Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 231348
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
948 AM EDT THU APR 23 2015

.SYNOPSIS...
A WEAKER SECONDARY COLD FRONT WILL CROSS THE AREA TODAY. A HIGH
PRESSURE SYSTEM WILL BRIEFLY BUILD OVER THE REGION FRIDAY INTO
EARLY SATURDAY. LOW PRESSURE IS THEN FORECAST TO PASS BY TO OUR
SOUTH FROM SATURDAY NIGHT INTO SUNDAY, TRACKING FROM AROUND THE
TENNESSEE VALLEY TO OFF THE CAROLINA COAST. ANOTHER HIGH PRESSURE
SYSTEM SHOULD BRIEFLY BUILD INTO THE AREA ON MONDAY AND TUESDAY.
THEN A LOW PRESSURE SYSTEM PREDICTED TO FORM IN THE GULF OF
MEXICO SHOULD REACH THE NORTH CAROLINA COASTAL WATERS ON
WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AN AREA OF LOW PRESSURE WILL REMAIN NEARLY STATIONARY AND CONTINUE
TO SPIN ACROSS SOUTHEASTERN CANADA TODAY. STRONG WESTERLY AND
NORTHWESTERLY WINDS WILL CONTINUE THROUGH THE AFTERNOON AND INTO
THE EARLY EVENING, WITH GUSTS AROUND 30 MPH POSSIBLE THROUGH THIS
TIME. A WEAK COLD FRONT/SURFACE TROUGH IS EXPECTED TO SLIDE
ACROSS THE AREA THIS AFTERNOON. AS THIS HAPPENS, LOW-MID LEVEL
LAPSE RATES ARE FORECAST TO INCREASE AND THERE IS SOME MOISTURE
FORECAST TO MOVE ACROSS THE AREA. THIS COULD LEAD TO SOME ISOLATED
SHOWER ACTIVITY DEVELOPING TO OUR WEST AND MOVING INTO OUR AREA.
FOR NOW, THE GREATEST POSSIBILITY IS FOR OUR NORTHWESTERN THIRD OF
THE AREA. ITS POSSIBLE SOME SPRINKLES COULD MAKE IT DOWN INTO THE
TIER OF COUNTIES DOWN, SO WE`VE INCLUDED A CHANCE OF SPRINKLES
THERE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
ANY SHOWERS AND/OR SPRINKLES ARE EXPECTED TO DISSIPATE BY THIS
EVENING AS DAYTIME INSTABILITY IS LOST AND THE SURFACE TROUGH MOVES
EASTWARD. SKIES WILL LIKELY REMAIN PRETTY CLOUDY FOR MUCH OF THE
NIGHT HOWEVER. WITH THE LOW REMAINING TO OUR NORTHEAST, THE PRESSURE
GRADIENT WILL REMAIN ACROSS THE AREA, KEEPING A STEADY BREEZE FOR
MUCH OF THE NIGHT. HOWEVER, WE STILL EXPECT COLD TEMPERATURES
TONIGHT AS COLD AIR ADVECTION WILL CONTINUE THROUGH THE NIGHT. WE`VE
ISSUED A FREEZE WARNING FOR AREAS WHERE WE ARE MOST CONFIDENT OF SUB-
FREEZING TEMPERATURES OCCURRING OVERNIGHT, AND A FREEZE WATCH FOR
THOSE AREAS WHERE WE ARE A LITTLE MORE UNCERTAIN. WITH THE BREEZE
EXPECTED, IT MAY BE HARD TO DEVELOP MUCH FROST, SO THAT`S WHY WE
HAVEN`T INCLUDED FRONT IS THE FORECAST OR ISSUED A FROST ADVISORY AT
THIS TIME.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
THE WRF-NMM INITIALIZATION LOOKED SLIGHTLY BETTER THAN THE GFS AT
500MB IN THE EASTERN CONUS AND THE REVERSE IN THE WESTERN CONUS. THE
NAM/WRF-NMMB INITIALIZATION AT 925MB AND 850MB LOOKED SLIGHTLY
BETTER. THE CORE OF THIS CHILLY AIR MASS WAS SLIGHTLY COLDER THAN
INITIALIZED.

