TEENS AND 20S ALREADY OVER THE POCONOS AND NW NJ. UNDERCUT
DEW POINTS SLIGHTLY THROUGH OUT THE DAY, BUT WILL WAIT UNTIL
UPSTREAM 12Z SOUNDINGS COME IN BEFORE MAKING ANY SIGNIFICANT
CHANGES.

PREVIOUS NEAR TERM DISCUSSION...THE COLD FRONT, AND ASSOCIATED
LOW, WILL CONTINUE TO SLIDE AWAY FROM THE REGION. IN IT`S WAKE, A
COOL AND VERY DRY AIR MASS WILL BUILD IN OVER THE REGION. SEE FIRE
WEATHER SECTION BELOW FOR A DISCUSSION OF FIRE WEATHER CONCERNS.
DESPITE THE COOLER AIR MASS, TEMPERATURES SHOULD ACTUALLY BE
PRETTY CLOSE, IF NOT A BIT ABOVE, NORMAL VALUES TODAY. THE UPPER
LEVEL JET IS EXPECTED TO REMAIN JUST NORTHEAST OF THE REGION
THROUGH THE DAY TODAY, LEADING TO PERSISTENT THICK CIRRUS CLOUDS,
SO WHILE IT WON`T BE COMPLETELY SUNNY, IT SHOULD STILL BE A NICE
DAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
500 MB SHORT WAVE RIDGE SLIDES OVER THE REGION, AS THE SURFACE HIGH
BUILDS CLOSER. ADDITIONALLY, THE 250MB LEVEL JET SLIDES FURTHER OFF
SHORE, ALL OF THIS WILL COMBINE FOR CLEARING SKIES OVERNIGHT. WINDS
SHOULD BE LIGHT, AND WITH THE RELATIVELY LOW DEW POINT TEMPERATURES,
SHOULD SEE CONSIDERABLE RADIATIONAL COOLING. AS A RESULT, EXPECT
LOWS IN THE UPPER 30S TO LOWER 40S. AT THIS TIME, HOWEVER, DO NOT
EXPECT FROST ADVISORY CONDITIONS IN LOCATIONS WHERE THE GROWING
SEASON HAS ALREADY STARTED (IN THESE AREAS EXPECT LOWS MOSTLY IN THE
LOWER 40S).

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
THE SYNOPTIC SETUP IS COMPRISED OF AN INITIAL RIDGE IN THE EAST THAT
TRANSITIONS TO SOME TROUGHING. AS THIS OCCURS, A CLOSED LOW ACROSS
THE WEST DROPS EAST-SOUTHEAST EVENTUALLY EJECTING ACROSS THE PLAINS.
THIS FEATURE BUILDS SOME RIDGING DOWNSTREAM, HOWEVER IT ALSO FORCES
SOME AMPLIFICATION OF THE TROUGH ACROSS THE NORTHEAST FOR A PORTION
OF THE WEEKEND. THE CLOSED LOW MAY THEN GET ABSORBED INTO A LARGE
SCALE TROUGH FROM THE MIDWEST AS IT UNDERGOES AMPLIFICATION EASTWARD
EARLY NEXT WEEK. PRIOR TO THIS OCCURRING, A SURFACE LOW IS FORECAST
TO DEVELOP NEAR THE NORTH CAROLINA COAST THURSDAY AND THEN TRACK
NORTHEASTWARD. THE DETAILS WITHIN THIS SETUP IS OF LOWER CONFIDENCE
AS THE MODEL GUIDANCE IS HAVING TROUBLE HANDLING THE SPLIT FLOW. THE
INTERACTION OF THE EJECTING CLOSED LOW AND THE NORTHERN STREAM
TROUGH AND ASSOCIATED ENERGY WILL HAVE AN IMPACT ON THE DOWNSTREAM
WEATHER. THIS IS MOST NOTED FOR OUR AREA DURING THE WEEKEND AND
ESPECIALLY EARLY NEXT WEEK. GIVEN THE LOWER CONFIDENCE, WE USED A
MODEL BLEND WITH CONTINUITY FOR WEDNESDAY THROUGH FRIDAY THEN WENT
WITH MOSTLY THE 00Z WPC GUIDANCE /BLEND OF THE MEANS SATURDAY, THEN
MOSTLY A NAEFS/ECMWF ENSEMBLE MEAN BLEND THEREAFTER/. SOME
ADJUSTMENTS WERE THEM MADE FOLLOWING ADDITIONAL COLLABORATION WITH
OUR NEIGHBORING OFFICES.

