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000
FXUS61 KPHI 192029
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
329 PM EST Sun Jan 19 2020

.SYNOPSIS...
A secondary cold front crosses our region during tonight with a much
colder and drier air mass behind it. While low pressure tracks near
the Canadian Maritimes Monday, strong high pressure from the Midwest
to the Tennessee Valley gradually builds east through Tuesday. The
high then settles right over our area Wednesday and Thursday before
weakening and shifting to our east during Friday. Low pressure
should then arrive from the southwest Saturday before moving away
Sunday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A shortwave trough will be moving through the Northeast tonight, and
an attendant cold front will shift quickly southeastward through the
CWA this evening. Snow showers downstream of the Great Lakes will
continue to impinge upon the Poconos, but enhanced lift along the
front may allow snow showers to penetrate farther southward into the
Lehigh Valley and adjacent northern New Jersey between 6 pm and
midnight. Have maintained a mention of slight chance of snow showers
in these areas, with somewhat higher chances in the Poconos, where
quick accumulation of a few tenths of an inch may occur in the
strongest bands. As the trough moves offshore late tonight, snow
showers should quickly wane, with nil PoPs across the area by
daybreak.

The pressure gradient will remain fairly strong overnight, so expect
breezy northwest winds to continue. This should allow wind chills to
fall below zero in the Poconos and into the single digits to low
teens elsewhere. The winds should keep temperatures from plummeting,
but they will still be quite cold. Lows will generally be in the
teens to low 20s, though possibly in the single digits in the
Poconos.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
A broad and quite strong (1044+ mb) surface high will be building
into the central Plains on Monday. Meanwhile, the surface low in the
Canadian Maritimes will continue to lift away from the region. The
pressure gradient will remain sufficiently strong in the Mid-
Atlantic (thanks to the intensity of both surface features) to
generate another breezy day across the area. However, chances of
precipitation should be minimal as large-scale descent encompasses
much of the eastern U.S. by this time. With continued cold advection
through the day, less favorable orientation of surface flow for
downsloping, and overall weaker mixing, highs on Monday should be
colder by several degrees. Generally used a continuity/statistical
blend for temperatures, as there was excellent agreement amongst the
guidance. Max temps may struggle to reach 20 in the Poconos and
should barely make freezing southeast of I-95.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Summary...A cold air mass Tuesday moderates from Wednesday right
into the weekend. Dry conditions continue however moisture will be
on the return for the weekend as a storm system arrives.

Synoptic Overview...An expansive upper-level trough in the East
gradually shifts offshore during Tuesday with an upper-level ridge
arriving in its place. The ridge will drive strong surface high
pressure eastward through Friday with it eventually weakening and
shifting to our east. This pattern results in a cold air mass giving
way to a warming trend for the second half of the week and including
the weekend, however it could get tricky over the weekend with the
next storm set to arrive.

For Monday night and Tuesday...An upper-level trough will dominate
the East during this time frame. At the surface, strong high
pressure builds into the Tennessee and Ohio valley`s through
Tuesday, however it will extend into our region with time. A north
to northwest flow of cold air will be maintained as a result with
temperatures below where they normally should be for the daytime
highs. Plenty of dry air in place especially in the lower levels,
although a northern stream upper-level trough glances our area to
the north by later Tuesday. This may allow for at least some mid to
high level clouds drifting through for a time. The winds will
diminish through this time as the aforementioned surface high builds
closer and the pressure gradient relaxes quite a bit.

For Wednesday and Thursday...The axis of an upper-level ridge is
forecast to slide across our region during Wednesday. This will
allow surface high pressure to crest across our region as well, then
as the ridge shifts east the surface high will also shift with it
and weaken as we go through Thursday and especially Friday. Given
the ridge aloft and some gradual light return flow becoming
established, some warm air advection will result in temperatures
moderating through this time frame. A significant upper-level trough
across the Plains Thursday will shift eastward through Friday, with
surface low development across the Tennessee to Ohio valley`s.
Another high pressure system then becomes situated across eastern
Canada.

For Friday through Sunday...A significant upper-level trough
continues to shift eastward and takes surface low pressure with it.
Some ridging across the region ahead of this storm positions high
pressure across eastern Canada with some of it extending down into
the Mid-Atlantic region. While a milder air mass will be in place,
this may change as the low-level flow turns more easterly Friday
night in advance of a warm front. A secondary surface low is
forecast to develop across the Carolinas to Virginia Friday night as
the primary low occludes in the upper Ohio Valley. This will all
result in increasing clouds especially later Friday with the chance
for some precipitation increasing later Friday night and especially
Saturday, some of which could be wintry especially across parts of
eastern Pennsylvania to northern New Jersey. These details are much
less certain as it will depend on the storm track, timing and
thermal/moisture profiles. As of now, the scope of the dry air does
not look as impressive compared to leading into yesterday`s
(Saturday) event. As of now, the storm is forecast to be moving away
as we start Sunday with improving conditions.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Mainly VFR, though snow showers may make it as far south
as ABE this evening (in which brief sub-VFR may occur).
Northwest winds 10 to 15 kt with gusts up to 30 kt this evening
becoming less frequent and lowering to around 20 kt overnight. High
confidence.

Monday...VFR with northwest winds 10 to 15 kt with gusts to 25 kt.
High confidence.

Outlook...
Monday night through Wednesday...VFR. Northwesterly winds diminish
to 10 knots or less Monday night and continue Tuesday before
becoming light and variable into Wednesday. High confidence.

Thursday...VFR. Light and variable winds to locally light
southwesterly. High confidence.

Friday...VFR with increasing and lowering clouds; MVFR/IFR ceilings
may develop during the night along with a chance of some
precipitation. Light and variable winds, becoming southeast to east
around 5 knots. High confidence during the day, then low to moderate
confidence at night.

&&

.MARINE...
Strong northwest winds continue over the waters this afternoon, and
these are expected to continue through tonight before slowly
decreasing on Monday. A few gusts may approach gale force through
the overnight hours, but conditions appear too infrequent/marginal
to warrant an upgrade of the small craft advisory to a gale warning.
Winds on Monday appear to remain sufficiently strong for
continuation of the advisory through the day. However, as offshore
winds continue, seas will gradually subside below 5 feet tonight and
remain below criteria on Monday.

Outlook...
Monday night...Northwest wind gusts to near 25 knots during the
early evening will then diminish through the night. It looks on the
marginal side, however a Small Craft Advisory may need to be
extended into the evening hours mostly for the Atlantic coastal
waters.

Tuesday through Thursday...The conditions are anticipated to be
below Small Craft Advisory criteria as high pressure gradually
builds over our region.

Friday...The conditions are anticipated to be below Small Craft
Advisory criteria during the day, then the winds become southeast
and east at night and start to increase. It looks like the winds
remain below advisory criteria, however seas may build to around 5
feet across the Atlantic coastal waters Friday night.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EST Monday for ANZ430-431-
     450>455.

&&

$$
Synopsis...Gorse
Near Term...CMS
Short Term...CMS
Long Term...Gorse
Aviation...CMS/Gorse
Marine...CMS/Gorse