510 
FXUS61 KPHI 021127
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
627 AM EST Mon Jan 2 2023

.SYNOPSIS...
High pressure will build to our south through today with 
temperatures remaining above normal. The high pressure will slide 
offshore tonight with southerly flow bringing increasing 
temperatures through the middle of the week. A frontal system will 
impact the region Tuesday through Wednesday bringing increasing 
chances for rain showers, fog, drizzle, and near record breaking 
warmth by Wednesday. Cooler and more seasonable conditions will 
return by the end of the week and into the weekend as colder high 
pressure builds to our west.

&&

.NEAR TERM /THROUGH TONIGHT/...
Some patchy fog is forming across portions of southeast New
Jersey and Delmarva. Any fog that does form should quickly
diminish shortly after sunrise.

Otherwise, high pressure is centered over the Southeast and 
Mid- Atlantic and will gradually slide offshore tonight. 
Meanwhile, a zonal flow aloft will keep Arctic air bottled to 
the north, and a mild airmass will continue to spread into the 
Northeast and Mid-Atlantic. 

Some shortwave energy will approach from the west and will pass
through the region this afternoon and evening. Hi-res models 
showing some light rain moving into southeast Pennsylvania late 
this afternoon. Will go ahead and add minimal PoPs, capped at 
slight chance, for southeast Pennsylvania. Any rain that falls 
will be light.

Highs today will be almost 20 degrees above the seasonal 
normals and will top off in the mid to upper 50s for most of the
area, and as high as the low 60s in southern New Jersey and 
southern Delmarva.

With the high offshore, a light southerly flow sets up across 
the area tonight. Surface dew points will creep up during the 
overnight hours, climbing into the mid 40s. With this increase 
in moisture, patchy fog is likely to develop across the region. 
Whether fog becomes dense remains to be seen.

Low pressure over the Midwest, and a warm front will extend out
from this low and will lift towards the region late tonight. 
Combined with some mid-level shortwave energy, some rain may 
move into far northern and western portions of the forecast area
prior to daybreak Tuesday. Will add some slight chance/low-end 
chance PoPs to the forecast for those areas.

Low temperatures tonight will be in the low to mid 40s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The short term period Tuesday through Wednesday night will be 
characterized by unseasonable warmth and several periods of showers, 
fog, and drizzle. Near record breaking warmth is expected on 
Wednesday.

High pressure is forecast to be offshore across the western Atlantic 
Tuesday morning. As low pressure approaches the central Great Lakes 
region early Tuesday, increasing low-level south to southwesterly 
warm advection is forecast to overspread our area. This is 
pronounced at the 925 mb level and will result in a northeastward 
developing warm front. The latest guidance has increased the support 
for widespread advection fog Tuesday morning as the warm advection 
ramps up. This fog may become locally dense in spots, particularly 
near coastal areas and along and north of I-78 where cooler surface 
air may persist longer and increase the intensity and duration of 
the fog.

The chance for showers during the daytime Tuesday will be greatest 
northwest of I-95. The latest guidance has continued to show 
stronger isentropic lift ahead of a warm front and near and 
north/west of an axis of robust low-level warm air advection. This 
should result in a ribbon of showers or even a period of rain as the 
main forcing for ascent quickly lifts north and northeast from 
Tuesday morning through early afternoon. PoPs were increased 
northwest of I-95, with the highest PoPs closest to the Poconos, 
decreasing southeastward. Aside from the showers, the other story 
will be the increasing temperatures. Cloud cover will limit more 
robust diurnal heating, but 925 mb temperatures increasing to +14C 
to +18C will support highs in the upper 50s to low 60s across much 
of the area. Some guidance shows a pocket of weak cold air damming 
across mainly north of I-78, however given the robust low-level warm 
air advection and southerly flow, this should weaken even more with 
time Tuesday. Winds will increase from the south to southwest around 
10-15 mph with some gusts near 25 mph possible.

Temperatures are unlikely to fall much Tuesday night with southerly 
flow and warm air advection continuing. In fact, temperatures could 
rise a few degrees overnight. We are currently forecasting low 
temperatures in the low to mid 50s for most of the region. As 
surface dew points continue to climb overnight, low clouds and some 
fog/drizzle should develop, especially along coastal areas and in 
the higher terrain of eastern Pennsylvania and northwest New Jersey. 
Some showers will remain across the entire area overnight as well.

As we go through Wednesday, the best forcing for widespread showers 
will arrive especially during the afternoon hours as the cold front 
gets closer to the area. The southwest flow will continue to advect 
warm and moist air into the region. We are expecting widespread 
temperatures in the mid 60s Wednesday afternoon along with dew 
points nearing 60 degrees. So it will be a warm and muggy January 
afternoon with showers. Any breaks in the clouds and showers could 
locally push temperatures toward 70 degrees across the urban 
corridor and interior portions of the coastal plain. Both high and 
low temperatures for the calendar day on Wednesday will be near 
record warmest values for all 9 of our climate stations. Details on 
these records can be found in the Climate section below.

Rainfall for the Tuesday through Wednesday looks to be generally 
near or less than a half inch. Precipitation chances will decrease 
late Wednesday night, however the latest trend in the guidance has 
been generally slower with the progression of the system moving 
offshore. The cold front may not move offshore until Thursday 
morning, which has implications for Thursday's high temperature 
forecast. Given the uncertainty, temperatures for Thursday were 
increased a few degrees. In any case, the cold front will eventually 
push through the area bringing an end to the shower activity and 
warm, muggy air.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Summary...Mild to start then temperatures trending closer to 
average; mainly dry with the exception of a possible coastal or 
offshore storm.

