Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180220
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
920 PM EST Fri Feb 17 2017

.SYNOPSIS...
High pressure situated over the Appalachians will gradually
move offshore tonight, allowing a warm front to lift north
across our region Saturday morning. A weak cold front will move
through our area on Sunday, followed by high pressure, which
will build southward out of Hudson`s Bay and into our region
through Tuesday. This high will move offshore on Wednesday, with
a cold frontal passage expected Thursday into Friday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
With clear skies and light to nearly calm winds, may areas are
radiating quite well, and temps are falling into the 20s and 30s
for most areas.

Some upper level energy may bring some mid and upper clouds
through the region after midnight tonight and into early
Saturday. This may result in temps holding steady and possibly
rising a bit.

Quiet conditions on tap for tonight. Lows will drop into the
teens across the Poconos, low to mid 20s for northern and
central NJ, mid and upper 20s in southern NJ, SE PA, and the
Delmarva. Lows will be in the low 30s around Philly.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Sunny skies and milder...by around 15 degrees which would be
also be about 16 degrees above normal. Southwest wind gusty
around 20 mph during the afternoon. Increasing high clouds
late. No record highs expected on Saturday.

FCST basis: 12z/17 50 50 blended GFS/NAM MOS and then raised
that by 3-4F per HIRES guidance which is only ~1 deg less than
our 330 am fcst.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
An initially split flow pattern across North America will
become more amplified late this weekend into early next week. A
southern stream closed low lifting out of the Rio Grande Valley
will traverse the mid-Atlantic states as an open wave on Sunday.
As phasing of the northern and southern streams takes place
across the inter-mountain west during this time frame, a high
amplitude ridge will build across the eastern conus on Monday
and Tuesday. By Wednesday, both streams decouple, with an active
northern stream near the US/ Canadian border, and a southern
stream closed low traversing the Gulf coast states. There is
some uncertainty regarding the placement of these features
through Friday.

The main story during the Sunday thru Friday portion of the
forecast will be continued above average temperatures. Across
our region, daily means will generally range from 5 to 15+
degrees above average, and overall will favor 10 to 15 degrees
across the entire period! In fact, some daily record high
temperatures may be in jeopardy on Sunday at our long term
climate sites. The primary chances for precipitation will be on
Saturday night across the southern half of the area (Delmarva, S
NJ, and SE PA), and again Tue night into Wed, albeit light in
both cases. There is also the potential for a wintry mix Tuesday
night and early Wednesday morning across N NJ and NE PA.
Looking further ahead, low confidence on precip chances on
Friday.

Saturday night thru Tuesday...The main uncertainty during this
time frame is the northward extent of light precipitation
associated with an open southern stream shortwave moving just to
our south Saturday night. In conjunction with this feature, a
weak cold front also crosses the region, which aids in drawing
low-level moisture northward. In addition, a vorticity streamer
provides modest lift for the generation of precipitation. At
this time, the highest PoPs (slight chance) are expected south
of the PA Turnpike and I-195, with some sprinkles possible
north. Rainfall amounts up to one-tenth of an inch are possible.

Otherwise, a dry, and partly to mostly sunny Sunday thru
Tuesday is expected. As for Sunday, some daily record highs may
be in jeopardy, especially at PHL and ILG, given westerly
surface flow and lack of snow cover.

Tuesday night thru Wednesday...Low pressure moving well
northwest of the area is expected to lead to a cold frontal
passage on Wednesday. With high pressure receding offshore, an
initially dry air mass will be in place on Tuesday night, which
would favor a period of radiational cooling. Given the weak
boundary layer winds in the warm sector, colder air, possibly
near freezing, will be harder to overcome northwest of the fall
line. If 2-meter temperatures maintain closer to freezing, and
precipitation is able to overcome the drier low-level air mass
in place, then there could be a short period of frozen precip
across portions of northeast PA and northern NJ. With the
uncertainty at this time range, confidence is very low in this
outcome. Stay tuned.

