Area Forecast Discussion

FXUS61 KPHI 172050
Area Forecast Discussion
National Weather Service Mount Holly NJ
350 PM EST Sat Feb 17 2018
Low pressure rapidly intensifies off the mid Atlantic coast 
this evening then races out to sea by Sunday morning. High 
pressure briefly builds across the area again on Sunday, then 
offshore Sunday night. A strong warm front lifts northward 
across our area later Monday into early Tuesday, followed by a 
cold front late Wednesday. The cold front stalls to our south by
next Thursday with a series of waves moving north and east 
along it late next week into early next weekend.
Clouds will continue to thicken and lower and precipitation 
will overspread our region from the west and southwest during 
the late afternoon and early evening hours. Temperatures are 
such that the precipitation should begin as snow in the Poconos 
and in far northern New Jersey. It is expected to begin as a 
brief period of rain in extreme northeastern Maryland, northern 
Delaware, southeastern Pennsylvania, and much of northern and 
central New Jersey before changing to snow. An all rain event is
anticipated for southeastern Maryland, southern Delaware and 
much of southern New Jersey.
Mid level short wave energy moving up the Ohio River Valley 
this afternoon will enhance precipitation rates this evening. A 
relatively brief period of moderate to heavy snow is expected 
with amounts in much of eastern Pennsylvania, far northeastern 
Maryland, northern Delaware and central and northern New Jersey 
ranging from 2 to 5 inches. The far upper Delmarva, extreme 
southeastern Pennsylvania and the southern part of central New 
Jersey should favor the low end of those values.
The guidance has trended a bit warmer with the system than in 
previous runs. As we get into the late evening hours, the 
rain/snow line may advance well into the Philadelphia 
metropolitan area and central New Jersey. We will indicate a 
change to rain before the precipitation ends. The rain will cut 
into snowfall amounts in parts of those areas.
Due to the expected location of the rain/snow line, our lowest 
area of confidence in our snowfall forecast extends from the 
upper Delmarva and extreme southeastern Pennsylvania into parts 
of southern and central New Jersey.
A mid level short wave trough located over Iowa and vicinity 
this afternoon will progress to the east and it should pass 
overhead late tonight. The feature will kick the last of the 
precipitation out to sea. It appears as though most of the rain 
and snow in our region will end by 2 or 3 o'clock in the 
The wind is forecast to be from varying directions at less than
10 MPH for much of the night, becoming northwest at 10 to 15 
MPH toward morning. Low temperatures are anticipated to range 
from the middle 20s in the Poconos to the middle 30s in southern
High pressure is forecast to build into our region from the 
west for Sunday. We are anticipating a mostly sunny day with a 
northwest to west wind around 10 MPH.
Sunday afternoon is expected to become relatively mild. Highs 
are forecast to be in the lower and middle 40s in the Poconos, 
the Lehigh Valley and northern New Jersey. Readings should get 
into the upper 40s and lower 50s in northeastern Maryland, 
Delaware, southeastern Pennsylvania, and southern and central 
New Jersey. Much of the new snow cover should melt by day's end.
**Record warmth possible Tue and expected Wed**
Sunday night through Wednesday....
To start the period Sunday evening, high pressure crests over 
the area in the evening before slowly moving east overnight. 
This will set up good conditions for radiational cooling due to 
light winds and mainly clear skies despite the airmass not being
all that cold. Lows by Monday morning should generally be in 
the 20s to low 30s. 
For Monday, the high continues to push off to the east through 
the day with a warm front approaching from the south and west 
ahead of the next system. This will bring increasing clouds with
some showers likely by afternoon...mainly over eastern PA. 
Highs will generally range from the mid 40s north to the 50s 
across the Delmarva and southern NJ. 
Some showers may continue into Monday evening before lifting 
out overnight as the front moves through. Temperatures will be 
quite mild with lows only dropping to the 40s to low 50s. This 
will be followed by near record warmth on Tuesday as a strong SW
flow takes hold. We continue to forecast temperatures above the
model consensus and are generally looking at highs ranging from
the 60s in the north to the low 70s across SE PA as well as 
much of the Delmarva and southern NJ. Areas right near the coast
will likely be cooler though. 
For Tuesday night into Wednesday, temperatures continue to warm
with record warmth forecast by Wednesday...highs currently 
forecast to reach the low to mid 70s over SE PA as well as much 
of the Delmarva and NJ. Conditions should be dry for the most 
part though by late Wednesday a cold front could bring some 
showers in from the west...mainly for eastern PA. 
Wednesday night through Saturday...
In the big picture, this period will be dominated by somewhat 
cooler, though still well above average temperatures as a long 
wave trough persists over the Rocky Mountains with the area in a
SW flow. Conditions will also trend more unsettled as a series 
of waves move north and east along a wavering front that will 
linger in the region.
For Wednesday night into Thursday, the aformentioned cold front
with some associated rain showers pushes south through the area
before stalling over the mid Atlantic. Forecast guidance then 
indicates a wave trying to move north along the front though 
there is uncertainty in how this all evolves as high pressure 
will also be building in to our north. The high could suppress 
precip mainly to our south into Thursday but again, these 
details are uncertain so we keep chances for showers in the 
forecast through Thursday. Beyond this time there may be a brief
break before a stronger low pressure system moves north along 
the front by later Friday into next Saturday. Highs Thursday and
Friday will generally be in the 40s and 50s with 60s possible 
again by next Saturday.
