Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 290854
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
354 AM EST MON DEC 29 2014

.SYNOPSIS...
A WEAK AREA OF LOW PRESSURE OVER NORTH CAROLINA WILL MOVE EAST AND
OFFSHORE LATER TODAY AND TONIGHT. A CANADIAN HIGH PRESSURE SYSTEM
WILL ENTER THE NORTHERN PLAINS ON TUESDAY AND SLOWLY BUILD TO THE
SOUTHEAST REACHING THE SOUTHERN MID ATLANTIC COASTAL WATERS ON
FRIDAY. A LOW PRESSURE SYSTEM AND WARM FRONT SHOULD ADVANCE
TOWARD OUR AREA ON SATURDAY. A NEW WAVE OF LOW PRESSURE ALONG ITS
COLD FRONT MIGHT DEVELOP AND PASS SOUTHEAST OF THE REGION ON
SUNDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
TODAY WILL BE THE TRANSITION DAY AS WE START TO STEP TOWARD COLDER
WEATHER. ON THE SYNOPTIC LEVEL, A COLD FRONT IS WELL SOUTH AND EAST
OF OUR AREA WITH IT TENDING TO STALL TO OUR SOUTH. THIS IS DUE TO
THE FLOW GENERALLY BECOMING PARALLEL WITH IT AS HIGH PRESSURE NEAR
THE MIDWEST THIS MORNING BUILDS EASTWARD. THERE IS AT LEAST ONE MAIN
SHORT WAVE MOVING THROUGH THOUGH.

THIS SHORT WAVE HAS HELPED PRODUCE SOME OVERRUNNING TYPE LIGHT RAIN
NORTH OF THE SURFACE FRONT. THIS ENERGY IS FORECAST TO SETTLE EAST
OF THE AREA THIS MORNING AS IT TENDS TO SHEAR OUT SOME. THERE IS
JUST ENOUGH MOISTURE AND MID LEVEL LIFT TO GENERATE A SWATH OF
MAINLY LIGHT RAIN ACROSS OUR SOUTHERN ZONES, ALTHOUGH THIS HAS BEEN
GRADUALLY WEAKENING EARLY THIS MORNING AT LEAST IN OUR AREA. AS A
RESULT, WE CONTINUED SOME LIKELY/CATEGORICAL POPS EARLY ACROSS
PORTIONS OF THE SOUTHERN AREAS THEN TAPER THESE TO NEARLY NOTHING
WITH A NORTHWARD EXTENT. THE CHC OF LIGHT RAIN ACROSS THE SOUTH
DECREASES THROUGH THE MORNING. GIVEN THE PRESENCE OF A
WEST-SOUTHWEST MID LEVEL FLOW, WE SHOULD HAVE A FAIR AMOUNT OF MID
TO HIGH CLOUDS AROUND ABOVE THE SOUTHEASTWARD CLEARING LOWER CLOUDS.
THE FORECAST SOUNDINGS DO SHOW ENOUGH DRYING FOR AWHILE TODAY
ESPECIALLY ACROSS THE NORTH TO ALLOW FOR MORE SUNSHINE COMPARED TO
FARTHER SOUTH. THE CAA AT 850 MB IS FORECAST TO CONTINUE THROUGH THE
DAY, WITH THIS MORE NOTABLE ACROSS THE CENTRAL AND NORTHERN ZONES.
THIS WILL RESULT IN A COOLER DAY ACROSS THE ENTIRE AREA.