Wednesday night thru Friday...A couple shortwaves cross the
region, with considerable cloudiness expected, and perhaps a
chance of showers by Friday.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...VFR. SCT clouds AOA 4000 feet possible after 06Z. W-SW
winds 5 KT or less, becoming LGT/VRB.

Saturday...VFR. SW winds increasing to 5-10 KT. Gusts to 18 KT
or so possible in the afternoon.

OUTLOOK...

Saturday night and Sunday...Predominantly VFR. West-northwest flow
with gusts 15 to 20 knots on Sunday.

Sunday night and Monday...There is a low potential of MVFR ceilings
developing below an inversion, mainly at ABE and RDG, otherwise VFR.
North-northwest flow around 10 knots may become northeast at PHL by
Monday afternoon, with gusts up to 20 knots.

Monday night and Tuesday...Predominantly VFR. There is a signal that
fog could develop Monday night, especially at the typically prone
TAF sites, such as MIV, RDG, and ABE. This could lead to brief
MVFR/IFR restrictions. With high pressure overhead, light and
variable winds.

Tuesday night into Wednesday...Clouds will lower in advance of a
cold front, with MVFR ceilings likely. There could be a period of
IFR late Tuesday night into early Wednesday morning. On Wednesday,
expect MVFR ceilings, with some improvement to VFR at times. Winds
will generally favor the southwest direction at 10 to 20 knots.

&&

.MARINE...
No headlines at this time through Saturday.

West to northwest winds 10-15 KT tonight will become SW on
Saturday with gusts to 20 KT in the afternoon.

OUTLOOK...

Saturday night and Sunday...Winds out of the southwest. Sub-SCA
winds and seas expected.

Sunday night and Monday...In the wake of a cold frontal passage,
winds shift from southwest to west-northwest early Sunday night.
With modest cold air advection and surface pressure rises, northwest
winds will increase, possibly to SCA levels. The highest probability
is generally across the northern NJ waters (ANZ-452 northward), with
a low probability further south and across the Delaware Bay.

Monday night and Tuesday...Winds gradually veer to the southwest.
Sub-SCA winds and seas expected.

Tuesday night and Wednesday...A cold front approaches the waters on
Wednesday. Southwest flow will increase, but there is uncertainty
with regard to reaching SCA criteria, given low-level inversion
and the gradient contribution (low confidence). Given an
anomalously warm and moist (high dew point) air mass traversing
the water, areas of fog may develop by Wednesday.

&&

.CLIMATE...
Updated 1035 AM Fri Feb 17. Next update possibly not til Sunday
or Monday when we recheck and adjust. We did spot check our
past 24 hr max/mins, as well as the new max/min fcst fm our
office issued at 330 AM and the FTPRHA guidance beyond. The fcst
numbers as they are now posted herein would be too low... and
so it could run warmer than our projections. However, there is
day to day variability in the guidance so we are making no
change in our data outlook for Feb and the winter (DJF) season.
The GFS/EC ENSEMBLED expected transition to a cooler more wintry
scenario at the end of the month or the first two weeks of
March continues likely. Whether that means anything more than an
inch or 3 of snow south of I-78 remains to be seen.

We have now added ILG information, despite some of those
questionably warm early years in the database back to 1893-94.

Projecting widespread top 10 warmest February on record in our
forecast area. Confidence: above average. Details below.

Seasonal average (DJF) temperature projecting widespread top
14. PHL is projecting #9 warmest, ABE #6 and ACY #12.
Confidence: above average.

February:

The month as a whole has so far averaged 3.4 to 5.5 degrees
above normal through the 15th, except 1.4 above normal at KMPO.
There still isn`t any sign of long duration substantially colder
than normal air coming this month and in fact some of the
guidance is suggesting near record warmth is possible either
this weekend and maybe the middle of next week (date and climate
location dependent).

Just the 7 day period of tomorrow through the 23rd should
average close to 10 degrees above normal.

The following projection is for Philadelphia with remainder of
the area relationship discussed.

