000 
fxus61 kphi 161213 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
813 am EDT Wed Aug 16 2017 


Synopsis... 
high pressure will build across the region today before moving 
offshore on Thursday. A warm front will lift northward towards the 
area late Thursday and then moves through the area on Friday. A cold 
front will approach from the west on Friday, pushing through the 
region Friday night through Saturday. High pressure returns for 
Sunday through Tuesday. 


&& 


Near term /until 6 PM this evening/... 
dense fog advisory that was up until 8 am was allowed to expire. 
Visibility across the region generally above 1 mile, but there are 
some patchy areas where visibility is less than a mile, and even less 
than 1/2 mile. Motorists should be aware for rapidly changing 
Road conditions, as lingering fog should burn off within the 
hour. 


Otherwise, high risk for dangerous rc formation continues per 
the 13 second 4-5 ft se swell from Gert, washing ashore. 


Shortly after sunrise...it becomes sunny for a time before 
scattered to broken clouds form late morning and afternoon. 


Light northwest wind trends west during the afternoon with sea 
breezes along the coast. 


With a weak wind shift (drier dewpoints) developing across our 
area very late this afternoon near or north of i78...its not 
impossible to see a sprinkle in parts of E central or se PA and 
central or S New Jersey toward sunset. Hrrrx and NSSL WRF have it. 
Blended probability of precipitation and review of ki suggest not forecasting a sprinkle 
in New Jersey or Delaware but instead leave it for the southern part of Delaware. 


Forecast basis was a 50 50 blend of the 00z/16 GFS/NAM MOS 
guidance. 


Max temps a couple of degrees above normal. 


Also: posted a short pns sampling of reports for rainfall ydy 
of 1" or greater. 


&& 


Short term /6 PM this evening through 6 am Thursday/... 
again, its not impossible to see isolated sprinkles vcnty 
philly to Acy at 00z down into S Delaware but not lasting long. 


Otherwise becoming mostly clear. 


The wind shift progresses southward to near phl by 12z Thursday. 
Light north-northeast wind to its north and and light south to 
southwest to its south. 


Cooler and much more comfortable i78 northward, though short 
lived. 


Patchy fog probably forms toward dawn Thursday, but not nearly 
to the extent we see it this morning and not expecting a dense 
fog advy situation. 


Forecast basis was a 50 50 blend of the 00z/16 GFS/NAM MOS 
guidance. 


&& 


Long term /Thursday through Tuesday/... 
high pressure will start to slide offshore on Thursday with a warm 
front developing across Virginia. The warm front will push northward 
on Thursday and will start to move into our area late Thursday, 
pushing through the region on Friday. Showers and thunderstorms will 
start to develop just north of and along the warm front on Thursday 
afternoon and evening and then will overspread the region Thursday 
night and Friday as a warmer and moister airmass moves into the mid- 
Atlantic. 


A cold front will approach the region from the west on Friday, 
crossing the region late Friday through Saturday. Another round of 
showers and thunderstorms are expected as the front moves through 
our area. Good shear and forcing across the area means some 
storms may be strong, possibly severe, and with pwats running 
high again, heavy rain will also be a threat. Storm Prediction Center has a marginal 
risk for severe storms just to our west at this time. 


Some cooler air should arrive behind the front but it isn't all 
that cool or dry so little relief is expected. A shortwave will 
cross through the region on Saturday keeping the chance for 
showers and thunderstorms throughout Saturday evening. As the 
wave pushes to the east, the showers/thunderstorms will decrease 
in coverage and drier air will start to move in. 


High pressure will build in for Sunday and a period of relatively 
nice weather should continue for the start of the week with the high 
shifting offshore on Monday. Another frontal system will approach 
the region for Tuesday/Wednesday with another chance for showers and 
thunderstorms. 


&& 


Aviation /12z Wednesday through Sunday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 


Remaining IFR stratus/fog dissipates by 14z. Then VFR sct-bkn 
clouds aoa 4000 ft develop midday with a west-northwest wind 
trending west to southwest late in the afternoon except sea 
breezes developing vcnty kacy. Isolated light showers possible 
se PA to S New Jersey after 21z. I think the NAM tsec is best for fcstg 
low lvl rh changes. Narre has completely missed the dense fog in 
our area, yet unexpectedly to ME has a stratus deck lingering 
to around 15z. 


Tonight...after any isolated light showers vcnty kilg/kphl/kacy 
southward end by 01z, a VFR night with a wind shift progressing 
southward to near kphl by 12z Thu. Winds turn light north-northeast 
north of the boundary and are light south to southwest to its 
south. 


Patchy IFR fog/stratus may form in the New Jersey and Delmarva Countryside 
between 07z-10z/17, but not nearly to the extent of what we see/saw 
this morning. 


Outlook: 
Thursday...mainly VFR conditions expected. Sub-VFR conditions in 
afternoon/evening showers and thunderstorms. Fog possible early 
Thursday morning and again late Thursday night. 


Friday...fog possible early morning. Sub-VFR conditions in showers 
and thunderstorms. 


Saturday...MVFR conditions expected scattered showers and 
thunderstorms possible. Improving conditions late. 


Sunday...mainly VFR conditions expected. 


&& 


Marine... 
seas are around 5 feet at the buoys off the New Jersey/Delaware coast as 
Hurricane Gert heads enewd well offshore toward the north 
central Atlantic. Longer period swell from Gert is reaching the 
buoys (generally 12-13 seconds) and will continue this morning 
then easing slowly this afternoon and evening. Small Craft 
Advisory for seas continues. 


Light northwest flow this morning becomes southeast to south 
sea breezes during this afternoon. A wind shift back to 
northerly should develop for the New Jersey coastal waters late 
Wednesday night. 


Some fog may develop near the coast and near Delaware Bay early 
today, with visibility restrictions possible. However, this fog 
should dissipate rapidly after sunrise with a nice day expected, 
save for the aforementioned higher seas. 


Outlook... 
Thursday thru Sunday...sub-Small Craft Advisory conditions 
expected on the area waters through Sunday. Some gusts around 
20-25 knots are possible Friday afternoon and evening. Showers 
and thunderstorms possible late Thursday through Saturday, with 
locally higher seas and winds. 




Rip currents... 
a high risk for the development of dangerous rip currents is 
in effect today. Long period swells from Hurricane Gert will 
continue to impact the coasts of Delaware and New Jersey. 


Swim only in the presence of lifeguards where safety prevails 
and if beaches are closed...respect the decisions of the local 
officials. Do we need a reminder? There have been numerous 
drowning fatalities this year along the New Jersey coast, and most of 
those at unguarded beaches. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...high rip current risk through this evening for njz014-024>026. 
Delaware...high rip current risk through this evening for dez004. 
Maryland...none. 
Marine...Small Craft Advisory for hazardous seas until 2 PM EDT this 
afternoon for anz450>455. 


&& 


$$ 
Synopsis...meola 



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