Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 240558
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1258 AM EST Fri Feb 24 2017

.SYNOPSIS...
A frontal boundary extended across northern Pennsylvania,
southeastern New York and New England and it should lift to the
north on Friday and Friday night. A strong cold front will move
through the Mid Atlantic on Saturday. High pressure will pass
through the region Sunday and Monday. A front will set up near
the area for much of next week, with several lows expected to
move along it. A strong low will move through the Great Lakes
and southeast Canada next Wednesday and Thursday, which will
pull another strong cold front through the region by late in the
week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The scattered rain showers associated with the frontal boundary
to the north of our region should continue to lift
northeastward during the balance of the night. The sky was
mostly cloudy over Berks County, the Lehigh Valley, the Poconos
and northern New Jersey around midnight. The sky was partly
cloudy to clear over southeastern Pennsylvania, central and
southern New Jersey, Delaware and northeastern Maryland.

While some patchy stratus and fog may develop in our region
overnight, it should not be nearly as widespread as it was on
Thursday morning. We are solidly in the warm sector and the
light southwest to south wind at most locations should keep the
atmosphere mixed.

Minimum temperatures are forecast to range from the upper 40s
to the middle 50s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM SATURDAY/...
The cold front will dissipate inland by the morning. Similar to
today, the day will start with low clouds and fog. The low-
level flow is forecast to be ever-so-slightly backed tomorrow
(Sly) compared to today (S-SWly), which may allow the stratus to
hang on an hour or two later into the day than today.
Regardless, there looks to be an opportunity for temperatures to
spike to near record levels in the mid to late afternoon hours
with clearing skies during peak heating. Trended warmer for
tomorrow (closer to the RGEM), yielding highs in the low to mid
70s south of I-78 and mid to upper 60s farther north.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
The long term period looks active, as several systems are
likely to affect the area through the middle part of next week.

At 00Z Saturday, a strong vorticity maximum will approach the
Great Lakes and Ohio Valley, with a 140-kt 250-mb jet streak
positioned across much of the southern U.S. As the nose of this
jet enters difluent flow near the Atlantic Coast, considerable
upper-level divergence will collocate with differential cyclonic
vorticity advection downstream of the aforementioned vort max.
Strongly forced convection will develop along an associated cold
front in the Midwest moving east into New York and Pennsylvania
by late Saturday morning. A downstream jet streak will develop
in the high-amplitude ridging nosing into eastern Canada,
providing additional lift via jet coupling to produce widespread
precipitation in Quebec, New York, and adjacent New England
Saturday afternoon. As the vort max impinges upon the high-
amplitude ridging, it will make a shift northward, leaving our
region on the southern fringes of the stronger dynamics/lift and
well within the warm sector of the system.

Given sufficient diabatic heating, marginal boundary-layer
based instability is expected by afternoon in our area, which
may act to compensate for the somewhat weaker large-scale
ascent. Vertical wind profiles will be quite strong, with deep-
layer shear 40-60 knots. Unidirectional wind profile and
orientation parallel to the initiating boundary will support a
line of convection moving through the area during the afternoon.
Strength of the wind profile and steep lapse rates near the
surface suggest isolated damaging wind gusts are possible as the
line moves through the region. The key to the extent of this
threat will be the degree to which the boundary layer
destabilizes during the day and the ability for updrafts to
withstand the strong vertical wind profile -- the usual players
in a high CAPE-low shear environment. Today`s simulations
suggest there will be a window of at least partial surface
heating just downstream of the cold front, with MUCAPE near 500
J/kg during peak heating. Maintained a threat of thunderstorms
in the grids for Saturday afternoon. Models have sped up the
timing of frontal passage a tad, and reflected this in the grids
somewhat by increasing PoPs a bit earlier in the day and
decreasing them a bit more Saturday evening/night.

Temperature forecast on Saturday is a big challenge, as sky
cover, precipitation, and timing of the frontal passage are all
highly complicating issues. I went pretty close to statistical
guidance, which was generally in good agreement despite the
complex scenario. Nevertheless, there is large uncertainty and
potential for error for highs Saturday, which currently are
around five degrees lower than the values in place for Friday.

A sprawling but progressive high will move in behind the front
for Sunday and Monday, so a period of dry weather and much
cooler (though still near to slightly above average)
temperatures are forecast during this period.

By Monday afternoon, model agreement becomes quite poor. These
large discrepancies exist owing to an unusually high degree of
spread associated with an upper-level low digging off the
California coast this weekend and progressing eastward early
next week. The GFS is very quick to move a perturbation from
this upper low into the central plains by 00Z Monday and to the
Mid-Atlantic States by 00Z Tuesday. Widespread precipitation
breaks out on the East Coast Monday night in advance of this
system. The ECMWF, meanwhile, is much weaker with this
perturbation and basically shows no precipitation at all with
its passage, but is more aggressive in breaking out
scattered/light precipitation on Tuesday afternoon/evening as
isentropic ascent increases downstream of a stronger system that
develops in the central plains into the Great Lakes by midweek.
As the low rapidly develops and lifts into southeast Canada by
Thursday, a cold front sweeps through the East Coast Wednesday
night and Thursday, bringing widespread precipitation through
the area. Meanwhile, the GFS moves this low/associated
precipitation mostly to the north of the area. Other guidance
provides little insight, as the CMC becomes a strong outlier
with the depth/orientation of the longwave trough beyond this
weekend, and the ensemble guidance shows that the GFS/ECMWF
solutions are nearly equally plausible.

