Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 130153
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
953 PM EDT SAT APR 12 2014

.SYNOPSIS...
A WARM FRONT WILL LIFT NORTH INTO THE REGION TONIGHT. TOMORROW, A
HIGH CENTERED IN THE NORTH ATLANTIC WILL BUILD, BECOMING THE
PREDOMINANT FEATURE FOR OUR WEATHER THROUGH MONDAY. LATE TUESDAY, A
STRONG COLD FRONT IS EXPECTED TO PUSH THROUGH THE REGION. HIGH
PRESSURE IS EXPECTED TO BUILD AND REMAIN ENTRENCHED OVER OUR REGION
THROUGH THE LATER HALF OF THE WORK WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
NO BIG CHANGES TO THE FORECAST SO FAR FOR THE OVERNIGHT PERIOD;
MAINLY HOURLY GRID ADJUSTMENTS INTO THE OVERNIGHT HOURS. HIGH
PRESSURE WILL CONTINUE TO SLIDE OFFSHORE TONIGHT WHILE A WARM
FRONT TO OUR SOUTH PUSHES NORTHWARD. AN INCREASE IN ATLANTIC
MOISTURE, ON THE NOSE OF A SOUTHEAST SURFACE FLOW, SHOULD ALLOW
FOR AREAS OF STRATUS TO DEVELOP BY EARLY SUNDAY MORNING AS A LOW-
LEVEL INVERSION LOWERS OVERNIGHT. PATCHY FOG, MAINLY IN THE
SHELTERED SPOTS AND RIVER VALLEYS, COULD ALSO FORM, BUT THINKING
TONIGHT IS MORE OF A STRATUS EVENT. THAT BEING SAID, THE MAVMOS,
WHICH HAS VERY LITTLE IN THE WAY OF LOWER CLOUDS, SEEMED A BIT TOO
COLD SO SIDED WITH THE WARMER MET NUMBERS. THIS SHOULD YIELD WELL
ABOVE OVERNIGHT LOWS AROUND 50F.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
THE WARM FRONT WILL SLIDE THROUGH THE REGION PLACING US IN THE WARM
SECTOR LATE TOMORROW MORNING. STRENGTHENING SOUTHERLY FLOW, COMBINED
WITH DAYTIME HEATING, SHOULD ALLOW THE STRATUS TO LIFT AND BURN-OFF.
THERE SHOULD BE A FAIR AMOUNT OF SUNSHINE WITHIN THE WARM SECTOR,
OTHER THAN FAIR WEATHER CUMULUS, AS LOW-LEVEL THERMAL FIELDS
INCREASE QUITE NICELY. A CURSORY LOOK AT THE 850 AND 925MB
TEMPERATURES SHOWED THAT BOTH THE NAM AND GFS WERE A TAD TOO COLD
JUST DOWNSTREAM, WHILE THE NAM WAS A BIT WARMER AND BETTER THAN THE
GFS. SEEING AS THOUGH WE MADE A PRETTY GOOD RUN AT 80F ON FRIDAY IT
LOOKS WE MAY HAVE ANOTHER SHOT TOMORROW BUT WITH THE WINDS BEING
MORE SOUTHERLY, WITHOUT MUCH OF A WEST COMPONENT DID NOT GO THAT
ROBUST BUT DID GO A COUPLE DEGREES ABOVE GUIDANCE.

SEA AND BAY BREEZES SHOULD NOT BE MUCH AN ISSUE BEYOND THE IMMEDIATE
SHORE POINTS TOMORROW GIVEN THE STRONGER LOW-LEVEL FLOW IN PLACE.
WINDS SHOULD BECOME GUSTY BY THE MID-AFTERNOON HOURS AS THE LAPSE
RATES INCREASE AND CONVECTIVE TEMPERATURES ARE CLOSE TO BEING MET.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
HE MAIN CONCERN THROUGH THIS PERIOD IS THE HEAVY RAIN POTENTIAL
MONDAY INTO TUESDAY AHEAD OF THE NEXT COLD FRONT.

