Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 042138 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 438 PM EST WED MAR 4 2015 .SYNOPSIS... SEVERAL WAVES OF LOW PRESSURE WILL TRACK NORTHEASTWARD ALONG A COLD FRONTAL BOUNDARY TONIGHT AND THURSDAY. THIS COLD FRONTAL BOUNDARY WILL MOVE OFFSHORE THURSDAY NIGHT AND WILL GIVE WAY TO AN AREA OF HIGH PRESSURE MOVING INTO THE REGION ON FRIDAY. FOR THE WEEKEND AND EARLY NEXT WEEK, WE WILL ALTERNATE BETWEEN AREAS OF HIGH PRESSURE AND COLD FRONTS MOVING THROUGH THE REGION. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... TRENDS VIA 18Z AND 20Z HRRR SHOW A HURRY UP CHANGE TO SNOW FROM NORTH TO SOUTH SUCH THAT PHL SHOULD BE SEEING SNOW ACCUM AROUND 08Z WITH 2-3 INCHES NEAR AND N OF I80 BY 09Z. COLD FRONT SHOULD BEGIN TO PUSH THROUGH THE REGION LATE THIS EVENING. AS IT DOES SO, THE PRECIPITATION TYPE WILL CHANGE FROM RAIN TO WINTRY PRECIPITATION. EXACTLY WHAT KIND OF WINTRY PRECIPITATION WILL DEPEND ON WHERE IN THE REGION AND WHAT TIME THE FRONT FINALLY COMES THROUGH. FOR THE POCONOS AND LEHIGH VALLEY IN PA AND NORTHWEST NJ, IT LOOKS LIKE A PRETTY FAST AND CLEAN TRANSITION FROM RAIN TO SNOW BY LATE THIS EVENING. FOR THE URBAN CORRIDOR, CENTRAL AND SOUTHERN NJ, AND FAR NORTHERN DELMARVA, A WARM NOSE IS EXPECTED TO DEVELOP AROUND OR JUST AFTER MIDNIGHT IN THE LOW LEVELS, MAKING A BRIEF PERIOD OF A WINTRY MIX OF SLEET AND SNOW POSSIBLE BEFORE CHANGING OVER TO ALL SNOW. SOUTHERN DELMARVA SHOULD STAY MOSTLY RAIN THROUGH THE OVERNIGHT HOURS UNTIL JUST BEFORE SUNRISE - WHICH IS DISCUSSED MORE IN THE SHORT TERM SECTION. THIS ALL DEPENDENT ON THE TIMING OF THE COLD FRONT AND THE TEMPERATURES, WHICH GUIDANCE HAS BEEN POOR FOR TEMPERATURES MOST OF THE DAY. AS FOR SNOW AMOUNTS, THE AXIS OF HEAVIEST QPF HAS SHIFTED FURTHER SOUTH, HOWEVER THIS WILL ALL BE DEPENDENT ON THE TIMING OF THE CHANGE OVER, WHICH AS MENTIONED BEFORE IS STILL UNCERTAIN. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... RECORD DAILY SNOWFALLS POSSIBLE AT KILG AND KACY. PLS SEE CLIMATE SECTION FOR DETAILS ON THE BIG FOUR. THE WARM NOSE WILL STILL BE PRESENT, AND SHOULD IN FACT BE A BIT DEEPER OVER SOUTHERN DELMARVA AS THEY DROP NEAR AND BELOW FREEZING NEAR SUNRISE. AS SUCH, COULD SEE A MIX OF FREEZING RAIN AND SLEET BEFORE IT CHANGES OVER TO ALL SNOW NO LATER THAN MID MORNING. ON THE OTHER SIDE OF THE REGION, DRIER AIR MOVING INTO THE POCONOS AND NW NJ COULD ERODE AND END THE PRECIPITATION FOR THOSE AREAS BY MID DAY. DRY AIR ADVECTION WILL TAKE OVER ACROSS MUCH OF THE REST OF THE AREA THROUGH THE AFTERNOON, ALLOWING THE PRECIPITATION TO TAPER OFF ALMOST EVERYWHERE BY LATE AFTERNOON. