Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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574
FXUS61 KPHI 201543
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1043 AM EST Tue Feb 20 2018

.SYNOPSIS...
High pressure off the East Coast will provide southwesterly
winds and unseasonably mild weather today and Wednesday. A cold
front is forecast to cross the area Wednesday night. This
frontal system is expected to remain across the mid- Atlantic
region through the latter part of this week and into the
weekend, with a chance for rain each day. Temperatures should
remain near or somewhat above normal through this period.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Fog is hanging in across the Lehigh Valley as of late morning.
We have allowed the Dense Fog Advisory to expire as visibility`s
improve, and replaced it with a Special Weather Statement thru
noontime for the remaining patchy fog. Breaks in the cloudiness
are evident across the coastal plain and downstream further to
the west. With increasing sunshine, we maintained the current
temperature forecast. Soundings indicate mixing only to 975 hPa
will result in near record high temperatures across portions of
the region.

Previous discussion...
A stationary/warm front extended from central New Jersey,
southward across the Delmarva, and southward across the east
coast, before looping back across the western Appalachians and
northward across western Pennsylvania. Areas south and east of
the front remain mostly fog free, while the areas north and west
of the front are socked in with low clouds and dense fog. This
front may push back eastward through daybreak, allowing for the
fog to spread toward the coast. So we will keep the Dense Fog
Advisory in place. We expect the front to lift north of the area
as a warm front during the daytime today. Once the front lifts
north of the area, we expect some clearing, and the fog and low
clouds to dissipate. However, this will likely be a slow trend
for many areas. This will make the forecast for the day tricky.
If the low clouds and fog do not burn off quick enough, daytime
temperatures will not have enough time to warm up. The current
expectation is that the clouds and fog will begin to dissipate
and lift by late morning or early afternoon, which will allow
for some warming. So we leaned closer to the warmer guidance
since we expect some clearing. Outside of some drizzle this
morning, we expect the area to remain precipitation free for
today as there are not any short waves/vorticity impulses
expected.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
Any clearing this afternoon is expected to be short lived as
clouds and fog/drizzle are expected to develop again tonight.
While the warm front is expected to have lifted north of the
area during the day today, our area will remain withing a
warm/moist southwest flow as high pressure remains off the east
coast. This warm/moist air will allow the low levels to saturate
again, and in turn allowing for the low clouds and fog/drizzle
to form. It is very possible that another night of dense fog is
in store for the area, and another Dense Fog Advisory may be
possible tonight. Outside of any drizzle overnight, we expect
the area to remain precipitation free overnight.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The long-term period begins with a continuation of unseasonably
mild weather, aided by southwesterly flow around and unusually
strong mid-/upper-level ridge along the East Coast. At least
some partial sunshine is expected to help temperatures reach the
low to mid 70s in most areas. A number of max temperature
records are likely to be broken; see the climate section below.


Later on Wednesday the upper ridge begins to be suppressed and a
cold front is forecast to push south across the forecast area
Wednesday night. There does not seem to be much forcing for UVV
with the front so we have included only a slight chance of
showers for most areas with the frontal passage. The front will
result in a return to more normal temps for late February.

This front is expected to stall somewhat south of Delaware.
However the cool air looks rather shallow and low level warm
advection develops above it by Thursday and and continues into
Friday/Saturday. This WAA plus some apparent weak impulses in
the continuing SW flow aloft should result in periods of rain
for the latter part of the week and into the weekend. Confidence
in the timing however is below average. Daytime highs should
gradually increased above normal.

By Sunday a stronger shortwave trof is forecast to approach from
the west, with the associated surface frontal system to cross
the mid-Atlantic region late in the day. More widespread rain is
expect ahead of the is system on Saturday night and Sunday,
followed by clearing on Monday.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today-tonight...Low clouds will persist across the TAF sites
through at least the late morning hours. While ACY and MIV do
not have the LIFR conditions the rest of the TAF sites do. We
expect an improvement to the conditions for a period this
afternoon. However, this improvement is expected to be temporary
as low clouds and fog/drizzle are once again expected to
develop after sunset and likely persist through the night. IFR
conditions are expected again tonight through Wednesday morning.