AS FOR HIGH TEMPERATURES, WE MOSTLY UTILIZED AN EVEN BLEND OF THE
NAM/GFS MOS. THE LAMP/LAV GUIDANCE WAS USED FOR THE HOURLY
TEMPERATURES AND DEW POINTS EARLY THIS MORNING. THE DRIER AIR IN THE
LOWER LEVELS CONTINUES TO ADVECT INTO THE AREA, AS EVIDENT BY THE
DECREASING SURFACE DEW POINTS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
AS A WEAK SHORT WAVE TROUGH ARRIVES LATE TONIGHT, A STRONGER SHORT
WAVE IS FORECAST TO ARRIVE MAINLY ACROSS THE CENTRAL AND SOUTHERN
ZONES. THE VORTICITY ASSOCIATED WITH THIS SHORT WAVE THOUGH IS MORE
CHANNELIZED AND THE MOISTURE IS NOT ALL THAT DEEP. IT WAS GENERALLY
THIS FEATURE DAYS AGO THAT SOME MODELS WERE SHOWING A DECENT
OVERRUNNING TYPE EVENT, HOWEVER IT APPEARS TO BE FARTHER SOUTH AND
WEAKER NOW. WHILE THERE IS SOME MID LEVEL LIFT ASSOCIATED WITH IT,
MUCH OF THIS MAY END UP IN THE PRODUCTION OF A MID LEVEL CLOUD DECK.
IF SOME LIGHT PRECIPITATION WERE TO DEVELOP LATE, IT WOULD BE ACROSS
THE DELMARVA AND POSSIBLY INTO FAR SOUTHERN NEW JERSEY. THE FORECAST
SOUNDINGS IN GENERAL HAVE A DRY LOOK TO THEM WITH PERHAPS SOME
VIRGA/SNIRGA MOVING THROUGH. SINCE THERE IS NOT MUCH TO LATCH ONTO
WITH THIS SHORT WAVE MOVING THROUGH LATE, WE MAINTAINED SOME SLIGHT
CHC POPS ACROSS THE FAR SOUTH. GIVEN THE CAA CONTINUING, IT DOES
BECOME COLD ENOUGH FOR THE PRECIPITATION TYPE TO BE SNOW.

OTHERWISE, A FAIR AMOUNT OF CLOUDS ACROSS THE CWA ALTHOUGH THE FAR
NORTH MAY END UP HAVING LESS CLOUDS FOR AWHILE BEING NORTH OF THE
CHANNELIZED SHORT WAVE. IF THERE IS LESS CLOUD COVER LONGER, THEN
TEMPERATURES WILL TEND TO BE COLDER GIVEN LIGHT ENOUGH WINDS AND
LOWERING DEW POINTS.

AS FOR LOW TEMPERATURES, WE USED A NAM/GFS MOS BLEND THEN MADE A FEW
TWEAKS FOR LOCAL AFFECTS.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
A COLD START AND UNSETTLED END TO THE LONG TERM IN MORE WAYS THAN
ONE. A HIGH PRESSURE SYSTEM ORIGINATING IN SIBERIA WILL ENTER THE
CONUS ON TUESDAY. THIS WILL SOLIDIFY COLDER WEATHER ENTERING THE
NEW YEAR. AS THIS MOVES OFFSHORE, A STORM SYSTEM FROM THE
SOUTHWEST IS PREDICTED TO AFFECT OUR AREA OVER THE WEEKEND. THE
GEFS MEAN IS PREDICTING A DUAL TELECONNECTION SWITCH WHICH IS A
FAIRLY CONFIDENT SIGNAL A PCPN EVENT.

AS FOR THE DETAILS, THE MODELS HAVE HAD A DIFFICULT TIME ON
KEYING ON THE CORRECT 500MB PATTERN MUCH MORE THAN 4 TO 5 DAYS IN
ADVANCE SINCE AUTUMN. GETTING DOWN TO THE SURFACE, THESE DIFFERENCES
HAVE NOT BEEN SOLIDIFIED MUCH BEFORE 72 HOURS. AS A RECENT EXAMPLE
THE NON-ECMWF MODELS DID NOT LOSE THEIR SNOWIER TUESDAY SOLUTION FOR
OUR CWA UNTIL THE 12Z RUN SATURDAY AND IN THE NAM`S CASE NOT UNTIL
YESTERDAY. SO IN ONE CORNER WE HAVE THE GFS, NOGAPS AND (INFERRING)
UKMET TAKE A VERY STRONG LOW THROUGH THE SAINT LAWRENCE VALLEY.
THERE IS A PLETHORA OF COLD AIR IN EASTERN CANADA AND HAVE LOW
CONFIDENCE THAT THIS WILL BE EASILY DONE. IN THE OTHER CORNER WE
HAVE THE ECMWF, PGFS AND CAN GGEM THAT TAKE A MUCH WEAKER LOW
INTO THE SAINT LAWRENCE VALLEY, HANG BACK ENERGY IN THE DESERT SW
AND THEN DO ANOTHER SHEARING VERSION OF OUR PRESENT SCENARIO OVER
THE WEEKEND. WHILE WE LIKE THE WEAKER SAINT LAWRENCE VALLEY TRACK
FORECAST, THE HANGING BACK OF ENERGY, ESPECIALLY WITH THE ECMWF,
OPENS UP A WHOLE NEW BOWL OF UNCERTAINTY. SO GIVEN THE DIVERGENT
SOLUTION WITH THIS PACKAGE, WE LEANED HEAVILY ON THE LATEST WPC
SOLUTION FOR ANY ADJUSTMENTS, WHICH FOR RIGHT NOW PAINTS A VERY
CLIMATOLOGICAL PICTURE OF SNOW TO RAIN TO SNOW FOR THE WEEKEND.

