Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 241338
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
938 AM EDT FRI APR 24 2015

.SYNOPSIS...
A HIGH PRESSURE SYSTEM OVER THE WESTERN GREAT LAKES WILL BUILD
SOUTHEAST AND REACH THE FORECAST AREA ON SATURDAY. A LOW
PRESSURE SYSTEM EMERGING FROM THE CENTRAL ROCKIES WILL MOVE
EAST THROUGH THE TENNESSEE VALLEY SATURDAY NIGHT AND OFF THE
CAROLINA COAST ON SUNDAY. AN UPPER LEVEL DISTURBANCE WILL THEN
OVER THE NORTHEAST ON MONDAY. A WEAK HIGH PRESSURE SYSTEM
THEN BUILDS OVER THE AREA ON TUESDAY. A LOW PRESSURE SYSTEM WILL
THEN MOVE ACROSS THE NORTHERN GULF OF MEXICO ON WEDNESDAY AND IS
PREDICTED TO MOVE OFF THE SOUTHERN MIDDLE ATLANTIC STATES WATERS
ON THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
930 AM UPDATE...NO MAJOR CHANGES ASIDE FROM INCREASING WIND
SPEEDS THROUGH THE DAY. MODELS APPEAR TO BE UNDERDONE ON WIND
SPEEDS IN THE LOW LEVELS AS COMPARED TO NEARBY 12Z SOUNDINGS.
EVEN WITH THE INCREASED WINDS, SHOULD STAY BELOW WIND ADVISORY
CRITERIA AS WINDS DON/T REACH 40KT UNTIL 4500 TO 5000 FT AGL.

PREVIOUS NEAR TERM DISCUSSION...LOW PRESSURE WILL REMAIN NEARLY
STATIONARY NEAR THE EASTERN MAINE/CANADA BORDER TODAY, WHILE HIGH
PRESSURE BUILDS TO OUR WEST. THIS WILL KEEP A TIGHT PRESSURE
GRADIENT ACROSS THE AREA THROUGH TODAY, LEADING TO BREEZY
CONDITIONS. WITH CONTINUED GOOD MIXING TODAY, WE WILL BE ABLE TO
MIX DOWN STRONGER WINDS FROM THE LOWEST 2,000-3,000 FEET, LEADING
TO GUSTS AROUND 25-35 MPH THROUGH THE DAY.

A DIFFUSE SURFACE TROUGH IS FORECAST TO CROSS THE AREA TODAY, WHILE
THE CHANNELIZED VORTICITY ALOFT SLIDES ACROSS THE AREA. WITH LIMITED
MOISTURE, PW`S LESS THAN ONE-QUARTER OF AN INCH AND LOW RH`S IN THE
LOW LEVELS, WE DO NOT EXPECT ANY PRECIPITATION. THERE COULD BE SOME
FLURRIES/SPRINKLES ACROSS THE WESTERN AREAS THIS MORNING, BUT DON`T
THINK THERE IS ENOUGH COVERAGE TO PUT IN FORECAST. CLOUD COVER WILL
CONTINUE THIS MORNING, BUT CLOUDS WILL BEGIN TO SCATTER OUT AND
DISSIPATE THROUGH THE DAY WITH SUNSHINE RETURNING BY THE AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
THE AREA OF LOW PRESSURE REMAINS TO OUR NORTHEAST TONIGHT, BUT
BEGINS TO MOVE EASTWARD SOME, WHILE THE HIGH PRESSURE TO OUR WEST
BEGINS TO WEAKEN. THE PRESSURE GRADIENT SHOULD BEGIN TO WEAKEN SOME,
BUT WE WILL LIKELY CONTINUE TO HAVE A LIGHT BREEZE OVERNIGHT. SKIES
ARE EXPECTED TO CLEAR OUT OVERNIGHT, AND WE`LL CONTINUE TO HAVE COLD
ADVECTION THROUGH THE NIGHT. TEMPERATURES SHOULD BE ABLE TO FALL
MORE TONIGHT THAN THEY DID LAST NIGHT. WE WILL CONTINUE WITH THE
FREEZE WATCH WHERE WE EXPECT TEMPERATURES TO REACH 32 OR LOWER, AND
KEEP MENTION OF FROST IN THE FORECAST FOR MUCH OF THE AREA AS WELL.
WE WILL LET LATER SHIFTS LOOK AT FUTURE GUIDANCE TO DETERMINE IF AND
WHERE WE WOULD NEED FREEZE WARNINGS/FROST ADVISORY OVERNIGHT.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
A BLOCKY WEATHER PATTERN WITH A POSSIBLE NOR`EASTER AT THE END
OF THE LONG TERM CONTINUES IN THIS LONG TERM PERIOD. WHILE
MODELING CONSENSUS REMAINS CONSISTENT ABOUT A RELATIVELY BENIGN
PASSAGE OF A SFC LOW OFF THE CAROLINA COAST ON SUNDAY, THERE
CONTINUES TO BE VIOLENT MODEL SOLUTION SWINGS WITH THE END OF THE
LONG TERM COASTAL SYSTEM.

