Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 020301 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1001 PM EST SUN MAR 1 2015 .SYNOPSIS... A COLD FRONT OVER THE OHIO VALLEY WILL MOVE INTO THE AREA BY MONDAY MORNING. HIGH PRESSURE BUILDS EASTWARD INTO THE MID ATLANTIC MONDAY AFTERNOON THROUGH TUESDAY MORNING. LOW PRESSURE IS ANTICIPATED TO MOVE ACROSS THE GREAT LAKES LATE TUESDAY, THEN DOWN THE SAINT LAWRENCE RIVER VALLEY BY EARLY WEDNESDAY. THIS LOW IS FORECAST TO PULL A COLD FRONT SLOWLY THROUGH OUR REGION ON WEDNESDAY. WEAK LOW PRESSURE IS EXPECTED TO RIDE ALONG THE FRONT ON THURSDAY BEFORE HIGH PRESSURE BUILDS INTO OUR AREA FROM THE WEST FOR FRIDAY INTO THE WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... WE HAVE CONVERTED ALL WARNINGS TO ADVISORIES WITH THIS UPDATE AND CONTINUE ADVISORIES EVERYWHERE THROUGH THE OVERNIGHT HOURS. A MAJORITY OF THE PRECIPITATION HAS CONCLUDED THIS EVENING, THOUGH SOME OF THE HI-RES MODELS SHOW SOME RE-FIRING OF PRECIPITATION AS THE COLD FRONT PUSHES THROUGH THE REGION AND WITH WEAK LOW-LEVEL TROUGHING. A LIGHT WINTRY MIX IS STILL POSSIBLE AFTER MIDNIGHT BUT BY DAYBREAK ANY RESIDUAL MOISTURE SHOULD BE ALL SNOW. CURRENTLY THERE ARE SEVERAL THOUSAND HOMES AND BUSINESSES WITHOUT POWER IN THE DELMARVA AND SOUTHERN NEW JERSEY COUNTIES ADDING TO SIGNIFICANCE OF THE ICING THIS EVENING. AS WAS STATED EARLIER, FORTUNATELY THE WINDS ARE EXPECTED TO REMAIN LIGHT AND VARIABLE TONIGHT WHICH WOULD HELP TO COMBAT ANOTHER FURTHER OUTAGES. OVERALL WE WILL CONTINUE TO DRY OUT WEST TO EAST TONIGHT AS TEMPERATURES SLOWLY CREEP TOWARDS THE FREEZING MARK FROM THE PHILLY METRO AREA SOUTHWARD...IT`LL TAKE A BIT LONGER NORTH AND WEST. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... THE COLD FRONT WILL HAVE MOVED WELL OFFSHORE BY 12 MON. HIGH PRESSURE FROM THE OHIO VALLEY WILL BEGIN TO BUILD EAST. FAIR WEATHER IS EXPECTED...WITH ONLY A FEW SNOW SHOWERS EARLY ACROSS THE SRN POCONOS. SKIES WILL BE MOSTLY SUNNY ACROSS MOST AREAS. IT WILL BE BREEZY AND COOLER THAN NORMAL WITH HIGHS ONLY IN THE MID/UPPER 30S ACROSS THE SOUTH AND LOW 30S NORTH. WINDS WILL BE WEST OR NORTHWEST AT 10 TO 20 MPH WITH SOME GUSTS UP TO 30 MPH AT TIMES. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... HIGH PRESSURE WILL BUILD IN FROM THE OHIO VALLEY MONDAY NIGHT. THE CENTER OF THIS 1030+ MB HIGH IS FORECAST TO SHIFT DIRECTLY OVERHEAD BY THE EARLY MORNING. MID AND HIGH CLOUDS ASSOCIATED WITH A STRONG UPPER JET MAX WILL SPREAD INTO THE AREA WHICH, IF THICK ENOUGH, MAY CURB RADIATIONAL COOLING A BIT DESPITE THE WINDS BECOMING CALM. MIN TEMPS RANGE FROM THE SINGLE DIGITS IN NE PA AND NW NJ WHERE A FRESH SNOWPACK IS EXPECTED TO BE ON THE GROUND TO AROUND 20F IN THE URBAN AND COASTAL LOCALES. THE HIGH WILL SHIFT OFFSHORE ON TUESDAY AS THE NEXT AREA OF LOW PRESSURE LIFTS INTO THE GREAT LAKES. THE PATTERN IS SIMILAR TO SEVERAL RECENT EVENTS (INCLUDING THE ONE TODAY) WHERE THE LOW CUTS TO OUR NORTHWEST, ALLOWING WARM AND MOIST AIR TO OVERRUN THE RESIDUAL ARCTIC AIR OVER THE MID ATLANTIC. THE RESULT IS A WINTRY MIX OF SNOW/SLEET AT THE ONSET LATE TUESDAY AFTERNOON AND EVENING CHANGING OVER TO FREEZING RAIN AND THEN RAIN FROM SOUTH TO NORTH TUESDAY NIGHT INTO WEDNESDAY AS THE WARMER AIR INFILTRATES THE AREA. THE MIDWEEK SYSTEM WILL CONSIDERABLY MORE AMPLIFIED THAN TODAY`S EVENT, INCLUDING AN IMPRESSIVE 70-80 KT LOW LEVEL JET THAT IS FORECAST TO DEVELOP OVERHEAD TUESDAY EVENING. ALSO THE COLD AIRMASS PRECEDING THIS EVENT WILL NOT BE AS COLD AND DRY RELATIVE TO TODAY`S EVENT. ACCORDINGLY, PRECIPITATION AMOUNTS WILL BE HEAVIER WITH THE MIDWEEK SYSTEM BUT A QUICKER TRANSITION FROM WINTRY PRECIP TO RAIN WILL ALSO OCCUR. THE FASTER CHANGEOVER WILL KEEP ANY SNOW AND SLEET ACCUMULATIONS LIGHT. THE BIGGER IMPACT WOULD BE FREEZING RAIN, WITH THE GREATEST ICING POTENTIAL ALONG AND WEST OF THE FALL LINE WHERE FREEZING RAIN MAY LINGER INTO THE OVERNIGHT AS THE HILLY TERRAIN WOULD HELP TRAP THE COLD AIR NEAR THE SURFACE. EXPECT ONLY ONE PTYPE DURING THE DAY ON WEDNESDAY- RAIN. THE RAIN MAY BE MODERATE TO HEAVY AT TIMES EARLY IN THE DAY BEFORE TAPERING OFF FROM NW TO SE IN THE AFTERNOON AS A COLD FRONT MOVES THRU. THERE IS STILL QUITE A BIT OF SPREAD IN QPF AMOUNTS, RANGING FROM UNDER A HALF INCH (12Z NAM AND A FEW 09Z SREF MEMBERS) TO AROUND TWO INCHES IN THE WETTEST SREF MEMBERS. WE FOLLOWED WPC QPF CLOSELY, WHICH IS CLOSER TO THE MEDIAN WITH AROUND AN INCH ACROSS OUR THE SOUTHERN TWO- THIRDS OF THE CWA. WENT A FEW DEGREES BELOW GUIDANCE FOR TEMPS ON WEDNESDAY, PARTICULARLY IN NE PA AND NW NJ WHERE THE COLDER AIR WILL BE MOST RESISTANT TO ERODING. FORECAST MAX TEMPS RANGE FROM NEAR 40F IN THE POCONOS TO THE MID 50S IN THE LOWER DELMARVA. COMPLEX FORECAST SHAPING UP DURING THE WED NGT AND THU TIME FRAME. NORTHERN STREAM S/WV ENERGY LEADS TO A COLD FROPA ON WED WITH MUCH COLDER AIR POISED TO MOVE INTO THE AREA. BUT THE FRONT WILL STALL INVOF THE MID-ATL AS THE MID-LEVEL FLOW BECOMES PARALLEL TO IT... AND WITH ADDITIONAL S/WV ENERGY ENTERING THE LONG WAVE TROUGH OVER THE ERN CONUS...THIS WILL LEAD TO SEVERAL WAVES OF LOW PRES