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
000
FXUS61 KPHI 101728
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1228 PM EST Sat Dec 10 2016

.SYNOPSIS...
A large surface high builds towards the region through tonight. By
late tomorrow, the high will shift off shore as a low pressure
system crosses the Great Lakes region, bringing to our region a
warm front late Sunday night followed quickly by a cold front on
Monday. A strong cold front is expected Wednesday. High pressure
builds east through the end of the work week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KDIX indicates light snow shower/flurry activity over northern
portions of the CWA early this afternoon, and this trend is
expected to continue til sunset. this activity is expected to
remain mostly north of i-78, and most places that see snow should
expect just a dusting...but up to one-half inch is possible in a
few spots...especially in the higher elevations. West to northwest
winds in the 10 to 15 mph range are expected, with a slightly
higher gust from time to time. Temperatures will remain cold,
mainly in the 30s.
&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Snow showers/flurries are expected to dissipate into the evening as
the steep lapse rates weaken and the enhanced moisture lifts out of
the area. Skies will temporarily scatter out in the evening before
clouds build back across the area overnight. High pressure builds
across the area overnight, so winds will lighten through the night
as well. Temperatures will cool quite a bit overnight/Sunday morning
and likely be cooler than Friday night/Saturday morning.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Main story through the long term remains the Sunday/Monday wintry
mix precipitation event.

Changes from previous forecast: latest model runs have trended
faster with the arrival of the warm front early Monday morning.
Additionally, both the GFS and ECMWF show a dry slot over Delmarva
and far southern NJ and far SE PA ahead of the arrival of the warm
front. If both of these trends continue, the I95 corridor and
locations south and east should see mostly (if not all) rain. For
locations northwest of the I95 corridor (especially along and
north of I78), this may unfortunately mean that they will have a
longer period in the transition zone, meaning a longer period of
freezing rain and sleet. As a result, the forecast snow amounts
have decreased slightly, while storm total ice forecast for I78
and further north have increased.

Hazards/impacts: At this point, while it looks like we might fall
short of warning criteria (either for ice storm or winter storm),
it will likely be a high end advisory event for I78 and north that
could result in treacherous travel conditions especially Sunday
night into at least the first half of the Monday morning commute.
Additionally, there may be enough ice accumulation to result in
some power outages in these locations.

For the rest of the region, if these trends hold, the main impacts
would be slippery conditions on area roads through the first half
of Sunday night (if the precip moves in that early). However, by
the time of the morning commute, precip should be all rain.

Confidence: This forecast is still very dependent on how quickly
the warm air will move in, so there is still considerable
uncertainty with the exact timing of the change over, and
consequently snow and ice amounts.

Monday afternoon/evening: dry air advection is expected on the
heels of the cold front, so precipitation should quickly come to
an end behind the cold front which should be off shore by the
evening hours. The one possible exception is that with the strong
northwesterly flow behind the front, there may be some lake effect
snow showers, which may get as far south and east as the southern
Poconos.

Tuesday through Saturday: Stayed close to model consensus to
focus on both the snow showers this morning and the Sunday/Monday
event. A brief period of snow is possible behind the next (and
stronger cold front on Wednesday.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Generally VFR conditions expected this afternoon...with cloud
bases 4,000-6,000 feet, with isolated / scattered snow mainly
north of I-78.

Winds will generally be west to northwest around 10 knots with gusts
15-20 knots. Gusts will drop off late in the afternoon into the
early evening.

VFR conditions expected to remain across the TAF sites tonight.
Winds will lighten to less than 5 knots overnight as high pressure
builds across the area.

Outlook...

Sunday and Monday...Widespread MVFR and even IFR conditions at times
with low ceilings and reduced visibilities. Precipitation could
begin as snow and may be a wintry mix for most TAF sites Sunday
night (with possible exception of KMIV and KACY, which may have all
rain). All precip should change over to rain no later than 18Z
Monday. Windy conditions will be possible behind the cold front on
Monday.

Monday night...conditions should gradually improve to VFR. Breezy
northwesterly winds possible during the evening hours.

Tuesday...VFR conditions expected.

Wednesday...MVFR or even IFR conditions are possible if wintry
precip moves into the region. Breezy northwesterly winds possible.

&&

.MARINE...
The Small Craft Advisory is now in effect for just the coastal
waters adjacent to northern New Jersey. Winds further south have
dropped below 25 knots as high pressure approaches from the west.

Sub-Small Craft Advisory conditions are expected overnight tonight
as the high builds across the waters, although winds could gust
around 20 knots during the evening hours.

Outlook...

Sunday...winds and seas should stay below SCA criteria.

Monday...Prolonged SCA conditions for both winds and seas possible
first with southerly winds behind a warm front early in the day,
then an abrupt shift to breezy northwesterly winds is expected late
in the day with a cold front. Gale force gusts are possible
especially on the ocean waters. A gale watch may be issued if
confidence remains this high as we get closer.

Tuesday...winds should drop below SCA criteria early in the day, and
sub SCA conditions should continue for the remainder of the day.

Wednesday...Mostly Sub-SCA conditions are expected through the day,
though a brief period of gusts above 25 kt will be possible behind a
cold front.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for ANZ450-
     451.

&&

$$
Synopsis...Johnson
Near Term...Robertson/Miketta
Short Term...Robertson/Miketta
Long Term...Johnson
Aviation...Johnson/Robertson
Marine...Johnson/Robertson


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.