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000
FXUS61 KPHI 022105
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
405 PM EST MON MAR 2 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVER OUR AREA TONIGHT, THEN SHIFT OFF THE
MID ATLANTIC COAST ON TUESDAY. A WARM FRONT IS EXPECTED TO LIFT
THROUGH OUR AREA ON TUESDAY EVENING. A COLD FRONT IS ANTICIPATED TO
ARRIVE WEDNESDAY AFTERNOON, THEN THE FRONT SHOULD SETTLE SLOWLY TO
THE SOUTHEAST WEDNESDAY NIGHT AND THURSDAY AS LOW PRESSURE RIDES
ALONG IT. ANOTHER ARCTIC HIGH IS FORECAST TO BUILD ACROSS OUR REGION
FOR FRIDAY INTO SATURDAY. A WARM FRONT MAY BEGIN TO APPROACH FROM
THE SOUTHWEST ON SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A STRONG AREA OF HIGH PRESSURE WILL BUILD OVER OUR AREA TONIGHT. AS
THIS OCCURS, THE PRESSURE GRADIENT WILL COLLAPSE AND THE MIXING WILL
DIMINISH. THIS IS EXPECTED TO RESULT IN THE WINDS DIMINISHING FAIRLY
QUICKLY THROUGH THIS EVENING.

GIVEN THE INITIAL CAA AND ALSO THE ADVECTION OF DRIER AIR ACROSS OUR
CWA, LITTLE IN THE WAY OF CLOUDS ARE ANTICIPATED THROUGH MUCH OF THE
NIGHT. THERE SHOULD BE SOME HIGH LEVEL CLOUDS THOUGH ESPECIALLY LATE
WITHIN THE FAST FLOW FROM OUR NEXT STORM SYSTEM ORGANIZING ACROSS
THE SOUTHERN PLAINS. THE COMBINATION OF LESSENING WIND, DRY AIR AND
LITTLE CLOUDS WILL CONTRIBUTE TO GOOD RADIATIONAL COOLING
CONDITIONS. AS A RESULT, WE WENT BELOW THE NAM/GFS MOS FOR LOW
TEMPERATURES ESPECIALLY NORTH AND WEST OF THE FALL LINE AND
INTERIOR SOUTHERN NEW JERSEY.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
THE START OF A RATHER UNSETTLED TIME FRAME BEGINS LATER TUESDAY.
THIS IS COURTESY OF AN UPPER-LEVEL TROUGH AMPLIFYING ACROSS THE
MIDWEST WITH ENERGY ALSO EJECTING OUT OF THE FOUR CORNERS REGION
INTO THE SOUTHERN PLAINS. THE MIDWEST ENERGY DRIVES LOW PRESSURE
MOSTLY NORTH OF THE GREAT LAKES DURING TUESDAY. THIS FEATURE HOWEVER
WILL BE PULLING A COLD FRONT TOWARD OUR AREA LATE IN THE DAY. AS
THESE FEATURES MOVE EASTWARD, STRENGTHENING WAA AND LIFT OCCURS
DOWNSTREAM.

THE FLOW IS FORECAST TO INCREASE QUITE A BIT ABOVE THE SURFACE BY
THE END OF THE DAY AS A SOUTHERLY LOW-LEVEL JET ARRIVES. THIS WILL
DRIVE STRONG WAA ALOFT AND ALSO RESULT IN A RIBBON OF STRONG LIFT.
THE FORECAST SOUNDINGS SHOW WARMING ALOFT MUCH FASTER THAN AT THE
SURFACE ACROSS MUCH OF THE AREA. THIS RESULTS IN A STRONG INVERSION,
WHICH WILL TEND TO HOLD IN THE COLDER AIR AT THE SURFACE. WE ARE
EXPECTING SOME MODERATION IN THE LOW-LEVEL AIRMASS DUE TO THE
SOUTHERLY FLOW DEVELOPING, HOWEVER THIS SHOULD BE LIGHT INITIALLY
AND INCOMING PRECIPITATION COMBINED WITH LOW DEW POINTS SHOULD
RESULT IN AN INITIAL DROP IN TEMPERATURES FOR MOST IF NOT ALL OF THE
AREA. THIS LEADS TO A FORECAST CHALLENGE REGARDING ICING POTENTIAL.

