Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 010225
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
925 PM EST SAT FEB 28 2015

.SYNOPSIS...
HIGH PRESSURE OVERHEAD TONIGHT WILL SHIFT OFFSHORE ON SUNDAY. A COLD
FRONT WILL APPROACH FROM THE WEST SUNDAY BEFORE IT MOVES THROUGH THE
REGION LATE SUNDAY NIGHT. HIGH PRESSURE BUILDS BACK INTO THE AREA
MONDAY AND MONDAY NIGHT. LOW PRESSURE WILL TRACK WELL TO OUR
NORTHWEST MIDWEEK. THE COLD FRONT ASSOCIATED WITH THIS SYSTEM
APPROACHES TUESDAY AND TUESDAY NIGHT BEFORE IT PASSES THROUGH OUR
AREA ON WEDNESDAY. THE FRONT WILL SLOW DOWN AS IT MOVES SOUTH OF THE
AREA WEDNESDAY NIGHT INTO THURSDAY. ARCTIC HIGH PRESSURE BUILDS IN
FROM THE WEST LATE IN THE WORK WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
THE 00Z SFC ANALYSIS SHOWS HIGH PRESSURE CENTERED OVER NJ AND ERN
PA RESULTING IN CALM OR LIGHT AND VARIABLE WINDS ACROSS THE AREA.
THE LIGHT WINDS AND CLEAR SKIES ALLOW FOR GOOD RADIATIONAL COOLING
AND TEMPS WILL CONTINUE TO FALL INTO/THRU THE TEENS...REACHING
SINGLE DIGITS IN SOME COLDER LOCATIONS. HWVR...HI/MID-LVL CLOUDS
ARE ADVANCING STEADILY EASTWARD AND HAVE REACHED WRN PA AS OF
0200Z OR 900 PM. CLOUDS SHOULD OVERSPREAD OUR FCST AREA STARTING
SHORTLY AFTER MIDNIGHT...PUTTING AN END TO MOST OF THE RADIATIONAL
COOLING. SNOW LAGS BEHIND THE CLOUDS AND SHOULD BE ENTERING WRN OH
SHORTLY.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
CLOUDS WILL HAVE OVERSPREAD THE ENTIRE AREA BY SUNDAY MORNING. A
FAST MOVING WEAK LOW PRESSURE SYSTEM WILL ZIP ACROSS THE AREA
SUNDAY AFTERNOON. A LARGE AREA OF MOISTURE WILL ACT UPON THE
DISORGANIZED DYNAMICS TO PRODUCE PCPN ACROSS THE REGION...BEGINNING
WEST BY MID/LATE MORNING AND DURING THE EARLY AFTERNOON FOR THE DEL
VALLEY/SRN NJ. P-TYPE ISSUES ABOUND WITH COLD MORNING TEMPS AND WAA
ALOFT...THE USUAL SUSPECTS...ON SCENE. MUCH OF THE PCPN WILL BE SNOW
ACROSS THE DEL VALLEY N/W AT THE ONSET WITH SLEET AND FREEZING RAIN
AT THE ONSET FAR S/E. THE FROZEN P-TYPE WILL SLOWLY YIELD TO
FREEZING PCPN FROM S TO N DURING THE AFTERNOON. IT APPEARS TO BE ALL
SNOW THRU 00Z NORTH OF I-80. P-TYPE ARE ALWAYS TRICKY...SO CHECK BACK
OVERNIGHT FOR THE LATEST.