THE ECMWF HAS GONE FROM A ROBUST NOR`EASTER TO FUGETABOUTIT TO
ROBUST NOR`EASTER IN THREE SUCCESSIVE 00Z SOUNDING MODEL RUNS.
INDICATIONS OF A DOUBLE TELECONNECTION SWITCH FAVORS A ROBUST EAST
COAST SOLUTION. THE QUESTION WILL BE DOWN THE ROAD HOW ROBUST FOR
US. WHILE LAST NIGHT`S OP ECMWF RUN WAS REFUTED BY ITS ENSEMBLE
BRETHREN, THIS ONE WE SUSPECT WILL GET SOME ENSEMBLE SUPPORT. THE
OTHER MEDIUM RANGE MODELS ALSO HAVE A LOW PRESSURE SYSTEM GOING
OFF THE EAST COAST, BUT ARE NOT AS STRONG AS THE ECMWF. BOTH THE
OP GFS AND CAN GGEM RUNS WERE CLOSE TO THE MIDDLE OF THE PACK
SOLUTIONS OF THEIR ENSEMBLE MEMBERS. ONCE AGAIN MODELING
DIFFERENCES HAVE MORE TO DO WITH THE UPSTREAM WRN NOAM RIDGING
COMING FROM THE BERING SEA CLOSED LOW AND NOT AS MUCH WITH THE
CLOSED LOW IN THE WESTERN ATLANTIC. STAY TUNED.

ITS A SIMILAR INITIALIZATION SCHEME TONIGHT WITH THE GFS BETTER AT
500MB WEST AND THE WRF/NAM BETTER EAST. ALSO THE WRF WAS SLIGHTLY
BETTER AT 850MB AND 925MB WITH THE GFS HAVING MORE NEGATIVE (COLD
BIAS) INITIALIZATION ERRORS. THE DP/DT WITH THE SAT NGT SYSTEM WITH
THE GFS IS DEFINITELY MORE SUBDUED WITH THE UKMET NOW ASSUMING THE
HONOR OF THE WETTEST/NORTHERNMOST SOLUTION. THE DP/DT IS ALSO
BLOCKIER SUGGESTING THAT OUR CURRENT CLOSED LOW SHOULD NOT GET
OUT OF THE WAY (THUS A MORE SUPPRESSED TRACK WITH LOW NUMBER ONE).

LIKE LAST NIGHT WE USED THE GFS DIAG TO ADJUST THE FCST AND THIS
COMES CLOSEST TO THE CAN GGEM OUTPUT IN OUR CWA. SREF ENSEMBLE
MEAN SUGGESTS THE OP WRF/NAM IS TOO SUPPRESSED.

EXCEPT FOR THE UKMET, ALL OTHER MODELS ARE DRY FOR SATURDAY DAY.
THE 250MB JET POSN PREDICTED BY THE UKMET LOOKS TO BE IN MODE
CONFLICT WITH PCPN ARRIVING. SO POPS WERE KEPT OUT OF OUR CWA THRU
SATURDAY AFTERNOON. THE POSN OF THE JET WHILE TOO CLOSE NORMALLY FOR
PCPN COULD HELP GENERATE THICKER CIRRUS ACROSS OUR CWA AS CLOUDS
OVERALL INCREASE. GREATER CONFIDENCE ABOUT MAX TEMPS BEING REACHED
NORTHEAST THAN SOUTHWEST. WITH THE SFC HIGH IN CLOSE PROXIMITY, WINDS
OVERALL WILL BE LIGHTER.