WE REMAIN IN THE WARM SECTOR ON MONDAY, AND COULD SEE A FEW SHOWERS
WITH SOME LEADING UPPER LEVEL SHORT WAVE TROUGHS.

MODEL PRECIPITABLE WATER VALUES ARE AROUND 1.25 TO 1.50 DURING THE
OVERNIGHT HOURS MONDAY NIGHT THROUGH MID DAY TUESDAY. WHILE NOT
UNPRECEDENTED, THESE VALUES WOULD BE HIGHER THAN THE 75TH PERCENTILE
FOR PWATS THIS TIME OF YEAR. IN ADDITION, ON TUESDAY MORNING
ESPECIALLY, THE 0 TO 6 KM MEAN FLOW IS NEARLY PARALLEL TO THE
APPROACHING COLD FRONT. THEREFORE IF THE COLD FRONT IS A SLOW MOVER
(NOT UNCOMMON FOR A LATE SPRING COLD FRONT), SOME LOCATIONS COULD
SEE SEVERAL HOURS OF TRAINING STORMS. THE MEAN RH IS ALSO QUITE HIGH
THROUGH THIS PERIOD (>90 PERCENT).

ON THE FLIP SIDE HOWEVER, THERE ARE LIMITING FACTORS FOR THE HEAVY
RAIN POTENTIAL. FIRST, THE WARM CLOUD LAYER AT ITS PEAK IS ABOUT
9000 FT DEEP, WHICH IS MARGINAL FOR AN ENHANCED HEAVY RAIN THREAT.
THE LOW LEVEL JET REMAINS A SOUTHWESTERLY JET THROUGH THE PERIOD,
WITH LITTLE TO NO ON SHORE FLOW, LIMITING MOISTURE TRANSPORT DURING
THE PRECIPITATION EVENT. THE MEAN FLOW IS ALSO RATHER FAST (40 TO
50KT) FOR AN ENHANCED HEAVY RAIN THREAT, BUT THIS COULD BE NEGATED
BY STORM TRAINING. FINALLY, AS MENTIONED BY THE PREVIOUS SHIFT, THE
MODELS HAVE RECENTLY TENDED TO BE A BIT TOO HIGH BOTH WITH QPF AND
FORECAST PWAT VALUES.

FOR NOW, AGREE WITH THE PREVIOUS SHIFT THAT THE POTENTIAL IS THERE
FOR MODERATE TO HEAVY RAIN, BUT AT THIS TIME THE THREAT FOR FLOODING
IS RATHER LOW. WHAT WOULD MAKE THIS THREAT HIGHER IS IF THE FRONT
SLOWS OR EVEN STALLS (THE ECMWF IS SHOWING A SLOWER FRONT) OR IF AN
AREA OF TRAINING CELLS DEVELOPS OVER A MORE URBANIZED LOCATION, LIKE
THE I95 CORRIDOR.

BEHIND THE FRONT, THE FORECAST PICTURE BECOMES A BIT MORE MUDDLED.
THE GFS SHOWS THE FRONT PUSHING ALL THE WAY THROUGH THE REGION BY
TUESDAY EVENING, WHILE THE ECMWF SLOWS AND EVEN STALLS THE FRONT OFF
THE COAST. THIS HAS IMPLICATIONS FOR OUR REGION IN TWO WAYS. FIRST,
WITH HIGHS ON TUESDAY; FOR NOW HAVE GONE WITH A MIDDLE OF THE ROAD
SOLUTION OF HIGHS IN THE 50S AND 60S BEING REACHED EARLY IN THE DAY.
IF THE GFS SOLUTION IS TRUE, HIGHS COULD ONLY BE A BIT LOWER. THE
OTHER IMPLICATION RELATES TO PRECIPITATION BEHIND THE FRONT. THE
ECMWF SHOWS A BROAD AREA OF PRECIPITATION LASTING 24 TO 36 HOURS
BEHIND THE FRONT, PRIMARILY FOR LOCATIONS NEARER THE SHORE. WITH HOW
COLD THE AIR IS EXPECTED TO BE BEHIND THE FRONT, THIS COULD MEAN A
WINTRY MIX FOR HIGHER ELEVATIONS IN THE POCONOS. HOWEVER, GIVEN THE
CONTINENTAL SOURCE REGION OF THE POLAR AIR MASS, EXPECT CONSIDERABLE
DRY AIR ADVECTION BEHIND THE FRONT, AND THUS HAVE TRENDED THE
FORECAST CLOSER TO THE GFS BEHIND THE FRONT.

