Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 150808 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 408 AM EDT TUE APR 15 2014 .SYNOPSIS... A STRONG COLD FRONTAL SYSTEM WILL MOVE THROUGH THE REGION TODAY AND BE LOCATED OFFSHORE TONIGHT. BY WEDNESDAY HIGH PRESSURE WILL BEGIN BUILDING INTO THE REGION WITH THE FRONTAL BOUNDARY LINGERING OFFSHORE THROUGH FRIDAY. ANOTHER FRONTAL BOUNDARY WILL APPROACH THE REGION ON SATURDAY. HIGH PRESSURE IS EXPECTED TO BUILD BACK INTO THE REGION FOR SUNDAY AND MONDAY OF NEXT WEEK WITH ANOTHER FRONTAL PASSAGE MONDAY NIGHT AND TUESDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... THE STRETCH OF WARM WEATHER WILL COME TO A RAPID END AS A STRONG COLD FRONT IS FORECAST TO SWEEP THROUGH LATER IN THE DAY. PRIOR TO THIS THOUGH, A MILD SOUTHERLY FLOW WILL CONTINUE AS A SHARP UPPER-LEVEL TROUGH APPROACHING FROM THE WEST HELPS TO STRENGTHEN THE DOWNSTREAM WIND FIELDS. THIS WILL ADVECT DEEPER MOISTURE ACROSS THE REGION AS PW VALUES ARE FORECAST TO INCREASE TO 1.0-1.5 INCHES. THIS INCREASING MOISTURE INTERACTING WITH AN INITIAL INVERSION WILL HELP PROMOTE THE DEVELOPMENT OF SOME STRATUS ESPECIALLY CLOSER TO THE COAST INITIALLY, WHICH SHOULD THEN EXPAND INLAND. THE INFLUX OF HIGHER DEW POINT AIR MOVING OVER THE COLDER WATERS WILL ALSO LEAD TO SOME FOG, ESPECIALLY ALONG THE COASTAL AREAS THROUGH THE MORNING. THE ARRIVAL OF A LOW-LEVEL JET OF 50-65 KNOTS /STRONGEST CLOSER TO THE COAST/ WILL HELP PROVIDE SOME LIFT, ALLOWING SOME SHOWERS TO CONTINUE ACROSS THE AREA EARLY THIS MORNING. THE MAIN LARGE SCALE LIFT THOUGH ARRIVES LATER IN THE MORNING ASSOCIATED WITH THE APPROACHING SHARP UPPER-LEVEL TROUGH. THIS IN COMBINATION OF A FAVORABLE UPPER-LEVEL JET WILL ALLOW FOR NUMEROUS SHOWERS TO OCCUR. THERE IS THE POTENTIAL FOR A BAND OF HEAVIER SHOWERS AND EMBEDDED THUNDER TO DEVELOP NEAR OR ALONG THE COLD FRONT AS IT ARRIVES. FOR MORE ON THE HEAVY RAIN ASPECT, SEE THE HYDROLOGY SECTION BELOW. THIS LINEAR FORCING COULD ALLOW FOR A BURST OF RAIN AND GUSTY WINDS, ESPECIALLY IF CONVECTIVE ELEMENTS DEVELOP AND CAN BE SUSTAINED AND TAP THE STRONG WINDS ABOVE THE SURFACE. THE FORECAST SOUNDINGS GENERALLY INDICATE THAT THE THERMAL PROFILES ARE MOIST, WHICH WOULD NOT FAVOR AS MUCH MOMENTUM TRANSFER DOWN TO THE GROUND AND LIMIT THE INSTABILITY. THEREFORE, WE MAY HAVE TO WAIT FOR THE ACTUAL FRONT TO PROVIDE A BETTER LOW-LEVEL MOMENTUM TRANSFER. THERE IS AN IMPRESSIVE THERMAL GRADIENT ALONG AND BEHIND THE COLD FRONT, AND THIS WOULD SUGGEST A RAPID INCREASE IN THE WINDS RIGHT BEHIND THE FRONT. THIS MAY RESULT IN WIND GUSTS TO AROUND 40 MPH AT TIMES WITH AND JUST BEHIND THE FRONT. THE PRE-FRONTAL WINDS WILL ALSO BE GUSTY, HOWEVER DEEPER MIXING IS NOT ANTICIPATED. SINCE