Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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767 FXUS61 KPHI 140246 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 946 PM EST SAT FEB 13 2016 .SYNOPSIS... ARCTIC HIGH PRESSURE CENTERED OVER THE MIDWEST LATE THIS EVENING WILL BUILD OVER OUR REGION THROUGH THE REMAINDER OF THE WEEKEND. THE HIGH THEN RETREATS OFF THE COAST SUNDAY NIGHT AND MONDAY. LOW PRESSURE IS FORECAST TO DEVELOP OVER THE NORTHERN GULF COAST STATES MONDAY AND THEN TRACK NORTHEASTWARD UP THE EASTERN SEABOARD MONDAY NIGHT AND TUESDAY. A COLD FRONT SHOULD PASS THROUGH THE MID- ATLANTIC REGION WEDNESDAY. HIGH PRESSURE RETURNS FOR THURSDAY AND FRIDAY. ANOTHER COLD FRONT MAY APPROACH FROM THE WEST EARLY NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... WITH INCOMING ARCTIC HIGH PRESSURE SPREADING EAST INTO THE MID- ATLANTIC, THE DRIER AIR MASS DEEPENS ACROSS OUR REGION. NOT MANY ADJUSTMENTS NEEDED TO OVERNIGHT LOW TEMPS AS THE FCST LOOKS ON TRACK, BUT WE DID USE THE LAV/LAMP GUIDANCE TO CAPTURE THE LATEST HOURLY DEWPOINT AND TEMP TRENDS INTO TONIGHT. GRADUAL CLEARING IS EXPECTED THROUGH THE NIGHT, AND THERE COULD BE SOME WEST- NORTHWEST WIND GUSTS TO AROUND 25 TO 30MPH THROUGH THE REMAINDER OF THE LATE EVENING. OTHERWISE, THE WIND CHILL HEADLINES CONTINUE AS MUCH OF THE FORECAST AREA WILL FEEL WIND CHILLS TO BETWEEN 10 TO 20 BELOW ZERO, WITH WIND CHILLS RANGING 20 TO 30 BELOW ZERO ACROSS THE POCONOS AND NORTHWEST NJ. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... HIGH PRESSURE WILL CREST OVER THE REGION SUNDAY. SKIES ARE EXPECTED TO BE CLEAR AND WINDS WILL BE RATHER LIGHT. VERY COLD MORNING TEMPERATURES WILL MODERATE ONLY INTO THE TEENS IN MOST AREAS. THERE MAY BE SOME LOW 20S ACROSS THE DELMARVA HOWEVER. WINDS WILL BE MOSTLY WEST OR NORTHWEST AT 5 TO 10 MPH. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... ARCTIC HIGH PRESSURE SETTLES OVER THE AREA SUNDAY EVENING. HIGH CLOUDS WILL START TO STREAM IN FROM THE WEST BUT SHOULD BE THIN AND NOT HAVE MUCH OF AN IMPACT ON RADIATIONAL COOLING. THEREFORE, TEMPS SHOULD DROP RATHER QUICKLY AFTER SUNSET UNDER LIGHT WINDS. THE HIGH WILL BEGIN TO MOVE OFF THE COAST OVERNIGHT WHILE CLOUDS WILL LOWER AND THICKEN AHEAD OF THE APPROACHING STORM SYSTEM. THEREFORE, TEMPS MAY NOT DROP AS MUCH AND EVEN RISE OVERNIGHT. REGARDLESS, IT WILL BE A COLD NIGHT WITH LOWS IN THE SINGLE DIGITS IN THE RURAL AREAS OF EASTERN PA AND NJ...AND TEENS IN THE CITIES, ALONG THE COAST AND IN THE DELMARVA. OUR ATTENTION THEN TURNS TO A POTENTIALLY SIGNIFICANT WINTER STORM THAT IS EXPECTED