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000
FXUS61 KPHI 020301
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1001 PM EST SUN MAR 1 2015

.SYNOPSIS...
A COLD FRONT OVER THE OHIO VALLEY WILL MOVE INTO THE AREA BY MONDAY
MORNING. HIGH PRESSURE BUILDS EASTWARD INTO THE MID ATLANTIC MONDAY
AFTERNOON THROUGH TUESDAY MORNING. LOW PRESSURE IS ANTICIPATED TO
MOVE ACROSS THE GREAT LAKES LATE TUESDAY, THEN DOWN THE SAINT
LAWRENCE RIVER VALLEY BY EARLY WEDNESDAY. THIS LOW IS FORECAST TO
PULL A COLD FRONT SLOWLY THROUGH OUR REGION ON WEDNESDAY. WEAK LOW
PRESSURE IS EXPECTED TO RIDE ALONG THE FRONT ON THURSDAY BEFORE
HIGH PRESSURE BUILDS INTO OUR AREA FROM THE WEST FOR FRIDAY INTO
THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
WE HAVE CONVERTED ALL WARNINGS TO ADVISORIES WITH THIS UPDATE AND
CONTINUE ADVISORIES EVERYWHERE THROUGH THE OVERNIGHT HOURS. A
MAJORITY OF THE PRECIPITATION HAS CONCLUDED THIS EVENING, THOUGH
SOME OF THE HI-RES MODELS SHOW SOME RE-FIRING OF PRECIPITATION AS
THE COLD FRONT PUSHES THROUGH THE REGION AND WITH WEAK LOW-LEVEL
TROUGHING. A LIGHT WINTRY MIX IS STILL POSSIBLE AFTER MIDNIGHT BUT
BY DAYBREAK ANY RESIDUAL MOISTURE SHOULD BE ALL SNOW. CURRENTLY
THERE ARE SEVERAL THOUSAND HOMES AND BUSINESSES WITHOUT POWER IN
THE DELMARVA AND SOUTHERN NEW JERSEY COUNTIES ADDING TO
SIGNIFICANCE OF THE ICING THIS EVENING. AS WAS STATED EARLIER,
FORTUNATELY THE WINDS ARE EXPECTED TO REMAIN LIGHT AND VARIABLE
TONIGHT WHICH WOULD HELP TO COMBAT ANOTHER FURTHER OUTAGES.

OVERALL WE WILL CONTINUE TO DRY OUT WEST TO EAST TONIGHT AS
TEMPERATURES SLOWLY CREEP TOWARDS THE FREEZING MARK FROM THE
PHILLY METRO AREA SOUTHWARD...IT`LL TAKE A BIT LONGER NORTH AND
WEST.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
THE COLD FRONT WILL HAVE MOVED WELL OFFSHORE BY 12 MON. HIGH
PRESSURE FROM THE OHIO VALLEY WILL BEGIN TO BUILD EAST. FAIR
WEATHER IS EXPECTED...WITH ONLY A FEW SNOW SHOWERS EARLY ACROSS
THE SRN POCONOS. SKIES WILL BE MOSTLY SUNNY ACROSS MOST AREAS. IT
WILL BE BREEZY AND COOLER THAN NORMAL WITH HIGHS ONLY IN THE
MID/UPPER 30S ACROSS THE SOUTH AND LOW 30S NORTH. WINDS WILL BE
WEST OR NORTHWEST AT 10 TO 20 MPH WITH SOME GUSTS UP TO 30 MPH AT
TIMES.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
HIGH PRESSURE WILL BUILD IN FROM THE OHIO VALLEY MONDAY NIGHT. THE
CENTER OF THIS 1030+ MB HIGH IS FORECAST TO SHIFT DIRECTLY OVERHEAD
BY THE EARLY MORNING. MID AND HIGH CLOUDS ASSOCIATED WITH A STRONG
UPPER JET MAX WILL SPREAD INTO THE AREA WHICH, IF THICK ENOUGH, MAY
CURB RADIATIONAL COOLING A BIT DESPITE THE WINDS BECOMING CALM. MIN
TEMPS RANGE FROM THE SINGLE DIGITS IN NE PA AND NW NJ WHERE A FRESH
SNOWPACK IS EXPECTED TO BE ON THE GROUND TO AROUND 20F IN THE URBAN
AND COASTAL LOCALES.