THE DURATION IS IN QUESTION ESPECIALLY POST-FRONTAL, WE HELD OFF ON A WIND ADVISORY ATTM. REGARDING THUNDERSTORMS, THERE LOOKS TO BE ENOUGH ELEVATED INSTABILITY TO GENERATE SOME LIGHTNING. HOWEVER, WE MAY END UP HAVING SOME SORT OF A LOW-TOPPED LINE RIGHT NEAR THE FRONT GIVEN THE LINEAR FORCING. THERE IS A BETTER CHC OF STRONGER STORMS FROM THE DELMARVA ON SOUTHWARD AS A BIT MORE INSTABILITY MAY BE REALIZED ACROSS THESE AREAS. IF SOME STRONGER CONVECTION IS ABLE TO DEVELOP, THEN LOCAL WIND DAMAGE IS POSSIBLE ESPECIALLY ACROSS THE SOUTHERN AREAS. THE COLD FRONT LOOKS TO TRAVERSE THE AREA FROM WEST TO EAST AFTER 18Z. AS THIS OCCURS, THE TEMPERATURES BY LATER IN THE AFTERNOON ARE ANTICIPATED TO START DROPPING RATHER QUICKLY AS LOW-LEVEL CAA RAPIDLY TAKES PLACE. THIS RAPID COOLING MAY ALLOW FOR A MIX OR CHANGE OVER TO SOME SNOW AND SLEET ACROSS THE HIGHER TERRAIN OF THE POCONOS LATER THIS AFTERNOON. ANY ACCUMULATIONS SHOULD BE LIGHT AND MAINLY ON NON-ROADWAY SURFACES. HIGH TEMPERATURES WERE GENERALLY INDICATED TO OCCUR THIS MORNING, THEN A MODEL BLEND AND MANUAL ADJUSTMENTS WERE MADE TO THE HOURLY TEMPERATURES TO INDICATE FALLING VALUES. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM WEDNESDAY/... THE CALENDAR INDICATES THAT IT IS SPRING, HOWEVER MOTHER NATURE HAS OTHER PLANS. AS A STRONG COLD FRONT SWEEPS TO OUR EAST EARLY ON, RAPID CAA WILL ALLOW FOR TEMPERATURES TO FALL QUITE A BIT THROUGH THE NIGHT. THIS IS FORECAST TO BE OCCURRING AS THE BAND OF PRECIPITATION WITH THE FRONT SHIFTS QUICKLY EAST AND ENDS. THERE LOOKS TO BE SOME SNOW AND EVEN SOME SLEET TO OCCUR ACROSS PARTS OF THE CWA FOR A TIME BEFORE THE PRECIPITATION ENDS FROM WEST TO EAST. OVERALL NO ACCUMULATION IS EXPECTED, EXCEPT UP TO AN INCH OF SNOW IS POSSIBLE ACROSS THE HIGHER TERRAIN OF THE POCONOS. THE FORECAST SOUNDINGS INDICATE THAT THE LOW-LEVEL CAA IS STRONGER, WHICH LEAVES A WARMER LAYER ABOVE FOR A TIME. IF THIS WERE TO OCCUR, THEN RAIN SHOWERS COULD MIX WITH OR CHANGE TO A BRIEF PERIOD OF SLEET FARTHER SOUTH AND EAST. THE MAIN STORY IS THE RAPID RETURN OF COLD AIR, WHICH WILL BE USHERED IN BY GUSTY NORTHWESTERLY WINDS. THE STRONGEST WIND FIELD SHOULD BE IN PLACE DURING THE EVENING, AND THIS IS WHEN THE CAA RAPIDLY INCREASES PLUS THERE ARE PRESSURE RISES ON THE ORDER OF NEARLY 6 MB IN 3 HOURS FORECAST. THE MOMENTUM TRANSFER LOOKS GOOD TO ALLOW FOR GUSTS UP TO 40 MPH FOR AWHILE, THEN THIS SHOULD SETTLE DOWN SOME OVERNIGHT. THE WIND GUSTS COULD BE CLOSE TO ADVISORY CRITERIA, HOWEVER THE STRONGEST WINDS MAY NOT LAST ALL THAT LONG THEREFORE WE HELD OFF ON A WIND ADVISORY. THIS WILL ADD TO RATHER COLD WIND CHILL VALUES ACROSS THE REGION, WHICH WILL FEEL WORSE GIVEN THE STRETCH OF RATHER WARM WEATHER WE JUST