fxus61 kphi 201955 

Area forecast discussion 
National Weather Service Mount Holly New Jersey 
355 PM EDT Wed Jun 20 2018 

a developing low pressure system and its associated fronts will 
traverse the region tonight. Canadian high pressure moves into the 
northeast late Thursday into Friday while a stalled front 
remains just to the south. Low pressure moving from the eastern 
Great Lakes into northern New England will lift a warm through 
the region on Saturday, followed by a cold frontal passage late 
Sunday. A sprawling area of Canadian high pressure builds into 
the area through the first half of next week. 

Near term /until 6 am Thursday morning/... 
looks to be an active night with the sfc front just to the west and 
a few weak vort maxs expected to move through. Weak low pressure 
will also cross the area. We expect increasing amts of showers this 
evening with tstms also expected. Locally heavy rains are also 
possible. Hopefully, the activity will move thru fast enough to 
preclude any significant flooding. Localized poor drainage flooding 
is possible however. It will remain warm and humid overnight. Lows 
will drop into the low/mid 60s north/west and hold in the upper 60s/low 70s 

Short term /6 am Thursday morning through 6 PM Thursday/... 
most of the showers associated with the system from Wednesday night 
will have moved S/east of the area by Thursday morning. A few showers 
may remain across ern Delaware and se New Jersey however. These showers will 
continue east and be offshore by noon. Clouds will decrease from 
northwest/southeast as drier air filters into the area. Temperatures will reach 
the low/mid 80s in most areas Thursday. Dew points will be somewhat 
less than Wednesday. Winds will be north to northeast around 10 

Long term /Thursday night through Tuesday/... 

Thursday night through Sunday... 

There will be a brief reprieve between systems Thursday night 
into Friday before the next system affects the area over the 
weekend. To start the period Thursday night, a quasi-stationary 
front will be situated just south of the area while a high 
pressure system moves from Ontario and Quebec into New England. 
This will set up a cooler east/NE flow over the area. Mainly clear 
to partly cloudy skies Thursday evening will give way to 
increasing clouds overnight as mid and upper level moisture 
begins streaming in ahead of the next system. In addition, there 
are some indications that a marine low stratus deck may form and 
effect portions of central and southern New Jersey into the Delmarva. 
The area should remain precip free for Thursday night however 
with lows mainly in the 60s, except 50s over the southern 

Tricky forecast for Friday. Moisture associated with the next 
approaching low over the Ohio Valley will continue to push 
eastward toward the region in the SW flow aloft. Meanwhile, at 
the surface, the stationary front remains stalled just to our 
south with cool east/NE winds over the area to its north. This will 
be associated with the westward extent of the ridge over New 
England. Despite the moisture advecting in aloft, there will be 
a dry layer in the lower levels associated with the ridge and 
this will tend to limit precip over the area. That said, still 
think there may be some scattered to isolated showers over the 
area under the mainly cloudy skies so we do have chance to 
slight chance pops in for most areas by Friday afternoon. We 
also trended the forecast cooler as there will be an inversion 
above the cooler NE flow. Generally expect highs in the low to 
mid 70s but it could even be a bit cooler than this. 

Friday night, low pressure supported by an upper trough 
advances northward toward lower Michigan slowly pushing a warm 
front toward the southern Delmarva by early Saturday. Expect 
an area of showers to move through associated with the 
isentropic lift and shortwave energy in the SW flow ahead of the 
upper trough. A few rumbles of thunder will be possible but this 
should be mainly confined to southern areas across the Delmarva 
closer to the front. Heading into Saturday, the warm front will 
continue to slowly make its way northward through the area but 
may not make it farther north than the I-78 / I-80 corridor by 
late day. The initial round of showers Friday night may last 
into Saturday morning before there should be a lull as much of 
the area breaks into the warm sector...so not looking like a 
continuous all day rain. Depending on how much sunshine breaks 
out temps south of the front should at least reach the low to 
mid 80s, if not a bit higher, with dew points climbing into the 
upper 60s to low 70s so it will be quite muggy once again! By 
the latter part of the afternoon into the evening attention will 
then turn to the thunderstorm threat ahead of a pre-frontal 
trough. At this point still looking at good deep layer forcing 
with ml convective available potential energy potentially reaching 1000-1500+ j/kg and deep 
layer shear reaching 30-50 knots. For these reasons still see 
the potential for severe weather given this set up...especially 
near and south of the I-95 corridor in the warm sector. 
Indications are for a round of late day showers and 
thunderstorms to affect this area before moving out Saturday 
night as the trough moves through. 

