Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 030250 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 950 PM EST MON MAR 2 2015 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD OVER OUR AREA OVERNIGHT, 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.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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930 PM ESTF: TEMPS ADJUSTED SLIGHTLY COLDER KSMQ THROUGH KFWN WHERE MODELED ECMWF/GFS 2M TEMPS SHOULD BE CLOSER TO REALITY THAN THE MOS GUIDANCE NEAR 10Z TUESDAY IN ASSOCIATION WITH RADIATIONAL COOLING AS DECOUPLING DEVELOPS OVERNIGHT. THICK CIRRUS ARRIVES AROUND SUNRISE. DIMINISHING NORTHWEST WIND TO LIGHT AROUND MIDNIGHT.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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**WINTER WEATHER ADVISORY ALREADY POSTED FOR LATE TUESDAY** THE QUESTION: DO WE NEED TO EXPAND THIS A TIER OF COUNTIES FURTHER SE IN THE 330 AM TUESDAY FCST. NO CHANGE AT 930 PM. AM FAVORING THE NAM THERMAL PROFILE AND THIS LOOKS LIKE IT HAS A BUNCH OF SLEET AT THE START IN PA/NJ SOUTH OF I78, THEN FZRA, WHILE ALONG AND N OF I78 SNOW TO SLEET TO FRZG RAIN. IN MD/DE IT WILL BE FREEZING RAIN PROBABLY CHANGING TO RAIN. FROM THE 330 PM DISCUSSION: 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.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... **A MORE POTENT WINTER WEATHER EVENT SHAPING UP FOR 03Z THU-19Z THU** THIS WILL NEED TO BE MONITORED FOR MUCH LONGER AND POSSIBLY GREATER PUBLIC IMPACT THAN THE TUESDAY EVENING EVENT. COMPLEX FORECAST SHAPING UP DURING THE TUE NIGHT THRU THU TIME FRAME WITH TWO CHANCES OF WINTER PRECIP. FOR TUE NIGHT...OVERRUNNING WILL LEAD TO SNOW CHANGING TO SLEET AND THEN FREEZING RAIN. CONFIDENCE IS GREATEST FOR FREEZING RAIN ALONG AND NORTHWEST OF THE I-95 CORRIDOR WHERE WE ARE HOISTING A WINTER WEATHER ADVISORY. THERE IS STILL SOME UNCERTAINTY IN THE FORECAST...AND THIS ADVISORY MAY BE NEED TO BE ADJUSTED SOUTHEAST. A COLD FRONT WILL MOVE THRU ON WED...AND THIS WILL SET THE REGION UP FOR ANOTHER OVERRUNNING EVENT WED NIGHT AND THURSDAY. THERMAL PROFILES AND QPF ARE STILL HIGHLY UNCERTAIN AT THIS POINT...BUT A RAIN TO SLEET TO SNOW SITUATION SEEMS MORE LIKELY. WHERE THE HEAVIEST SNOW SLEET ACCUMULATION AXIS SETS UP IS ALSO UNCERTAIN...BUT SEVERAL INCHES OF COMBINED SNOW AND SLEET ARE EXPECTED. SOME MODEL THERMAL PROFILES SUGGEST A POSSIBLE EXTENDED PERIOD OF SLEET. THIS SYSTEM IS PROJECTED TO MOVE OFFSHORE BY LATE THU OR EARLY FRIDAY...WITH THE NEXT COLD FRONT APPROACHING OVER THE WEEKEND. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...VFR WITH CIRRUS CIGS POSSIBLE AFTER 09Z. NORTHWEST WINDS DIMINISHING TO 10 KNOTS OR LESS AROUND 05Z/3, THEN LOCALLY BECOMING LIGHT AND VARIABLE OVERNIGHT. TUESDAY...ICING SHOULD BE A DEICING PROBLEM FOR AIRCRAFT LATE TUESDAY AFTERNOON AT MANY TAF LOCATIONS BUT ALSO IN FLIGHT AOB ROUGHLY 6000 FT AS AN ABOVE FREEZING LAYER ARRIVES AT 6000-8000 FT LATE IN THE DAY WHILE MODELED THERMAL PROFILES MAINTAIN TEMPS WELL BELOW FREEZING BELOW 5000 FT LATE IN THE DAY. VFR CIGS LOWER TO MVFR/IFR IN -FZRAPLSN LATE IN THE AFTERNOON FROM WEST TO EAST. 00Z/3 TAFS ATTEMPT TO DEFINE THAT A PERIOD OF LIGHT SNOW WOULD PRIMARILY OCCUR AT KABE/KTTN WITH PL AND FZRA AT ALL OTHER TAF SITES; MAYBE MOSTLY PL AT KRDG THROUGH 00Z/4. LIGHT WIND BECOMING SOUTHEAST NEAR KNOTS. ISOLATED GUSTS 15 KT MID AND LATE AFTN. OUTLOOK... TUESDAY NIGHT...MAINLY IFR CONDITIONS WITH SN/PL QUICKLY CHANGING TO ZR AND THEN RA FROM SOUTH TO NORTH IN THE EVE. ZR MAY HOLD ON UNTIL AFTER MIDNIGHT AT RDG/ABE. LLWS WILL BE THE OTHER PROBLEM DUE TO A STRONG SWLY LOW-LEVEL JET THAT IS FORECAST TO DEVELOP OVERHEAD. LLWS IS IN THE PHL TAF WHEN A WIND OF 210-220 AT 50 KT IS MODELED BY THE NAM AROUND 03Z/4. LLWS MOST PREDOMINANT OVER S NJ WHERE STRONGER SW WINDS ARE FORECAST NEAR 2000 FT. WEDNESDAY...OCNL MVFR AND IFR CONDITIONS IN PERIODS OF RAIN. WEDNESDAY NIGHT AND THURSDAY...MVFR AND IFR CONDITIONS IN RAIN. THE RAIN IS EXPECTED TO MIX WITH AND THEN CHANGE TO SNOW FROM NORTHWEST TO SOUTHEAST. THERE IS STILL LOWER CONFIDENCE ON TIMING OF THE CHANGEOVER BUT ABE/RDG LOOK TO CHANGE OVER FIRST WEDNESDAY NIGHT AND THEN THE I-95 TERMINALS EITHER LATE WEDNESDAY NIGHT OR THURSDAY MORNING. IFR/LIFR IF HEAVIER SNOW DEVELOPS. GUSTY NW WINDS DEVELOP. THURSDAY NIGHT THROUGH SATURDAY...MAINLY VFR.