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... FAIRLY QUIET WITH A GENERAL NORTHWEST FLOW PATTERN OF ALTERNATING COLD FRONTS AND WEST-SOUTHWESTERLY FLOW WARM-UPS AHEAD OF THESE FRONTS. SLIGHT TO LOW PRECIPITATION CHANCES AHEAD OF THESE FRONTS, FOCUSED NORTH. THURSDAY NIGHT THROUGH SATURDAY: A COLD FRIDAY MORNING IS ON TAP WITH SNOWCOVER IN PLACE, CLEAR SKIES AND MAINLY LIGHT WINDS UNDER 10 MPH. RADIATIONAL COOLING SHOULD ALLOW FOR A QUICK TEMPERATURE DROP AFTER CLOUDS CLEAR. WENT COLDER THAN MAV AND MET GUIDANCE SETS CLOSER TO THE MODELED TWO METER TEMPERATURES FROM THE GFS. HIGH PRESSURE BUILDS INTO THE REGION KEEPING THIS PERIOD DRY WITH A EVENTUAL SWING FROM NORTHWEST TO SOUTHWEST WINDS AND MODERATING TEMPERATURES BY SATURDAY. TRENDED COLDER THAN THE MET AND MAV AT NIGHT DUE TO SNOWCOVER AND WARMER DURING THE DAY. THESE GUIDANCE SETS HAVE BEEN RUNNING WITH A COLD BIAS IN THE DAYTIME. SOUNDINGS ALSO YIELD THE POTENTIAL FOR SOME WIND GUSTS AROUND 15 MPH SATURDAY AFTERNOON. SATURDAY NIGHT AND SUNDAY: A COLD FRONT WILL DECAY INTO A TROUGH ACROSS NEW ENGLAND BY SUNDAY MORNING PROVIDING AN INCREASE IN CLOUDS AND PERHAPS A LOW CHANCE FOR RAIN AND SNOW SHOWERS ACROSS FAR NORTHERN PARTS OF THE REGION, CLOSER TO THE FRONT. A FEW 06Z GEFS MEMBERS HAVE MOISTURE FROM THE GULF COMING NORTH AS WELL, FOR NOW WILL GO WITH THE MODEL CONSENSUS AWAY FROM THIS IDEA. SNOWCOVER SHOULD LESS OF A CONCERN WITH TEMPERATURES BY SUNDAY. WITH MORE CLOUDS AROUND THE ENSEMBLE GUIDANCE FROM WPC IS PREFERRED FOR MOST ELEMENTS. WINDS ARE MORE IN LINE WITH THE NAM/GFS MODELS THOUGH. SUNDAY NIGHT THROUGH WEDNESDAY: ONCE AGAIN HIGH PRESSURE IS IN CONTROL IN THE REGION WITH GENERAL WEST WINDS. THIS WILL RESULT IN A BRIEF PERIOD OF COOLER TEMPERATURES SUNDAY NIGHT BEFORE SPRING LIKE DAYS ON MONDAY THROUGH WEDNESDAY. A WEAK FRONTAL BOUNDARY AGAIN LOOKS TO FOCUS ON NEW ENGLAND FOR MONDAY, ANOTHER LOW CHANCE OF PRECIPITATION. THEN THIS WILL BE FOLLOWED BY ANOTHER HIGH PRESSURE SYSTEM. THE AIRMASS BY TUESDAY AND WEDNESDAY WILL BE THE WARMEST IN SOME TIME ACROSS THE REGION. LIKED THE DIRECTION OF THE ENSEMBLE GUIDANCE TO TREND TEMPERATURES SEVERAL DEGREES WARMER THAN THE MODELED TWO METER TEMPERATURES. THE MODELED TWO METER TEMPS LOOK TO COOL SHOULD SOME SOUTHERLY COMPONENT GET INVOLVED, THIS LOOKS LIKE IT HAS A FAIR CHANCE OF OCCURRING BY WEDNESDAY. FORECAST HIGH OF 56 AT PHL WEDNESDAY, I`M SURE THIS WILL BE WELCOME TO MANY. LOW PRESSURE THAT FORMS IN THE GULF OF MEXICO TUE-WED