THE OVERALL QPF AMOUNTS ARE NOT THAT MUCH...USING THE 12Z GFS AS
GUIDANCE...TOTALS OF 1/4 TO 1/2 INCH ARE EXPECTED. THESE TOTALS
WOULD LEAD TO AN ADVISORY LEVEL SNOW EVENT (NORTH - IN THE ALL SNOW
AREA)...AND AT LEAST SOME ICE (ONLY A TRACE IS NEEDED FOR AN
ADVISORY) ELSEWHERE. ITS POSSIBLE THAT 1/10 TO 2/10TH OF AN INCH OF
ICE MAY OCCUR IN PERSISTENT FREEZING RAIN AREAS. WE WILL THEREFORE
ISSUE A WSW (ADVISORY) FOR ALL AREAS FROM 15Z SUN THRU 09Z MONDAY.
THE END TIME IS PROBABLY WELL AFTER THE PCPN ENDS...BUT THERE COULD
BE SOME RESIDUAL SLICK AREAS...AND THE OPTION TO EXTEND INTO THE MON
AM DRIVE TIME IS THERE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
A COLD FRONT WILL CROSS THE APPALACHIANS SUNDAY EVENING.  PRECIP IS
EXPECTED TO BE WIDESPREAD EARLY IN THE EVENING AS THE BEST
ISENTROPIC LIFT AND LOW-LEVEL JET DYNAMICS IS EXPECTED PROGRESS THRU
THE FORECAST AREA. USED THERMAL PROFILES FROM THE COLDER NAM/ECMWF
TO POPULATE OUR WX GRIDS AS COLDER AIR ANCHORED NEAR THE SURFACE
WILL BE SLOW TO ERODE. THIS WILL ALLOW FREEZING RAIN TO CONTINUE
ALONG THE I-95 CORRIDOR WHERE AN ADDITIONAL ICE ACCUMULATION OF UP
TO ONE-TENTH ARE FORECAST DURING THE EVENING. FARTHER NORTH AND WEST
ACROSS THE I-78, PREDOMINANT PTYPE WILL BE SNOW AND SLEET BUT IT CAN
CHANGEOVER TO FREEZING RAIN FOR A SHORT PERIOD. THE HIGHEST SNOWFALL
ACCUMULATIONS ARE EXPECTED ALONG THE I-80 CORRIDOR WHERE PRECIP
SHOULD REMAIN ALL SNOW.

THE COLD FRONT WILL PASS THRU THE REGION OVERNIGHT SUNDAY NIGHT. THE
TREND WAS TO END PRECIP FROM WEST TO EAST EARLIER. EXPECT THE LAST
OF THE PRECIP TO HAVE MOVED OFFSHORE BEFORE THE START OF THE MORNING
COMMUTE ON MONDAY.

ONCE THE FRONT MOVES OFFSHORE, A STRONG PRESSURE GRADIENT THAT
DEVELOPS BETWEEN THE LOW NEAR THE GULF OF MAINE AND HIGH PRESSURE
OVER THE MIDWEST WILL PRODUCE A BRISK W-NW WIND ON MONDAY. FORECAST
SOUNDINGS FOR MONDAY MORNING SHOW THE COLUMN DRYING AND COOLING
RAPIDLY IN WAKE OF FROPA IN CONCERT WITH THE POST-FRONTAL SURGE. FOR
SOME LOCATIONS, HIGHS MAY OCCUR OVERNIGHT (CLOSE TO FROPA TIME)
BEFORE TEMPS DECREASE DURING THE DAY. THERE WILL LIKELY BE AT LEAST
BKN CAA STRATOCU THAT DEVELOPS DURING THE DAY BUT AT LOCATIONS THAT
ARE ABLE TO RECEIVE MORE APPRECIABLE BREAKS IN THE CLOUDS, SOLAR
INSOLATION SHOULD OFFSET CAA, THUS ALLOWING TEMPS TO REMAIN STEADY
OR EVEN INCREASE SLIGHTLY DURING THE PEAK HEATING HOURS.

HIGH PRESSURE BUILDS IN FROM THE OHIO VALLEY MONDAY EVENING BEFORE
MOVING OVERHEAD BY EARLY TUESDAY MORNING. THE SETUP FOR RADIATIONAL
COOLING WILL BECOME FAVORABLE, ESPECIALLY OVERNIGHT, WHEN THE HIGH
MOVES OVERHEAD AND THE WINDS BECOME CALM. THE FORECAST FOR MIN TEMPS
MONDAY NIGHT WEIGHTED TOWARD THE COLDER END OF GUIDANCE. IN THIS
SETUP (THE HIGH CENTERED RIGHT ON TOP OF US AND A PRE-EXISTING SNOW
PACK), WE TYPICALLY TRY TO UNDERCUT EVEN THE COLDEST GUIDANCE BY A
FEW DEGREES BUT DID NOT WANT TO GO QUITE THAT AGGRESSIVE WITH MID
AND HI CLOUDS SPREADING INTO THE AREA BY EARLY MORNING, WHICH COULD
CURB TEMP DROP OFF).