THE LONG TERM MODEL GUIDANCE HAS HAD LATITUDINAL FLIPPING OF
SYSTEMS AND TONIGHT WAS NO DIFFERENT. WHILE THERE HAS BEEN SOME
SETTLING OF FEATURES FOR SATURDAY AND SUNDAY, THE POTENTIAL
NOR`EASTER AT THE END OF THE LONG TERM NOW FINDS THE GFS AS THE
MOST AGGRESSIVE MODEL WITH THE OP ECMWF SUPPRESSED BEYOND BELIEF.
THE DIFFERENCE IS NOT A SLOWER EXIT OR MORE INTENSE SATURDAY
SYSTEM, BUT A DE-AMPLIFICATION OF THE FLOW ACROSS CENTRAL AND
WESTERN NOAM. WOULD BE SHOCKED IF THE ECMWF ENSEMBLE MEAN IS NOT
MORE AMPLIFIED. CONVERSELY, THE 00Z OPERATIONAL GFS WAS ALONG THE
NW OR NRN FRINGE OF GEFS MEMBERS WITH BOTH THE SATURDAY AND END OF
LONG TERM SYSTEM. STAY TUNED.

NO BACKING AWAY FROM A CHILLY/FROSTY START TO THE LONG TERM.
ON FRIDAY, A CHANNELIZED VORT MAX WILL BE MOVING NEWD AND LIFTING
TOWARD THE NERN EDGE OF OUR CWA. WHILE CONVECTIVE TEMPS ARE
PREDICTED TO BE REACHED, THERE IS LESS CERTAINTY THAN TODAY,
ESPECIALLY THE SWRN HALF OF OUR CWA. SO AN OVERALL SUNNIER DAY IS
EXPECTED. MAX TEMPS ARE TOWARD THE HIGH END OF STAT GUIDANCE AND
IF YESTERDAY WAS ANY INDICATION, MAYBE NOT HIGH ENOUGH. WINDS ARE
STILL EXPECTED TO BE BRISK AND THIS IS A FIRE WEATHER CONCERN
GIVEN LOW RELATIVE HUMIDITY LEVELS PREDICTED. PLEASE SEE FIRE
WEATHER SECTION BELOW.

FOR FRIDAY NIGHT WE HAVE ISSUED A FREEZE WATCH FOR MOST OF OUR PA
AND NJ ZONES WHERE THE GROWING SEASON HAS STARTED. EXCEPTION
IMMEDIATE COAST AND PHL AREA. WE ARE NOT AS SURE ABOUT DELMARVA. SFC
HIGH PRESSURE SHOULD BE CLOSE ENOUGH TO DECOUPLE WINDS. ANOTHER
SIGNAL IS THE WAA PREDICTED ABOVE THE BOUNDARY LAYER. BECAUSE WINDS
WILL BE LIGHTER, WE HAVE INCLUDED FROST IN THE GRIDS. STAT GUIDANCE
IS PRETTY CLOSE AND WE FOLLOWED THEM FOR MINS.

LOOKING AT THE GFS DIAGS FOR SATURDAY AND SATURDAY NIGHT, OTHER THAN
MID LEVEL QVEC CONVERGENCE, MOST OTHER PREDICTED FORCING (MID
LEVEL WAA, 300K ISENTROPIC LIFT. LOCATION OF THE 250MB JET)
MECHANISMS SUGGEST THE MODEL IS TOO FAR NORTH WITH ITS QPF. ERGO
WE ARE REMAINING PRETTY CLOSE TO CONTINUITY WITH A SHARP CUT-OFF
OF POPS NEAR THE MASON-DIXON LINE. IRONICALLY AGAIN GFS MOS IS
WARMER THAN NAM MOS WITH MAX TEMPS ON SATURDAY IN SPITE OF BEING
FASTER AND FARTHER NORTH WITH THE CLOUDS AND PCPN. DEFINITE UPSIDE
POTENTIAL OVER STAT GUIDANCE FOR MAX TEMPS SATURDAY AND WE WERE
NEAR THEM SOUTH AND ALONG THEN COAST, BUT OVERALL WARMER
ELSEWHERE. CONSENSUS IS FOR GREATEST PCPN CHANCES ON SATURDAY
NIGHT AND AN EXIT OF PCPN BY SUNDAY MORNING BY ALL OF THE MODELS.

THE CURRENT CLOSED LOW OVER ONTARIO THAT IS GOING TO HELP STEER THE
WEEKEND SFC SYSTEM WELL TO OUR SOUTH IS PREDICTED TO RETROGRADE
WWD AT THE LEAST INTO NEW ENGLAND ON SUNDAY AND THEN LINGER CLOSE
BY ON MONDAY AND TUESDAY. SOME INSTABILITY SHOWERS ARE POSSIBLE
UNDER THIS COLD POOL. BUT THE THERMAL PROFILE CLOSER TO THE
SURFACE WILL BE MILDER. SO WHILE TEMPS SHOULD STILL BE BELOW
NORMAL, THEY SHOULD BE A CATEGORY OR TWO HIGHER THAN TODAY AND
FRIDAY.