ONCE THE FRONT FULLY CLEARS THE REGION, EXPECT A SURFACE HIGH TO
BUILD, AND THEN TRANSITION TO A POSITIVELY TILTED RIDGE BY FRIDAY.

THE NEXT LOW PRESSURE SYSTEM COULD AFFECT THE REGION AS EARLY AS
SATURDAY OR SUNDAY, BUT THERE ARE CONSIDERABLE DIFFERENCES AMONG
THE LONG RANGE MODELS IN THE TRACK OF THIS SYSTEM.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

TONIGHT...VFR TO START THEN TRENDING TOWARDS THE MVFR/IFR RANGE BY
OVERNIGHT INTO THE PRE-DAWN HOURS SUNDAY. SOUTHERLY WINDS WILL
SLIGHTLY VEER TOWARDS THE SOUTHEAST TONIGHT ALLOWING MORE MOISTURE
TO MOVE INTO THE REGION. A WARM FRONT MOVING INTO THE REGION FROM
THE SOUTH WILL ALLOW A LOW- LEVEL TEMPERATURE INVERSION TO SETUP
BY TOMORROW MORNING POOLING MOISTURE NEAR THE SURFACE. THIS COULD
PROVIDE AREAS OF STRATUS AND PATCHY FOG THROUGH THE LATE MORNING
HOURS. WE MAY NOT BE LOW ENOUGH, BUT CONFIDENCE ON IFR CONDITIONS
IS NOT EXTREMELY HIGH, SO KEPT ONLY MVFR CIGS/VSBYS AT THIS TIME.

TOMORROW...STRATUS/FOG LIFT AND BURN OFF BY MID-LATE MORNING GIVING
WAY TO POCKETS OF FAIR WEATHER CUMULUS. WINDS TURN TOWARDS THE
SOUTH-SOUTHWEST BEHIND THE WARM FRONT PASSAGE AND STRENGTHEN
BECOMING GUSTY, AROUND 20 KNOTS, BY THE AFTERNOON HOURS.

OUTLOOK...

MONDAY...MOSTLY VFR. MVFR CONDITIONS IN -SHRA POSSIBLE LATE MONDAY
AFTERNOON.

MONDAY NIGHT AND TUESDAY...DETERIORATING CONDITIONS TO WIDESPREAD
MVFR AND POSSIBLY WIDESPREAD IFR. RAIN COULD BE HEAVY AT TIMES, AND
ISOLATED THUNDERSTORMS ARE POSSIBLE DURING THE DAY TUESDAY.

WEDNESDAY...CONDITIONS IMPROVING TO VFR FROM WEST TO EAST.

&&

.MARINE...
WARM FRONT WILL LIFT THROUGH THE REGION LATE TONIGHT TURNING THE
WINDS FROM SOUTHEAST TO SOUTH AND STRENGTHENING THEM. SEAS AND WINDS
SHOULD INCREASE ENOUGH TOWARDS THE AFTERNOON HOURS SUNDAY TO
REACH SMALL CRAFT CRITERIA THROUGH THE REMAINDER OF THE DAY.

OUTLOOK...
MONDAY AND TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY TO
CONTINUE.

WEDNESDAY...WINDS DECREASING BELOW SCA CONDITIONS BY MID DAY.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 6 AM EDT MONDAY FOR
     ANZ450>455.

&&

$$
SYNOPSIS...JOHNSON
NEAR TERM...HEAVENER/ROBERTSON
SHORT TERM...HEAVENER
LONG TERM...JOHNSON
AVIATION...HEAVENER/JOHNSON
MARINE...HEAVENER/JOHNSON



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