Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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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...

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