THE HIGH WILL SHIFT OFFSHORE ON TUESDAY AS THE NEXT AREA OF LOW
PRESSURE LIFTS INTO THE GREAT LAKES. THE PATTERN IS SIMILAR TO
SEVERAL RECENT EVENTS (INCLUDING THE ONE TODAY) WHERE THE LOW CUTS
TO OUR NORTHWEST, ALLOWING WARM AND MOIST AIR TO OVERRUN THE
RESIDUAL ARCTIC AIR OVER THE MID ATLANTIC. THE RESULT IS A WINTRY
MIX OF SNOW/SLEET AT THE ONSET LATE TUESDAY AFTERNOON AND EVENING
CHANGING OVER TO FREEZING RAIN AND THEN RAIN FROM SOUTH TO NORTH
TUESDAY NIGHT INTO WEDNESDAY AS THE WARMER AIR INFILTRATES THE
AREA. THE MIDWEEK SYSTEM WILL CONSIDERABLY MORE AMPLIFIED THAN
TODAY`S EVENT, INCLUDING AN IMPRESSIVE 70-80 KT LOW LEVEL JET THAT
IS FORECAST TO DEVELOP OVERHEAD TUESDAY EVENING. ALSO THE COLD
AIRMASS PRECEDING THIS EVENT WILL NOT BE AS COLD AND DRY RELATIVE
TO TODAY`S EVENT. ACCORDINGLY, PRECIPITATION AMOUNTS WILL BE
HEAVIER WITH THE MIDWEEK SYSTEM BUT A QUICKER TRANSITION FROM
WINTRY PRECIP TO RAIN WILL ALSO OCCUR. THE FASTER CHANGEOVER WILL
KEEP ANY SNOW AND SLEET ACCUMULATIONS LIGHT. THE BIGGER IMPACT
WOULD BE FREEZING RAIN, WITH THE GREATEST ICING POTENTIAL ALONG
AND WEST OF THE FALL LINE WHERE FREEZING RAIN MAY LINGER INTO THE
OVERNIGHT AS THE HILLY TERRAIN WOULD HELP TRAP THE COLD AIR NEAR
THE SURFACE.

EXPECT ONLY ONE PTYPE DURING THE DAY ON WEDNESDAY- RAIN. THE RAIN
MAY BE MODERATE TO HEAVY AT TIMES EARLY IN THE DAY BEFORE TAPERING
OFF FROM NW TO SE IN THE AFTERNOON AS A COLD FRONT MOVES THRU.
THERE IS STILL QUITE A BIT OF SPREAD IN QPF AMOUNTS, RANGING FROM
UNDER A HALF INCH (12Z NAM AND A FEW 09Z SREF MEMBERS) TO AROUND
TWO INCHES IN THE WETTEST SREF MEMBERS. WE FOLLOWED WPC QPF
CLOSELY, WHICH IS CLOSER TO THE MEDIAN WITH AROUND AN INCH ACROSS
OUR THE SOUTHERN TWO- THIRDS OF THE CWA. WENT A FEW DEGREES BELOW
GUIDANCE FOR TEMPS ON WEDNESDAY, PARTICULARLY IN NE PA AND NW NJ
WHERE THE COLDER AIR WILL BE MOST RESISTANT TO ERODING. FORECAST
MAX TEMPS RANGE FROM NEAR 40F IN THE POCONOS TO THE MID 50S IN THE
LOWER DELMARVA.

COMPLEX FORECAST SHAPING UP DURING THE WED NGT AND THU TIME
FRAME. NORTHERN STREAM S/WV ENERGY LEADS TO A COLD FROPA ON WED
WITH MUCH COLDER AIR POISED TO MOVE INTO THE AREA. BUT THE FRONT
WILL STALL INVOF THE MID-ATL AS THE MID-LEVEL FLOW BECOMES
PARALLEL TO IT... AND WITH ADDITIONAL S/WV ENERGY ENTERING THE
LONG WAVE TROUGH OVER THE ERN CONUS...THIS WILL LEAD TO SEVERAL
WAVES OF LOW PRES TRAVERSING THE FRONT. BOTH THE AMERICAN AND
EUROPEAN MODELS HAVE ADVERTISED THIS SCENARIO OVER THE LAST
SEVERAL DAYS...BUT THERE IS CONSIDERABLE UNCERTAINTY AS WE ENTER
THE D+4 TIME FRAME... WITH REGARD TO THE PLACEMENT OF THE FRONT,
LOW-LEVEL THERMAL PROFILE, AND QPF.