TO IMPACT THE MID-ATLANTIC REGION EARLY IN WEEK. THE TREND HAS BEEN FOR A SLIGHTLY QUICKER ARRIVAL OF PRECIP ON MONDAY AS A STRENGTHENING SLY WINDS ALOFT PRODUCES ISENTROPIC LIFT. THE OVERRUNNING PRECIP WILL BE COLD ENOUGH TO START AS SNOW EVERYWHERE. IT MAY COME IN QUICK ENOUGH TO BRING LIGHT SNOW ACCUMULATIONS THAT COULD IMPACT THE MORNING COMMUTE ON PRESIDENT`S DAY, ESPECIALLY TOWARD THE DELMARVA. THE SYNOPTIC SETUP TO LOCK THE COLD AIR IN PLACE WILL NOT BE THERE WITH THIS EVENT AS THE HIGH IS RETREATING FARTHER OFFSHORE ON MONDAY. THE BIG QUESTION IS HOW QUICKLY WILL IT TAKE FOR THE DOME OF RESIDUAL ARCTIC AIR IN THE LOW-LEVELS TO RETREAT? THE MODELS FROM YESTERDAY`S RUNS WERE SHOWING A MORE AMPLIFIED UPSTREAM TROUGH WITH A NEGATIVE TILT THAT ALLOWED FOR A STRONGER LOW TO DEVELOP AND TRACK FARTHER INLAND (OVER CENTRAL PA ON TUESDAY). THE ECMWF HAS HELD ONTO THIS IDEA AS WELL EVEN WITH THE LATEST RUN. ASIDE FROM THE ECMWF, TODAY`S 12Z RUNS HAVE TRENDED A BIT MORE PROGRESSIVE WITH THE TROUGH, WHICH WOULD RESULT IN A WEAKER LOW THAT TRACKS CLOSER TO THE I-95 CORRIDOR. A TRACK LIKE THIS WOULD IMPLY THAT THE WARM FRONT WILL NOT HAVE MUCH RESISTANCE REACHING AREAS TO THE EAST OF THE FALL LINE AND THUS THE CHANGEOVER FROM SNOW TO RAIN WOULD OCCUR QUICKLY ALONG AND EAST OF I-95 MONDAY AFTERNOON AND EVENING FROM SE TO NW. STILL CANNOT RULE OUT A BRIEF PERIOD OF SLEET/FREEZING RAIN THOUGH DURING THE TRANSITION, ESPECIALLY WITH THE NEAR RECORD COLD LEADING UP TO IT. AN INCH OR TWO OF SNOW IS POSSIBLE BEFORE THE CHANGEOVER. FARTHER NORTH AND WEST TOWARD BERKS COUNTY, THE LEHIGH VALLEY, POCONOS AND NORTHWEST NJ, THERE WILL LIKELY BE MORE RESISTANCE FROM THE SHALLOW COLD AIR IF THE LOW TRACKS ALONG OR JUST TO THE EAST AS CONSENSUS INDICATES. THUS, THE THREAT FOR AN EXTENDED PERIOD OF MIXED WINTRY PRECIP IS HIGHEST IN NORTHEAST PA AND NORTHWEST NJ WITH THIS EVENT. THE CHANGEOVER TO SNOW MAY BE DELAYED UNTIL MONDAY NIGH FOR THESE INLAND AREAS AND WOULD BE FOLLOWED BY A PERIOD OF SLEET AND FREEZING RAIN. SOME OF THE GUIDANCE HAS THE WARMER AIR INFILTRATING THESE FAR NORTHWESTERN AREAS, ALLOWING TEMPS TO RISE ABOVE FREEZING AND FOR PRECIP TO CHANGE TO RAIN MUCH EARLIER THAN WE FORECAST. AM A BIT SKEPTICAL OF THESE WARM SOLUTIONS AS THE COLD AIR TENDS TO HANG ON LONGER THAN MODELED IN NORTHEAST PA AND NORTHWESTERN NJ, WHERE THE OROGRAPHY PLAYS A ROLE IN TRAPPING THE SHALLOW COLD AIR NEAR THE SURFACE ESPECIALLY IN SHELTERED VALLEYS. WOULD NOT BE SURPRISED TO SEE TEMPERATURES STRUGGLING TO GO ABOVE FREEZING THROUGHOUT THE DURATION OF THE EVENT TOWARD THE