NOT MUCH OF A CHANGE TO POPS FOR SATURDAY NIGHT WITH THE CUT-OFF
RIGHT AROUND THE LATITUDE OF PHL AND THE ACY EXPRESSWAY. THE LIKELY
POPS IN DELMARVA WERE DETERMINED BY WHERE THE GFS HAS PREDICTED
LLVL THETA E CONVERGENCE, MID LEVEL WAA AND WEAK 300K ISENTROPIC
LIFT. THE DEEPER PREDICTED QVEC CONVERGENCE CUT-OFF HAS PHL NOW ON
THE NORTHERN EDGE (WAS THRUT OUR CWA LAST NIGHT). WOULD EXPECT
CLOUDS TO KEEP MIN TEMPS UP VS THE MUCH CHILLIER NIGHT TONIGHT.

AS THE SURFACE LOW MOVES EASTWARD IN THE TENNESSEE VALLEY A SECONDARY
IS PREDICTED TO FORM EAST OF NORTH CAROLINA AND BECOME "THE LOW".
SOME REMNANT PCPN FROM THE PRIMARY LOW COULD LINGER IN DELMARVA
ON SUNDAY. WE EDGED POPS SOUTHWARD AND LOWER AS THE DAY PROGRESSES.
MENTION IS IN DELMARVA ONLY. FARTHER NORTH THE CONVECTIVE TEMP IS
PREDICTED TO BE REACHED, SO PARTIAL SUNSHINE WILL SUFFICE. WE ARE
ASSUMING THE GFS FAST BIAS IS IN FORCE WITH THE APPROACHING SHORT
WAVE TO THE NORTH, SO NO POPS. MAX TEMPS BASED ON PREDICTED 925MB
TEMPS. ONCE AGAIN BETTER CONFIDENCE NORTH THAN SOUTH.

WE KEPT SUNDAY NIGHT DRY, BANKING ON THE LACK OF DAYTIME HEATING WILL
NEGATE SHOWERS FROM DEVELOPING. BUT ON MONDAY WITH THE COLD POCKET
STILL CLOSE TO OUR CWA AND CONVECTIVE TEMPS WITHIN REACH, WE KEPT
IN THE CHANCE FOR SHOWERS. AN INCREASING GRADIENT FROM THE
OFFSHORE LOW SHOULD ALSO MAKE IT BREEZIER.

WITH WEAK HIGH PRESSURE BUILDING INTO OUR CWA, WE KEEP TUESDAY
THROUGH WEDNESDAY DAY DRY. THEN WE ARE CLOSE TO WPC GUIDANCE FOR
WEDNESDAY NIGHT AND THURSDAY. THIS COASTAL SYSTEM HAS THE
POTENTIAL TO HAVE AN IMPACT ON OUR CWA, PENDING ITS FINAL TRACK
AND INTENSIFICATION RATE. BUT THE FACT THAT BOTH THE PNA AND NAO
WILL BE IN THE CORRECT LOADING POSN PRIOR TO THIS SYSTEM DOES ADD
HIGHER CONFIDENCE OF IT OCCURRING. OF COURSE IF THE WRN ATLC
CLOSED LOW REMAINS TOO CLOSE TO THE NOAM COAST, THIS NEXT SYSTEM
TOO MAY NOT BE ABLE TO MAKE A SHARP TURN UP THE EAST COAST.

&&

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

VFR CONDITIONS WILL PREVAIL ACROSS THE TAF SITES THROUGH THE PERIOD.
CLOUD COVER THIS MORNING WILL BEGIN TO SCATTER OUT AND DISSIPATE
THROUGH THE DAY WITH MOSTLY CLEAR SKIES RETURNING BY THIS AFTERNOON.