LOOKS TO STAY SOUTH OF OUR REGION ATTM. && .AVIATION /22Z WEDNESDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. CEILINGS WILL GRADUALLY LOWER TO IFR CONDITIONS BY 00Z. VISIBILITIES WILL BE VARIABLE BETWEEN IFR AND MVFR THROUGH MUCH OF THIS EVENING, THEN LOWER TO STEADY IFR AS PRECIPITATION CHANGES FROM RAIN TO A WINTRY MIX TO EVENTUALLY ALL SNOW. EXACTLY WHEN THIS WILL HAPPEN IS STILL UNCERTAIN AND WILL START FROM KABE AND KRDG AND MOVE SOUTHEAST THROUGH THE OVERNIGHT HOURS. FOR THE TAF SITES, EXPECT A 1 TO 2 HOUR WINDOW FOR A MIX OF SLEET AND SNOW, BEFORE IT CHANGES OVER TO ALL SNOW. CONDITIONS SHOULD SLOWLY IMPROVE, AGAIN FROM NORTHWEST TO SOUTHEAST BETWEEN 15 AND 00Z THROUGH THE DAY TOMORROW. OUTLOOK... THURSDAY NIGHT: IMPROVING TO VFR BY MID-EVENING. NORTHWEST WIND AROUND 10 KNOTS. FRIDAY AND FRIDAY NIGHT: VFR, NORTHWEST WIND 10 KNOTS OR LESS. SATURDAY THROUGH SUNDAY NIGHT: VFR, WEST TO SOUTHWEST WIND AROUND 10 KNOTS, GUSTS AROUND 15 KNOTS SATURDAY AFTERNOON. MID-LEVEL CLOUDS SATURDAY NIGHT AND SUNDAY MORNING, PASSING RAIN/SNOW SHOWER CAN NOT BE RULED OUT FOR ABE. MONDAY AND MONDAY NIGHT: VFR, MID-LEVEL CLOUDS. && .MARINE... THIS SECTION UPDATES BY 5P. OUTLOOK.. SEAS LOOK TO REMAIN BELOW FIVE FEET THROUGHOUT THE ENTIRE OUTLOOK PERIOD, WITH SEAS NEAR FIVE FEET EARLY THURSDAY NIGHT. THE FORECAST IS ABOUT A FOOT HIGHER THAN WAVEWATCH. NORTHWEST WIND GUSTS AROUND 20 KNOTS MAY OCCUR THURSDAY EVENING. OTHERWISE WIND GUSTS SHOULD STAY UNDER 20 KNOTS. SOME FREEZING SPRAY MAY OCCUR THURSDAY NIGHT AND EARLY FRIDAY IN ICE FREE WATERS. CONFIDENCE IS NOT HIGH FOR ANY MODERATE FREEZING SPRAY IN TERMS OF DURATION AND LIKELIHOOD, MAY JUST LAST A FEW HOURS IF IT OCCURS. WITH SOME MODERATE FREEZING SPRAY IN THE GRIDS, DID INCLUDE MENTION IN THE HWO. && .HYDROLOGY... MODELS CONTINUE TO SHOW A DECENT AMOUNT OF QPF ACROSS THE AREA TONIGHT INTO THURSDAY. IN GENERAL AND BREAKING THE CWA INTO THIRDS, A CHANGEOVER TO SLEET OR SNOW IS EXPECTED ACROSS THE NORTHERN THIRD BY AROUND MIDNIGHT, THE MIDDLE THIRD BY DAYBREAK, AND THE SOUTHERN THIRD BY MID-MORNING TOMORROW. WITH THE GROUND BEING FROZEN EVERYWHERE, ANY RUNOFF WILL BE VERY EFFICIENT BEFORE THE CHANGEOVER. MORNING MODELS CONTINUE TO PRODUCE BETWEEN 0.50 TO 1.00 INCH OF QPF BEFORE THE CHANGEOVER. WITH THIS AMOUNT, WE FEEL NUISANCE POOR DRAINAGE AND LOW LYING FLOODING WILL BE THE MOST LIKELY OUTCOME. WITH MORE SNOW OR SLEET EXPECTED ACROSS THE NORTHERN HALF OF THE CWA, WE`RE LESS CONCERNED ABOUT FLOODING THERE. MODELED SOLUTIONS SUGGEST WE WOULD NEED BETWEEN 1.50 TO 2.00 INCHES OF LIQUID (OVER A 6 TO 12 HOUR PERIOD), EITHER IN THE FORM OF ALL RAIN OR RAIN AND MELTING SNOW TO HAVE OUR SOUTHERN CREEKS AND STREAMS LEAVE THEIR BANKS. NONE OF OUR RIVER FORECAST POINTS ARE FORECAST TO HIT FLOOD STAGE OR EVEN CAUTION STAGE. THE SHORT TERM GOOD NEWS IS THAT RAIN WILL CHANGE OVER TO SNOW QUICKER ACROSS PLACES THAT HAVE A SNOWPACK AND WHERE MORE RAIN IS EXPECTED, THERE IS LESS SNOW PACK. THE LONGER TERM BAD NEWS IS THAT WE`RE POTENTIALLY KICKING THE CAN DOWN THE LINE AND JUST ADDING TO OUR SNOWPACK FOR A FUTURE MELT. WITH THE RAINFALL, THE FLOW ON AREA CREEKS AND STREAMS WILL INCREASE. THIS COULD START TO MOVE ICE, AND IN A WORST CASE SCENARIO, CREATE RESTRICTIONS OR JAMS. THE GOOD NEWS IS WE`VE SEEN SOME RECESSION/MELT THE LAST FEW DAYS. && .CLIMATE... CLIMATE: WITH A SNOWCOVER IN PLACE AND ANOTHER ARCTIC AIRMASS SETTLING INTO THE REGION AND RADIATIONAL COOLING OCCURRING, WE HAVE ANOTHER CHANCE FOR MORE RECORD LOWS ACROSS THE REGION. FRIDAY 3/6 RECORD LOWS ACY 10 1888 PHL 10 1978 ILG 11 1926 ABE 7 1960 TTN 7 1872 GED 10 1978 RDG 7 1978 MPO -5 1909 THE CURRENT FORECAST CURRENTLY HAS MOST LOCATIONS BREAKING THERE RECORD LOW ON FRIDAY MORNING. THE ONE EXCEPTION WOULD BE MOUNT POCONO. SATURDAY 3/7 RECORD LOWS ACY 10 1890 PHL 9 1960 ILG 11 1960 ABE 1 1960 TTN 7 1890 GED 3 1960 RDG 10 1989 MPO -18 1911 MOST LOCATIONS ARE FORECASTED TO BE SEVERAL DEGREES WARMER THAN THE RECORD LOWS FOR SATURDAY MORNING. RECORD DAILY SNOWFALL FOR THURSDAY MARCH 5 KACY 0.3 - 1960 KILG 3.7 - 1981 KABE 7.0 - 1917 KPHL 8.8 - 1981 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR PAZ054-055- 061-062. WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR PAZ060- 101>106. WINTER STORM WARNING FROM 11 PM THIS EVENING TO 7 PM EST THURSDAY FOR PAZ070-071. NJ...WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR NJZ001-007- 008. WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR NJZ009-010- 012-015. WINTER STORM WARNING FROM 11 PM THIS EVENING TO 7 PM EST THURSDAY FOR NJZ013-014-016>027. DE...WINTER STORM WARNING FROM 11 PM THIS EVENING TO 7 PM EST THURSDAY FOR DEZ001-002. WINTER STORM WARNING FROM 3 AM TO 7 PM EST THURSDAY FOR DEZ003- 004. MD...WINTER STORM WARNING FROM 11 PM THIS EVENING TO 7 PM EST THURSDAY FOR MDZ008-012-015-019-020. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ450>455. && $$ SYNOPSIS...GAINES NEAR TERM...JOHNSON/DRAG 438 SHORT TERM...JOHNSON LONG TERM...GAINES/O`HARA AVIATION...GAINES/JOHNSON/O`HARA MARINE...GAINES/JOHNSON/O`HARA HYDROLOGY... CLIMATE... 438

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