Scientific Forecaster Discussion
fxus61 kphi 111738
Area forecast discussion
National Weather Service Mount Holly New Jersey
1238 PM EST Mon Nov 11 2019
a strong cold front extended from northern New England to the
southern Great Plains early this morning. Low pressure is
forecast to develop along the front in the Ohio River valley
today. It is expected to progress northeastward, reaching New
England late tonight. The low is anticipated to pull the cold
front through our region early on Tuesday. Cold high pressure is
expected to follow for the mid week period. A warm front
approaching from the west is 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.
Near term /until 6 PM this evening/...
12:30 PM update: no significant changes made. Updated
temperatures and dewpoints to reflect current trends.
At the surface a largely stalled front will remain displaced to
our west today while an area of low pressure develops to our
southwest and moves from the Ohio Valley into central
Pennsylvania. At mid- levels the flow aloft will back more
southwesterly ahead of a deepening h5 trough over the western
Great Lakes/upper Midwest. This configuration will result in an
uneventful day weather-wise with cloud cover largely limited to
cirrus (albeit, potentially thick at times) streaming in from
the SW ahead of the next storm system. Light, but warm southerly
flow on the eastern periphery of the developing low will keep
temperatures mild, with highs largely in the upper 50s to lower
60s (e.G. About 5 degrees above normal).
Short term /6 PM this evening through 6 PM Tuesday/...
the surface low will track northeastward tonight, passing just
west of the area in the predawn hours Tuesday morning. As the
low progresses the attendant and fairly robust cold front will
approach the area from the west. Guidance currently has the cold
front entering far western portions of the forecast area early
Tuesday morning, reaching the I-95 corridor around or just after
sunrise, and then clearing the coast by mid-morning.
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 will begin as rain everywhere but will likely
transition to a rain-snow mix or potentially (mainly north and
west of the I-95 corridor) all snow later in the event as the
column cools. There is a small chance that some areas
(particularly the Poconos and northwest nj) see a brief period of
freezing rain or sleet between the rain-snow transition, but
this would likely be quite brief as the surface cooling should
not greatly outpace the cooling aloft. Although, do think much
of the area will at least see some flakes on the tail end of the
event, the initially warm temperatures combined with
postfrontal drying should largely prevent accumulations south of
approximately the I-78 corridor. Even in areas that do see some
accumulating snow, the limited moisture associated with the
system coupled with the initially low snow ratios should hold
totals to less than an inch. The exception could be the higher
terrain of the Poconos and northwest New Jersey where amounts could be around
an inch. Precipitation will taper off from west-east Tuesday, and
expect the area will be largely dry by mid-afternoon Tuesday.
Strong cold advection will occur immediately behind the front
and, therefore, tuesday's high temperatures are both rather
uncertain (particularly for areas around the I-95 corridor and
points east), and also not particularly meaningful as these
highs will occur early in the morning and therefore not be
representative of temperatures most of the day. Think that by
mid afternoon temps will have largely settled into the mid to
upper 30s over most of the region (apart from the Poconos and northwest
Long term /Tuesday night through Sunday/...
high pressure is forecast to be located in the middle
Mississippi River valley on Tuesday evening. The high will move
eastward and its center should reach our region on Wednesday
evening. It will be the coldest air mass to influence our
weather, so far this season.
The pressure gradient between the departing low to our
northeast and the approaching high should result in windy
conditions from Tuesday night into Wednesday morning. As the low
moves farther away from US on Wednesday afternoon, and as the
high drifts closer, wind speeds are expected to begin
Low temperatures on Tuesday night are expected to favor the
teens and lower 20s. Wind chill values early on Wednesday
morning are anticipated to fall a bit below zero in the elevated
terrain of the Poconos and far northern New Jersey and they
should range from 5 to 15 in much of the rest of our region.
High temperatures are forecast to range from the middle 20s on
the Pocono plateau to the middle 30s in northeastern Maryland,
Delaware and southern New Jersey on Wednesday.
The high is expected to move to the waters off Nova Scotia on
Thursday, putting our region in a return southerly flow at that
time. Clouds should be on the increase as a warm front
approaches from the west. Temperatures on Thursday afternoon are
forecast to be noticeably warmer than those on Wednesday
afternoon. Highs should range from the middle and upper 30s in
the north to the middle and upper 40s in the south.
The warm front is forecast to pass through our region on
Thursday night. We are expecting a mostly cloudy sky with a very
limited chance for precipitation, mainly on the coastal plain.
Conditions on Friday are anticipated to be even milder than
those on Thursday with highs mostly in the 40s and lower 50s.
A cold front is expected to arrive from the northwest on Friday
night with limited moisture associated with it.
High pressure is forecast to build from the Great Lakes to New
England and canada's maritime provinces over the weekend with
low pressure developing off the southeast coast. The expected
weather pattern should result in a prolonged northeasterly
surface flow in our region. Some of the model guidance is
suggesting that the northwestern edge of the clouds and
precipitation shield associated with the low will affect our
region. The forecast temperature profiles indicated that the
precipitation type would strongly favor rain.
Aviation /18z Monday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Today...VFR, with prevailing southerly winds around 5 kts. High
Tonight...VFR conditions for much of the night with sub-VFR
conditions in initially rain spreading west-east starting around
08-09z at krdg and kabe. Winds generally SW 5-10kts, shifting northwest
10-15kts at ridge and Abe just before daybreak. Moderate
Tuesday... sub-VFR conditions for most of the morning in some
combination of rain and/or snow. Conditions likely improving to
VFR (w-e) late morning into early afternoon. Winds from the northwest
sustained 10-15kts, with gusts 20-25 kts. Generally high
confidence apart from precipitation types which is moderate
Tuesday night and Wednesday...mainly VFR. Northwest wind 10 to
20 knots with gusts of 25 to 30 knots. High confidence.
Wednesday night...mainly VFR. Northwest to northeast wind 5 to
10 knots. High confidence.
Thursday... mainly VFR. Northeast to east wind 5 to 10 knots
becoming southeast to south. Medium confidence.
Thursday night... mainly VFR. South wind 5 to 10 knots becoming
west. Medium confidence.
Friday... mainly VFR. West wind 5 to 10 knots. Medium
today... winds and seas will remain below Small Craft Advisory criteria during
the daytime hours, with SW wind gusts around 15-20kts and seas
generally 2-3 ft.
Tonight/Tuesday... Small Craft Advisory conditions are expected to begin this
evening with SW winds gusting 25-30 kts and seas building to
around 5 ft by Tuesday morning. Winds will shift to the northwest late
Tuesday morning with gusts over 30 kts possible Tuesday
Tuesday night...a gale watch is in effect for northwest wind
gusts around 35 knots.
Wednesday...a northwest wind is expected to gust around 25 to
Wednesday night through Friday...no marine headlines are
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...gale watch from Tuesday evening through late Tuesday night for
Small Craft Advisory from 6 PM this evening to 6 PM EST
Tuesday for anz430-431-450>455.