AN EXAMINATION OF THE FORECAST SOUNDINGS IS POINTING TOWARD MORE
SLEET IN GENERAL. THIS IS DUE TO THE ROBUST WAA ALLOWING FOR A
DEEPER WARM LAYER ABOVE A DECENT COLD LAYER. THE INITIAL RATHER DRY
LOW-LEVEL AIRMASS THOUGH SHOULD RESULT IN SOME EVAPORATIONAL
COOLING, THEREFORE WE ARE THINKING SOME SNOW TO START BEFORE
TRANSITIONING TO SOME SLEET FROM SOUTH TO NORTH BY EARLY EVENING.
THE OVERALL START TIME ACROSS THE AREA APPEARS TO BE AFTER 18Z. THIS
WILL LIKELY HAVE AN IMPACT ON THE EVENING COMMUTE ACROSS A GOOD
PORTION OF THE CWA.

GIVEN THE ABOVE /EVEN THOUGH AMOUNTS BY EARLY EVENING SHOULD BE ON
THE LIGHTER SIDE/, FACTORING IN THE EVENING COMMUTE IMPACT AND A
TRANSITION TO FREEZING RAIN BEYOND THE DAYLIGHT HOURS LEADS US TO
ISSUING A WINTER WEATHER ADVISORY. THE ADVISORY WAS PLACED WHERE
CONFIDENCE WAS HIGHEST FOR MIXED PRECIPITATION, HOWEVER SOME
EXPANSION MAY BE NEEDED IF FREEZING RAIN LOOKS MORE LIKELY.

AS FOR HIGH TEMPERATURES, WE MOSTLY USED AN EVEN BLEND OF THE
GFS/NAM MOS BUT DID ADJUST THE HOURLY TEMPERATURES DOWN SOME BY LATE
AFTERNOON TO ACCOUNT FOR SOME EVAPORATIVE COOLING.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
STRONG WARM ADVECTION IS ANTICIPATED ALOFT FROM INTO TUESDAY
EVENING. WARMING AT THE SURFACE WILL LAG A BIT. THERE SHOULD BE A
GRADUAL TRANSITION FROM A WINTRY MIX TO RAIN FROM SOUTH TO NORTH.
HOWEVER, TRAPPED COLD AIR IN OUR FAR NORTHERN COUNTIES COULD
RESULT IN SEVERAL HOURS OF FREEZING RAIN THERE ON TUESDAY NIGHT
INTO EARLY WEDNESDAY MORNING. OUR LATEST PROJECTIONS FOR TUESDAY
INTO TUESDAY NIGHT BRING 1 TO 3 INCHES OF SNOW ACROSS OUR NORTHERN
COUNTIES AND LESS THAN AN INCH TO OUR CENTRAL AND SOUTHERN
COUNTIES WHERE ACCUMULATION MAY BE CUT DOWN BY THE PRESENCE OF
SLEET. FREEZING RAIN SHOULD CAUSE A PROBLEM ONLY ACROSS OUR
NORTHERN COUNTIES WHERE UP TO A TENTH OF AN INCH OF ICE MAY
ACCUMULATE ON TOP OF THE NEW SNOWFALL.

IT CONTINUES TO APPEAR AS THOUGH THE PRECIPITATION WILL CHANGE TO
ALL RAIN FOR WEDNESDAY. A BIT OF DRYING MAY BEGIN TO WORK ITS WAY
DOWN FROM THE NORTHWEST ON WEDNESDAY AFTERNOON. IT SEEMS POSSIBLE
THAT SOME LOCATIONS, ESPECIALLY IN THE CENTRAL AND SOUTHERN PARTS
OF OUR FORECAST AREA MAY PICK UP A HALF INCH TO AN INCH OF
RAINFALL DURING THE PERIOD. THE RAIN IN COMBINATION WITH SNOWMELT
AND THE FROZEN GROUND, ALONG WITH ICE MOVEMENT IN AREA WATERWAYS
MAY RESULT IN A BIT OF MINOR FLOODING.