THE HIGH IS FORECAST TO SHIFT OFFSHORE TUESDAY. STRENGTHENING S-SWLY
RETURN FLOW AROUND THE HIGH AND AHEAD OF A SYNOPTIC TROUGH THAT WILL
BE AMPLIFYING OVER THE CENTRAL CONUS WILL DRAW MILDER AIR UP THE
EASTERN SEABOARD TUESDAY AFTERNOON THROUGH WEDNESDAY. PRECIP LOOKS
TO OVERSPREAD THE FORECAST AREA IN THE LATE IN THE AFTERNOON
(PRIMARILY IN OUR FAR WESTERN ZONES) AND IN THE EVENING WHEN A WARM
FRONT LIFTS THRU THE MID ATLANTIC. THE AIRMASS PRECEDING THE ARRIVAL
OF THE WARM AIR AND PRECIP WILL BE COLD, SO THERE IS A POTENTIAL FOR
IT TO START AS A WINTRY MIX OF SNOW AND SLEET. A QUICK TRANSITION TO
FREEZING RAIN AND THEN RAIN IS EXPECTED DURING THE EVENING IN THE
DELMARVA AND NEAR THE COAST. THE COLD AIR TRAPPED NEAR THE GROUND IS
OFTEN MORE STUBBORN TO RETREAT WEST OF THE FALL LINE THAN MODELS
SHOW DUE TO THE COMPLEX OROGRAPHY. AFTER TAKING INTO ACCOUNT THIS
MODEL BIAS, THERE IS A CONCERN FOR FREEZING RAIN TUESDAY NIGHT WITH
NE PA AND NW NJ FACING A LONGER DURATION OF FREEZING RAIN COMPARED
TO THE I-95 CORRIDOR. WE WILL ATTEMPT TO HEIGHTEN THE WORDING FOR
AN ICING THREAT IN THE HWO.

THE PRE-FRONTAL WARM SECTOR IS EXPECTED TO BE ESTABLISHED OVER THE
MID-ATLANTIC REGION ON WEDNESDAY. IF THE AFOREMENTIONED SHALLOW
LAYER OF COLD AIR HANGS AROUND A BIT LONGER THAN CURRENTLY FORECAST,
THEN FREEZING RAIN COULD PERSIST INTO THE MORNING IN THE SHELTERED
VALLEYS OF THE I-80 CORRIDOR. OTHERWISE MOST, IF NOT ALL, OF THE
AREA SHOULD SEE PERIODS OF RAIN DURING THE DAY. THE THREAT FOR
FLOODING WITH THIS EVENT IS DISCUSSED IN THE HYDRO SECTION OF THE
AFD. UNDERCUT TEMP GUIDANCE BY A FEW DEGREES FOR WEDNESDAY
ESPECIALLY INLAND SINCE THE COLD AIR WILL NOT GO WITHOUT A FIGHT AND
CLOUDS WILL INHIBIT STRONGER HEATING. FORECAST MAX TEMPS RANGE FROM
NEAR 40F IN THE POCONOS TO MID 50S IN THE DELMARVA.

A COLD FRONT IS FORECAST TO SAG SEWD THRU THE AREA LATE WEDNESDAY.
THE LEADING EDGE OF ARCTIC AIR WILL SURGE INTO THE AREA SOMETIME
WEDNESDAY NIGHT INTO THURSDAY UNDER NW WINDS BEHIND THE BOUNDARY.
HOWEVER, THE FLOW ALOFT IS STILL OUT OF THE SW SINCE THE UPPER
TROUGH HANGS BACK TOWARD THE MIDWEST/GREAT LAKES. WHILE THERE IS
STILL CONSIDERABLE MODEL DIFFERENCES BETWEEN THE PROGRESSION OF THE
COLD AIR, MAJORITY OF GUIDANCE DOES DEVELOP ANAFRONTAL PRECIP (RAIN
CHANGING TO SNOW) ON THE BACK END OF THIS EVENT. THE POTENTIAL FOR
ACCUMULATING SNOW IS HIGHER UNDER THIS SETUP THAN IN MOST CASES
WITH RAIN ENDING AS SNOW.