FOR THURSDAY...HIGH PRESSURE AT THE SURFACE IS FORECAST TO SHIFT TO
OUR EAST DURING THIS TIME FRAME. THIS WILL SET THE STAGE FOR
SOUTHEASTERLY LOW-LEVEL FLOW THAT WILL ALLOW FOR MOISTURE ADVECTION
TO INCREASE. IT APPEARS THAT A PRESSURE TROUGH DEVELOPS ALONG THE
NORTH CAROLINA COAST AS DEPARTING HIGH PRESSURE WEDGES SOUTHWESTWARD
FOR A TIME. AS A RESULT, LOW PRESSURE IS FORECAST TO DEVELOP NEAR OR
ALONG THE NORTH CAROLINA COAST. THERE MAY BE A CONDUIT OF MOISTURE
PULLED NORTHWESTWARD FROM THIS SURFACE LOW AS IT SLOWLY TRACKS
NORTHEASTWARD. OTHERWISE, AN INCOMING COLD FRONT SHOULD ALSO HAVE
SOME SHOWERS WITH IT. OVERALL, MUCH OF THIS TIME FRAME SHOULD BE DRY
WITH ANY SHOWERS TENDING TO HOLD OFF UNTIL LATER THURSDAY NIGHT AND
THIS IS WHEN THE POPS INCREASE.

FOR FRIDAY AND SATURDAY...IT MAY START OUT RATHER UNSETTLED FRIDAY
AS MOISTURE GETS PULLED NORTHWARD FROM LOW PRESSURE NEAR THE NORTH
CAROLINA COAST. THIS FEATURE WILL THEN TRACK FARTHER AWAY FROM THE
COAST LATER FRIDAY AND SATURDAY, ALTHOUGH A SECONDARY COLD FRONT
SHOULD ARRIVE DURING SATURDAY. THERE IS LESS CONFIDENCE IN THE
AMOUNT OF SHOWERS FRIDAY AS IT WILL DEPEND ON HOW MUCH INTERACTION
THE SURFACE LOW TO OUR SOUTH HAS WITH ENERGY SLIDING BY FARTHER TO
THE NORTH. AS A RESULT, WE KEPT POPS BELOW LIKELY AND WENT WITH
SCATTERED WORDING FOR NOW. THE SECONDARY FRONT ON SATURDAY MAY NOT
HAVE MUCH MOISTURE LEFT TO WORK WITH, THEREFORE WE KEPT POPS ON THE
LOWER SIDE. IT DOES APPEAR THAT THE AIRMASS MODERATES PRIOR TO THE
COLD FRONTAL PASSAGE WITH MANY AREAS GETTING TO AROUND 70 DEGREES
DURING THE DAY.

FOR SUNDAY THROUGH TUESDAY...HIGH PRESSURE AT THE SURFACE SHOULD
BUILD IN BRIEFLY SUNDAY. AS ENERGY EJECTS EASTWARD FROM A CLOSED LOW
AND ALSO FROM THE MIDWEST, A COMPLEX SYSTEM MAY EVOLVE EASTWARD WITH
TIME. WE KEPT SUNDAY DURING THE DAY DRY DUE TO THE PRESENCE OF HIGH
PRESSURE, THEN WAA AND MOISTURE ADVECTION BEGINS TO OVERTAKE THE
AREA AT NIGHT. THIS MAY ALLOW FOR SOME SHOWERS TO ARRIVE, ALTHOUGH
IT STILL LOOKS LIKE THE MORE UNSETTLED TIME FRAME MAY BE MONDAY AND
TUESDAY. THIS WILL DEPEND ON THE EVOLUTION OF THE SPLIT FLOW AS IT
MAY TURN INTO AN AMPLIFIED UPPER-LEVEL TROUGH IN THE EAST. AS OF
NOW, THE HIGHEST POPS ARE FOR MONDAY HOWEVER THIS WILL PROBABLY
CHANGE. GIVEN THE UNCERTAINTY WITH THE DETAILS, WE DID NOT GO ANY
HIGHER THAN HIGH CHC POPS. SOME COOLER TEMPERATURES SHOULD RESULT,
ESPECIALLY IF THE RAIN IS MORE WIDESPREAD.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. ONLY LINGERING
HIGH CIRRUS CLOUDS ARE POSSIBLE, PRIMARILY THROUGH 00Z. NORTHERLY
WINDS MAY BRIEFLY GUST NEAR 20 KT THROUGH 21Z, BUT OTHERWISE
WINDS SHOULD BE NEAR OR BELOW 10KT. WINDS ARE EXPECTED TO
GRADUALLY SHIFT TO EAST NORTHEASTERLY OVERNIGHT TONIGHT.

