Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KPHI 200234

Area Forecast Discussion
National Weather Service Mount Holly NJ
934 PM EST Sun Feb 19 2017

A cold front will move south through our region early Monday. High
pressure will build over the Mid Atlantic Monday afternoon through
Tuesday before shifting offshore. A warm frontal passage occurs
early Wednesday. It will be followed by a cold front dropping down
into Pennsylvania and New Jersey early Friday which should return
north as a warm front early Saturday. Low pressure is probably
going to move from the Great Lakes region into southeast Canada
Saturday and sweep a cold front off the east coast this weekend.


930 pm update: Made a few more modifications to the temperature
forecast based on latest couple of hours of obs. Trouble spots
were about as expected: the Pine Barrens/Millville,
Somerset/Sussex Airports, and portions of the Lehigh Valley --
where nocturnal radiational cooling has been quite pronounced.
Millville has dropped 30+ degrees this evening, for example.

Surface analysis at 02Z indicates the cold front in New England
is progressing southward nicely -- now generally along a line
from Buffalo, NY, to Manchester, NH. WV loop shows main vort max
approaching Maine with pronounced subsidence/drying and a
developing jet streak on the upstream side. IR satellite imagery
showing low clouds are developing on the north side of the
front, but the question remains how far south these clouds get.
So far...see little reason to change sky cover forecast much
from previous forecast.

Previous discussions below...

630 pm: Vort max over northern New England and adjacent
southeast Canada will continue to dig southeastward overnight,
with 23Z surface analysis showing associated cold front moving
south through northern New England at this time. Strong diabatic
heating and downsloping effects more than compensated for weak
near-surface cold air advection today, allowing for temperatures
to soar to record or near-record territory in much of the Mid
Atlantic south of this front.

Main forecast concern this evening is timing the temperature
drop with decreasing winds and mostly clear skies. Suspect spots
notoriously prone to radiational cooling (such as the Pine
Barrens) may see plummeting temperatures this evening before a
brief period of thickening upper-level clouds occurs as the vort
max makes its closest approach late this evening and overnight.
Already starting to see evidence of this at Millville. Made a
few adjustments to the temperature grids through the evening
hours, and suspect more modifications will be needed in the next
couple of hours once the details become clearer. Did not make
much change to morning lows, but did lower them a degree or two
in a couple spots based on the favorable radiational cooling
conditions expected this evening.

Other main concern is sky cover later tonight as a low-level
subsidence inversion becomes established as a transient/high-
amplitude ridge moves into the East. Boundary layer moisture may
be sufficient to develop some low-level clouds, especially in
the southern Poconos. This may also wreak havoc with
temperatures, as the cold air advection behind the front will
fight against the emission of radiation back to the surface
from any low clouds that develop. Latest high-resolution
guidance does not appear particularly aggressive with this low
cloud development, so made no changes to the forecast at this
time. But it will be something to watch during the overnight

330 pm: Yet another spring-like day across the entire area,
with even some new record high temperatures occurring.

An upper-level trough in eastern Canada is forecast to amplify
southward some especially across New England. This will push a cold
front down from the north, also known as a backdoor front, later
tonight. As this occurs, cold air advection will strengthen
somewhat later tonight; however, this is more notable across
the northern zones. This will allow temperatures to drop much
more later tonight.

As surface high pressure begins to build in from the west and
northwest overnight, a subsidence inversion is forecast to
strengthen with some moisture pooling beneath it. This moist layer
looks rather shallow; however, some guidance indicates some low
clouds developing toward daybreak especially for portions of
northeastern Pennsylvania into northwestern New Jersey. Areas
farther to the south, the moist layer looks delayed and
therefore no low cloud development is expected. A north-
northwest wind will be light tonight despite some cold air
advection on the increase, as surface high pressure draws

Low temperatures were mostly a blend of MOS and continuity. The
hourly temperature and dew point grids are being adjusted this
afternoon based on the latest obs, then the LAMP/LAV guidance was
blended with continuity through early this evening. A forecast
challenge through this evening could be just how quickly the
boundary layer cools.


A strong upper-level trough/closed low is forecast to exit New
England through about early afternoon on Monday. This will allow
surface high pressure to slide across our area, although it remains
centered well to our north. This will provide a northerly wind
across the entire region, although this should be on the light side
given a loose pressure gradient. Some cold air advection is forecast
to continue through much of the day, with the coldest air aloft
found over our northern zones. This all translates into a cooler
day, however highs will still be several degrees above where we
should be for this time of year.

