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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 151329

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

A cold front will stall south of our area through today while
high pressure weakens to our west. A weak area of low pressure
slides by our region on Monday. High pressure builds across the
Northeast Tuesday into Wednesday, then shifts southward across
the Mid- Atlantic region Thursday. The high is forecast to shift
to our south Friday, then offshore next weekend.


930 AM update...The back edge of the cloud cover initially 
thinned out into portions of the I-95 corridor, however with a 
moist boundary layer combined with brief heating resulted in the
redevelopment of some low clouds. This is expected to shift 
southeastward and erode this morning as drier air moves in from 
the northwest. The cloud cover was adjusted upward into the I-95
corridor for awhile longer to account for this. The PoPs were 
adjusted based on radar trends, and showers continue to shift 
east and southeastward. The cold front looks to be currently 
moving through the southeastern part of the region, with a more 
northerly wind in its wake.

Otherwise, a weak cold front continues to move through the area
this morning. Given the slow movement of the front, 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.

The sky will improve upstream of the front rather quickly 
through 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.

Today...Lingering MVFR/IFR conditions through 15z especially
from the PHL area south/east, then improvement to VFR. The sub-
VFR conditions linger the longest south and east of PHL and
especially in the MIV to ACY areas. Light and variable winds
becoming northerly up to 10 kt. The wind direction is 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. Low confidence on timing of improving
conditions especially near and south/east of PHL, but high
confidence for the forecast this afternoon.

Tonight...Mainly VFR with light/variable winds. There are some 
indications lower CIGs may develop near the coast, but not
expecting this to affect the terminals at this point. High

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/Gorse
Short Term...CMS
Long Term...Robertson