Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 140802 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 402 AM EDT MON APR 14 2014 .SYNOPSIS... HIGH PRESSURE LOCATED OVER THE WESTERN NORTH ATLANTIC WILL CONTINUE TO INFLUENCE OUR WEATHER FOR TODAY. A STRONG COLD FRONT IS FORECAST TO APPROACH FROM THE WEST AND IT SHOULD PASS THROUGH OUR REGION FROM LATE TUESDAY AFTERNOON INTO EARLY TUESDAY EVENING. HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS THE NORTHEASTERN STATES ON WEDNESDAY AND OVER ATLANTIC CANADA AND THE ADJACENT WATERS FOR THURSDAY AND FRIDAY. A FRONTAL BOUNDARY APPROACHING FROM THE WEST IS EXPECTED TO PASS THROUGH OUR REGION ON SATURDAY NIGHT. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... OUR REGION REMAINS BETWEEN A RIDGE TO THE EAST AND SOUTHEAST AND A SHARPENING UPPER-LEVEL TROUGH TO THE WEST. AS THE LATTER GRADUALLY SLIDES EASTWARD THROUGH TODAY, THE RIDGE WILL BE PUSHED FARTHER OFFSHORE. THIS WILL RESULT IN THE HEIGHTS LOWERING SOME THROUGH THE COURSE OF THE DAY. MEANWHILE, A DEEP SOUTH-SOUTHWEST FLOW OF WARM AIR WILL BE MAINTAINED ACROSS THE ENTIRE REGION. THIS WILL RESULT IN ANOTHER WARM DAY, HOWEVER WITH SOME COOLING FORECAST TO START TAKING PLACE ALOFT, HIGH TEMPERATURES SHOULD BE A LITTLE COOLER THAN WHAT WAS OBSERVED YESTERDAY. DESPITE THIS, WE DID GO A LITTLE BIT ABOVE GUIDANCE /CLOSER TO CONTINUITY/ ESPECIALLY AS THE BOUNDARY LAYER IS FORECAST TO BE WELL MIXED ONCE AGAIN. THE SOUTHERLY WIND COMPONENT THOUGH WILL ALLOW FOR COOLER TEMPERATURES ONCE AGAIN ALONG THE ATLANTIC COAST AND ALSO THE NORTH COAST OF DELAWARE BAY. THE LOW-LEVEL MOISTURE WHILE INCREASING, THE OVERALL FLOW IS STILL ON THE STRONGER SIDE AND IS ACTUALLY FORECAST TO INCREASE SOME THROUGH THE DAY. THERE LOOKS TO BE A BATTLE BETWEEN THE INVERSION AND THE MOISTURE TRYING TO POOL BENEATH IT. IT APPEARS THAT JUST ENOUGH TURBULENT MIXING BELOW AND NEAR THE INVERSION WILL KEEP ANY STRATUS DEVELOPMENT LIMITED EARLY THIS MORNING. WE ARE ALSO BANKING ON MOST PLACES STILL MAINTAINING SOME WIND THROUGH DAYBREAK TO KEEP ANY FOG RATHER LIMITED. A STRONG COLD FRONT IS FORECAST TO REMAIN WELL TO OUR WEST THROUGH TODAY, AND THIS IS WHERE THE GREATEST FORCING IS LOCATED. THERE IS THE POTENTIAL FOR SOME SHOWERS TO EITHER DEVELOP ACROSS OUR WESTERN ZONES OR APPROACH FROM THE WEST ESPECIALLY LATER THIS AFTERNOON. THIS MAY BE ASSOCIATED WITH AN UPTICK IN THE LOW-LEVEL WIND FIELD AS THE BOUNDARY LAYER MOISTENS SOME MORE BELOW A DRY LAYER. BASED ON THE SOUNDINGS AND SOME GUIDANCE RUNNING A BIT TO HIGH WITH THE SURFACE DEW POINTS SO FAR, THIS MAY END UP STAYING TO OUR WEST AND DELAYED MORE FOR THE NIGHTTIME HOURS. THEREFORE, WE OPTED TO MAINTAIN A DRY FORECAST THROUGH THE DAYTIME HOURS. ANOTHER ROUND OF DEEP MIXING IS EXPECTED TO DEVELOP AS THE BOUNDARY LAYER WARMS AND THE LOW-LEVEL LAPSE RATES STEEPEN QUITE A BIT. GIVEN ABOUT 30 KNOTS OF WIND AVAILABLE TO BE MIXED DOWN, SURFACE GUSTS SHOULD NEAR 35 MPH AT