POCONOS/ DELAWARE WATER GAP/HIGH POINT. THE LATEST SNOWFALL FORECAST THAT WENT OUT WITH THE AFTERNOON UPDATE IS FOR 3-5 INCHES OF SNOW IN OUR FAR NORTHERN AND WESTERN ZONES AS WELL AS ONE- TO TWO-TENTHS INCH OF ICE. LOCALLY HIGHER AMOUNTS ABOVE ONE-QUARTER INCH SEEMS POSSIBLE IN THE ICE-STORM PRONE POCONOS. SINCE THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY THIS FAR OUT REGARDING SNOW/ICE AMOUNTS AND IMPACTS, WE WILL HOLD OFF ON A WINTER STORM WATCH FOR NOW. THERE IS A POTENTIAL FOR HEAVY RAIN, PARTICULARLY TUESDAY MORNING, AND THUS THE OTHER CONCERN IS FLOODING. PLEASE SEE OUR HYDRO SECTION BELOW FOR MORE DETAILS. NORTHWEST FLOW WILL DEVELOP AFTER THE WAVE OF LOW PRESSURE TRACKING ALONG THE FRONT MOVES NORTH OF US INTO THE NORTHEAST STATES. THIS WILL CAUSE THE COLD FRONT TO MOVE OFFSHORE TUESDAY AFTERNOON. THE RAIN (EXCEPT POSSIBLY A WINTRY MIX IN THE FAR NORTHWESTERN ZONES) WILL END FROM SOUTHWEST TO NORTHEAST DURING THIS TIME. AFTER A LULL IN PRECIP LATE TUESDAY, ANOTHER ROUND OF LIGHTER PRECIP IN ASSOCIATION WITH THE TRAILING UPPER SHORTWAVE TROUGH WILL PIVOT THROUGH THE AREA ON WEDNESDAY. COLDER AIR WILL ALSO WORK INTO THE AREA SO THE PRECIP MAY CHANGE OVER TO SNOW IN THE HIGHER ELEVATIONS AND EITHER RAIN/SNOW MIX OR JUST RAIN ELSEWHERE. HIGH PRESSURE BUILDS IN THURSDAY AND FRIDAY RESULTING IN DRY CONDITIONS. BELOW NORMAL TEMPS ON THURSDAY RETURN TO NEAR NORMAL FRIDAY. THE HIGH MOVES OFFSHORE BY THE START OF THE WEEKEND AS A STORM SYSTEM APPROACHES FROM THE GREAT LAKES. THE TRACK OF THE LOW FAVORS MAINLY RAIN FOR US EXCEPT MAYBE SNOW AT THE ONSET IN INTERIOR SECTIONS. THE SYSTEM LOOKS TO BE EMBEDDED IN A RATHER FAST ZONE FLOW PATTERN, SO WE ARE CURRENTLY NOT ANTICIPATING A SIGNIFICANT RAINFALL EVENT. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS WILL CONTINUE AT THE TAF SITES TONIGHT AND SUNDAY. THE DRYING AIRMASS SHOULD YIELD LESS IN THE WAY OF SNOW SHOWER ACTIVITY TONIGHT, AS COMPARED TO EARLIER DURING SATURDAY. THE WINDS WILL REMAIN GUSTY THROUGH THE EVENING TO AROUND 25 OR EVEN 30 KT AND THEN GRADUALLY DIMINISH SOME LATE TONIGHT. ON SUNDAY, VFR CONDITIONS WITH MOSTLY CLR SKIES ARE EXPECTED. WINDS W TO NW AT 8 TO 12 KNOTS, THEN DECREASING LATE-DAY. OUTLOOK... SUNDAY NIGHT...VFR AND LIGHT WINDS. MONDAY AND MONDAY NIGHT...SNOW OVERSPREADING THE AREA DURING THE DAY (PERHAPS MORNING ACROSS THE SOUTHERN TERMINALS IN THE MORNING AND AFTERNOON TOWARD ABE. THE SNOW MAY START TO MIX WITH OR CHANGE TO RAIN LATE IN THE DAY, ESPECIALLY AT ILG-MIV-ACY. THE TRANSITION TO RAIN WILL WORK INTO THE REST OF THE I-95 TERMINALS BY EVENING. IFR