767  
FXUS61 KPHI 192054  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
354 PM EST THU JAN 19 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE OVER THE MID-ATLANTIC WILL MOVE OFFSHORE TONIGHT  
THROUGH FRIDAY MORNING. WEAKENING LOW PRESSURE WILL LIFT  
NORTHEAST THROUGH THE REGION LATE FRIDAY. WEAK HIGH PRESSURE  
RETURNS FOR SATURDAY. A STRONG AND COMPLEX AREA OF LOW PRESSURE  
WILL IMPACT THE NORTHEAST AND MID-ATLANTIC FROM SUNDAY THROUGH  
TUESDAY. A SERIES OF FRONTAL BOUNDARIES WILL IMPACT THE AREA  
LATE NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
CONSIDERABLE CLOUDINESS DEVELOPED TODAY BELOW THE LOW-LEVEL  
INVERSION. WITH THE LOSS OF DAYTIME HEATING AND A CONTINUED  
BUILDING OF THE MID-LEVEL RIDGE ACROSS THE AREA, EXPECT THE  
CLOUDS TO DIMINISH THIS EVENING WITH MOSTLY CLEAR SKIES  
DEVELOPING. THEN A CIRRUS SHIELD WILL BEGIN OVERSPREADING THE  
REGION, AROUND MIDNIGHT IN DELMARVA, AND REACHING NORTHWEST NJ  
BY SUNRISE. THESE CLOUDS WILL WORK THEIR WAY OVER THE  
AFOREMENTIONED RIDGE, IN ADVANCE OF THE NEXT STORM SYSTEM TO  
IMPACT THE REGION FRIDAY.  
 
IN SPITE OF THE CLOUDINESS, WE SHOULD RADIATE EFFICIENTLY IN  
THE NORMALLY COLDER SPOTS NORTH OF I-78, AS WELL AS IN THE  
PINELANDS, AS HIGH PRESSURE CENTERS OVER THE REGION, MAINTAINING  
LIGHT AND VARIABLE WINDS. IN THE AFOREMENTIONED LOCATIONS, LOW  
TEMPERATURES WILL BE IN THE MID TO UPPER 20S, WITH LOW TO MID  
30S ELSEWHERE.  
 
WE ALSO EXPECT ADDITIONAL PATCHY FOG, MAINLY NORTH OF I-78 AND  
IN THE PINELANDS, PARTICULARLY WHERE IT OCCURRED THURSDAY  
MORNING, GIVEN A SIMILAR AIR MASS.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/
 
 
LOW PRESSURE MOVING THROUGH THE OHIO VALLEY ON FRIDAY BEGINS TO  
UNDERGO REDEVELOPMENT OFFSHORE OF THE NC/VA BORDER DURING THE  
AFTERNOON. AS THE MID-LEVEL RIDGE MOVES EAST OF THE AREA IN THE  
MORNING, AN OVERRUNNING REGIME WILL SETUP ACROSS THE REGION,  
WITH MODEST ISENTROPIC ASCENT ALONG THE 300K SURFACE. PRIOR TO  
THAT, WITH HIGH LEVEL CLOUDINESS HAVING OVERSPREAD THE REGION,  
THERE IS A SHARP GRADIENT IN THE REMAINING COLUMN MOISTURE,  
SUGGESTING THE DAY WILL START OUT WITH SUNSHINE, FOLLOWED BY  
OVERCAST SKIES ACROSS THE REGION BY LATE MORNING.  
 