THE MODELS ARE COMING TOGETHER ON THE IDEA OF A WAVE OF LOW
PRESSURE RIDING ALONG THE SLOW MOVING COLD FRONT. IT SHOULD BRING
US ANOTHER ROUND OF PRECIPITATION FOR WEDNESDAY NIGHT INTO
THURSDAY. AS COLD AIR FILTERS DOWN INTO OUR REGION FROM THE NORTH
AND NORTHWEST, THE PRECIPITATION TYPE WILL LIKELY TRANSITION TO
SNOW. THERE IS ENOUGH SPREAD IN THE GUIDANCE SOLUTIONS TO MAKE THE
DETAILS A BIT UNCERTAIN AT THIS POINT. HOWEVER, IT IS LOOKING
INCREASINGLY POSSIBLE THAT WE WILL SEE ACCUMULATING SNOW IN MUCH
OF OUR FORECAST AREA AT THAT TIME.

HIGH PRESSURE FROM THE WEST IS ANTICIPATED TO BRING DRY WEATHER
AND BELOW NORMAL TEMPERATURES FOR THURSDAY NIGHT INTO SATURDAY
NIGHT.

THE 0000 UTC GFS AND THE 0000 UTC ECMWF ARE BOTH SUGGESTING THE
POTENTIAL FOR PRECIPITATION TO BE NEARING OUR REGION FROM THE
SOUTHWEST ON SUNDAY DUE TO A WEAK AREA OF LOW PRESSURE ALONG WITH
A WARM FRONT.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

REST OF THIS AFTERNOON...VFR. NORTHWEST WINDS AROUND 15 KNOTS WITH
GUSTS TO AROUND 25 KNOTS, DIMINISHING TOWARD EVENING.

TONIGHT...VFR. NORTHWEST WINDS DIMINISHING TO 10 KNOTS OR LESS THIS
EVENING, THEN LOCALLY BECOMING LIGHT AND VARIABLE OVERNIGHT.

TUESDAY...VFR FOR MUCH OF THE DAY WITH INCREASING CLOUDS. THE
CONDITIONS SHOULD LOWER TO MVFR/IFR LATE IN THE AFTERNOON FROM WEST
TO EAST AS SNOW AND SLEET OVERSPREADS THE REGION. LIGHT AND VARIABLE
WINDS, BECOMING NORTHEAST THEN SOUTHEAST AT 5-8 KNOTS. A SOUTHERLY
LOW-LEVEL JET /2000 FEET/ NEAR 40 KNOTS SHOULD ARRIVE LATE IN THE
AFTERNOON, THEREFORE INCLUDED LOW-LEVEL WIND SHEAR IN THE 30-HOUR
KPHL TAF.

OUTLOOK...
TUESDAY NIGHT...MVFR AND IFR CONDITIONS WITH A WINTRY MIX OF
PRECIPITATION CHANGING TO RAIN FROM SOUTH TO NORTH. THE RAIN MAY
BE MODERATE TO HEAVY AT TIMES. LOW LEVEL WIND SHEAR IS POSSIBLE
DUE TO A SOUTHWESTERLY LOW LEVEL JET THAT IS FORECAST TO DEVELOP
OVERHEAD.

WEDNESDAY...MVFR AND IFR CONDITIONS IN RAIN. THE RAIN MAY BE
MODERATE TO HEAVY AT TIMES, ESPECIALLY SOUTH OF KPHL.

WEDNESDAY NIGHT...MVFR AND IFR CONDITIONS IN RAIN, MIXING WITH
THEN CHANGING TO SNOW FROM NORTH TO SOUTH.

