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Area Forecast Discussion
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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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