TIMES ESPECIALLY FROM MIDDAY ON. THE HOURLY GRIDS WERE ADJUSTED EARLY THIS MORNING USING THE LAMP/LAV GUIDANCE TO ASSIST WITH TRENDS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... THE STRETCH OF DRY AND WARM WEATHER WILL START TO COME TO AN END TONIGHT AS A STRONG COLD FRONT GRADUALLY APPROACHES FROM THE WEST LATE. THE STRENGTHENING LOW TO MID LEVEL FLOW WILL HELP DRIVE ADDITIONAL MOISTURE NORTHWARD. IT APPEARS THAT SOME INITIAL SHOWERS MAY BE SIMPLY TIED TO THE INCREASE IN THE LOW-LEVEL JET IN COMBINATION WITH A SURGE IN THETA-E ADVECTION. THE BULK OF THE FORCING APPEARS TO BE LINKED CLOSER TO THE ACTUAL COLD FRONT AND AS THE REAR RIGHT QUADRANT OF THE 250 MB JET ARRIVES. THEREFORE, WHILE SHOWERS ARE ANTICIPATED TO DEVELOP AND INCREASE IN COVERAGE SOME, THE BULK OF THE WET WEATHER SHOULD BE AT AND AFTER DAYBREAK TUESDAY. WE THEREFORE GRADUALLY INCREASED THE POPS FROM WEST TO EAST WITH THE HIGHER VALUES TOWARD DAYBREAK. SOME OF THE HIGH RESOLUTION GUIDANCE INDICATE A DECENT RAMP UP IN SHOWERS OVERNIGHT, WITH AN AREA ACROSS THE WESTERN ZONES AND ANOTHER ALONG THE COAST ASSOCIATED WITH THETA-E SURGES AND INCOMING SHORT WAVE ENERGY, THEN CONGEALING TOWARD DAYBREAK. IF THIS OCCURS THEN POPS WILL NEED TO BE INCREASED ESPECIALLY FARTHER EAST. AS THE MOISTURE ADVECTION INCREASES THROUGH THE NIGHT AND BOUNDARY LAYER WARMTH IS MAINTAINED ENOUGH, THE FORECAST SOUNDINGS INDICATE THAT SOME INSTABILITY DEVELOPS THROUGH THE NIGHT. THIS HOWEVER DOES NOT APPEAR TO BE ALL THAT HIGH, WHICH RAISES THE QUESTION REGARDING CHARGE SEPARATION. AS OF NOW, WE DO NOT THINK THE INSTABILITY WILL BE SUFFICIENT ENOUGH FOR CHARGE SEPARATION AND THEREFORE LIMITED THE SLIGHT CHC OF THUNDER TO THE WESTERN AREAS TOWARD DAYBREAK. OTHERWISE, CLOUDS WILL CONTINUE TO THICKEN AND LOWER THROUGH THE NIGHT AS THE LOWER LEVELS TURN A BIT MORE HUMID. THIS MAY ALLOW FOR A STRATUS DECK TO OVERSPREAD THE AREA ESPECIALLY AS THE THETA-E SURGE ARRIVES LATER ON. THIS AGAIN THOUGH COULD BE HINDERED SOME BY ENOUGH TURBULENT MIXING BEING MAINTAINED. BASED ON THIS IDEA, WE DID NOT CARRY A FOG MENTION. AS FOR LOW TEMPERATURES, WE GENERALLY USED AN EVEN BLEND OF THE GFS/NAM MOS. && .LONG TERM /TUESDAY THROUGH SUNDAY/... THE AXIS OF A DEEP MID LEVEL TROUGH IS EXPECTED TO EXTEND FROM THE WESTERN GREAT LAKES TO THE TEXAS GULF COAST ON TUESDAY MORNING. THE FEATURE SHOULD LIFT NORTHEASTWARD WITH ITS AXIS PASSING OVER OUR REGION LATE ON TUESDAY NIGHT. THE GUIDANCE CONTINUES TO FOCUS ON THE LATE TUESDAY AFTERNOON INTO EARLY TUESDAY EVENING TIME FRAME FOR THE PASSAGE OF THE STRONG SURFACE COLD FRONT ASSOCIATED WITH THE MID LEVEL TROUGH. WE HAVE GONE WITH A 100 PERCENT CHANCE OF RAIN SHOWERS FOR TUESDAY. THERE WILL LIKELY BE PERIODS OF MODERATE TO HEAVY RAINFALL THROUGH THE DAY ALONG WITH A CHANCE OF THUNDER DUE TO THE ROBUST NATURE OF THE SYSTEM. THE 0000 UTC NAM AND THE 0000 UTC GFS ARE BRINGING GENERALLY ONE TO TWO INCHES OF RAIN TO OUR REGION ON TUESDAY