OUTLOOK...
THURSDAY THROUGH SATURDAY...VFR THURSDAY WITH INCREASING CLOUDS,
THEN CONDITIONS TENDING TO LOWER TO MVFR WITH SCATTERED SHOWERS
LATER THURSDAY NIGHT AND FRIDAY. OUR CONFIDENCE IS ON THE LOWER SIDE
WITH THE TIMING AND HOW MUCH RAIN OCCURS. A SECONDARY COLD FRONT
MOVES THROUGH DURING SATURDAY, HOWEVER THIS MAY HAVE LIMITED
MOISTURE WITH IT.

SUNDAY...OVERALL VFR AS HIGH PRESSURE BRIEFLY BUILD IN.

&&

.MARINE...
SMALL CRAFT ADVISORY HAS BEEN CANCELLED. WINDS AND SEAS HAVE
DROPPED BELOW CRITERIA. A FEW GUSTS NEAR 20 KT WILL BE POSSIBLE
THROUGH THE DAY ON THE COASTAL WATERS, BUT SHOULD REMAIN BELOW
SCA CRITERIA.

OUTLOOK...
THURSDAY AND FRIDAY...THE WINDS AND SEAS ARE EXPECTED TO BE BELOW
SMALL CRAFT ADVISORY CRITERIA AS THE FLOW OVERALL IS FORECAST TO BE
LIGHT ENOUGH.

SATURDAY AND SUNDAY...A COLD FRONT MOVES THROUGH DURING SATURDAY
THEN HIGH PRESSURE ARRIVES BRIEFLY FOR SUNDAY. THE WINDS APPEAR TO
REMAIN BELOW ADVISORY CRITERIA, HOWEVER THE SEAS COULD NEAR 5 FEET
FOR A TIME ON THE OCEAN MAINLY IF THE NORTHERLY FLOW AHEAD OF HIGH
PRESSURE LASTS LONG ENOUGH AND IS A BIT STRONGER.

&&

.FIRE WEATHER...
ALMOST ALL OF THE REGION (WITH THE EXCEPTION OF A FEW COASTAL
LOCATIONS) WILL SEE MINIMUM RELATIVE HUMIDITY VALUES NEAR OR BELOW
20 PERCENT.  MUCH OF DELMARVA AND FAR SOUTHERN NJ HAD RAIN TOTALS
NEAR OR ABOVE 1 INCH YESTERDAY, LEADING TO HIGHER FUEL MOISTURES.
FOR THE REST OF THE REGION HOWEVER, THE LIGHT RAIN YESTERDAY DID
NOT HAVE MADE A SIGNIFICANT IMPACT ACROSS CENTRAL/NORTHERN NJ AND
EASTERN PA ON FUEL MOISTURE AND DRYING OF THE FUEL MOISTURE WILL
CONTINUE TODAY.

AS FOR WINDS, GUSTS NEAR 20 KT ARE LIKELY ACROSS THE REGION.
HOWEVER, THE TIGHTEST PRESSURE GRADIENT, AND THUS THE STRONGEST
WINDS ARE EXPECTED IN THE MORNING BUT MAY LINGER INTO THE
AFTERNOON. WE HAVE ISSUED A RED FLAG WARNING FOR EASTERN PA,
NORTHERN/CENTRAL NJ UNTIL 7 PM DUE TO A COMBINATION OF LOW
MOISTURE IN FINE FUELS, LOW RH 20% OR LOWER AND WIND GUSTS AROUND
25 MPH THROUGH THE AFTERNOON.

FOR THURSDAY, THE RELATIVE HUMIDITY VALUES ARE FORECAST TO DROP TO
25-35 PERCENT IN THE AFTERNOON MAINLY FOR NEW JERSEY /AWAY FROM THE
COAST/ AND EASTERN PENNSYLVANIA, HOWEVER THE WINDS ARE CURRENTLY
FORECAST TO BE 15 MPH OR LESS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...RED FLAG WARNING UNTIL 7 PM EDT THIS EVENING FOR PAZ054-055-
     060>062-070-071-101>106.
NJ...RED FLAG WARNING UNTIL 7 PM EDT THIS EVENING FOR NJZ001-
     007>010-012>015.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GORSE
NEAR TERM...GAINES/JOHNSON
SHORT TERM...JOHNSON
LONG TERM...GORSE
AVIATION...GORSE/JOHNSON
MARINE...GORSE/JOHNSON
FIRE WEATHER...GAINES/JOHNSON



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