A strong subsidence inversion to start the morning may trap in some
lower clouds across mainly portions of northeastern Pennsylvania and
northwestern New Jersey, otherwise this should weaken as the
boundary layer warms enough. Otherwise, plenty of sunshine should
become dominant as the forecast soundings indicate the column
overall dries out through the day. High temperatures are mostly a
continuity and MOS blend. The winds may turn a bit more
northeasterly along the coast to assist with cooling off the chilly
ocean waters.


500 MB: A strong ridge in the Great Lakes Monday night slides east.
A weak short wave cuts eastward into the ridge across New England
Wednesday. In the wake of the short wave, a ridge dominates over the
mid Atlantic States Thursday into Saturday before a strong short
wave moves into the Great Lakes over the weekend.

Temperatures: As our forecast area proceeds to a 1st or 2nd
warmest February on record and a top 10 warmest winter in the
period of record dating back to the late 19th century, the coming
week of Tuesday through Sunday should average 12 to 17 degrees
above normal. The coolest day is expected to be Tuesday...only
several degrees above normal, but thereafter, some model guidance
points to a three day period of temperatures 15 to 25 degrees
above normal between Thursday and Saturday. BUT... a wrinkle has
developed. After near record warmth on Thursday and max temperatures
25 to 30 degrees above normal, a cold front will probably interrupt
the excessive warmth one day with a cooler east-southeasterly
flow on Friday.

Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/19
GFS/NAM MOS guidance Monday night-Tuesday night, thereafter the
12z/18 15z/18 WPC guidance Wednesday - Sunday, raising the fcst
temps by 3-4 degrees due to the recent cool bias in the guidance,
lack of snow cover and expected westerly isobaric gradient.

The dailies including any possible significant insight...

Monday night...Fair.. some high cloudiness that may slightly limit
otherwise ideal radiational cooling. nearly calm wind.

Tuesday...WAA increasing high clouds limiting max temperature
potential. Chance showers may invade ne PA late in the day in the
leading portion of the instability burst. Wind southeast to south.
Max gust 15 MPH.  Confidence: average on max temps.

Tuesday night...Chance of light showers during the evening ahead of
a warm front. Low probability there could be a touch of freezing
rain highest terrain above 1500 feet north of I-80. This ice risk
isn`t in the HWO or zones since confidence is below average and
guidance favors above freezing min temps during any rain.
Confidence: average or below average regarding the occurrence of
any rain.

Wednesday...Becoming mostly sunny and warmer. Near record warmth
(vulnerable records). Forecast temps may end up a degree or
warmer than now predicted. This fcst is above all available
guidance and reflects the recent cool bias in max temps the past
several days... the warm regime with a 550 1000-500mb
thickness. cooler coastal seabreezes likely. West wind.
Confidence: above average.

Wednesday night...Fair (thin high clouds). patchy fog possible in a
few countryside locations.

Thursday...mixed clouds and sun with near record warmth. Some
cirrus as per the GFS. Max temps may end up 2f warmer than the
now I95 predicted 70 to 75F. However cooler coastal sea breezes
embedded within the west southwest wind gradient. Confidence:
above average.

Friday...early morning stratus/fog possible along a cool front
that has settled into our area. maybe a shower north of the
boundary during the afternoon or maybe the boundary doesn`t make
it down into our forecast area? otherwise considerable clouds.
Confidence: below average on the scenario. Note: considerable
instability is showing up in the GFS and ECMWF.

Friday night...a good chance of showers ahead of the cold front
moving east toward our area and/or the quasi-stationary front
moving north as warm front from I-78. Shower timing and
temperature uncertainty as well as wind uncertainty, though
probably southeast turning south to southwest, depending on
latitude in our area. Note: considerable instability is showing
up in the GFS and ECMWF. Confidence: average.

Saturday...Maintained continuity. I think we need a 90 pop
it should rain ahead of the cold front and there may be a tstm.
Dewpoints probably close to 60 in a sliver ahead of the cold
front. Operational EC and GGEM as well as the 12z/19 GEFS are
slower and at this time, did not want to raise hopes for the GFS
blustery dry westerly flow on Saturday. The UKMET is kind of
unsettling and if idea of a low way back in Ohio is correct...
we will need to rethink progressive cold frontal passage for
Saturday morning. Confidence: average.

Sunday...Becoming mostly sunny and cooler but still above normal
temps as the sfc low moves northeast into Canada taking the primary
chunk of colder air northeast with it, making it difficult to
import too much of the cold air here from the midwest. Breezy
with west winds gusting 20 to 25 mph. Confidence: average.


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

For the 00Z TAFs...VFR conditions expected through the period;
however, there is a chance of some CIGs near MVFR around
daybreak north/west of KPHL -- including KABE/KRDG. Confidence
too low to include in the TAF at this time, but this will be
monitored closely. Any low clouds will dissipate by mid morning.
Winds generally northwest around or below 10 kts, with an
occasional gust to 20 kts possible tomorrow afternoon.