AND TUESDAY EVENING. THE 0000 UTC ECMWF IS MORE CONSERVATIVE WITH AMOUNTS MAINLY IN THE 0.6 TO 1.0 INCH RANGE. WE WILL CONTINUE TO FOCUS ON THE 0.75 TO 1.25 INCH RANGE FOR RAINFALL AMOUNTS. THE EXPECTED AMOUNTS COULD PRODUCE SOME FLOODING IN AREAS OF POOR DRAINAGE AND PONDING OF WATER ON ROADWAYS. SPOTTY SMALL STREAM FLOODING IS POSSIBLE. HOWEVER, THE ANTICIPATED AMOUNTS WOULD PRECLUDE ANY CONCERN FOR WIDESPREAD FLOODING BASED ON ANTECEDENT CONDITIONS. A 60 PLUS KNOT LOW LEVEL SOUTH SOUTHWESTERLY JET IS FORECAST TO DEVELOP OVER OUR REGION IN ADVANCE OF THE FRONT ON TUESDAY. WHILE THE STRONGEST OF THE WINDS ARE NOT EXPECTED TO MIX TO THE SURFACE, CONDITIONS SHOULD BECOME QUITE BREEZY WITH SOUTHERLY WIND GUSTS GETTING AT LEAST INTO THE 30 TO 35 MPH RANGE FOR A TIME. THE LATEST GUIDANCE SUGGESTS THAT MOST OF THE PRECIPITATION WILL BE OFF THE COAST BEFORE MIDNIGHT ON TUESDAY NIGHT, IN ADVANCE OF THE MID LEVEL TROUGH AXIS. HOWEVER, SOME LIGHT SHOWERS MAY LINGER IN PARTS OF NEW JERSEY AND DELAWARE UNTIL ABOUT 2:00 OR 3:00 AM. AFTER THE FRONT PASSES, TEMPERATURES WILL BEGIN TO DROP SHARPLY AS A GUSTY NORTHWEST WIND DEVELOPS. IT CONTINUES TO APPEAR AS THOUGH THE PRECIPITATION WILL END AS A BRIEF PERIOD OF SNOW SHOWERS IN MUCH OF THE POCONO REGION, THE LEHIGH VALLEY AND NORTHWESTERN NEW JERSEY. A FEW SNOW FLAKES COULD FALL AS FAR SOUTH AS SOUTHEASTERN PENNSYLVANIA AND CENTRAL NEW JERSEY. AMOUNTS SHOULD BE NEGLIGIBLE EXCEPT PERHAPS IN THE ELEVATED TERRAIN OF THE POCONOS AND NORTHWESTERN NEW JERSEY WHERE A FEW TENTHS OF AN INCH OF SNOW MAY ACCUMULATE. THE NORTHERN AND MOST OF THE CENTRAL PART OF OUR FORECAST AREA SHOULD FALL BELOW FREEZING LATE ON TUESDAY NIGHT. OUR RECENT WARM SPELL HAS CAUSED PLANTS TO START FLOWERING, ESPECIALLY IN SOUTHEASTERN PENNSYLVANIA, CENTRAL NEW JERSEY AND POINTS TO THE SOUTH. THE COLD TEMPERATURES COULD HAVE A NEGATIVE IMPACT AND WE MAY NEED TO CONSIDER ISSUING A FREEZE WATCH FOR PARTS OF OUR AREA. COOL HIGH PRESSURE FROM THE WEST IS FORECAST TO BUILD ACROSS THE NORTHEASTERN STATES ON WEDNESDAY AND OVER ATLANTIC CANADA AND THE ADJACENT WATERS FOR LATE IN THE WEEK. A SURFACE RIDGE AXIS IS ANTICIPATED TO DEVELOP DOWN THE LEE OF THE APPALACHIANS. THE PATTERN WILL KEEP OUR REGION IN A COOL NORTH TO NORTHEAST SURFACE FLOW. TEMPERATURES WILL BE BELOW NORMAL. A MOSTLY CLEAR SKY IS ANTICIPATED FOR WEDNESDAY NIGHT. THE WIND MAY BECOME LIGHT ENOUGH ALONG THE INTERSTATE 95 CORRIDOR AND INTO SOUTHEASTERN PENNSYLVANIA TO RESULT IN THE DEVELOPMENT OF SOME PATCHY FROST THERE DURING THE EARLY MORNING HOURS ON THURSDAY. AS THE HIGH PULLS TO THE NORTHEAST AND FARTHER AWAY FROM OUR REGION A MID LEVEL TROUGH AND ITS ASSOCIATED SURFACE FRONT ARE EXPECTED TO APPROACH FROM THE WEST. THE FRONTAL BOUNDARY MAY PASS THROUGH OUR REGION ON SATURDAY NIGHT. WE HAVE MENTIONED A CHANCE OF RAIN SHOWERS FROM FRIDAY NIGHT INTO SATURDAY NIGHT. TEMPERATURES ARE FORECAST TO RETURN TO NEAR NORMAL LEVELS FOR THE WEEKEND. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...A CHANCE FOR SOME LOCAL STRATUS/FOG EARLY. OTHERWISE, VFR WITH CEILINGS MOSTLY AT OR ABOVE 10,000 FEET. SOUTH-SOUTHWEST WINDS 5 TO 10 KNOTS, INCREASING TO AROUND 15 KNOTS WITH GUSTS UP TO 30 KNOTS. THE HIGHEST GUSTS SHOULD OCCUR FROM MIDDAY ON. TONIGHT...VFR TO START, THEN CEILINGS LOWERING TO MVFR AND THEN PROBABLY IFR LATE. THE MOISTURE WILL BE ON THE INCREASE AS THE LOW TO MID LEVEL WIND FIELDS STRENGTHEN. SURFACE WINDS SHOULD REMAIN IN THE 10 TO 15 KNOT RANGE, WITH MOST OF THE GUSTINESS DROPPING OFF DURING THE EVENING. HOWEVER, A SOUTHWEST FLOW AROUND 2,000 FEET WILL BE IN THE 40 TO 50 KNOT RANGE. AS OF NOW, WE HELD OFF INCLUDING A LOW-LEVEL WIND SHEAR MENTION IN THE TAFS. SOME SHOWERS ARE EXPECTED TO OVERSPREAD THE AREA ESPECIALLY LATE FROM WEST TO EAST. OUTLOOK... TUESDAY...MVFR AND IFR CONDITIONS IN RAIN SHOWERS. THE RAIN WILL BECOME MODERATE TO HEAVY AT TIMES. SCATTERED THUNDER IS POSSIBLE. A SOUTH TO SOUTHWEST WIND AT 15 TO 20 KNOTS MAY GUST NEAR OR IN EXCESS OF 30 TO 35 KNOTS AT TIMES. TUESDAY NIGHT...MVFR AND IFR CONDITIONS IN RAIN SHOWERS IN THE EVENING, IMPROVING TO VFR OVERNIGHT. A NORTHWEST WIND AT 15 TO 20 KNOTS GUSTING TO 25 OR 30 KNOTS AT TIMES. WEDNESDAY THROUGH FRIDAY...MAINLY VFR. && .MARINE... A SOUTHERLY FLOW WILL BE MAINTAINED THROUGH TONIGHT WELL IN ADVANCE OF A STRONG COLD FRONT. THE FLOW ABOVE THE SURFACE IS FORECAST TO STRENGTHEN, ESPECIALLY TONIGHT WITH 925 MB WINDS ON THE ORDER OF 40 TO 50 KNOTS. THIS WILL ALLOW FOR THE SURFACE WINDS TO INCREASE THROUGH THE DAY, HOWEVER A WARM AIR MASS REMAINS AND THIS WILL ONCE AGAIN TEND TO LIMIT THE VERTICAL MIXING. THE BEST MIXING WILL GENERALLY BE NEAR SHORE, AND THEREFORE THE HIGHER GUSTS TO ADVISORY LEVELS. IT MAY TAKE SOME TIME TO OCCUR, ESPECIALLY ACROSS DELAWARE BAY, HOWEVER WE WILL MAINTAIN THE SMALL CRAFT ADVISORY FOR ALL AREAS THROUGH TONIGHT. THE SEAS WILL ALSO GRADUALLY RESPOND TO THE PERSISTENT SOUTHERLY FLOW, WITH THE OCEAN SEAS GETTING TO 5 FEET OR ABOVE THROUGH TONIGHT. OUTLOOK... TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED. THE WIND WILL BE FROM THE SOUTH. ISOLATED GALE FORCE GUSTS ARE POSSIBLE. TUESDAY NIGHT AND WEDNESDAY MORNING...A STRONG NORTHWEST WIND IS FORECAST WITH FREQUENT GALE FORCE GUSTS. A GALE WATCH IS IN EFFECT. WEDNESDAY AFTERNOON THROUGH FRIDAY...SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED ON OUR OCEAN WATERS. A NORTHEAST FLOW WILL KEEP SEAS AT OR IN EXCESS OF 5 FEET. OCCASIONAL WIND GUSTS NEAR 25 KNOTS ARE POSSIBLE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...GALE WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY MORNING FOR ANZ430-431-450>455. SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR ANZ430-431- 450>455. && $$ SYNOPSIS...IOVINO NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...IOVINO AVIATION...GORSE/IOVINO MARINE...GORSE/IOVINO

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