THE MODEL INITIALIZATION LOOKED PRETTY GOOD AND A WRF-NMMB AND GFS
BLEND WAS USED FOR THE START OF THE LONG TERM.

AS FOR SOME DAY TO DAY DETAILS...

ON TUESDAY A CHANNELIZED VORT MAX IS STILL EXPECTED TO PASS ACROSS
THE FAR SOUTHERN PART OF OUR CWA. MID LEVEL MOISTURE IS STILL
SUFFICIENT AS IS PREDICTED MID LEVEL QVEC CONVERGENCE TO GENERATE
PCPN. THE LOWER LEVEL SOUNDINGS ARE DRY AND NOT SURE HOW MUCH OF
THAT PCPN WOULD BE ABLE TO MAKE IT TO THE GROUND. POPS WERE KEPT AS
CHANCE OR LOWER. BECAUSE OF THE LIGHT PCPN INTENSITY, PTYPE MACROS
SUGGEST RAIN OR SNOW COULD OCCUR BECAUSE OF THE WARM BOUNDARY LAYER.
AS TUESDAY DAY CONTINUES, MOISTURE IS PREDICTED TO BECOME MORE
LIMITED AND WE ENDED THE CHANCES DURING THE AFTERNOON. STAT GUIDANCE
LOOKED DECENT AND WAS SUPPORTED BY MODEL SOUNDINGS AND WAS FOLLOWED.

THE DOWNWARD PROGRESSION OF TEMPERATURES WILL CONTINUE ON TUESDAY
NIGHT. THE PREDICTED GRADIENT IS BORDERLINE FOR DECOUPLING SO IN
OUTLYING AREAS WE MET MIN TEMPERATURE POTENTIALS HALFWAY.

ON WEDNESDAY, A SECONDARY SURGE OF ARCTIC AIR WILL OCCUR. FCST
1000-850MB THICKNESSES ARE IN THE 1250M RANGE. THERE IS ANOTHER VORT
MAX PREDICTED TO PASS THROUGH AND CONVECTIVE TEMPS PREDICTED TO BE
REACHED NORTHWEST, MODEL DIFFERENCES CENTRAL AND NOT THERE
DELMARVA/SOUTHEAST. GRANTED THAT THE SHORT WAVE TIMING COULD BE
OFF, BUT ARCTIC THICKNESSES HAVE A WAY OF GENERATING FLURRIES AND
MAYBE EVEN SNOW SHOWERS. WE ADDED THE CHANCE OF FLURRIES AS A
STARTER. LOOKS LIKE LESS DECOUPLING CHANCES ON NEW YEARS EVE. NO
PCPN RELATED ISSUES, BUT IT WILL BE OVERALL COLDER.

A SUNNY, BUT BRISK AND COLD DAY FOR NEW YEARS DAY. THE LAKE
EFFECT TRAJECTORY IS PREDICTED TO REMAIN NORTH OF OUR CWA. A
BETTER RADIATING NIGHT IS POSSIBLE ON THURSDAY NIGHT WITH A SLIGHT
AIR MASS RECOVERY ON FRIDAY.

BECAUSE OF THE OVERALL SLOWER TIMING, WE REMOVED POPS FROM FRIDAY
NIGHT. WE ARE KEEPING THE FORECAST OF A ONE-TWO PUNCH OF THE
INITIAL LOW AND COLD FRONT PCPN ON SATURDAY WITH THE SECONDARY
SHEARING LOW PCPN POSSIBLE ON SUNDAY. THE GEFS MEMBERS ARE PRETTY
MUCH ALL CLUSTERED SIMILARLY TO THE OP GFS. THE CAN GEPS HAS ABOUT
THREE QUARTERS OF ITS MEMBERS SIMILAR TO THE GEFS AND A QUARTER
SIMILAR TO ITS OPERATIONAL AND ECMWF SOLUTION. THE ECMWF ENSEMBLE
MEAN DOES NOT HAVE MUCH OF A SECONDARY LOW SUNDAY AS IT OPENS UP
THE CLOSED SW CONUS LOW MUCH FASTER THAN THE OP. THERE IS A SWATH
OF DEEP PURPLE UNCERTAINTY ABOUT SFC PRESSURE OVER NEW ENGLAND
SUN EVE, NOT EXACTLY SMOKING ON THE WATER. OPERATIONALLY SEVEN
DAYS AWAY, THIS HAS BEEN MORE THE RULE THAN THE EXCEPTION THIS
COLD SEASON FOR ALL OF THE MODELS.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