THE GFS, EURO, AND THEIR RESPECTIVE ENSEMBLES HAVE CONSISTENTLY
INDICATED A FAIR AMOUNT OF QPF AND THERMAL PROFILES SUPPORTIVE
OF SNOW OVER THE CENTRAL AND SOUTHERN TIER OF THE CWA. BUT WHERE
THE FRONT ULTIMATELY STALLS WILL DETERMINE JUST HOW FAR SOUTH
THE COLD AIR MAKES IT...WITH A FRONTAL PLACEMENT FURTHER TO THE
NORTH LEADING TO A WARMER SOLUTION. THIS SYSTEM WILL ALSO TAP
GULF MOIST...BUT WITH HIGH PRESSURE BUILDING IN FROM THE WEST...
DRY LOW-LEVEL AIR WOULD LEAD TO A SHARP NORTHERN GRADIENT IN
PRECIP. THIS IS REFLECTED IN RUN-TO-RUN OSCILLATIONS OF MODEL QPF.
IF CURRENT MODEL RUNS VERIFY /AND KEEP IN MIND THERE IS A LOT OF
UNCERTAINTY/...COLDER AIR ADVECTING IN AT LOW-LEVELS WOULD LEAD
TO A ROBUST OVERRUNNING REGIME SETTING OVER THE MID-ATL WED NGT
AND THU...FED BY GULF MOISTURE AND SUPPORTED BY THE LF QUADRANT
OF A VIGOROUS 250 HPA JET. STAY TUNED.

THIS SYSTEM IS PROJECTED TO FINALLY MOVE OFFSHORE BY LATE THU
OR EARLY FRIDAY...BUT THE MODELS MAY BE A BIT TOO PROGRESSIVE
WITH THIS TIMING...AS THERE IS SOME EVIDENCE OF HIGH-LATITUDE
BLOCKING. HIGH PRESSURE SHOULD BUILD IN OVER THE WEEKEND WHEN
TEMPERATURES MAY ACTUALLY REACH SEASONAL LEVELS.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

NOT MUCH CHANGE WITH THE 00Z TAFS AT THIS TIME. MOSTLY IFR
CONDITIONS PRESENT AT OUR TERMINALS. BACK EDGE OF MAIN
PRECIPITATION IS MOVING THROUGH OUR REGION NOW THOUGH THERE IS
STILL AMPLE LOW-LEVEL MOISTURE AROUND THE REGION SO NOT THINKING
WE COMPLETELY DRY OUT THIS EVENING...SOME FREEZING DRIZZLE
POSSIBLE DURING THE OVERNIGHT HOURS. WE CONTINUE THE SLOW
IMPROVEMENT BACK TO VFR MOSTLY AROUND DAWN TOMORROW. LIGHT WINDS
TODAY AND TONIGHT THEN W OR NW 10-15KT WITH G25KT MONDAY.

OUTLOOK...

MONDAY NIGHT...VFR AND LIGHT WINDS.

TUESDAY AND TUESDAY NIGHT...CIGS/VSBYS LOWER TO MVFR AND THEN IFR
LATE IN THE AFTN WHEN A MIX OF SN/PL MOVE IN. PRECIP SHOULD QUICKLY
TRANSITION TO A PERIOD OF FZRA AND THEN RA DURING THE EVE FOR THE I-
95 TERMINALS AND FARTHER S/E. A WINTRY MIX (PL/FZRA) MAY PERSIST
CLOSER TO MIDNIGHT NEAR RDG/ABE BEFORE IT CHANGES TO RA. FORECAST
SOUNDINGS SHOW THE POTENTIAL FOR LLWS TO DEVELOP BY EVE WITH A
STRONG SW LLVL JET DEVELOPING ABOVE A SHARP FRONTAL INVERSION.

WEDNESDAY...MVFR AND IFR ESPECIALLY EARLY IN THE DAY WHEN STEADY RA
IS EXPECTED. RAIN TAPERS OFF FROM NW TO SE LATER IN THE MRNG AND
AFTN.

WEDNESDAY NIGHT AND THURSDAY...RA MAY CHANGE TO SN FROM NORTH TO
SOUTH. CHANCE FOR MVFR/IFR IF SN DOES DEVELOP BUT STILL A LOT OF
UNCERTAINTY WITH THIS PERIOD. BETTER CONFIDENCE FOR GUSTY NW
WINDS.

THURSDAY NIGHT AND FRIDAY...VFR.