THURSDAY...MVFR AND IFR CONDITIONS IN MORNING SNOW. CONDITIONS
IMPROVING GRADUALLY TO VFR WITH A LESSING CHANCE OF SNOW IN THE
AFTERNOON.

THURSDAY NIGHT AND FRIDAY...MAINLY VFR.

&&

.MARINE...
STRONG HIGH PRESSURE WILL BUILD OVER THE AREA LATER TONIGHT, HOWEVER
A LINGERING PRESSURE GRADIENT WILL KEEP THE WINDS UP SOME FOR AWHILE
LONGER. WE ARE SEEING SOME DIMINISHING ALREADY ESPECIALLY ACROSS THE
SOUTHERN WATERS. AS A RESULT, WE TRIMMED BACK THE END TIME OF THE
SMALL CRAFT ADVISORY TO 00Z FOR DELAWARE BAY AND THE FAR SOUTHERN
COASTAL WATERS, THEN 03Z ELSEWHERE. THE SEAS HAVE BEEN RUNNING A BIT
LOWER AS WELL, THEREFORE ADJUSTED THEM DOWN A BIT QUICKER WHICH IS
CLOSER TO THE LATEST GUIDANCE. AS THE BOUNDARY LAYER COOLS TONIGHT,
SOME FREEZING RAIN IS EXPECTED HOWEVER THIS SHOULD BE LIGHT AS THE
WINDS SUBSIDE. A SOUTHERLY FLOW DEVELOPS ON TUESDAY AHEAD OF THE
NEXT SYSTEM, AND WHILE A LOW-LEVEL JET WILL BE ARRIVING LATER IN THE
DAY IT APPEARS THE WINDS AT THE SURFACE WILL REMAIN BELOW ADVISORY
LEVELS DURING THE DAYLIGHT HOURS ON TUESDAY.

OUTLOOK..
TUESDAY NIGHT AND WEDNESDAY...A SMALL CRAFT ADVISORY MAY BE
NECESSARY DUE TO A GUSTY SOUTH TO SOUTHWEST WIND.

WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...A SMALL CRAFT ADVISORY
MAY BE NEEDED TO DUE TO GUSTY NORTHWEST WIND.

FRIDAY...NO MARINE HEADLINES ARE ANTICIPATED.

&&

.HYDROLOGY...
THE NEXT ROUND OF PRECIPITATION IS FORECAST TO MOVE INTO OUR AREA
ON TUESDAY AFTERNOON AND IT WILL CONTINUE INTO WEDNESDAY AND
THURSDAY.

THIS MIDWEEK EVENT APPEARS TO START AS A WINTRY MIX BEFORE
CHANGING OVER TO RAIN AS TEMPERATURES RISE WELL ABOVE FREEZING ON
WEDNESDAY. THE QPF AMOUNTS FOR TUESDAY INTO WEDNESDAY FAVOR THE
0.25 TO 0.75 INCH RANGE.

THE COMBINATION OF THE BRIEF WARM-UP ON WEDNESDAY, LOCALLY
MODERATE TO 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.

THE RAIN IS FORECAST TO CHANGE BACK TO SNOW ON WEDNESDAY NIGHT.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 6 AM EST
     WEDNESDAY FOR PAZ054-055-060>062.
     WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 1 AM EST
     WEDNESDAY FOR PAZ070-071-101>106.
NJ...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 6 AM EST
     WEDNESDAY FOR NJZ001-007>009.
     WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 1 AM EST
     WEDNESDAY FOR NJZ010-012-015>019.
DE...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 1 AM EST
     WEDNESDAY FOR DEZ001.
MD...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 1 AM EST
     WEDNESDAY FOR MDZ008-012.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     ANZ450>453.
     SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ430-
     431-454-455.

&&

$$
SYNOPSIS...GORSE/IOVINO
NEAR TERM...GORSE
SHORT TERM...GORSE/ROBERTSON
LONG TERM...IOVINO
AVIATION...GORSE/IOVINO
MARINE...GORSE/IOVINO
HYDROLOGY...