Using this mornings low of 33 and the NWS forecast through the
22nd (see SFTCTP), and then FTPRHA max/min for PHL D8-11, and
the normal the last two days of February (max min of 47/30) we
project a monthly average of 41.9 degrees at PHL (2 degrees
higher than the current first 15 day average). Normal for
February is 35.7 or a projection of 6.2 degrees above normal.
This would make February the 2nd warmest in our period of record
dating back to 1874. The warmest February on record was 42.2F
in 1925. Ninth warmest is 40.1 degrees, so you see that we have
1.7 degrees to give = be wrong, and still enjoy a top 10 warmest
February.

Average temperatures at all our other climate sites should
average at least a degree warmer than what has occurred through
the first 15 days.

Lack of snow cover is partly to blame and goes in tandem with
the primary storm track northwest of our area across the Ohio
Valley-Great Lakes this winter (DJF) as evidenced by above
normal pcpn fm KY northward into the Great Lakes.

Detailing ACY ABE and ILG for February as per PHL data process
input.

ACY projects #2 warmest at 41.1F with the record being 41.6F in
1890. The 30 normal is 35.3 or a positive departure of nearly 6
degrees. The projection has 1.2 degrees to give on the down
side for a #9 rank with the POR back to 1874. ACY climate is
subject to radiational cooling which at times may force a colder
solution so confidence on ACY maintaining a #2 projection is
less than PHL. Still, if the pattern doesn`t change
significantly from the outlook of the past three days...it will
be a noteworthy top 10 warmest February on record through most
of our Mount Holly forecast area.

ABE projects 7th warmest with a 36.1 average, or 5.4 degrees
above the norm of 30.7. ABE has less room to give on the down
side.

ILG projects 41.4 or 2nd warmest on record...6.3 above the norm
of 35.1. The record is 42.3 in 1903. This projection has 1.9
degrees to give on the low side to drop to about #10. Highly
unlikely.

Winter (DJF)

Finally...PHL for the winter season (DJF) is projecting an average
of 39.6 degrees...the 9th warmest DJF in the period of record
dating back to 1873-1874. Room to give is 0.4 degrees on the down
side to #10 warmest winter. Essentially its going to take all of
at least a 1.2 degree warm side error to drop back to #10 warmest
seasonal average. While this could happen, am thinking via ensemble
guidance that this is unlikely.

Projected seasonal rankings for ACY, ABE and ILG follow:

ABE seasonal average temp projects 34.9 or #6 in the POR back
to the winter 1922-23. 0.7 to give to drop out of top 10 so #6
looks pretty solid.

ACY seasonal average temp projects to 39.2 or #12 in the POR
back to the winter 1873-74. 0.6F to give to drop back to #14.

ILG seasonal average temp projects to 38.9 or #9 in the POR
back to the winter 1893-94. 0.4 to give to drop back to #10
warmest winter.

Past two years: PHL through February 2017 will have recorded
above average temperatures for 22 of the last 23 months. May 2016
was below normal. Then we have to go back to Jan Feb March 2015
for below normal monthly temps.

For ABE: 23 consecutive months of above normal temps through
February of this year with last below normal period, again JFM
2015!

For ACY 19 of the past 23 months have been above normal.
For ILG 17 of the past 23 months have been above normal.

Split flow = no snow was something I heard in Boston and it
seems to apply for the next 10 days as the pattern is devoid of
much phasing of the northern and southern streams.

Change is ensembled sometime between the 25th and the first
week of March with a storm track nearby and a better chance for
colder temps and some winter wx. Because of that, i hesitate to
look at seasonal snowfall records. Allentown current #7 least
snowy winter will most likely drop out of the top 10, needing
only 1.5" the rest of the snow season. PHL ILG are already out
of the top 10 least snowy.

&&

.EQUIPMENT...
Marine platforms: 44009 is not expected to be operational until
sometime in May 2017.

The pier for Brandywine Shoal is under reconstruction after
being nearly destroyed by a storm last year. RTS unknown.

&&

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

&&

$$
Synopsis...Franck
Near Term...Drag/MPS
Short Term...Drag
Long Term...Franck
Aviation...Drag/Franck/MPS
Marine...Drag/Franck/MPS
Climate...
Equipment...



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