TODAY...VFR CEILINGS. NORTH-NORTHWEST WINDS BECOMING NORTH-NORTHEAST
AT 5-10 KNOTS. SOME LIGHT RAIN EARLY THIS MORNING SOUTH OF KILG.

TONIGHT...VFR CEILINGS MAINLY AROUND 10000 FEET. NORTH-NORTHEAST
WINDS GENERALLY 4-8 KNOTS.

OUTLOOK...
TUESDAY...VFR CONDITIONS EXPECTED. GUSTY NORTH WINDS 20 TO 25
KNOTS. AIRPORTS IN DELMARVA SOUTH OF KILG AND IN NEW JERSEY SOUTH
OF KACY AND KMIV THERE IS A RISK OF MVFR CEILINGS AT TIMES.

TUESDAY NIGHT THROUGH FRIDAY...MOSTLY VFR CONDITIONS EXPECTED.
GUSTY WEST WINDS EXCEEDING 20 KNOTS POSSIBLE DURING THE DAY ON
BOTH WEDNESDAY AND THURSDAY.

&&

.MARINE...
OUR AREA WILL BE NORTH OF A STALLED FRONTAL BOUNDARY TODAY AND
TONIGHT. A WEAK SYSTEM IS TRACKING ALONG IT EARLY THIS MORNING AND
WILL SHIFT OFF THE DELMARVA COAST THROUGH THIS MORNING. THERE IS CAA
OCCURRING TODAY AND THAT WILL STRENGTHEN SOME BY LATE TODAY AND
TONIGHT. AS ANOTHER WEAK SYSTEM SLIDES BY TO OUR SOUTH LATER TONIGHT
AND HIGH PRESSURE BUILDS INTO THE GREAT LAKES, THE PRESSURE GRADIENT
WILL TIGHTEN ACROSS OUR AREA. THIS COMBINED WITH CAA WILL ALLOW FOR
BETTER MIXING. THIS WILL RESULT IN A NORTH-NORTHEAST WIND INCREASING
TONIGHT ESPECIALLY ACROSS THE SOUTHERN WATERS. IT DOES APPEAR TO
GENERALLY BE MARGINAL, HOWEVER WIND GUSTS LOOK TO NEAR ADVISORY
CRITERIA ACROSS THE SOUTHERN WATERS TOWARD 12Z TUESDAY. THEREFORE, A
SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE LOWER DELAWARE BAY AND
THE COASTAL WATERS SOUTH OF LITTLE EGG INLET STARTING AT 10Z TUESDAY.

OUTLOOK...
TUESDAY...WE HAVE THE SMALL CRAFT ADVISORY ONGOING FOR LOWER
DELAWARE BAY AND THE SOUTHERN ATLANTIC WATERS FOR A SURGE OF
AROUND 25 KT GUSTS OCCURRING AS THE LOW PRESSURE SYSTEM MOVES
FARTHER OFFSHORE AND INTENSIFIES. PEAK GUSTS SHOULD OCCUR MAINLY
DURING TUESDAY MORNING. UPPER DELAWARE BAY AND NORTHERN COASTAL
WATERS CONDITIONS ARE EXPECTED TO STAY BELOW SCA THRESHOLDS.

TUESDAY NIGHT AND WEDNESDAY...SUB SCA CONDITIONS EXPECTED. MAY
COME CLOSE LATE IN THE AFTERNOON WEDNESDAY.

WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WESTERLY WINDS WITH GUSTS
NEAR SMALL CRAFT ADVISORY CRITERIA ARE POSSIBLE, PRIMARILY ON THE
ATLANTIC COASTAL WATERS.

FRIDAY...SUB SCA CONDITIONS EXPECTED.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM TO 4 PM EST TUESDAY FOR ANZ431-
     452>455.

&&

$$
SYNOPSIS...GIGI/JOHNSON
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...GIGI
AVIATION...GIGI/GORSE/JOHNSON
MARINE...GIGI/GORSE/JOHNSON





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