By Sunday morning, area should be in another lull however the 
actual cold front and associated upper level trough will still 
be upstream. For this reason expect that a mainly dry start to 
the day with a mix of sun/clouds will give way to increasing 
chances for showers and storms arriving from the west by late 
afternoon as the front and the main shortwave energy aloft 
approaches. Still another very warm, muggy day with temps and 
humidity levels similar to Saturday. 

Sunday night through Wednesday... 

Showers and storms with the cold front discussed above will 
sweep through the area with the front Sunday night into early 
Monday followed by clearing skies by late Monday along with 
falling dew points and temperatures near seasonal. Beyond this 
time, a sprawling area of high pressure looks to build in from 
the north bringing mainly clear skies with seasonable 
temperatures and comfortable humidity levels through mid week. 

Aviation /19z Wednesday through Monday/... 

The following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 

Rest of afternoon/early evening...scattered showers moving east from 
south central PA will affect the Delaware valley tafs for awhile, 
but significant vsby or cig restrictions are not expected. Winds 
mostly S to SW around 10 knots. 

Tonight...more showers and scattered tstms will arrive overnight 
affecting most taf sites in the 04z/05z thru 09z/10z time frame. 
Cigs and vsbys will likely drop to MVFR, but upper end IFR is 
possible too. Winds will generally shift from srly direction to nrly 
towards dawn. 

Thursday...improvement from northwest/southeast through the morning with most 
showers done by 12/13z. Winds will be north to NE at 5 to 10 knots. 


Thursday night...MVFR ceilings possible at Acy and miv, with 
northeast wind gusts up to 20 mph. Elsewhere, VFR. Medium 

Friday...predominantly VFR. Cannot rule out brief MVFR ceilings in 
rain showers. Easterly wind gusts up to 20 mph, especially Acy and phl. 
Medium confidence. 

Friday night...low clouds and fog will lead MVFR, with IFR possible, 
especially late. Easterly wind gusts up to 20 mph. Low confidence. 

Saturday...conditions gradually improving to MVFR, with VFR possible 
by afternoon, especially I-95 corridor terminals. But rain showers and thunderstorms and rain 
will lead to brief ceiling/visibility restrictions. Southwest winds. 
Medium confidence. 

Saturday night...a return to low clouds and fog with MVFR, and even 
IFR possible. Winds shifting to the northwest. Low confidence. 

Sunday...low clouds and fog will dissipate with a return to 
mainly VFR until a late day risk of storms could bring brief 
restrictions. Winds west- southwest. Medium confidence. 

Sunday night...showers, storms possible along with associated 

Monday...becoming mainly VFR. 

overall, conditions will remain below Small Craft Advisory criteria tonight. Winds 
tonight will be mostly southeast to S around 10 to 15 knots this evening 
and 5 to 10 knots overnight. Scattered showers and tstms tonight. 
Locally higher winds and seas near tstms. 

Thursday, showers will end during the morning and then fair weather 
will arrive for the afternoon. Winds will be north to northeast at 
around 10 knots. 

Rip currents...low expected. 


Winds and seas may reach Small Craft Advisory levels late Thursday night as low 
pressure develops offshore. The pressure gradient between high 
pressure to the north and an approaching warm front to the south 
likely leads to continued Small Craft Advisory winds/seas Friday and Friday 
night. As the warm front moves across the waters, a brisk 
southwest flow promotes Small Craft Advisory level seas through at least 
Saturday. A return to more tranquil, sub-Small Craft Advisory boating conditions 
is expected Sunday into early next week. 

Phi watches/warnings/advisories... 
New Jersey...none. 



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