Scientific Forecaster Discussion
fxus61 kphi 120527
Area forecast discussion
National Weather Service Mount Holly New Jersey
1227 am EST Tue Nov 12 2019
developing low pressure over the Ohio Valley will move northeast
tonight into Tuesday as it tracks through Pennsylvania towards
New England. This will drag a strong cold front through the
region Tuesday morning. Cold high pressure is expected to follow
for the mid week period. A warm front approaching from the west
is then forecast to pass through our region on Thursday night
with a cold front arriving from the northwest on Friday night.
High pressure should move from eastern Ontario to canada's
maritime provinces over the weekend with low pressure developing
off the southeast coast. This low is progged to move north over
the western Atlantic early next week.
Near term /until 6 am this morning/...
cold front is through most of western and central New York and
western Pennsylvania. Temperatures continue to drop behind the
front, and expect the same trend as the front crosses the region
early this morning. By 8:00 am, the front should be somewhere
near or along the Delaware River.
Prefontal precipitation will move into the Lehigh Valley after
1:00 am. The front is expected to be frontogenetic as it passes
the area (at least in the 925-850 layer) with instability above
the level of enhanced positive frontogenesis (as deduced from
saturated geostrophic potential vorticity). Just behind the
front enhanced ul divergence associated with an approaching
150kt jet will nose into the area Tuesday morning, and
potentially keep the precipitation going for a few hours after
the front passes. Deep layer moisture will not be overly
impressive, but pwats do approach an inch or so just ahead of
the boundary. Given these factors, guidance is in fairly good
agreement that total liquid amounts with this system will
generally be in the 0.1-0.25 inch range, with some locally
higher spots possible (the Poconos and Delmarva being the best
candidates for > 0.25 inch totals).
Precipitation should remain all rain through the 6 am period
when looking at forecast surface temperatures and soundings.
The exception is the Poconos, where the first changeover is
expected to begin.
Short term /6 am this morning through 6 PM Wednesday/...
after 8:00 am, lingering precipitation is expected to begin
changing over to light snow. There could be a few heavier bands
across the Poconos, but given the warm temperatures today and
the timing of the changeover being during daytime, accumulation
is not expected outside of the Poconos and Sussex County, New Jersey. A
quick dusting is possible across the Lehigh Valley and into
northern New Jersey, but this is not expected to cause
significant impacts. Elsewhere into the philly Metro, a few wet
snowflakes or a quick snow shower is likely late morning into
the early afternoon.
By 4:00 PM, precipitation should begin to move offshore, with
conditions beginning to clear after that. Winds will be the big
story with wind gusts nearing 25 mph. Temperatures will be
falling through the day with, thus the high is not expected to
occur in the afternoon under a normal diurnal trend.
Temperatures will be falling from the 40s into the 30s and even
20s in the Poconos through the afternoon. Overnight temperatures
will become quite cold as well, dropping into the low 20s and
teens. Wind chills will also be a factor into Tuesday night with
values into the teens and single digits across much of the
Long term /Wednesday night through Monday/...
Wednesday through Thursday...
The main story for this period will be the cold...at least to
start the period for Wednesday. The strong Arctic high
responsible for the cold will crest over the region Wednesday
resulting in generally sunny skies and light winds but
unseasonably cold temperatures. Highs will range from the 20s
across the southern Poconos, where there will also be a bit more
cloud cover and possibly a few flurries, to the low to mid 30s
The center of the high with its associated Arctic airmass will
begin to shift offshore through Wednesday night but it will
still be dominant enough over the area to result in another
mainly clear and very cold night. Lows by Thursday morning
should range from the mid teens over the southern Poconos to the
upper teens to the mid 20s farther south. The urban corridor
should generally see lows in the low to mid 20s.
For Thursday, a disturbance in the upper levels will approach
from the west and this will result in increasing mid and high
level cloudiness through the day. However there won't be much of
a reflection of this disturbance at the surface as it moves
into ridging still holding on over the area so don't expect any
precip. Temperatures will also warm by a good 10 or so degrees
compared to Wednesday as the winds turn southerly.
Thursday night through Monday...
An upper level wave moves through Thursday night into early Friday
and as this occurs it will tap into some moisture off the coast.
This could bring a little light rain to the southern Delmarva into
far southern New Jersey. Otherwise it should be mainly dry through Friday.
Friday looks to be a little warmer than Thursday with highs in the
40s to low 50s.
The forecast becomes a bit trickier heading through next weekend.
Another cold front moves through Friday night with high pressure
building into the north Saturday. This will result in fair weather
with sunshine for Saturday but temperatures about 10 degrees colder
compared to Friday. However there will be a slow moving low pressure
system off the southeast coast and some of our guidance is
indicating moisture from this could make its way into our region by
Sunday. Any precip that occurs Sunday looks to be mainly in the form
of rain and light with the best chances being for areas S/east of the I-
95 corridor. Rain chances increase Sunday night into next Monday as
the low looks to move north over the western Atlantic. The marine
air with this system should also moderate temperatures back to more
Aviation /05z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight... VFR most of the night with lowering ceilings perhaps reaching
MVFR late. Light S winds this evening then becoming more SW by
midnight. Lower ceilings and -shra for krdg/kabe 08/09z then later
10z/11z for kttn-kpne-kphl-kilg.
Tuesday... low MVFR of IFR with showers rain and then snow/rain mix
before ending midday. Winds shift early to northwest and become gusty
g25 kts expected. Colder air arriving. VFR returns 16z/17z west
and 18z or so del valley sites and by 21z S/E.
Wednesday...VFR with northwest winds generally around 10-15 knots.
Wednesday night...mainly VFR. Winds variable but generally around 5
knots or less. High confidence.
Thursday... mainly VFR. Winds becoming southerly around 5 knots.
Thursday night... mainly VFR except around kacy where MVFR cigs
could develop. South winds around 5 knots becoming west. Medium
Friday... mainly VFR. West wind 5 to 10 knots. Medium confidence.
Friday night through Saturday...mainly VFR. Northwest winds 5-10 knots
Friday night shifting to NE Saturday.
tonight and Tuesday...Small Craft Advisory conditions continue
through the afternoon with southwest winds through the morning,
switching to northwest in the late morning around 20 knots. Gusts to
25 to 30 knots are possible. Seas from 3 to 5 feet, especially
tomorrow morning and afternoon.
Tuesday night...gale force gusts are likely with northwest winds
from 20 to 30 knots. Seas from 3 to 6 feet.
Wednesday...northwest winds 20 to 25 with gusts to 30 knots early in
the day will diminish with time and expect winds and seas to be
below Small Craft Advisory levels by mid afternoon.
Wednesday night through Friday...no marine headlines are
Friday night - Saturday...N/NE winds increase Friday night
behind a cold front and could reach gale force overnight Friday
night into Saturday.
here are the record low temperatures for Wednesday and
Climate sitenov 13
allentown18 in 1996
Atlantic city22 in 2001, 1996, and 1995
atl. City Marina 24 in 1920
georgetown21 in 1986
mount pocono12 in 1911
philadelphia24 in 1986
reading21 in 1976
Trenton 23 in 1920, 1911
wilmington18 in 1911
Climate sitenov 14
allentown17 in 1986
Atlantic city15 in 1986
atl. City Marina 23 in 1874
georgetown22 in 1986, 1950
Mount Pocono 5 in 1905
philadelphia19 in 1986
reading16 in 1986
Trenton 20 in 1905
Wilmington 20 in 1986, 1911
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-
Gale Warning from 6 PM this evening to 6 am EST Wednesday for