Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 271915
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
215 PM EST SAT DEC 27 2014

.SYNOPSIS...
A HIGH PRESSURE SYSTEM CENTERED OVER THE CAROLINAS WILL DRIFT SLOWLY
OUT TO SEA TODAY. A COLD FRONT WILL CROSS THE AREA ON SUNDAY, THEN
STALL TO OUR SOUTH AS A LOW PRESSURE SYSTEM RIDES ALONG IT MONDAY
AND MONDAY NIGHT. A STRONG CANADIAN HIGH PRESSURE SYSTEM WILL REACH
THE NORTHERN PLAINS BY TUESDAY AND IS THEN EXPECTED TO GRADUALLY
BUILD SOUTH AND THEN EAST REACHING KANSAS ON WEDNESDAY AND THE
CAROLINAS ON FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
TRANQUIL NIGHT EXPECTED AS SURFACE RIDGING CONTINUES TO MOVE
OFFSHORE WITH US STILL UNDER ITS INFLUENCE FOR A BIT LONGER. LIGHT
SOUTHWESTERLY WINDS WILL CONTINUE TO USHER IN A SOMEWHAT MOISTER
AIRMASS, AHEAD OF AN APPROACHING COLD FRONT. SKIES WILL CONTINUE TO
THICKEN AND LOWER WITH TIME. THE POSITION OF THE FRONT LOOKS TO
BE JUST TO OUR WEST RIGHT AROUND SUNRISE SUNDAY MORNING...THIS IS
WHEN WE INCREASE POPS INTO THE LIKELY RANGE. THERMAL PROFILES SHOW
ALL AN LIQUID PTYPE FOR THE REGION AS SURFACE TEMPERATURES WILL
ONLY DROP INTO THE MID TO UPPER-30S IN A LOT OF PLACES. WE COULD
RADIATE A BIT MORE TOWARDS THE NEW JERSEY/PINE BARRENS, EVEN WITH
THE INCREASING CLOUD COVER EXPECTED...DEPENDING ON HOW FAST WE CAN
BECOME OVERCAST.

&&

.SHORT TERM /SUNDAY/...
COLD FRONT WILL WORK ITS WAY THROUGH THE REGION FROM LATE MORNING
THROUGH THE EVENING HOURS. HAVE INCREASE POPS TO CATEGORICAL FOR AT
LEAST THE SOUTHERN HALF OF THE CWA BY SUNDAY AFTERNOON. SOME WEAK
MID-LEVEL ENERGY SLIDES ALONG THE FRONT LATER TOMORROW AFTERNOON
WHICH COULD ULTIMATELY SLOW ITS DEPARTURE DOWN A BIT. A MAJORITY OF
THE GUIDANCE HAS US DRYING OUT FROM NORTHWEST TO SOUTHEAST BY LATE
SUNDAY EVENING, JUST AHEAD OF THE BETTER LOW-LEVEL CAA KICKING IN.
THERE COULD BE SOME RAIN/SNOW MIX ACROSS OUR NORTHWEST ZONES LATE IN
THE PERIOD, DEPENDING ON HOW FAST WE CAN COOL BELOW 850MB AND HOW
MUCH MOISTURE REMAINS. TEMPERATURES WILL BE ABOVE NORMAL ONCE AGAIN
THOUGH SEVERAL DEGREES COOLER THAN TODAY WITH THE AMOUNT OF CLOUD
COVER EXPECTED AND THE RAIN SHOWERS MOVING IN.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A LOWER CONFIDENCE LONG TERM FORECAST CONTINUES FOR THE WAVE ON THE
COLD FRONT AS WE KICKED THE PROBLEMATICAL PTYPE CAN FROM SUNDAY
NIGHT TO MONDAY NIGHT. OTHER THAN THE OPERATION ECMWF, THE MODELING
CONSENSUS IS COMING CLOSER TO OUR CWA BEING AFFECTED BY A WAVE OF
LOW PRESSURE FORMING ON THE CDFNT. THIS FRONT WILL COME THRU OUR
AREA ON SUNDAY. THERE ARE STILL MULTIPLE ISSUES OF STRENGTH,
TIMING AND THERMAL FIELDS. A FASTER PROGRESSING SYSTEM LIKE THE
UKMET HAS IS WARMER AND RAINIER, SLOWER PROGRESSING SYSTEM LIKE
THE CAN GGEM HAS IT SNOWIER. THE WRF-NMMB IS BOTH SLOWER AND
WARMER WHICH LOOKS LIKE ITS USUAL MODEL BIAS OF PLACING LOWS TOO
DEEP IN THE COLD AIR. ADD TO THE MIX THE OP ECMWF STILL HAS NO
SECOND SYSTEM AT ALL.