ARCTIC HIGH PRESSURE BUILDS INTO THE AREA THURSDAY NIGHT AND FRIDAY.
TEMPS WILL BE 10-20F BELOW NORMAL TO END THE WORK WEEK. THE HIGH IS
THEN FORECAST TO SHIFT SOUTHWARD TOWARD THE SOUTHEAST STATES BY
SATURDAY. A MODERATING TREND WOULD BE IN STORE FOR START OF THE
WEEKEND WITH W-SW FLOW DEVELOPING AROUND THE HIGH.

&&

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

THE 00Z TAFS CONTINUE TO FEATURE VFR CONDITIONS THE REST OF THIS
EVENING AND TONIGHT. SKY COVER WILL REMAIN MOSTLY SCATTERED CI/CS
THROUGH THE EVENING...BEFORE CLOUDS LOWER AND THICKEN TOWARDS
DAWN ON SUNDAY MORNING. WE HAVE COMPOSED THE TAFS ALONG THE
GFS/LAMP LINES...SO LOWER CONDITIONS ARRIVE MID-MORNING FAR WEST
AND THEN DURING THE AFTERNOON DEL VALLEY AND EAST. SNOW WILL
DEVELOP OVER THE AREA FIRST...THEN CHANGE TO SLEET/FREEZING RAIN
LATER DURING THE AFTERNOON. THE 30-HR PHL TAF HAS A PRELIM
TIMELINE FOR THAT CHANGE-OVER...WHICH MAY OCCUR SOMEWHAT SOONER AT
MIV/ACY AND LATER OR NOT AT ALL AT ABE/RDG. WINDS LOOK LIGHT
THROUGH THE PERIOD... VARIABLE DIRECTION TONIGHT AND SE/E SUNDAY.

OUTLOOK...

SUNDAY NIGHT...WINTRY MIX CHANGING TO ZR AND THEN TO R FROM SE TO NW
IN THE EVENING. RDG AND ABE MAY HAVE ENOUGH COLD AIR FOR S/IP TO
CONT INTO MUCH OF THE NGT. FLUCTUATIONS BETWEEN MVFR AND IFR ARE
EXPECTED.

MONDAY...DRYING TREND WITH A GENERAL IMPROVEMENT TO VFR EXPECTED.
HOWEVER, STRATOCU AROUND 3-4 KFT AGL MAY LEAD TO MVFR CIGS FOR SOME
LOCATIONS. W-NW WINDS GUSTING TO 25 KT.

MONDAY NIGHT AND TUESDAY MORNING...VFR AND LIGHT WINDS.

TUESDAY AFTERNOON THROUGH WEDNESDAY...PRECIP OVERSPREADS LATE IN THE
AFTN AND EVE. HIGH CONFIDENCE IN CONDITIONS DETERIORATING TO MVFR
AND IFR DURING THIS TIME. PRECIP MAY BEGIN AS A WINTRY MIX BEFORE
CHANGING TO RA LATE TUESDAY NIGHT AND WED. THE RAIN COULD BE MOD TO
HVY AT TIMES. LLWS POSSIBLE, ESPECIALLY TUE NIGHT WITH A 60 KT SWLY
JET DEVELOPING AT 2 KFT AGL.

WEDNESDAY NIGHT AND THURSDAY...PRECIP MAY TRANSITION BACK TO SN FOR
A PERIOD BEFORE ENDING. TIMING OF THIS CHANGEOVER STILL UNCERTAIN.
IFR LIKELY IN SN.

&&

.MARINE...
WINDS AND SEAS ARE SUB-SCA AND ARE EXPECTED TO REMAIN SO THROUGH
TONIGHT AND SUNDAY. HIGH PRESSURE OVER THE WATERS THIS EVENING
WILL MOVE EAST OVERNIGHT. WINDS INTO THE EVENING WILL BE MOSTLY
NORTH OR NORTHWEST AND THEN THEY WILL SWITCH AROUND TO EAST OR
SOUTHEAST SUNDAY. WINDS SPEEDS WILL REMAIN UNDER 10 KNOTS MOST OF
THE TIME. SNOW/SLEET AND FREEZING RAIN WILL OVERSPREAD THE AREA
SUNDAY AFTERNOON. VSBY RESTRICTIONS POSSIBLE.

OUTLOOK...

SUNDAY NIGHT...NO MARINE HEADLINES ARE ANTICIPATED.