THERE IS GOOD MODEL AGREEMENT IN TERMS OF MASS FIELDS AND POPS  
FOR PRECIPITATION OVERSPREADING THE REGION FROM WEST TO EAST  
BETWEEN MID-MORNING AND NOON. INITIALLY, WE EXPECT 2-METER  
TEMPERATURES TO BE COLD ENOUGH (LOWER 30S) FOR A BRIEF PERIOD OF  
LIGHT FREEZING RAIN ACROSS CARBON AND MONROE COUNTIES, ENDING  
AROUND NOONTIME. THE MORE SUBSTANTIAL PRECIP SHOULD HOLD OFF  
UNTIL EARLY AFTERNOON ACROSS THIS AREA, WHICH WILL LIMIT  
FREEZING RAIN ACCUMULATIONS. AT THIS TIME, OUR ICE GLAZE MAP  
MAINTAINS A CHANCE FOR A TRACE TO ONE-HUNDREDTH OF AN INCH FOR  
PORTIONS OF CARBON AND MONROE COUNTIES. THIS IS LESS THAN  
PREVIOUSLY FORECAST, PER COLLABORATION WITH OUR SURROUNDING  
OFFICES AND WPC WWD. THERE IS STILL SOME POTENTIAL FOR  
ADDITIONAL FREEZING RAIN IN THE EARLY EVENING IF THE COLUMN WET-  
BULBS MORE THAN EXPECTED, BUT THAT IS A LOW PROBABILITY, AS  
EVEN THE HIGH RESOLUTION MODELS AND ENSEMBLES HAVE TRENDED  
WARMER. IN TERMS OF RAINFALL AMOUNTS, GENERALLY TWO TO THREE-  
TENTHS OF AN INCH ACROSS THE REGION.  
 
HIGH TEMPERATURES WILL STILL AVERAGE ABOVE NORMAL, GENERALLY  
MID 30S TO UPPER IN THE POCONOS AND NORTHWEST NJ, WITH 40S  
ELSEWHERE.  
 

 
   
LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/
 
 
WEAKENING LOW PRESSURE CONTINUES TO LIFT NE THROUGH THE REGION  
FRIDAY EVENING. PRECIP WILL TAPER OFF OVER SE PA, NE MD, DE, AND  
S NJ BY MIDNIGHT, AND THEN PRECIP GRADUALLY TAPERS OFF OVER N  
NJ PRIOR TO DAYBREAK.  
 
LATEST TREND IS FOR TEMPS TO REMAIN ABOVE FREEZING, AT LEAST  
DURING THE PRECIP, SO WILL NOT HAVE FREEZING RAIN IN THE  
FORECAST, AND WILL KEEP PRECIP AS PLAIN RAIN. LATEST  
NAM/GFS/ECMWF HAVE THE PRECIP WORKING THROUGH THE REGION FROM  
00-06Z, SO EARLY IN THE PERIOD WILL CARRY LIKELY POPS FOR N NJ  
AND THE POCONOS, AND GENERALLY CHANCE POPS ELSEWHERE.  
 
WEAK HIGH PRESSURE BUILDS IN FROM THE WEST AFTER MIDNIGHT  
FRIDAY NIGHT AND INTO SATURDAY MORNING. WITH ABUNDANT LOW LEVEL  
MOISTURE IN PLACE, AND LIGHT TO NEARLY CALM WINDS, CAN EXPECT  
AREAS OF FOG TO DEVELOP, AND DEPENDING ON HOW MUCH RAIN FALLS  
THROUGH FRIDAY EVENING, FOG COULD BE LOCALLY DENSE.  
 
DRY CONDITIONS ON SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE  
REGION AND MOVES OFFSHORE LATE.  
 
STORM DEVELOPS OVER THE GULF COAST ON SUNDAY AND BEGINS TO LIFT  
TO THE NORTH AND EAST SUNDAY NIGHT. ALTHOUGH MODELS IN GENERAL  
AGREEMENT, THERE ARE SOME KEY DIFFERENCES BETWEEN THE GFS AND  
THE ECMWF THAT HAVE SHOWN UP WITH THE MORNING MODEL CYCLE.  
 