TRAVERSING THE FRONT. BOTH THE AMERICAN AND EUROPEAN MODELS HAVE ADVERTISED THIS SCENARIO OVER THE LAST SEVERAL DAYS...BUT THERE IS CONSIDERABLE UNCERTAINTY AS WE ENTER THE D+4 TIME FRAME... WITH REGARD TO THE PLACEMENT OF THE FRONT, LOW-LEVEL THERMAL PROFILE, AND QPF. THE GFS, EURO, AND THEIR RESPECTIVE ENSEMBLES HAVE CONSISTENTLY INDICATED A FAIR AMOUNT OF QPF AND THERMAL PROFILES SUPPORTIVE OF SNOW OVER THE CENTRAL AND SOUTHERN TIER OF THE CWA. BUT WHERE THE FRONT ULTIMATELY STALLS WILL DETERMINE JUST HOW FAR SOUTH THE COLD AIR MAKES IT...WITH A FRONTAL PLACEMENT FURTHER TO THE NORTH LEADING TO A WARMER SOLUTION. THIS SYSTEM WILL ALSO TAP GULF MOIST...BUT WITH HIGH PRESSURE BUILDING IN FROM THE WEST... DRY LOW-LEVEL AIR WOULD LEAD TO A SHARP NORTHERN GRADIENT IN PRECIP. THIS IS REFLECTED IN RUN-TO-RUN OSCILLATIONS OF MODEL QPF. IF CURRENT MODEL RUNS VERIFY /AND KEEP IN MIND THERE IS A LOT OF UNCERTAINTY/...COLDER AIR ADVECTING IN AT LOW-LEVELS WOULD LEAD TO A ROBUST OVERRUNNING REGIME SETTING OVER THE MID-ATL WED NGT AND THU...FED BY GULF MOISTURE AND SUPPORTED BY THE LF QUADRANT OF A VIGOROUS 250 HPA JET. STAY TUNED. THIS SYSTEM IS PROJECTED TO FINALLY MOVE OFFSHORE BY LATE THU OR EARLY FRIDAY...BUT THE MODELS MAY BE A BIT TOO PROGRESSIVE WITH THIS TIMING...AS THERE IS SOME EVIDENCE OF HIGH-LATITUDE BLOCKING. HIGH PRESSURE SHOULD BUILD IN OVER THE WEEKEND WHEN TEMPERATURES MAY ACTUALLY REACH SEASONAL LEVELS. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. NOT MUCH CHANGE WITH THE 00Z TAFS AT THIS TIME. MOSTLY IFR CONDITIONS PRESENT AT OUR TERMINALS. BACK EDGE OF MAIN PRECIPITATION IS MOVING THROUGH OUR REGION NOW THOUGH THERE IS STILL AMPLE LOW-LEVEL MOISTURE AROUND THE REGION SO NOT THINKING WE COMPLETELY DRY OUT THIS EVENING...SOME FREEZING DRIZZLE POSSIBLE DURING THE OVERNIGHT HOURS. WE CONTINUE THE SLOW IMPROVEMENT BACK TO VFR MOSTLY AROUND DAWN TOMORROW. LIGHT WINDS TODAY AND TONIGHT THEN W OR NW 10-15KT WITH G25KT MONDAY. OUTLOOK... MONDAY NIGHT...VFR AND LIGHT WINDS. TUESDAY AND TUESDAY NIGHT...CIGS/VSBYS LOWER TO MVFR AND THEN IFR LATE IN THE AFTN WHEN A MIX OF SN/PL MOVE IN. PRECIP SHOULD QUICKLY TRANSITION TO A PERIOD OF FZRA AND THEN RA DURING THE EVE FOR THE I- 95 TERMINALS AND FARTHER S/E. A WINTRY MIX (PL/FZRA) MAY PERSIST CLOSER TO MIDNIGHT NEAR RDG/ABE BEFORE IT CHANGES TO RA. FORECAST SOUNDINGS SHOW THE POTENTIAL FOR LLWS TO DEVELOP BY EVE WITH A STRONG SW LLVL JET DEVELOPING ABOVE A SHARP FRONTAL INVERSION. WEDNESDAY...MVFR AND IFR ESPECIALLY EARLY IN THE DAY WHEN STEADY RA IS EXPECTED. RAIN