THE ENSEMBLING CLUSTERING PUTS THE OP GFS IN THE MIDDLE OF THE
ROAD. ABOUT A QUARTER OF THE MEMBERS ARE WETTER FARTHER TO THE
NORTHWEST WHILE A QUARTER OF THE MEMBERS ARE SIMILAR TO THE ECMWF
SOLUTION. CONVERSELY MOST OF THE 20 CAN GGEM ENSEMBLE MEMBERS ARE
MORE MUTED THAN THE OP OR CONTROL, ONLY ABOUT ONE OR TWO ARE MORE
BULLISH. THE "NOISE` IN THE ECMWF ENSEMBLE MEAN IS STILL NORTHWEST
OF THE OP. BUT NOT AS MUCH AS THE 12Z RUN WAS.

PART OF THE ISSUE REMAINS THE POSSIBILITY OF CONVECTION IN THE
NORTHWEST GULF. ALSO WHILE THE LOW IS HEADING TOWARD A CONFLUENT
FLOW, NOT SURE THE SYSTEM WILL GET AS SUPPRESSED AS THE OP ECMWF.
FOR THIS FCST PACKAGE WE ARE CLOSEST TO THE PGFS WHICH HAS A
SLIGHTLY SLOWER AND LESS ROBUST SOLUTION THAN THE OP GFS. WE HAVE
GAINED ANOTHER DAY TO GET A BETTER HANDLE, WHICH WE HOPE
SUBSEQUENT SOUNDING RUNS WILL DO.

THE SOUNDING INITIALIZATION IN THE SOUTHWEST LOOKED GOOD. THE TROF
ITSELF LOOKS BAGGIER, BUT THE INITIAL ENERGY SURGE IS HEADING TO THE
GREAT LAKES. ITS THE SHORT WAVES ALONG THE CALIFORNIA COAST THAT
WILL INITIATE THE SECONDARY LOW. THERMALLY THE GFS LOOKED BETTER
AT BOTH 850MB AND 925MB. ANOTHER REASON MONDAY NIGHT WE WERE NOT
AS WARM AS THE WRF-NMMB.

BETTER MODELING CONSENSUS ON SUNDAY AND SUNDAY NIGHT. THE INITIAL
SURGE OF MOISTURE IS EXITING FASTER AND LESS OF A PTYPE ISSUE IS
EXPECTED ON SUNDAY NIGHT. IN FACT NORTHWEST OF THE FALL LINE/I95
CORRIDOR IT LOOKS LIKE A RACE FOR WHICH WILL HAPPEN FIRST, PCPN END
OR A CHANGE TO SNOW JUST BEFORE ENDING. WHERE PCPN SHOULD LINGER
DEEPER INTO THE NIGHT, THERMAL FIELDS SUPPORT JUST RAIN SOUTH.
BACKING UP TO SUNDAY DAY, THERE IS DECENT MODEL CONSENSUS OF A SHORT
WAVE MOVING THROUGH THE SOUTHERN HALF OF OUR CWA DURING THE
AFTERNOON AND WE UPPED POPS TO LIKELY SOUTH. LIKELY POPS WERE
CARRIED INTO THE EVENING SOUTH AS THE PCPN TAKES MORE OF AN ANAFRONT
LOOK TO IT.

A PRECIPITATION BREAK IS EXPECTED ON MONDAY, OUR BREAK TIMING IS
CENTERED AROUND THE MIDDLE OF THE DAY. THERE MIGHT BE SOME
SUNSHINE NORTH, LESS CONFIDENT ABOUT SEEING THE SUN SOUTH. ONCE
THE BREAK ENSUES, DRIER AIR WILL START WORKING ITS WAY SOUTHWARD.
THIS WILL MAKE IT EASIER FOR THE NORTHERN PART OF THE PCPN TO
TRANSITION TO SNOW AFTER BOUNDARY LAYER TEMPERATURES FALL.

FOR NOW WE ARE CENTERING THE BEST CHANCE FOR PCPN ASSOCIATED WITH
THE FRONT TO OCCUR ON MONDAY NIGHT. THERE ARE MANY MOVING PARTS TO
THIS FORECAST, BUT SUFFICE THAT THE POSSIBILITY FOR ACCUMULATING
SNOW WHICH WAS NORTHWEST ON SUNDAY NIGHT HAS SHIFTED TO AROUND THE
DELAWARE VALLEY CORRIDOR ON MONDAY NIGHT. BASICALLY A TIGHTENING
FGEN BAND COUPLED WITH A JET STREAK ALOFT IS THE TRIGGER FOR PCPN IN
OUR AREA. ISENTROPIC LIFT IS NOT THERE AND NEITHER IS A TROWAL.
THE PREDICTED MOISTURE TRANSPORT AT 290K IS ABOUT A FOURTH OF WHAT
IS HEADING OUR WAY ON SUNDAY WHICH MAY STAND AS A GOOD PCPN FCST PROXY.
SOME OF THE MORE AGGRESSIVE MODELS BRING A COUPLE OF INCHES OF
SNOW TO OUR REGION. WE SHIFTED OUR HWO MENTION TO THE DELAWARE
VALLEY AND IF THERE WAS TO BE AN IMPACT WOULD BE WITH THE TUESDAY
MORNING COMMUTE,

WE LINGER A CHANCE OF MAINLY SNOW SOUTHEAST ON TUESDAY MORNING, MORE
SO FOR TIMING INCONSISTENCIES AND NOT THAT IT WOULD BE THAT A
PROTRACTED A PCPN EVENT. REGARDLESS OF THE PTYPE OUTCOME INTO TUESDAY
MORNING, THE REST OF THE WEEK WILL FEATURE COLDER WEATHER. THE
VORT MAX ON WEDNESDAY LOOKS MORE CHANNELIZED THAN WAS PREDICTED
YESTERDAY, SO A COLD, BUT DRY END OF THE LONG TERM WAS CONTINUED.