As a result, broadbrushed PoPs/sky cover/temps/winds Monday
night through Thursday, with generally slight chance to chance
PoPs during this period. There is at least some chance for a mix
of rain and snow in the southern Poconos Monday night if the
GFS solution pans out. Then again, if the ECMWF solution is
closer to reality, there may be no precipitation at all... Temps
during this period should be well above average.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conditions were being reported around 0600Z at and around
all eight of our TAF sites. Patchy fog and stratus are forecast
to develop. However, the low conditions are not expected to be
nearly as widespread as they were on Thursday morning. We have
indicated a period of low end MVFR conditions for now. Any low
clouds and fog should dissipate by 1400Z or so with VFR
conditions anticipated for the balance of the day into this
evening.

The computer guidance is suggesting another more substantial
round of low conditions for late Friday night. The solution
seems reasonable as the surface flow may be a little east of
south and more off the ocean that it is currently.

A light southwest to south wind should increase around 8 to 10
knots for late this morning and this afternoon. The wind
direction is forecast to back toward the south and southeast for
this evening and tonight at speeds generally less than 10
knots.

OUTLOOK..

Friday night...Sub-VFR conditions possible with areas of low
clouds and fog.

Saturday and Saturday night...Line of showers/storms likely
will move through the area during the day, with gusty/erratic
winds and sub-VFR conditions likely during passage. South winds
may gust at times above 20 kts before frontal passage. Winds
will rapidly switch to west or northwest after the front passes,
with gusts above 20 kts likely. Rapid improvement to VFR after
frontal passage.

Sunday...VFR with winds northwest 10-20 kts with gusts to 30
kts possible.

Sunday night and Monday...VFR with winds near/below 10 kts
becoming southerly by Monday. Conditions may become sub-VFR late
in the day as another system approaches, but this is very low
confidence.

Monday night and Tuesday...Potential for sub-VFR conditions
with precipitation, low ceilings, and reduced visibilities
possible at times. Very low confidence.

&&

.MARINE...
A S-SW wind around 10-15 kt then turn south or southeast Friday
afternoon with a few gusts near 20 kt possible at any time.

Another round of dense fog may occur over the waters either
very late tonight or more likely Friday. No marine dense fog
advisory yet due to uncertainty regarding when the dense fog
forms and how widespread it will become. There is a potential
for the dense fog..if it forms..to persist all day a few miles
off the Atlantic coast.

OUTLOOK...

Friday night through Saturday night...Fog may again develop on
the coastal waters, with at least some potential for
visibilities less than one mile, as very warm/moist air remains
over the relatively cold waters. A line of storms will likely
move through Saturday afternoon and evening, with any fog
rapidly dissipating as this occurs. Seas are expected to build
to small craft advisory (SCA) thresholds on Saturday, and winds
will become westerly and become gusty after cold frontal
passage. Gusts may approach gale levels late Saturday night.

Sunday and Sunday night...SCA northwest winds continue but
should decrease below advisory thresholds Sunday evening.

Monday through Tuesday...Generally sub-SCA conditions expected,
though winds may approach advisory levels for a brief period
Monday afternoon.

&&

.CLIMATE...
**Many records today contribute to a record warm Feb and a top 10
  warmest winter in the period of record for Mount Holly FA**

Records were set today 2/23/17, at GED 75, MPO 63, RDG 73, ABE
72 and records were equaled at ACY 72, ILG 73

For reference, here are/were the high temperature records for
today, Friday and Saturday (not including the new records so far
today).

Location    Thursday 2/23   Friday 2/24   Saturday 2/25

ACY         72-1985         75-1985       77-1930

PHL         75-1874         74-1985       79-1930

ILG         72-1985         78-1985       78-1930

ABE         71-1985         76-1985       74-1930

TTN         74-1874         74-1985       76-1930

GED         67-1985/1990    72-1961       76-1975

RDG         72/1932/1922    77-1985       77-1930

MPO         60-1977         60-1984       70-1930


The following are the monthly and seasonal expectations.

It is virtually certain that these values will be at or below
reality and that our forecast area is experiencing a record warm
February and a top 10 warmest winter.

Records date back to the late 19th century. Details below.

February:

PHL 43.9 #1  Normal 35.7 Record 42.2-1925 POR 1874

ABE 38.9 #1  Normal 30.7 Record 38.6-1998 POR 1922

ACY 42.9 #1  Normal 35.3 Record 41.6-1890 POR 1874

ILG 43.1 #1  Normal 35.1 Record 42.3-1903 POR 1895

Note for ABE: There is a pretty good chance ABE will end up
warmer and possibly very close to their monthly temp record.


Winter (DJF)

PHL 40.3 #7 and solid. It wont slip.

ABE 35.8 #5 and solid. It wont slip.

ACY 39.8 #9 and may rise

ILG 39.4 #5 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.)


Snow:

Atlantic City should end up tied for 5th least snowiest
February on record 0.3"

&&

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

&&

$$

Synopsis...CMS
Near Term...Iovino
Short Term...Klein
Long Term...CMS
Aviation...CMS/Iovino
Marine...CMS/Drag/Klein
Climate...Drag


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