HAD. SINCE THE WINDS ARE EXPECTED TO REMAIN ELEVATED THROUGH THE ENTIRE NIGHT, FROST IS NOT A CONCERN. THE CAA THOUGH WILL DRIVE TEMPERATURES AT OR BELOW FREEZING FOR MUCH OF THE AREA PRIOR TO DAYBREAK WEDNESDAY. THERE IS SOME CONCERN THE GUIDANCE IS TO COLD GIVEN THE WIND MAINTAINING MIXING, HOWEVER THE RATHER ROBUST CAA SHOULD GENERALLY TAKE CARE OF THAT. AS A RESULT, THE FREEZE WATCH WAS UPGRADED TO A WARNING. A FREEZE WARNING WAS ALSO ISSUED FOR THE OTHER AREAS WHERE THE GROWING SEASON HAS STARTED. AREAS TO THE NORTH OF THE WARNING, TEMPERATURES ARE FORECAST TO DROP BELOW FREEZING HOWEVER THE GROWING SEASON HAS NOT OFFICIALLY STARTED YET. AS FOR LOW TEMPERATURES, WE GENERALLY USED A BLEND OF THE NAM/GFS MOS WITH SOME TWEAKS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... WEDNESDAY AND WEDNESDAY NIGHT: A COLD FRONTAL BOUNDARY WILL CONTINUE MOVING OFFSHORE WEDNESDAY MORNING RESULTING IN CLEARING WITH A STRONG PUSH OF CAA. WENT MORE IN LINE WITH MET GUIDANCE ON HIGH TEMPERATURES AS THE MAV SEEMED A BIT WARM GIVEN THE AIRMASS BEHIND THE FRONT. THIS WILL BE QUITE THE SHOCK TO THE SYSTEM GIVEN THE RECENT SPRING WARMTH. MOSTLY CLEAR SKIES WILL CONTINUE INTO WEDNESDAY NIGHT AND WITH SOME RADIATIONAL COOLING LIKELY LOWS MAY BE NEAR OR BELOW FREEZING IN MANY LOCATIONS AWAY FROM THE SHORE. A LIMITATION TO FROST DEVELOPMENT MAY BE A FIVE MPH WINDS NORTHEAST WIND. HEADLINES FOR FROST/FREEZE MAY HAVE TO CONSIDERED AFTER TONIGHT`S THREAT HAS CONCLUDED AND THIS THREAT WILL BE MENTIONED IN THE UPDATED NPW PRODUCT. THURSDAY THROUGH FRIDAY NIGHT: LOOKS TO BE A RELATIVELY QUIET PERIOD UNDER NORTHEASTERLY FLOW FROM THE FRONTAL BOUNDARY OFFSHORE AND HIGH PRESSURE TO OUR NORTH. THE ONE CONCERN MAY BE SOME LOW CLOUDS AND DRIZZLE THAT ADVECT IN FROM THE OCEAN ALONG THE IMMEDIATE COAST. FOR NOW LEFT IT LESS THAN A SLIGHT CHANCE FOR THE FAR SE PORTIONS OF THE CWA IN LINE WITH THE 21Z SREF. SPLIT THE DIFFERENCE BETWEEN THE WARMER MEX GUIDANCE AND THE COOL MODELED TWO METER TEMPERATURES BOTH DAYS AND ON THE COLDER END OF GUIDANCE AT NIGHT. WITH LOW TEMPERATURES IN THE MID 30`S FROST MAY BE CONCERN AGAIN THURSDAY NIGHT THOUGH THE THREAT DOES NOT LOOK AS WIDESPREAD AS THE PREVIOUS TWO NIGHTS. SATURDAY AND SATURDAY NIGHT: A FRONTAL BOUNDARY WILL MOVE FROM THE OHIO VALLEY THROUGH THE SOUTHEAST STATES TOWARD OUR REGION. FORECAST THINKING REMAINS UNCHANGED THAT SOME UNCERTAINTY IS PRESENT ON WHICH FEATURE WILL BE MORE DOMINANT. IF THE LOW IN THE LAKES IS MORE DOMINANT THAN WE COULD HAVE A HIGHER CHANCE FOR SOME RAIN SHOWERS WITH THE FRONTAL PASSAGE. IF THE SOUTHERN LOW IS MORE DOMINANT A LOW PRESSURE COULD TRACK UP THE COAST OR OUT TO SEA. RIGHT NOW THE 00Z RUNS HAVE COME IN WITH A STRONGER SOUTHERN