CONDITIONS LIKELY. THERE IS A POTENTIAL FOR A BRIEF PERIOD OF FREEZING RAIN DURING THAT TRANSITION. THE BIGGER CONCERN IS FOR SEVERAL HOURS OF FREEZING RAIN TOWARD RDG AND ABE. POTENTIAL FOR LLWS MONDAY NIGHT WITH A STRONG THERMAL INVERSION ALOFT AND A SLY JET NEAR 60 KT AT 2 KFT AGL. TUESDAY...RAIN MAY BE HEAVY AT TIMES IN THE MORNING. IFR CONDITIONS LIKELY. THE RAIN WILL EXIT THE AREA DURING THE AFTERNOON FROM SW TO NE AND IMPROVE TO VFR IN ITS WAKE. TUESDAY NIGHT AND WEDNESDAY...MAINLY VFR. HOWEVER, LIGHT RAIN MAY MOVE IN AND COULD BE ACCOMPANIED BY LOCAL RESTRICTIONS TO MVFR. WEDNESDAY THROUGH FRIDAY...VFR. && .MARINE... MARINE HEADLINES WILL CONTINUE WITH GALES AND FREEZING SPRAY THE HAZARDS WHICH WILL CONTINUE THROUGH THE NIGHT AND INTO SUNDAY MORNING. THERE MAY BE A FEW SCATTERED SNOW SHOWERS, BUT OTHER THAN THAT JUST COLD GUSTY WINDS AND FAIR WEATHER. OUTLOOK... SUNDAY NIGHT AND MONDAY...NO MARINE HEADLINES EXPECTED. MONDAY NIGHT AND TUESDAY...SLY WINDS INCREASE BUT MIXING POTENTIAL WILL BE LIMITED WITH WARM AIR ATOP THE COLDER WATERS. SUSTAINED WINDS 25-30 KT IN OUR COASTAL WATERS MAY STRUGGLE TO BRING DOWN GALE FORCE GUSTS OUTSIDE OF CONVECTIVE TRANSPORT. SEAS WILL BUILD TO 6-10 FT IN THE ATLANTIC COASTAL WATERS MONDAY NIGHT AND TUESDAY. TUESDAY NIGHT AND WEDNESDAY...WINDS WILL WEAKEN BUT SEAS MAY REMAIN ELEVATED TO AOA 5 FT, WHICH WOULD WARRANT A SMALL CRAFT ADVISORY. WEDNESDAY AND THURSDAY....NW WINDS LATE WEDNESDAY AND THURSDAY BEHIND A COLD FRONT MAY GUST TO NEAR SCA THRESHOLD. && .HYDROLOGY... THERE IS POTENTIAL FOR FLOODING ACROSS THE HSA INTO THE EARLY PART OF THIS WEEK AS HEAVIER PRECIPITATION IS EXPECTED TO OVERSPREAD THE REGION LATE MONDAY NIGHT THROUGH TUESDAY. THERE`S STILL A LOT THAT NEEDS TO UNFOLD, BUT THE 5-DAY WPC QPF OF 1.25 TO 2.50 INCHES OF LIQUID COMBINED WITH ANOTHER 0.25 TO 0.50 INCH OF SWE ON THE GROUND WOULD VERY LIKELY CAUSE NUISANCE LOW-LYING FLOODING/POOR DRAINAGE FLOODING AND POSSIBLY SOME MINOR TO PERHAPS MODERATE RIVER FLOODING (RIVERS ASSOCIATED WITH OUR FORECAST POINTS). THIS ASSUMES MOST, IF NOT ALL, THE PRECIPITATION FALLS AS RAIN. HOWEVER, IF THE PRECIPITATION STARTS OFF AS SNOW OR ICE, THE EXTENT OF THE FLOODING THREAT DECREASES. AT THIS TIME, THE RARITAN AND PASSAIC BASINS HAVE A SOMEWHAT HIGHER POTENTIAL FOR POSSIBLE RIVER FLOODING AS THESE AREAS MAY BE ON THE HIGHER END OF EXPECTED QPF AMOUNTS, BUT THERE COULD ALSO BE SOME POSSIBLE FLOODING CONCERNS INTO EASTERN PA. THE UNCERTAINTY WITH THIS SET-UP IS LARGE. THE PRECIPITATION IS HEAVIEST LATE MONDAY NIGHT THROUGH TUESDAY. THE TRACK OF THE LOW