HIGH PRESSURE OVER NE CANADA WILL BEGIN TO NOSE ITS WAY  
SOUTHWARD TOWARDS NORTHERN NEW ENGLAND. WHERE THIS HIGH SETS UP  
WILL HAVE A PROFOUND IMPACT ON THE FORECAST. LATEST GFS HAS THE  
HIGH A BIT FARTHER SOUTH THAN THE ECMWF, AS A RESULT, SUPPRESSES  
THE APPROACHING MORE THAN THE ECMWF DOES. THE GFS HOLDS OFF ON  
THE HEAVIEST PRECIP UNTIL LATE MONDAY/MONDAY NIGHT, WHEREAS THE  
ECMWF HAS BANDS OF HEAVY PRECIP SLIDING ALONG THE COAST STARTING  
ON SUNDAY. AS OF NOW, FEEL BEST WAY TO APPROACH THIS IS BY  
PLANNING ON HAVING PERIODS OF MODERATE TO HEAVY RAIN FROM SUNDAY  
NIGHT THROUGH MONDAY NIGHT. ANOTHER ASPECT TO CONSIDER: IF THAT  
HIGH NOSES A BIT FARTHER SOUTH, THEN MUCH COLDER TEMPERATURES  
WOULD FILTER INTO THE REGION, AND THERE IS THE POTENTIAL FOR  
FREEZING RAIN SOMETIME DURING THE PERIOD. FOR NOW, WILL HAVE A  
FEW HOURS OF FREEZING RAIN IN THE FORECAST FOR CARBON AND MONROE  
COUNTIES MONDAY MORNING, AS THIS FOLLOWS WITH THE DIURNAL  
TEMPERATURE CURVE.  
 
WITH A TIGHT EASTERLY GRADIENT DEVELOPING BETWEEN THE  
APPROACHING LOW AND THE AFOREMENTIONED HIGH, THERE IS THE  
POTENTIAL FOR WIND ADVISORY LEVEL WINDS FOR MUCH OF EASTERN NJ  
AND INTO DE, GENERALLY TO THE SOUTH AND EAST OF I-95, WITH  
SUSTAINED WINDS OF 25-35 MPH WITH GUSTS UP TO 50 MPH. THE REST  
OF THE FORECAST AREA CAN EXPECT EAST WINDS 15-25 MPH WITH GUSTS  
UP TO 40 MPH.  
 
ONCE THE LOW LIFTS THROUGH THE REGION MONDAY NIGHT, PRECIP WILL  
COME TO AN END FAIRLY QUICKLY.  
 
UNSETTLED WEATHER ON TAP FOR THE MID TO LATE WEEK PERIOD AS  
SEVERAL WEAK BOUNDARIES IMPACT THE REGION. COLDER AIR LOOKS TO  
MAKE A RETURN BY THE END OF NEXT WEEK. UNTIL THEN, TEMPERATURES  
LOOK TO REMAIN AT ABOVE NORMAL LEVELS.  
 

 
   
AVIATION /21Z THURSDAY THROUGH TUESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...OCCASIONAL MVFR CEILINGS EARLY WILL LIFT FOR A TIME,  
THEN POSSIBLY SCATTERED IFR CEILINGS TOWARD SUNRISE. THERE MAY  
ALSO BE SOME PATCHY FOG AS WELL. NORTHWEST WINDS BECOMING LIGHT  
AND VARIABLE.  
 
FRIDAY...SCATTERED MVFR CEILINGS IN THE MORNING LOWERING TO IFR  
IN THE AFTERNOON. WITH RAIN ARRIVING AT THE TAF SITES FROM LATE  
MORNING INTO THE AFTERNOON, WE EXPECT SOME VISIBILITY  
RESTRICTIONS BELOW 3SM. WINDS WILL BE EAST AT 5 TO 10 KNOTS.  
 
OUTLOOK...  
FRI NIGHT...SUB-VFR CONDITIONS POSSIBLE IN -RA. MODERATE  
CONFIDENCE. FOG POSSIBLE FRI NIGHT. LIGHT WINDS.  
 