SYSTEM HEADING OUT TO SEA EARLY SATURDAY. THE 00Z GFS DOES BRING SOME SHOWERS WITH THE FRONTAL PASSAGE SO WILL CONTINUE WITH THE SHOWER CHANCE IN THE FORECAST. NOT MUCH SPREAD AMONG GUIDANCE ON TEMPERATURES IN THESE PERIODS. SUNDAY AND SUNDAY NIGHT: LOOKS LIKE A GOOD WEATHER DAY ACROSS THE REGION. WITH PLENTIFUL SUNSHINE WENT MORE TOWARD MEX/WPC GUIDANCE ON TEMPERATURES. MONDAY AND MONDAY NIGHT: NEXT SYSTEM WILL BE A COLD FRONT APPROACHING FROM THE WEST BY MONDAY NIGHT WILL INCLUDE A CHANCE OF SHOWERS. STUCK CLOSE TO WPC GUIDANCE IN THIS PERIOD AS THE 00Z MODELS HAVE INTO GOOD AGREEMENT ON A FRONTAL BOUNDARY PASSING THROUGH IN THE MONDAY NIGHT TIMEFRAME. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...CEILINGS ARE EXPECTED TO LOWER TO IFR, EVEN LOCALLY TO LIFR, THROUGH ABOUT MIDDAY. THE STRATUS IS MOST PREVALENT FIRST AT KACY AND KMIV. SHOWERS WILL INCREASE IN COVERAGE AS A STRONG COLD FRONT ARRIVES, AND SOME OF THE RAIN CAN BE HEAVY AT TIMES. THE LOWER VISIBILITIES SHOULD GENERALLY BE TIED TO THE RAIN INTENSITY, ALSO SOME FOG WILL OCCUR ESPECIALLY AT KACY AND KMIV. SOUTH WINDS IN THE 10 TO 20 KNOT RANGE WILL GUST UP TO 30 KNOTS ESPECIALLY FROM LATE MORNING ON, THEN SHIFT TO THE SOUTHWEST. A SHARP WIND SHIFT TO THE NORTHWEST SHOULD START TAKING PLACE FROM WEST TO EAST LATER THIS AFTERNOON. A LOW-LEVEL JET ON THE ORDER OF 45 TO 60 KNOTS WILL ACROSS MUCH OF THE AREA TODAY /STRONGEST CLOSER TO THE COAST/, AND THEREFORE A LOW-LEVEL WIND SHEAR MENTION IS MAINTAINED. SOME THUNDERSTORMS ARE POSSIBLE ESPECIALLY LATER THIS MORNING AND THIS AFTERNOON, HOWEVER CONFIDENCE IN COVERAGE IS LOW THEREFORE IT WAS NOT INCLUDED AT THIS TIME. STRONG SURFACE GUSTS TO AROUND 35 KNOTS ARE POSSIBLE MOSTLY STARTING AROUND 20Z AS THE STRONG COLD FRONT CROSSES OUR AREA. TONIGHT...CEILINGS IMPROVE TO MVFR AS SHOWERS COME TO AN END THROUGH THE EVENING. IT IS POSSIBLE THAT SOME WET SNOW AND SLEET OCCURS BEFORE THE PRECIPITATION ENDS, ESPECIALLY NORTH AND WEST OF KPHL. THE CEILINGS SHOULD THEN QUICKLY LIFT TO VFR AND CLEAR OUT DURING THE NIGHT. NORTHWESTERLY WINDS AROUND 20 KNOTS WITH GUSTS TO AROUND 30 KNOTS, THEN DIMINISHING SOME ESPECIALLY LATE. OUTLOOK... WEDNESDAY THROUGH FRIDAY NIGHT...MAINLY VFR CONDITIONS EXPECTED. NORTHWEST WIND GUSTS AROUND 20 KNOTS WEDNESDAY AFTERNOON. FRIDAY NIGHT AND SATURDAY: MAINLY VFR, POSSIBLE BRIEF PERIODS OF MVFR IN SCATTERED SHOWERS. && .MARINE... STRENGTHENING SOUTHERLY FLOW WILL OCCUR TODAY AHEAD OF A STRONG COLD FRONT. WHILE A POTENT LOW-LEVEL JET IS FORECAST TO OVERSPREAD THE AREA TODAY, THE THERMAL PROFILE SHOULD KEEP MUCH OF THE STRONGER WINDS ABOVE THE SURFACE. WHILE THERE COULD BE SOME GUSTS TO GALE FORCE THROUGH THE DAY, THIS SHOULD BE LOCALIZED AND TIED TO