&&

.MARINE...
SUB-SCA CONDITIONS THE REST OF THE AFTERNOON AND MOST OF
TONIGHT...THEN WINDS AND SEAS INCREASE AS LOW PRESSURE DEEPENS
OFFSHORE. SCA WINDS DEVELOP AROUND DAWN AND CONTINUE THRU THE DAY.
PRESENT SCA FLAG ISSUED EARLIER WILL CONTINUE AS IS. SNOW/SLEET AND
FREEZING RAIN TODAY AND EARLY TONIGHT...PERHAPS ALL RAIN FOR AWHILE
ACROSS THE SRN WATERS. PCPN DIMINISHES BEFORE DAWN.

OUTLOOK...

MONDAY NIGHT...SCA CONTINUES THRU THE EVENING. NW WINDS WILL
DIMINISH RATHER QUICKLY DURING THIS TIME SO THE SCA MAY BE ABLE TO
BE CANCELLED A FEW HOURS EARLIER (ESPECIALLY FOR THE DE BAY).

TUESDAY...NO MARINE HEADLINES EXPECTED WITH LIGHT WINDS.

TUESDAY NIGHT AND WEDNESDAY...SCA WILL LIKELY BE NEEDED WITH A
STRENGTHENING SWLY FLOW. SOUNDINGS CONTINUE TO SHOW VERY STRONG
WINDS JUST ABOVE THE SURFACE BUT THE WARMER AIR MOVING ATOP THE COLD
WATERS DOES NOT PROVIDE A FAVORABLE SETUP FOR MIXING DOWN THESE
WINDS.

WEDNESDAY NIGHT AND THURSDAY...SCA LIKELY WITH GUSTY NW WINDS.

THURSDAY NIGHT AND FRIDAY...NO MARINE HEADLINES ARE ANTICIPATED.

&&

.HYDROLOGY...
AFTER TODAY`S WINTRY MIX, THE NEXT ROUND OF PRECIPITATION IS
FORECAST TO MOVE INTO THE AREA TUESDAY AFTERNOON AND CONTINUE INTO
WEDNESDAY.

THIS MIDWEEK EVENT APPEARS TO START AS A WINTRY MIX BEFORE
CHANGING OVER TO RAIN AS TEMPERATURES RISE WELL ABOVE FREEZING ON
WEDNESDAY. ALTHOUGH THIS EVENT IS A FEW DAYS AWAY, WE WANT TO
HIGHLIGHT THAT SOME OF THE MODEL GUIDANCE IS SUGGESTING LOCALLY
HEAVY RAINFALL. THERE IS STILL QUITE A BIT OF SPREAD IN QPF
AMOUNTS, RANGING FROM UNDER A HALF INCH TO AROUND TWO INCHES IN
THE WETTEST RUNS. WE FOLLOWED WPC QPF CLOSELY, WHICH IS CLOSER TO
THE MEDIAN WITH AROUND AN INCH ACROSS OUR THE SOUTHERN TWO-THIRDS
OF THE CWA.

THE COMBINATION OF A BRIEF WARM-UP ON WEDNESDAY, LOCALLY HEAVY
RAINFALL, MELTING SNOW, A FROZEN GROUND, AND ABOVE NORMAL ICE IN
CREEKS, STREAMS, AND RIVERS COULD LEAD TO INCREASED RUNOFF AND
POSSIBLE FLOODING. WHERE THE DEPTH OF THE SNOWPACK IS GREATEST (IN
NE PA AND N NJ), RAPID SNOWMELT IS NOT EXPECTED SINCE TEMPS WILL
NOT RISE AS SHARPLY AS IN 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.

CONTINUE TO MONITOR THE FORECAST. KEEP IN MIND THAT SNOWMELT AND
WARMTH BY THEMSELVES TYPICALLY DO NOT CAUSE FLOODING. THE AMOUNT
OF RAIN THAT WE RECEIVE WILL BE THE DETERMINING FACTOR.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR PAZ054-055-
     060>062-070-071-101>106.
NJ...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR NJZ001-
     007>010-012>027.
DE...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR DEZ001>004.
MD...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR MDZ008-012-
     015-019-020.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 2 AM EST TUESDAY FOR
     ANZ430-431-450>455.

&&

$$
SYNOPSIS...KLEIN
NEAR TERM...HEAVENER/O`HARA
SHORT TERM...O`HARA
LONG TERM...FRANCK/KLEIN
AVIATION...HEAVENER/KLEIN/O`HARA
MARINE...KLEIN/O`HARA
HYDROLOGY...