Synoptic Overview...An upper-level trough in the East is forecast to 
be in place, although it may end up lifting out during the weekend. 
This should trend temperatures much closer to average. As the main 
trough axis crosses our area later Thursday into Friday, associated 
energy should activate an offshore baroclinic zone leading to 
surface low development. This feature looks progressive though and 
tending to be on the weaker side, therefore impacts as of now look 
to be on the low side.

For Thursday and Friday...The upper-level trough axis is forecast to 
be arriving along the East Coast by Friday afternoon. Some guidance 
is tighter with this feature with a fairly compact closed low. 
Strong shortwave energy ahead of this feature along with colder air 
aloft will assist in energizing an offshore baroclinic zone. This 
should result in surface low pressure development offshore. Overall 
this surface looks to be on the weaker side and also the entire 
system looks to be progressive, therefore impacts should be limited 
especially given a lack of blocking to our northeast. Given the 
uncertainty though with the details, will continue with a period of 
either slight chance or chance PoPs. Temperatures should be close to 
average, although may be colder if thicker cloud cover and 
precipitation actually occurs especially with a north to northeast 
low-level wind.

For Saturday and Sunday...While one upper-level trough has lifted 
well to our northeast, another one may slide across the Northeast 
Saturday. At the surface, high pressure is forecast to build across 
our region Saturday before shifting offshore during Sunday. An upper-
level trough tracking across the Plains and into the Great Lakes to 
Ohio Valley Sunday may send a developing warm front toward our area. 
It looks to be dry overall, however some warm air advection induced 
lift Sunday will send in some more clouds and perhaps eventually 
some showers. Temperatures are forecast to continue to be close to 
average.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, 
KRDG, KILG, KMIV, KACY and surrounding areas.

Today (12Z through 00Z)...Some fog is developing at KMIV and 
possibly KACY, but fog should dissipate by 13Z to 14Z. VFR 
otherwise. CIGs gradually lower through the day to around 3500 
to 4000 feet by this evening. Some light rain with no VSBY 
restrictions possible at KRDG/KABE late this afternoon. Light SW
winds. Moderate confidence.

Tonight (00Z through 12Z)...VFR initially, but MVFR or lower 
CIGs/VSBYs possible after 03Z as low clouds and fog develop. Will 
include MVFR CIGs for now, but conditions may end up being much 
lower than that. Light S winds. Low confidence.

Outlook...

Tuesday...MVFR and IFR restrictions likely with a period of rain 
likely northwest of I-95. LIFR possible, especially Tuesday morning 
and Tuesday night. Areas of fog and drizzle in the morning. Fog and 
drizzle is anticipated to develop again Tuesday night along with 
increasing chances for showers. Winds south around 10-15 kts. LLWS 
possible. Low confidence on timing and coverage of any restrictions.

Wednesday...MVFR to IFR restrictions likely with rain showers and 
areas of drizzle and fog also likely at times. South to southwest 
winds around 10-15 kts. Moderate confidence on occurrence of 
restrictions.

Thursday through Friday...Mainly VFR, but sub-VFR conditions are 
possible late Thursday and Friday along with a chance of 
precipitation. Northerly winds around 10-15 kts. Low confidence.

&&

.MARINE...
Sub-Small Craft Advisory conditions today through tonight. SW 
winds 5 to 10 kt, becoming NW this afternoon, then becoming S 
tonight. Seas 2 to 3 feet.

VSBY restrictions possible in fog this morning, but more 
widespread VSBY restrictions will develop in fog tonight. A 
Marine Dense Fog Advisory is now in effect starting at midnight 
tonight for all waters.

Outlook...

Tuesday through Wednesday...Small Craft Advisory conditions likely 
developing Tuesday and persisting into Wednesday night. Southerly 
winds increasing to 15-20 kts with gusts up to 30 kts possible and 
seas building to 4-6 feet. Periods of rain showers likely during 
this period, especially on Wednesday. Areas of dense fog and drizzle 
may develop with visibility 1 nautical mile or less both Tuesday 
morning and Tuesday night through Wednesday.

The Marine Dense Fog Advisory is in effect until 1 PM Tuesday
for Delaware Bay and the Atlantic coastal waters south of 
Atlantic City and through 4 PM Tuesday for the Atlantic coastal
waters near and north of Atlantic City. A Small Craft Advisory 
is in effect from 1 PM Tuesday through Tuesday night.

Thursday through Friday...Small Craft Advisory conditions possible. 
North to northeast winds around 15 kts with gusts up to 25 kts 
possible and seas 3-6 feet. Chance of rain Thursday night through 
Friday.

&&

.CLIMATE...
Near record breaking temperatures are forecast for Wednesday, 
January 4th. Record warmest high and low temperatures for 
January 4th are listed below:

                   Warmest High        Warmest Low
Site                Record/Year        Record/Year
Allentown (ABE)         66/1950            51/1950
AC Airport (ACY)        68/1950            52/1950
AC Marina (55N)         67/1998            52/2000
Georgetown (GED)        71/2000            59/1950
Mount Pocono (MPO)      59/1950            50/1950
Philadelphia (PHL)      68/1950            57/1950
Reading (RDG)           67/1950            57/1950
Trenton (TTN)           68/2000            57/1950
Wilmington (ILG)        69/1950            56/1950

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory from midnight tonight to 1 PM EST Tuesday 
     for ANZ430-431-453>455.
     Dense Fog Advisory from midnight tonight to 4 PM EST Tuesday 
     for ANZ450>452.
     Small Craft Advisory from 1 PM Tuesday to 6 AM EST Wednesday 
     for ANZ450>455.

&&

$$
SYNOPSIS...Staarmann
NEAR TERM...MPS
SHORT TERM...Gorse/Staarmann
LONG TERM...Gorse/Staarmann
AVIATION...MPS/Staarmann
MARINE...MPS/Staarmann
CLIMATE...