WINDS WILL BE THE MAIN CONCERN AGAIN TODAY AS WINDS GUSTS WILL ONCE
AGAIN GUST MID TO UPPER 20 KNOT RANGE AT TIMES TODAY. THE GUSTS
SHOULD DROP OFF AFTER SUNSET AND OVERNIGHT, ALTHOUGH A STEADY BREEZE
SHOULD REMAIN FOR MOST AREAS.

OUTLOOK...
SATURDAY...MAINLY VFR.

SATURDAY NIGHT...MAINLY VFR CONDITIONS NORTHERN AIRPORTS AND
TERMINALS. SOME RAIN AND SUB-VFR CONDITIONS ARE POSSIBLE,
MAINLY SOUTH OF A KILG/KACY LINE.

SUNDAY AND SUNDAY NIGHT...BECOMING VFR DELMARVA AIRPORTS SUNDAY DAY
AND MAINLY VFR REMAINING AIRPORTS AND TERMINALS.

MONDAY...MAINLY VFR WITH SOME GUSTY NORTH TO NORTHWEST WINDS. SOME
ISOLATED SHOWERS OCCURRING.

MONDAY NIGHT AND TUESDAY...MAINLY VFR WITH LESS OF A WIND IMPACT,

&&

.MARINE...
WINDS ON THE BAY WHICH WERE GUSTING NEAR GALE CONDITIONS EARLY
THIS MORNING HAD BEEN ON A DOWNWARD TREND BUT OVER THE LAST HALF
HOUR HAVE STARTED TRENDING UPWARD AGAIN. THUS...ISSUED A GALE
WARNING ON THE BAY THROUGH 5 PM EDT. THE SMALL CRAFT ADVISORY
REMAINS IN EFFECT FOR TODAY AND TONIGHT ON THE OCEAN AS WINDS
WILL REMAIN ELEVATED WITH THE PRESSURE GRADIENT REMAINING ACROSS
THE AREA AND SOME WINDS FROM ALOFT MIXING DOWN TO THE SURFACE.
WITH THE NORTHWEST FLOW, SEAS ARE NOT EXPECTED TO BUILD
SIGNIFICANTLY AND SHOULD BE AROUND 3-6 FEET.

OUTLOOK...
SATURDAY THROUGH SUNDAY...SUB SMALL CRAFT ADVISORY CONDITIONS
EXPECTED. THE LOW PRESSURE SYSTEM SHOULD PASS TOO FAR TO THE SOUTH
TO GENERATE HIGHER SEAS OR WINDS. LOWEST CONFIDENCE ON DELAWARE
OCEAN WATERS.

SUNDAY NIGHT THROUGH MONDAY...NEAR SCA CRITERIA AS THE GRADIENT
TIGHTENS BETWEEN THE OFFSHORE LOW AND APPROACHING HIGH PRESSURE
SYSTEM.

MONDAY NIGHT AND TUESDAY...SUB SMALL CRAFT ADVISORY CONDITIONS
EXPECTED.

&&

.FIRE WEATHER...
DRY AND GUSTY CONDITIONS ARE EXPECTED TODAY WITH RH VALUES EXPECTED
TO DIP INTO THE LOW/MID 20S AND WINDS GUSTING AROUND 25-35 MPH.
THE LIMITING FACTOR REMAINS HOW MOIST THE FUELS ARE. DRYING WAS
LIMITED YESTERDAY WITH THE CLOUDY AND COOL CONDITIONS. THEREFORE,
AFTER COORDINATION WITH STATE PARTNERS, HAVE EXTENDED THE SPS
THROUGH 8 PM EDT.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
     PAZ060>062-101>106.
NJ...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
     NJZ001-007>010-012-013-015>022-027.
DE...NONE.
MD...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
     MDZ008.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SATURDAY FOR ANZ450>455.
     GALE WARNING UNTIL 5 PM EDT THIS AFTERNOON FOR ANZ430-431.

&&

$$
SYNOPSIS...GIGI
NEAR TERM...JOHNSON/ROBERTSON
SHORT TERM...ROBERTSON
LONG TERM...GIGI
AVIATION...GIGI/JOHNSON/ROBERTSON
MARINE...GIGI/JOHNSON/ROBERTSON
FIRE WEATHER...JOHNSON/ROBERTSON


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