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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 150714

Area Forecast Discussion
National Weather Service Mount Holly NJ
314 AM EDT Sun Sep 15 2019

A cold front will move to the south of the area today while 
high pressure weakens to our west through the day. A clipper 
type system moves into the Mid Atlantic region on Monday and 
weakens as it moves across the area and to our south. High 
pressure builds across the northeast states on Tuesday into 
Wednesday, then shifts southward across the Mid Atlantic region
Thursday. The high is forecast to shift to our south Friday, 
then offshore over the weekend.


A weak front is moving through the area early this morning, 
with a few showers (and occasionally an isolated storm) in the 
areas immediately downstream of it. There are some indications 
that these showers will expand in coverage over eastern New 
Jersey early this morning before moving offshore, aided by a 
low-amplitude perturbation moving through the area at this time.
These showers should generally be offshore by late morning as 
the perturbation departs stage east. However, the front's 
movement is slow, and would not be surprised to see more showers
develop in Delmarva and southern New Jersey through mid 
afternoon before the front eventually migrates southeast of the 
region. Have maintained some slight-chance to low-chance PoPs in
these areas.

Meanwhile, patchy fog continues early this morning in the 
Lehigh Valley, southern Poconos, and northwest New Jersey. This 
should dissipate rapidly after daybreak, as the front pushes off
to the east, diurnal heating commences, and somewhat drier air 
filters into the region.

Skies will improve upstream of the front rather quickly today, 
with temperatures actually expected to be warmer than yesterday 
owing to the sunnier skies and improved mixing. MOS guidance is 
in good agreement with temperatures upstream of the front today,
and have used a continuity/statistical blend for the forecast.

Along the coast, a sea breeze will likely be able to penetrate 
inland owing to overall weak surface flow. As such, the 
temperatures may be curbed from climbing compared to areas 
farther west. Additionally, cloud cover may linger in the far 
southern portions of the CWA longer, which may keep temperatures
down here compared to areas farther northwest.


Northwest midlevel flow will become established by tonight, as 
a shortwave trough moves east of New England. Another vort max 
will be upstream in Ontario and western Quebec, but will still 
remain well northwest of the area overnight. As a result, 
expecting a dry night across the area as the northern Mid-
Atlantic lies in a nebulous surface col.

Skies will be clear, which should aid in some decent 
radiational cooling, especially during the evening. However, 
clouds will likely increase in the northern CWA in advance of 
the upstream perturbation overnight. Additionally, there are 
indications some weak moist advection will occur in the southern
CWA, synoptically induced by the northwest-flow system to move 
through the Northeast on Monday. Thus, stayed close to a 
consensus blend for tonight's lows. 


A mostly quiet long term period is expected, with only a small 
chance of precipitation at the beginning of the period..

The only chance of precipitation is expected to be on Monday 
for portions of northeast Pennsylvania and northern New Jersey 
as a clipper type system is forecast to move across the area 
during the day. This system is fairly weak and the strongest 
energy associated with it is forecast to pass to our north, so 
precipitation chances will not be very high. There may also be a
slight chance of showers across far southern Delmarva as the 
system weakens and pushes to our south overnight Monday.

Nice weather is then expected for the rest of the week as high 
pressure is forecast to affect the east coast through the week. 
The high forecast to build across New England Tuesday into 
Wednesday, then shift southward across the Mid Atlantic region 
on Thursday. Then the high is expected to build to our south on 
Friday, then offshore over the weekend. With the high pressure 
near the east coast most of the week into next weekend, dry 
conditions are currently forecast, although there will likely be
periods of cloud cover at times.

Temperatures through the extended will be a bit of a roller 
coaster ride. Monday will be well above normal, before dropping 
closer to normal Tuesday, Wednesday, and Thursday, before rising
back above normal Friday and especially next weekend.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas.

Rest of tonight...Still a chance of showers through about 10z 
at the Philly terminals, MIV, and ACY, with brief restrictions 
possible. Meanwhile, sub-VFR CIGs may settle in after the 
showers move out. Some IFR is possible, but CIGs may 
predominantly be MVFR. If lower CIGs do not become more 
prevalent, sub-VFR VSBYs should be expected to develop (already 
occurring at RDG/ABE). Light/variable winds. Low confidence.

Sunday...Quick improvement to VFR expected as winds become 
northwesterly up to 10 kt, though directions are expected to 
become more westerly or even variable in the afternoon. A sea 
breeze is likely to affect ACY in the afternoon, with quick 
switch to south winds. High confidence.

Sunday night...Mainly VFR with light/variable winds. There are 
some indications lower CIGs may develop near the coast, but 
confidence on this happening is low.


Monday...VFR conditions expected. Slight chance of showers for 
northeast Pennsylvania and northern New Jersey. West to 
southwest winds 5-10 knots early, becoming west to northwest 
during the day.

Monday night...VFR early, then MVFR conditions may develop 
overnight. north to northwest winds 5-10 knots early, becoming 
northeast overnight. 

Tuesday-Wednesday night...Mostly VFR during the day, with a 
chance of MVFR conditions overnight. East to northeast winds 
5-10 knots Tuesday-Tuesday night, becoming east to southeast 
during the day Wednesday.

Thursday-Thursday night...Generally VFR conditions expected. 
Variable winds through the day.


A front will move through the waters today, with showers and an
isolated storm possible. Winds will veer from southwest to 
northwest during frontal passage but remain well below advisory 
criteria (outside of the strongest showers). However, flow will 
quickly return to southeast or south by afternoon. Expect winds 
to become southwesterly overnight. Seas will generally range 
from 2 to 4 feet. 


Monday-Monday night...Conditions are expected to remain below 
advisory levels. Seas will remain 3-4 feet and winds could gust 
around 20 knots at times, especially later Monday night. 

Tuesday-Wednesday night...Small Craft Advisory conditions 
likely as wind gusts increase to 25-30 knots and seas increase 
to 5-6 feet for portions of the Atlantic Coastal waters.

Thursday-Thursday night...Winds may lower below advisory 
levels, however, seas may remain above 5 feet.

Winds will be variable today, from northwesterly this morning 
to southeasterly this afternoon. Speeds are expected to remain 
fairly light, generally under 15 mph. With seas lowering to 2 to
4 feet in the surf zone, a moderate risk of rip currents is 





Near Term...CMS
Short Term...CMS
Long Term...Robertson