PRESSURE WILL PLAY A ROLE IN DETERMINING TEMPERATURES AND NOT ONLY AFFECT WHAT TYPE OF PRECIPITATION FALLS, BUT ALSO AFFECT WHAT REMAINING SWE MELTS. THERE`S ABOUT 0.25 TO 0.50 INCH OF SWE SCATTERED ACROSS THE AREA. WE ARE IN A BETTER SPOT AS COMPARED TO THE 3RD AND 4TH WHEN THERE WAS IN EXCESS OF 2.00 OF SWE ALONG THE I- 78 CORRIDOR. AS AN FYI, ONE OF THE MAIN REASONS WE DIDN`T SEE THE FLOODING, THAT MODELS SUGGESTED, ON THE 3RD AND 4TH WAS BECAUSE ALL THE SWE DID NOT RAPIDLY COME OUT OF THE SNOWPACK. SNOWMELT CAN BE A TOUGH NUT TO CRACK. WHILE THE LACK OF SWE IS LOOKING BETTER ACROSS THE HSA, NOT ALL THE RIVERS HAVE RECEDED BACK TO WHERE THEY WERE PRIOR TO THE 3RD. SO RIVERS WILL START HIGHER AND THE COLD THIS WEEKEND WILL SURELY GET THE GROUND HARD FOR A VERY EFFICIENT RUNOFF. && .CLIMATE... NEAR RECORD COLD IS STILL EXPECTED FOR PORTIONS OF OUR AREA TOMORROW MORNING...AND THE COLDEST AIR OF THE SEASON SO FAR. BEST CHANCE FOR RECORD EQUALING OR EXCEEDING FOR VALENTINES DAY: KABE, KTTN, KPHL AND KMPO. RECORD LOW MAX`S CAN ONLY OCCUR FOR THIS EVENT ON SUNDAY THE 14TH, IF AT ALL. THOSE HAVE BEEN ADDED RECENTLY BELOW. SITE 2015-16 COLDEST SO FAR RECORD LOW FEB. 14TH RER LOW MAX --------------------------- -------------------- ----------- ABE 8 -1 IN 1979 14-1979 ACY 10 -6 IN 1979 13-1979 PHL 12 +2 IN 1979 14-1979 ILG 12 -4 IN 1979 13-1979 RDG 10 -4 IN 1983 TTN 9 0 IN 1916 GED 13 -7 IN 1979 MPO -1 -12 IN 1970 && .EQUIPMENT... WE ARE EXPERIENCING DIFFICULTY UPLOADING OUR LATEST STORM TOTAL SNOW AND ICE MAPS TO OUR WEBSITE THIS EVENING. WE ARE WORKING TO IDENTIFY THE SOURCE OF THIS PROBLEM AND TO CORRECT THIS ISSUE SO THAT THESE IMAGES WILL POST TO OUR WEBSITE SOON. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WIND CHILL ADVISORY UNTIL 9 AM EST SUNDAY FOR PAZ060>062-070- 071-101>106. WIND CHILL WARNING UNTIL 1 PM EST SUNDAY FOR PAZ054-055. NJ...WIND CHILL ADVISORY UNTIL 9 AM EST SUNDAY FOR NJZ007>010- 012>027. WIND CHILL WARNING UNTIL 1 PM EST SUNDAY FOR NJZ001. DE...WIND CHILL ADVISORY UNTIL 9 AM EST SUNDAY FOR DEZ001>004. MD...WIND CHILL ADVISORY UNTIL 9 AM EST SUNDAY FOR MDZ008-012-015- 019-020. MARINE...HEAVY FREEZING SPRAY WARNING UNTIL 9 AM EST SUNDAY FOR ANZ450>453. GALE WARNING UNTIL 10 AM EST SUNDAY FOR ANZ430-431-450>455. FREEZING SPRAY ADVISORY UNTIL 10 AM EST SUNDAY FOR ANZ430-431- 454-455. && $$ SYNOPSIS...KLEIN NEAR TERM...KLINE SHORT TERM...O`HARA LONG TERM...KLEIN AVIATION...KLEIN/KLINE/O`HARA MARINE...KLEIN/O`HARA HYDROLOGY...KRUZDLO/KLINE CLIMATE...DRAG EQUIPMENT...STAFF

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