ANY CONVECTIVE ELEMENTS. AS THE STRONG FRONT CROSSES THE AREA LATE THIS AFTERNOON AND EARLY THIS EVENING, RAPID CAA IS FORECAST TO OCCUR IN CONJUNCTION WITH DECENT 3-HOUR PRESSURE RISES. THIS ALLOWS MIXING TO INCREASE A LOT AND BECOME DEEPER THROUGH THE EVENING. THE FORECAST SOUNDINGS SHOW GUSTS TO AROUND 40 KNOTS FOR AWHILE, AND GIVEN THE STRENGTH OF THE COLD FRONT THIS LOOKS DOABLE. THEREFORE, WE WILL UPGRADE THE GALE WATCH TO A WARNING FOR ALL ZONES STARTING EARLY THIS EVENING. WE OPTED TO DROP THE LEADING IN SMALL CRAFT ADVISORY AND FOCUS ON THE GALES. A SHARP WIND SHIFT WILL ACCOMPANY THE COLD FRONT AS IT SWEEPS ACROSS THE AREA. SEAS WILL CONTINUE TO BUILD AS WELL AHEAD OF THE FRONT, THEN HIGHER SEAS WILL TEND TO GET PUSHED FARTHER OFFSHORE AS THE FLOW TURNS TO THE NORTHWEST TONIGHT. OUTLOOK... WEDNESDAY...STRONG NORTHWESTERLY WINDS WITH GALE FORCE GUSTS POSSIBLE THROUGH 16Z. THE GALE WATCH FOR THIS PERIOD CONTINUES. SEAS DECREASING TO AROUND FIVE FEET LATE WITH GUSTS FALLING BELOW SCA CRITERIA IN THE AFTERNOON. WEDNESDAY NIGHT: SEAS AND GUSTS ARE EXPECTED TO BE BELOW SCA CRITERIA ATTM. THURSDAY THROUGH FRIDAY NIGHT: SCA SEAS AND SOME SCA GUSTS POSSIBLE THURSDAY MORNING. SATURDAY: SUB SCA SEAS AND WINDS. && .HYDROLOGY... A RIBBON OF HIGH PW VALUES WILL BE IN PLACE TODAY INTO TONIGHT AHEAD OF A STRONG COLD FRONT. THE ENHANCED LIFT ESPECIALLY WITH THE ARRIVAL OF THE ACTUAL COLD FRONT WILL PRODUCE AREAS OF HEAVIER RAIN. WE WENT WITH RAINFALL TOTALS GENERALLY ON THE ORDER OF 0.75 TO 1.50 INCHES. THESE EXPECTED AMOUNTS SHOULD RESULT IN SOME FLOODING IN AREAS OF POOR DRAINAGE AND PONDING OF WATER ON ROADWAYS, ESPECIALLY DURING TIMES OF HEAVIER RAINFALL. SOME OF THE GUIDANCE /I.E GFS/ COULD HAVE SOME CONVECTIVE FEEDBACK ADDED IN. WHILE SOME ENHANCEMENT TO THE RAINFALL COULD OCCUR ALONG THE FRONT, IT WAS FELT THE MOVEMENT OF THE SYSTEM WAS ENOUGH TO KEEP ANY TRAINING CELLS LIMITED. SOME SPOTTY SMALL STREAM FLOODING IS POSSIBLE, HOWEVER WIDESPREAD FLOODING IS NOT EXPECTED BASED ON ANTECEDENT CONDITIONS. THEREFORE, NO FLOOD WATCH ISSUED ATTM. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FREEZE WARNING FROM 2 AM TO 9 AM EDT WEDNESDAY FOR PAZ060-070- 071-101>104-106. NJ...FREEZE WARNING FROM 2 AM TO 9 AM EDT WEDNESDAY FOR NJZ012-013- 015>023-027. DE...FREEZE WARNING FROM 2 AM TO 9 AM EDT WEDNESDAY FOR DEZ001>003. MD...FREEZE WARNING FROM 2 AM TO 9 AM EDT WEDNESDAY FOR MDZ008-012- 015-019-020. MARINE...GALE WARNING FROM 6 PM THIS EVENING TO NOON EDT WEDNESDAY FOR ANZ430-431-450>455. && $$ SYNOPSIS...GAINES NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GAINES AVIATION...GAINES/GORSE MARINE...GAINES/GORSE HYDROLOGY...GORSE

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