&&

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

TODAY - TONIGHT...VFR. LIGHT SOUTHWESTERLY WINDS, LESS THAN 8 KNOTS,
WILL CONTINUE THROUGH THIS EVENING BEFORE DECREASING A BIT AND
BACKING MORE TOWARDS THE WEST. ALTOCU DECK EXPECTED TO ARRIVE LATER
THIS EVENING AND LOWER THROUGHOUT THE OVERNIGHT HOURS. CONFIDENCE:
HIGH.

SUNDAY...MOSTLY VFR, DECREASING TO MVFR LATE IN THIS CYCLE. COLD
FRONT WILL SLOWLY APPROACH FROM THE WEST-NORTHWEST BY SUNDAY MORNING
TOUCHING OFF SOME RAIN SHOWERS. CONDITIONS SHOULD START TO
DETERIORATE INTO THE MVFR RANGE AS THE SHOWERS MARCH TOWARDS THE
EAST-SOUTHEAST. TIMING OF THE SHOWERS AND MVFR ONSET COULD VARY BY A
COUPLE HOURS SOONER/LATER. CONFIDENCE: MEDIU

OUTLOOK...
SUNDAY NIGHT...MVFR, POSSIBLY IFR, CONDITIONS POSSIBLE AT TIMES
AS A COLD FRONT MOVES THROUGH THE REGION WITH SHOWERS.

MONDAY AND MONDAY NIGHT...LOW CONFIDENCE. A SECOND WAVE OF
PRECIPITATION COULD BRING MVFR TO IFR CONDITIONS BACK INTO THE
REGION. MOST LIKELY TO OCCUR AT SOUTHERN AIRPORTS AND TERMINALS.
SOME PRECIPITATION COULD FALL AS SNOW.

TUESDAY...VFR NORTH, BECOMING VFR SOUTH.

TUESDAY NIGHT AND WEDNESDAY...VFR.

&&

.MARINE...
TODAY - SUNDAY...SUB-SCA CONDITIONS EXPECTED. SEAS WILL CONTINUE
AROUND 3 FEET THROUGH LATE THIS EVENING BEFORE AN INCREASE TO AROUND
4 FEET IS POSSIBLE...BETTER FARTHER NORTH. WINDS WILL REMAIN
RELATIVELY LIGHT OUT OF THE SOUTH-SOUTHWEST AROUND 10 TO MAYBE 15
KNOTS, THOUGH GUSTS SHOULD BE KEPT BELOW 20 KNOTS. WINDS BACK TOWARDS
THE WEST LATER TOMORROW EVENING AS A SURFACE COLD FRONT MOVES
THROUGH.

OUTLOOK...
SUNDAY MORNING...A SLIGHTLY STRONGER SOUTHWEST FLOW PRECEDING A COLD
FRONT WILL BRING WIND GUSTS CLOSER TO SMALL CRAFT ADVISORY CRITERIA
ON THE OCEAN.

SUNDAY AFTERNOON AND NIGHT...SUB SMALL CRAFT ADVISORY CONDITIONS
EXPECTED.

MONDAY THROUGH TUESDAY...THERE IS A CHANCE FOR SEAS TO REACH SMALL
CRAFT ADVISORY CRITERIA MONDAY NIGHT AND TUESDAY. SUB SMALL CRAFT
ADVISORY WINDS ARE STILL PREDICTED. LOWER CONFIDENCE AS A WAVE OF
LOW PRESSURE WILL FORM SOUTH OF THE AREA WATERS ON THE PREVIOUSLY
MENTIONED FRONT. ITS POSSIBLE THAT WIND RELATED SMALL CRAFT
ADVISORY CONDITIONS MIGHT ALSO OCCUR IF THIS LOW INTENSIFIES
FASTER THAN WE ARE CURRENTLY FORECASTING.

TUESDAY NIGHT THROUGH WEDNESDAY...SUB SMALL CRAFT ADVISORY
CONDITIONS EXPECTED.

&&

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

&&

$$
SYNOPSIS...GIGI/MIKETTA
NEAR TERM...HEAVENER
SHORT TERM...HEAVENER
LONG TERM...GIGI
AVIATION...GIGI/HEAVENER
MARINE...GIGI/HEAVENER






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