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&& .MARINE...
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EXTENDED SCA NNJ WATERS THRU 06Z/3 PER OBSERVED WIND AT 40065 AND WX FLOW SANDY HOOK. 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...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 TO THE SURFACE. SEAS IN OUR COASTAL ZONES INCREASE TO 4-6 FT. WEDNESDAY NIGHT AND THURSDAY...SCA LIKELY WITH GUSTY NW WINDS AND AT LEAST LIGHT FREEZING SPRAY. THURSDAY NIGHT THROUGH SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED.
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&& .HYDROLOGY...
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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. BUT 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. IN ADDITION, CURRENT MODEL SOLUTIONS HAVE THE GREATEST AMOUNTS OF RAINFALL ACROSS THE COASTAL PLAIN WHERE THERE IS MUCH LESS LIQUID WATER EQUIVALENT IN THE SNOWPACK. LOOKING AT THE MMEFS SOLUTIONS, ENSEMBLE QPF IS RUNNING HIGHER THAN THE OPERATIONAL. RUNNING WITH THE 0.25 TO 0.75 INCH OVER A SNOWPACK OR NOT, WE FEEL NUISANCE POOR DRAINAGE AND LOW LYING FLOODING IS THE MOST LIKELY OUTCOME. MODELED SOLUTIONS SUGGEST 1.50 INCHES OF RAINFALL ALONG WITH ABOUT AN INCH OF SNOW SMELT COULD GET SOME SMALLER STREAMS AND CREEKS TO LEAVE THEIR BANKS. STILL, INCREASED FLOW ON 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 SLEET AND THEN SNOW ON WEDNESDAY NIGHT/THURSDAY MORNING AS MUCH COLDER AIR ARRIVES FROM THE NORTH.
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&& .CLIMATE... SECOND COLDEST FEBRUARY ON RECORD FOR ALLENTOWN, PA... AVG TEMP YEAR 1 16.5 1934 2 18.9 2015* 3 20.4 1979 4 21.3 1936 5 22.0 1963 6 22.3 1978 7 22.4 1923 8 23.9 2007 9 24.3 1967 10 24.6 1958 POR 1922 TO PRESENT ALSO, THIS 18.9 AVERAGE IS THE 3RD COLDEST MONTH ON RECORD DATING BACK TO 1922 FOR ALLENTOWN WITH JAN 1977 18.6 RANKING NUMBER 2. JANUARY 2015 HAD AN AVERAGE TEMPERATURE OF 25.9, 7 DEGREES WARMER THAN FEBRUARY! SEVENTH COLDEST FEBRUARY ON RECORD FOR PHILADELPHIA, PA... AVG TEMP YEAR 1 22.2 1934 2 23.0 1979 3 24.3 1885 4 24.6 1978 5 25.4 1895 6 25.7 1875 7 25.8 2015* 8 26.3 1905 9 26.4 1963 10 27.1 1907 POR 1872 TO PRESENT THE FEBRUARY AVERAGE AT PHILADELPHIA`S 5.1 DEGREES COLDER THAN JANAURY`S 30.9 AVERAGE. FOURTH COLDEST FEBRUARY ON RECORD FOR ATLANTIC CITY, NJ... AVG TEMP YEAR 1 21.6 1979 2 23.6 1934 3 23.8 1978 4 24.4 2015* 5 25.5 1875 6 25.7 1905 7 25.8 1885 8 26.0 1895 9 26.8 1968 10 26.9 1904 POR 1874 TO PRESENT FOR ATLANTIC CITY THIS TIED FOR THE 7TH COLDEST MONTH ON RECORD. THE FEBRUARY AVERAGE WAS 5.8 DEGREES COLDER THAN THE AVERAGE OF 30.2 IN JANUARY. TO OUR KNOWLEDGE THIS IS THE FIFTH COLDEST FEBRUARY ON RECORD FOR WILMINGTON, DE... AVG TEMP YEAR 1 20.2 1934 2 22.1 1979 3 22.7 1978 4 24.6 1936 5 24.8 2015* 6 27.2 1895 7 27.3 1958 8 27.5 1963 9 27.8 1947 10 28.1 2007 *NEW THE FEBRUARY AVERAGE WAS 5.5 DEGREES COLDER AT WILMINGTON THAN THE 30.3 OF JANUARY 2015. THE POR 1894 TO PRESENT BUT IS MISSING A NUMBER OF YEARS OF DATA. && .PHI WATCHES/WARNINGS/ADVISORIES...
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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 1 AM EST TUESDAY FOR ANZ450-451.
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&& $$ SYNOPSIS...FRANCK NEAR TERM...DRAG 950 SHORT TERM...DRAG/GORSE 950 LONG TERM...DRAG/FRANCK AVIATION...DRAG/KLEIN 950 MARINE...DRAG/KLEIN HYDROLOGY...KRUZDLO CLIMATE...MEOLA/DRAG 950

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