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas.
Through 0600Z...Conditions becoming IFR early this evening in 
snow at KRDG, KABE, KTTN, KPNE, KPHL and KILG. Accumulating snow
is expected at the airfields (up around 4 inches at KRDG, KABE 
and KTTN, and up around 2 or 3 inches at KILG, KPHL and KPNE). A
mix or change to rain is expected at KILG, KPHL and KPNE late 
this evening before the precipitation ends. Conditions lowering 
to IFR in rain at KMIV and KACY this evening. East to southeast 
wind around 5 to 10 knots.
Late tonight (0600Z-1200Z)...Precipitation ending from 
southwest to northeast with conditions gradually improving to 
VFR. Wind become northwest 10 to 15 knots with gusts around 20 
Sunday...VFR. Mostly clear with a northwest wind around 10 
Sunday night...VFR. Confidence: Well above average. 
Monday...VFR early, lowering to MVFR or IFR during the 
afternoon or evening with rain. South to southwest wind. 
Confidence: above average.
Monday night...MVFR/IFR conditions continue with rain possible 
in the evening, and low clouds/dense fog possible overnight. 
Confidence: Above average. 
Tuesday...MVFR/IFR conditions possible through midday in low 
clouds/fog. Conditions improving to VFR during the afternoon. 
Southwest winds may gust around 20-25 knots in the afternoon. 
Confidence: average.
Tuesday night...VFR early, then possibly lowering to MVFR/IFR 
as low clouds/fog may develop overnight. Confidence: average.
Wednesday...MVFR/IFR conditions possible early with low 
clouds/fog. Conditions improving to VFR during the day. chance 
of showers late in the day. Southwest winds may gust around 
20-25 knots. Confidence: Average.
Wednesday night through Thursday...Chance of showers with 
associated restrictions. Confidence: Below average.
Low pressure will pass off the Virginia Capes this evening 
before moving quickly out to sea. A gusty northwest wind is 
expected to develop on the coastal waters of New Jersey and 
Delaware in the wake of the low. As a result, we will issue a 
Small Craft Advisory for our ocean waters and for Delaware Bay. 
It will be in effect from 4:00 AM until 11:00 AM Sunday. The 
wind is forecast to diminish gradually on Sunday afternoon. 
Sunday night through Monday...Sub Small Craft Advisory south 
winds. Confidence: Well above average. 
Monday night...Sub Small Craft Advisory conditions expected, 
although southwest winds may gust around 20 knots. Confidence: 
Above average. 
Tuesday-Wednesday...Winds should stay below advisory levels, 
but seas may increase to near 5 feet. Confidence: Average.
Wednesday night - Thursday...Winds should stay below SCA levels
with seas persisting in the 3 to 5 foot range.
Record high temperatures could be challenged on Tuesday, 
February 20th and probably will be equaled or exceeded Wednesday
February 21st. These records are listed below.
February 20:
Atlantic City...70 in 1930
Philadelphia....70 in 1939
Wilmington......71 in 1930
Allentown.......68 in 1930
Trenton.........70 in 1930
Georgetown......68 in 2002
Mount Pocono....59 in 1930
Reading.........72 in 1930
February 21:
Atlantic City...74 in 1930
Philadelphia....72 in 1930
Wilmington......70 in 1953
Allentown.......67 in 1953
Trenton.........70 in 1930
Georgetown......71 in 2014
Mount Pocono....60 in 1930
Reading.........71 in 1930
We are not posting the monthly records at this time since our 
forecast is 3 to 7 degrees below the monthly record. We'll check
again Sunday and Monday to see if our forecast edges warmer. 
The following are the record warm mins for Wednesday Feb 21. 
Barring a sudden immediate cool down behind the cool front at 
1159PM Wednesday, there is a good chance of record warm daily 
minimum temperatures as well the previously referenced record 
Record high mins for 2/21
ABE 46-1981
ACY 49-1954
PHL 49-2002
ILG 47-2002
RDG 48-1930
TTN 48-2002 
Atlantic City rainfall already ranks 11th wettest in February 
history with 6.50" in 2010 the wettest. By sunrise Sunday, 
Atlantic City should rank about 8th wettest in its historical 
The February average temp for PHL projects 41.0 or 5.3F above 
normal or 8th warmest on record. This placement can change 
anywhere from 3rd to 12th depending on a 1 degree change in the 
eventual average. Bottom line...we're likely on our way to a top
10 warmest February on record. The warmest was last year with a
44.2F average. Years 2002 and 2012 flank our currently 
projected 8th warmest.
PA...Winter Weather Advisory until 4 AM EST Sunday for PAZ054-055-
NJ...Winter Weather Advisory until 4 AM EST Sunday for NJZ001-
DE...Winter Weather Advisory until 4 AM EST Sunday for DEZ001.
MD...Winter Weather Advisory until 4 AM EST Sunday for MDZ008.
MARINE...Small Craft Advisory from 4 AM to 11 AM EST Sunday for ANZ430-
Near Term...Iovino
Short Term...Iovino
Long Term...Fitzsimmons