Monday night...VFR with some cirrus. Light mostly north through east
wind or calm.  Confidence: Much above average.

Tuesday...Cirrus ceilings may briefly lower to MVFR during the late
evening in scattered rain showers. South wind max gust around
15 kt during the afternoon becoming southwest at night.
Confidence: average.

Wednesday...VFR. This cirrus afternoon and night. west wind.
Confidence: Above average.

Thursday...Patchy fog possible early with mvfr vsby. Otherwise,
VFR occasional cigs. West southwest wind. Confidence: Above

Friday...Patchy IFR or MVFR CIGS along a cold front that stalls and
begins returning north at night. Chance of a shower at night. Wind
east turning southeast to south. Confidence: Below average.


930 pm update: No changes to the marine forecast tonight.

High pressure will gradually build in from the west and northwest
later tonight and Monday. This will result in a northerly wind,
however an increase in cold air advection overnight and Monday
morning should result in some increase in the winds especially
across the northern coastal waters. It appears that any gusts to 25
knots mainly across the northern ocean zones look to be short in
duration; therefore, we opted to hold off on a Small Craft
Advisory. Otherwise, the conditions are expected to remain below
advisory criteria through the day Monday.


Monday night...northerly winds may gust near or above 20 kt at
times, but should stay just below 25 kt during the evening then
diminish during the night and turn northeast to east.  Confidence:
above average.

Tuesday through Thursday...winds and seas will remain below SCA
criteria. Winds southeast Tuesday turning southwest Tuesday night
and continuing west to southwest Wednesday and Thursday with local
southerly afternoon sea breezes. Confidence: Above average.

Friday...easterly becoming southerly. Confidence: below average
with considerable uncertainty regarding direction and speed.


New records for this date have been established at PHL ILG ABE
TTN and RDG.

Here are/were the previous record highs for Sunday:

PHL 68-1948 now 70-2017
ILG 67-1997 now 71-2017
ABE 63-1997 now 68-2017
TTN 68-1948 now 69-2017
GED 74-1976
ACY 73-1961
RDG 67-1997 now 68-2017
MPO 58-1981

Wednesday 2/22    Thursday 2/23

ACY 68-1991       72-1985

PHL 68-1997/1974  75-1874

ILG 69-1997/1974  72-1985

ABE 68-1974       71-1985

TTN 66-1997       74-1874

GED 72-1997       no data

RDG 70-1974       72/1932/1922

MPO 56-1997       60-1977

The following monthly and seasonal expectations were number
crunched with our forecast at 9am this morning. We will tweet
and Facebook this post tomorrow morning around 10 am with
basically one final check of the numbers, which could run even
warmer than what we now have posted.

We did check our past 24 hr max/mins through 7AM, as well as
the new max/min fcst fm our office issued at 330 AM and the
FTPRHA guidance beyond. That also accounts for possible midnight
mins tonight at PHL ILG ACY, and also possible midnight mins
Saturday night the 25th.

The only day in significant uncertainty over the next 7 days is
Friday, when a cold front could settle south to the Delmarva
and leave us in cooler southeasterly flow, thereby lowering the
forecast average temperature by 7 degrees. Even so that would
only lower the monthly average by half a degree and that might
be made up by warmer than fcst temps on a couple of other days,
especially on the 28th.

So, the forecast numbers continue warming. There is guidance
variability but its virtually certain we`re looking at a widespread
top 2 warmest February on record in our forecast area and a top
10 warmest winter season... records dating back to the late 19th
century. Confidence: well above average. Details below.


PHL 43.3. #1   Normal 35.7   Record 42.2-1925     POR 1874

ABE 37.6  #2   Normal 30.7   Record 38.6-1998     POR 1922

ACY 42.2  #1   Normal 35.3   Record 41.6-1890     POR 1874

ILG 42.3  #1 tie  Normal 35.1 Record 42.3-1903    POR 1895

Winter (DJF)

PHL 40.1 #7

ABE 35.4 #5

ACY 39.6 #10

ILG 39.1 #6 tie

Past two years of monthly average temperatures through February
2017, a summary of above normal months listed below:

For ABE: 23 consecutive months of above normal temps!

FOR PHL: 22 of the past 23 months have been above normal.

For ACY: 19 of the past 23 months have been above normal.

For ILG: 17 of the past 23 months have been above normal.

(Jan Feb March 2015 was the last time we had significant and
persistent below normal monthly temps.)


February least on record:

Atlantic City may end up tied for 5th with very little opportunity
for snow on the horizon?




Near Term...CMS/Gorse
Short Term...Gorse
Long Term...Drag
Climate...CMS/Drag is the U.S. government's official web portal to all federal, state and local government web resources and services.