MONDAY AND MONDAY NIGHT...HIGH CONFIDENCE FOR SCA-LEVEL NW WINDS.
THE 12Z GFS IS INDICATING THE POTENTIAL FOR 35 KT GUSTS ON MONDAY
BUT THIS SOLUTION IS AN OUTLIER FOR GALES SO NO WATCH WAS ISSUED
ATTM.

TUESDAY...NO MARINE HEADLINES ARE ANTICIPATED.

TUESDAY NIGHT AND WEDNESDAY...SCA WILL LIKELY BE NEEDED WITH A
STRENGTHENING SWLY FLOW. SOUNDINGS OFF THE 12Z GFS SHOWS STORM-FORCE
WINDS ONLY 600 FT OFF THE GROUND TUESDAY NIGHT. WARMER AIR MOVING
OVER THE COLD WATERS WILL NOT PRODUCE A FAVORABLE MIXING SETUP FOR
THESE WINDS ALOFT TO BE TRANSPORTED DOWNWARD BUT CANNOT LOOK OVER
MECHANICAL MIXING BRINGING DOWN STRONGER GUSTS GIVEN THE IMPRESSIVE
SPEED SHEER.

WEDNESDAY NIGHT AND THURSDAY...NW WINDS MAY GUST TO NEAR SCA
CRITERIA.

&&

.HYDROLOGY...
TWO PRECIPITATION EVENTS ARE EXPECTED OVER THE NEXT FIVE DAYS,
ONE ON SUNDAY AFTERNOON/NIGHT AND A SECOND ONE ON TUESDAY
AFTERNOON INTO WEDNESDAY NIGHT.

THE INITIAL EVENT LOOKS TO BE ONE WITH SNOW OR MIXED WINTRY
PRECIPITATION. THE SECOND EVENT ON TUESDAY NIGHT INTO WEDNESDAY
NIGHT LOOKS TO BE ON THE LIQUID SIDE WITH TEMPERATURES BY
WEDNESDAY ABOVE FREEZING AFTER AN INITIAL WINTRY START. ALTHOUGH
THIS SECOND EVENT IS ABOUT 4 DAYS OUT, WE WANTED TO HIGHLIGHT THAT
SOME OF THE SOLUTIONS WE`RE SEEING ARE PRODUCING LOCALLY HEAVY
RAINFALL.

THE COMBINATION OF A BRIEF WARM UP ON WEDNESDAY, LOCALLY HEAVY
RAIN, MELTING SNOW, A FROZEN GROUND, ABOVE NORMAL ICE IN CREEKS,
STREAMS, AND RIVERS COULD LEAD TO INCREASED RUNOFF AND FLOODING.
WHERE THE DEPTH OF THE SNOW PACK IS HIGHEST (IN NW PA AND N NJ),
RAPID SNOW MELT IS NOT EXPECTED SINCE TEMPS WILL NOT RISE AS
SHARPLY AS AREAS TO THE SOUTH.

INCREASED FLOW 0N AREA CREEKS, STREAMS, AND RIVERS COULD ALSO
START TO MOVE ICE, AND IN A WORST CASE SCENARIO, CREATE
RESTRICTIONS OR JAMS.

AGAIN, THIS SECOND EVENT BRINGING WARMTH AND RAIN IS ABOUT 4 DAYS
OUT. THINGS CAN CHANGE. CONTINUE TO MONITOR FORECASTS. KEEP IN
MIND THAT SNOW MELT AND WARMTH, BY THEMSELVES, TYPICALLY DON`T
CAUSE FLOODING. HOW MUCH RAIN WE GET WILL BE THE DETERMINING
FACTOR.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 4 AM EST MONDAY
     FOR PAZ054-055-060>062-070-071-101>106.
NJ...WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 4 AM EST MONDAY
     FOR NJZ001-007>010-012>027.
DE...WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 4 AM EST MONDAY
     FOR DEZ001>004.
MD...WINTER WEATHER ADVISORY FROM 10 AM SUNDAY TO 4 AM EST MONDAY
     FOR MDZ008-012-015-019-020.
MARINE...NONE.

&&

$$
SYNOPSIS...KLEIN
NEAR TERM...AMC
SHORT TERM...O`HARA
LONG TERM...KLEIN
AVIATION...KLEIN/O`HARA
MARINE...KLEIN/O`HARA
HYDROLOGY...KRUZDLO/KLEIN


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