WE LEFT IN THE CHANCE FOR RAIN ON WEDNESDAY ASSOCIATED WITH THE NEXT
LOW PRESSURE SYSTEM/POSSIBLE NOR`EASTER. NOT THAT WE EXPECTED
CONSENSUS AT THIS JUNCTURE, BUT THE SPREAD IN TRACK (AND TIMING
ALSO) SOLUTIONS HAS INCREASED FROM LAST NIGHT.

&&

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

VFR CONDITIONS WILL CONTINUE AT THE TAF SITES THROUGH THE PERIOD,
ALTHOUGH CLOUD COVER WILL INCREASE THIS AFTERNOON INTO TONIGHT. A
FEW VERY LIGHT RAIN SHOWERS/SPRINKLES WILL BE POSSIBLE THIS
AFTERNOON PRIMARILY FOR KTTN AND KABE. HOWEVER, VFR CONDITIONS ARE
EXPECTED TO CONTINUE EVEN UNDER THESE SHOWERS.

WINDS WILL BE THE MAIN CONCERN AS WIND GUSTS WILL INCREASE
THROUGH THE DAY AND WILL GUST AROUND 25 KNOTS AT TIMES TODAY. THE
SPEED OF THE GUSTS MAY DROP OFF A BIT THIS EVENING AND OVERNIGHT,
BUT WE COULD STILL GET SOME GUSTS ROUND 20 KNOTS THROUGH THE NIGHT
FOR MANY AREAS.

OUTLOOK...
FRIDAY...CONTINUED VFR CONDITIONS, WITH GUSTY WEST-NORTHWEST WINDS
TO AROUND 25 KNOTS, ESPECIALLY LATE MORNING AND THROUGH THE
AFTERNOON.

FRIDAY NIGHT...VFR CONDITIONS WITH LIGHTER WINDS.

SATURDAY AND 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 THROUGH MONDAY...MAINLY VFR CONDITIONS ARE EXPECTED.

&&

.MARINE...
THE SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR TODAY AND TONIGHT 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 4-5 FEET.

OUTLOOK...
FRIDAY AND FRIDAY NIGHT...THE SMALL CRAFT ADVISORY WAS EXTENDED
THROUGH THE DAY FRIDAY ALL WATERS AND MIGHT NEED AN EXTENSION
INTO FRIDAY NIGHT, OR AT LEAST FRIDAY EVENING.

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.

SUNDAY NIGHT THROUGH MONDAY...CONTINUED SUB-SCA CONDITIONS;
ALTHOUGH, SOME WIND GUSTS TO AROUND 20 KNOTS PLUS ARE POSSIBLE.

&&

.FIRE WEATHER...
DRY AND GUSTY CONDITIONS ARE EXPECTED TODAY WITH RH VALUES EXPECTED
TO DIP INTO THE MID/UPPER 20S AND WINDS GUSTING AROUND 25-30 MPH.
AFTER COORDINATION WITH THE STATE PARTNERS HAVE DECIDED TO ISSUE A
SPS FOR TODAY AS FINE FUELS ARE ALREADY BEGINNING TO DRY OUT. THE
SPS IS VALID THROUGH 7 PM EDT AS WE SHOULD SEE QUICK RH RECOVERY
EARLY THIS EVENING.

CONDITIONS MAY BE ENHANCED ON FRIDAY FOR THE POTENTIAL OF WILDFIRE
SPREAD ACROSS THE REGION. FRIDAY`S RELATIVE HUMIDITY VALUES ARE
PROGGED TO DROP BELOW 30 PERCENT FOR A TIME FROM LATE FRIDAY MORNING
AND THROUGH THE AFTERNOON TO EARLY EVENING. IN ADDITION, SUSTAINED
WEST-NORTHWEST WINDS BETWEEN 15 TO 20 MPH ARE FORECAST DURING THIS
TIMEFRAME, WITH GUSTS REACHING BETWEEN 25 TO 30 MPH AT TIMES. WE
WILL CONTINUE TO MONITOR THE LATEST GUIDANCE AND COORDINATE WITH OUR
FIRE WEATHER PARTNERS IF ANY ADDITIONAL PRODUCTS BECOME NECESSARY.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY MORNING
     FOR PAZ060>062-101>106.
     FREEZE WARNING FROM 2 AM TO 9 AM EDT FRIDAY FOR PAZ061-062-105.
     FREEZE WATCH FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR
     PAZ060-101>104-106.
NJ...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY MORNING
     FOR NJZ001-007>010-012-013-015>022-027.
     FREEZE WARNING FROM 2 AM TO 9 AM EDT FRIDAY FOR NJZ001-007>010.
     FREEZE WATCH FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR
     NJZ012-013-015>022-027.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ430-431-
     450>455.

&&

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


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