SAT/SAT NIGHT...IMPROVING CONDITIONS SATURDAY MORNING,  
OTHERWISE VFR. HIGH CONFIDENCE.  
 
SUN...E WINDS 10-15 KT. CONDITIONS DETERIORATING FROM S TO N  
DURING THE DAY WITH IFR CONDITIONS POSSIBLE BY AFTERNOON.  
MODERATE CONFIDENCE.  
 
SUN NIGHT THRU MONDAY NIGHT...IFR AND LOWER CONDS POSSIBLE IN  
RA. E WINDS 15-20 KT WITH 20-30 KT GUSTS AT TERMINALS NORTH AND  
WEST OF I- 95, AND 20-30 KT WITH 30-50 KT SOUTH AND EAST OF I-95  
POSSIBLE. MODERATE CONFIDENCE.  
 
TUESDAY...MAINLY VFR, BUT CANNOT RULE OUT PASSING SHOWERS. LOW  
CONFIDENCE.  
 

 
   
MARINE
 
 
SCA FOR HAZARDOUS SEAS HAS BEEN EXTENDED THROUGH THIS EVENING  
AS OCEAN SEAS REMAIN AT 5-6 FEET DUE TO THE LONG PERIOD SWELL.  
GUIDANCE HAS BEEN WELL UNDERDONE.  
 
OTHERWISE, WE EXPECT SUB-SCA CRITERIA FOR THE WATERS LATE  
TONIGHT INTO FRIDAY.  
 
OUTLOOK...  
FRI THROUGH SUN MORNING...NO MARINE HEADLINES ANTICIPATED  
DURING THIS TIME. SEAS WILL GENLY BE AROUND 2 FT WITH WIND 10  
KTS OR LESS.  
 
SUN AFTN THRU MON NIGHT...EASTERLY FLOW INCREASES TO 15-20 KT  
WITH 25-30 KT GUSTS STARTING SUN AFTN, AND THEN GALE FORCE GUSTS  
OF 35-40 KT LIKELY MONDAY AND MONDAY NIGHT. MODERATE TO HEAVY  
RAIN WITH LOW VSBY EXPECTED. STORM FORCE WINDS POSSIBLE,  
ESPECIALLY ON MONDAY. CONDITIONS BEGIN TO IMPROVE LATE MONDAY  
NIGHT, AND WINDS DECREASE TO SCA LEVELS. HOWEVER, SEAS ON THE  
OCEAN SHOULD REMAIN ABOVE SCA CRITERIA.  
 
MON NIGHT THRU WED...WIND DECREASES BELOW HEADLINE CRITERIA,  
BUT OCEAN SEAS WILL REMAIN ABOVE SCA CRITERIA. IT IS POSSIBLE  
THAT SOME AREAS, ESPECIALLY ACROSS SOUTHERN WATERS, MAY DROP  
BELOW SCA SEAS ON WED.  
 

 
   
TIDES/COASTAL FLOODING
 
 
DUE TO THE PERSISTENT AND INCREASING EASTERLY FLOW AROUND A  
COASTAL LOW SUNDAY-MONDAY, THERE COULD BE SEVERAL TIDAL CYCLES  
OF COASTAL FLOODING, BUT THIS WILL ALSO BE DEPENDENT ON THE  
TRACK OF THE LOW AND WILL BECOME MORE EVIDENT AS WE APPROACH  
SUNDAY NIGHT AND MONDAY. LATEST GUIDANCE INDICATES THE POTENTIAL  
FOR WIDESPREAD MINOR COASTAL FLOODING, BUT THAT WILL COME INTO  
BETTER FOCUS THIS WEEKEND.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 1 AM EST  
FRIDAY FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...MPS  
NEAR TERM...FRANCK  
SHORT TERM...FRANCK  
LONG TERM...MPS  
AVIATION...FRANCK/MPS  
MARINE...FRANCK/MPS  
TIDES/COASTAL FLOODING...  
 
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