528 
FXUS61 KPHI 102330
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
630 PM EST Tue Nov 10 2020

.SYNOPSIS...
An area of low pressure will move across the Great Lakes into 
Canada tonight as high pressure moves further offshore. A cold 
front associated with this area of low pressure will move toward
the region Wednesday before completely pushing offshore 
Thursday afternoon. High pressure will briefly build across the 
region into the weekend, quickly moving off to the east as 
another area of low pressure moves across the Great Lakes. A 
warm front accompanying this low will push northward across the 
region Sunday before another cold front crosses the area Monday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
While temperatures will cool tonight, the trend will be for a 
more gradual, less strikingly robust drop than what we have been
seeing the past several evenings. Clouds will be on the 
increase at nearly all levels ahead of a cold front well to our 
west across the Mid- Mississippi Valley. This will lead to a 
warmer night as well with lows in the upper 50s to low 60s. With
dew points nearing 60F, and less cloud cover today, am leaning 
more on the foggy side of things with the expectation that more 
appreciable radiational cooling will take place tonight ahead of
the cloud cover to our south, which is still only building into
the Carolinas. Thus, be prepared for morning fog and 
potentially longer commutes. 

Things begin to change tomorrow as we stay partly to mostly 
cloudy. Fog will be slower to burn off than past days as well. 
Another mild day at least, though cooler than today with highs 
making it into the upper 60s to near 70s across much of 
southeast Pennsylvania and northern New Jersey, and into the low
70s on the Coastal Plain. Temperatures could waver a degree or 
two if skies clear enough in the late morning after residual fog
lifts. 

The large-scale pattern remains much the same as the longwave 
trough across the western U.S. stays mostly put, with the more 
notable change being a flattening and slight shift eastward in 
the ridge axis over the eastern U.S. that has led to the 
incredible dry stretch of weather as of late. A shortwave trough
currently ejecting out of this longwave trough will continue to
move across the Midwest and Great Lakes tonight into tomorrow 
morning before moving into Ontario. At the surface, an area of 
low pressure will, perhaps more colloquially termed a Colorado 
Low, will develop along the pre- existing frontal boundary 
draped across the mid-section of the CONUS. As this low deepens 
into Ontario, reinvigoration of the cold front will continue to 
propel it eastward into the Ohio and Tennessee Valleys closer to
the Mid-Atlantic. Tropical Storm Eta's positioning with respect
the surface high over the western Atlantic will be most 
formidable for funneling prolific moisture into the region, 
which can be summarized by the rise in PWATs to near 2 inches by
tomorrow evening. Expect a precip shield to blossom over the 
Mid-Atlantic given a strengthening vort max to our southwest 
across the Carolinas Wednesday afternoon and evening. The 
initial rain shield looks to push across central Pennsylvania 
into our region in the early afternoon, with additional rain 
developing from the southwest, overtaking much of the CWA by 4-6
pm. This sets the stage for a wet night, so be alert for 
slippery driving conditions with wet leaves in the roadways.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Wed night thru Thu night...Unsettled conditions with low 
pressure passing well north of the area and its associated front
moving W to E across the area later Wed. A subtle weak wave 
moves along the front Thu prolonging the arrival of the drier 
and cooler air behind the system. The mild and humid airmass in 
place Wed will yield decent QPF across the area with 1.5 to 2.0 
inches for the NE PA and nrn NJ areas and 2.0 to 2.5 inches for 
srn NJ, metro Philadelphia and Delmarva. Probably not enough to 
produce widespread flooding, but can;t completely rule out some 
localized flooding concerns for the period. Temperatures some 5 
to 10 degrees above normal Thu then trending close to normal Thu
night. 

Friday...Fair weather expected, can't completely rule out a 
scattered shower early, so we'll just keep pops in the slight 
chc range for now. Low pressure pulls away offshore while high 
pressure begins to build from the central part of the U.S. High 
temps a few degrees above normal with maxs in the upper 50s/low 
60s most areas and some mid 60s for Delmarva.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Fri night/Saturday...High pressure will be across the region 
with fair weather expected thru the period. Increasing clouds 
late Sat. as the next system develops to the SW. Seasonable 
temperatures overall, maybe a degree or two below normal, with 
highs Sat. mostly in 50s for the forecast area and some upper 
40s for the higher elevations NW. 

Sat night thru Monday...Unsettled conditions with an upper 
trough moving towards the region and the last of the remnant 
moisture associated with TS Eta moving up across the East Coast.
Pops are in the chc range Sat night then increase to low 
likelies for Sunday as the best dynamics arrive for the Middle 
Atlantic. Beyond that the upper energy is more scattered so 
mostly chc pops for Sun night and Monday. The precipitation will
be rain for most areas most of the time but a few snow flakes 
are possible up across the higher elevations of the Poconos late
Sat night/Sun morning. Temperatures will be close to normal Sat
night, but then turn above normal for the rest of the (Sun-Mon)
period. 

Monday night/Tue... Fair weather behind the departing deep low 
across the Canadian Maritime Provinces and high pressure across 
the Central Plains. Colder air will be arriving with 
temperatures around 5 degrees below normal.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas. 

Tonight...Mainly VFR until around 06Z, with conditions lowering
to MVFR/IFR after 06Z in stratus and fog. Southerly wind 6 
knots or less. High confidence in the overall trend but low 
confidence in the specific timing.

Wednesday...Mainly MVFR/IFR conditions. Rain arriving from the 
west after 18Z. The rain will become moderate to heavy late in 
the period. Southerly wind 5 to 10 knots. Medium to high 
confidence.

.Outlook...

Wed night thru Thu night...Lower CIGS/VSBYS with showers. 

Fri thru Saturday...Mostly VFR. Morning fog possible. 

Sat night/Sunday...Restrictions possible. Showers.

&&

.MARINE...
Tonight through Wednesday...Sub-advisory conditions are 
expected with southerly winds from 10 to 15 knots and gusts to 
15 knots. Seas from 1 to 3 feet building to near 4 feet by 
Wednesday night. 

.Outlook...

Wed night thru Thu night...SCA conditions possible. Showers. 

Fri/Sat...sub-SCA. Fair weather. 

Sat night thru Sunday...sub-SCA. Showers possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

Synopsis...Davis
Near Term...Davis
Short Term...O'Hara
Long Term...O'Hara
Aviation...Iovino/O'Hara
Marine...Davis/O'Hara