Winds this morning will be light and variable for many
locations, although some areas will continue with southwest
winds around 5-10 knots. All areas are expected to have their
winds increase to 10-15 knots out of the southwest today. Some
areas will even see some gusts around 20 knots, especially where
the clouds break up and dissipate. The southwest winds will
continue into tonight, with some areas becoming light and
variable.

Confidence: Average.

OUTLOOK...

Wednesday...Fog and stratus dissipate in the morning, giving way
to VFR conditions. SW winds 10-15 kt with gusts to 20 kt.
Confidence: Above average.

Wednesday night...Scattered showers and patchy fog possible with
sub-VFR conditions. Winds shift from SW to N in the evening.
Confidence: Average.

Thursday...Sub-VFR conditions possible in scattered showers. NE
winds 10-15 kt. Confidence: Average.

Thursday night...Sub-VFR conditions possible in scattered
showers. Confidence: Below average.

Friday through Saturday...Sub-VFR conditions in periods of rain.
Confidence: Below average.

&&

.MARINE...
The Dense Fog Advisory was allowed to expire as visibilities are
improving greater than one Nautical Mile, and will be replaced
with a Marine Weather Statement for lingering fog through this
evening.

Dense fog will likely redevelop overnight, so another Dense Fog
Advisory will likely be needed for visibilities at or below one
Nautical Mile.

A Small Craft Advisory is now in effect for all of Delaware
Bay, where frequent southwest wind gusts up to 25 knots are
likely through 6 PM this evening.

On the Atlantic Waters of Delaware and New Jersey, Winds and
seas are expected to remain below advisory levels for today and
tonight. However, winds may gust around 20 knots at times and
seas will be around 3-4 feet.

OUTLOOK...

Wednesday...SCA conditions possible on the ocean with gusty SW
winds.

Wednesday night...Sub-SCA conditions expected.SW winds turning
NW overnight.

Thursday...SCA conditions possible on the ocean waters.

Friday through Saturday...Sub-SCA conditions anticipated.

&&

.CLIMATE...
Record high temperatures are possible today and Wednesday.

Tuesday, 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

Wednesday, 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

A record warm minimum temperature may be set for Atlantic City
on Tuesday. The current record is 44 in 1949.

The following are the record warm minimum temperatures for
Wednesday, all which should be exceeded.

ABE 46-1981
ACY 49-1954
PHL 49-2002
ILG 47-2002
RDG 48-1930
TTN 48-2002

The all time February max temps may be approached on Wednesday
at ILG, TTN, GED RDG MPO. All the all time monthly max`s are
listed below:

ACY 77 2/25/30
PHL 79 2/25/30
ILG 78 2/24/85
ABE 77 2/24/17
TTN 76 2/25/30
GED 77 2/25/17
RDG 77 2/24/17
MPO 70 2/25/30

Our expectation is that ACY will exceed the previous all time
record rainfall for February, by the end of the weekend. The
record is 6.50 inches in 2010. #2 is 1958 with 5.98 inches.

And...adding only half an inch to PHL and ILG will put both
locations in the top 9 ranking for Feb rainfall.

Have rechecked the monthly projection at PHL and the avg temp
continues at 41.0 or 5.3F above avg which is 8th warmest on
record, if it holds. Add or subtract a degree to the
average/departure and the ranking changes from 3rd to 11th. The
forecast 5.3F departure is ~2f warmer than the current
departure. I`d expect similar for the rest of our area...a bit
less in the north which will have better chances for colder air,
and a bit more warming in the south where the positive
departure as of yesterday was already 5F above normal, heading
for 7+. So all in all it appears we`re heading for a top 10
warmest February. Last year was the warmest on record, a
whopping 3+F degrees warmer than our current projection.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ430-
     431.

&&

$$
Synopsis...Franck
Near Term...Franck/Robertson
Short Term...Robertson
Long Term...AMC
Aviation...AMC/Franck/Robertson
Marine...AMC/Franck/Robertson
Climate...Staff



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