TAPERS OFF FROM NW TO SE LATER IN THE MRNG AND AFTN. WEDNESDAY NIGHT AND THURSDAY...RA MAY CHANGE TO SN FROM NORTH TO SOUTH. CHANCE FOR MVFR/IFR IF SN DOES DEVELOP BUT STILL A LOT OF UNCERTAINTY WITH THIS PERIOD. BETTER CONFIDENCE FOR GUSTY NW WINDS. THURSDAY NIGHT AND FRIDAY...VFR. && .MARINE... SUB-SCA CONDITIONS THE REST OF THE AFTERNOON AND MOST OF TONIGHT...THEN WINDS AND SEAS INCREASE AS LOW PRESSURE DEEPENS OFFSHORE. SCA WINDS DEVELOP AROUND DAWN AND CONTINUE THRU THE DAY. PRESENT SCA FLAG ISSUED EARLIER WILL CONTINUE AS IS. SNOW/SLEET AND FREEZING RAIN TODAY AND EARLY TONIGHT...PERHAPS ALL RAIN FOR AWHILE ACROSS THE SRN WATERS. PCPN DIMINISHES BEFORE DAWN. OUTLOOK... MONDAY NIGHT...SCA CONTINUES THRU THE EVENING. NW WINDS WILL DIMINISH RATHER QUICKLY DURING THIS TIME SO THE SCA MAY BE ABLE TO BE CANCELLED A FEW HOURS EARLIER (ESPECIALLY FOR THE DE BAY). TUESDAY...NO MARINE HEADLINES EXPECTED WITH LIGHT WINDS. 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. WEDNESDAY NIGHT AND THURSDAY...SCA LIKELY WITH GUSTY NW WINDS. THURSDAY NIGHT AND FRIDAY...NO MARINE HEADLINES ARE ANTICIPATED. && .HYDROLOGY... AFTER TODAY`S WINTRY MIX, THE NEXT ROUND OF PRECIPITATION IS FORECAST TO MOVE INTO THE AREA TUESDAY AFTERNOON AND CONTINUE INTO WEDNESDAY. THIS MIDWEEK EVENT APPEARS TO START AS A WINTRY MIX BEFORE CHANGING OVER TO RAIN AS TEMPERATURES RISE WELL ABOVE FREEZING ON WEDNESDAY. ALTHOUGH THIS EVENT IS A FEW DAYS AWAY, WE WANT TO HIGHLIGHT THAT SOME OF THE MODEL GUIDANCE IS SUGGESTING LOCALLY HEAVY RAINFALL. THERE IS STILL QUITE A BIT OF SPREAD IN QPF AMOUNTS, RANGING FROM UNDER A HALF INCH TO AROUND TWO INCHES IN THE WETTEST RUNS. WE FOLLOWED WPC QPF CLOSELY, WHICH IS CLOSER TO THE MEDIAN WITH AROUND AN INCH ACROSS OUR THE SOUTHERN TWO-THIRDS OF THE CWA. THE COMBINATION OF A BRIEF WARM-UP ON WEDNESDAY, LOCALLY 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. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR PAZ054-055- 060>062-070-071-101>106. NJ...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR NJZ001- 007>010-012>027. DE...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR DEZ001>004. MD...WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR MDZ008-012- 015-019-020. MARINE...SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 2 AM EST TUESDAY FOR ANZ430-431-450>455. && $$ SYNOPSIS...KLEIN NEAR TERM...HEAVENER/O`HARA SHORT TERM...O`HARA LONG TERM...FRANCK/KLEIN AVIATION...HEAVENER/KLEIN/O`HARA MARINE...KLEIN/O`HARA HYDROLOGY...

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