Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1002 PM EDT Fri Oct 21 2016
low pressure will consolidate near southern New England tonight,
then intensify as it tracks northward through late Saturday.
Another cold front arrives Sunday night, then high pressure
gradually builds in late Tuesday and Wednesday. A warm front to
our southwest Thursday is then forecast to lift across our area
Near term /until 6 am Saturday morning/...
low pressure was centered off eastern Long Island this evening.
The low is forecast to drift northward overnight. The cold front
associated with the low had passed through all of eastern
Pennsylvania, northeastern Maryland, Delaware and much of New
Jersey by 9:30 PM. The boundary will continue to move eastward
and out to sea overnight.
Temperatures will drop in the wake of the front. Lows are
expected to be mostly in the 40s to the northwest of the
Interstate 95 corridor and into the lower 50s elsewhere in our
forecast area. A northwest wind will be on the increase
overnight. Sustained wind speeds should reach 15 to 20 miles per hour by
daybreak with gusts around 30 miles per hour.
A mid level low was taking shape over southwestern Pennsylvania
and vicinity this evening. The feature is anticipated to reach the
lower Susquehanna River valley around daybreak. As the mid level
low approaches our region, the associated lift will help to
develop additional showers with the continued inflow of moisture
from the south and southwest aloft.
Short term /6 am Saturday morning through 6 PM Saturday/...
as upper low lifts to the north and east on Saturday, upper
trough remains over the area. Surface low pressure over the
Canadian Maritimes will intensify, deepening from a 990 mb low
Saturday morning to a 980 mb low by Saturday evening. Meanwhile,
1022 mb high pressure will build into the Gulf Coast states. As a
result, a tight pressure gradient will form across the entire
northeast U.S. Strong northwest winds develop fairly quickly Saturday
morning, increasing to 20- 30 miles per hour winds with 35-45 miles per hour gusts.
Based on latest NAM and GFS forecast soundings, think wind gusts
will fall short of Wind Advisory criteria, so will not issue a
Wind Advisory. Will keep the mention in the hwo, as it will be
close, and cannot rule out a few 45-50 miles per hour reports Saturday
afternoon, especially in the higher elevations, and near the
For temps, with strong cold air advection underway, looking as if the highest
temps of the day will occur just after midnight, as temps will be
in the upper 50s to low 60s. By Saturday morning, temps will be in
the upper 40s to low 50s, and should hold mainly steady from
Long term /Saturday night through Friday/...
the synoptic setup is comprised of a deep upper-level trough in
the east to start Saturday night into Sunday, however this feature
is forecast to lift out during Sunday. A secondary short wave
amplifies the trough once again Sunday night and Monday as another
cold front pushes through. The trough weakens thereafter with
surface high pressure building in later Tuesday and Wednesday,
then another trough tracks across the Midwest and upper Great
Lakes regions Wednesday and Thursday before pushing eastward. This
should send a developing warm front northbound across our area
Thursday night and Friday. Overall, it looks to be a cooler time
frame given a trough that wants to remain in the northeast. We
used a model/continuity blend Saturday night into Monday, then
blended in the 12z wpc guidance thereafter. Some adjustments were
then made following additional collaboration with our neighboring
For Saturday night and Sunday...a deepening upper-level trough
will swing to our east during this time frame. This will drive
intensifying surface low pressure up across New England and then
into Canada through Sunday. The best low-level cold air advection
wanes through Saturday night, then some moderation is forecast at
least at 850 mb during Sunday. Meanwhile, high pressure centered
well to our southwest will result in a tight pressure gradient.
This will result in gusty winds continuing through this time
frame. However, there should be enough decoupling Saturday night
and early Sunday to allow the winds to diminish some. Despite a
strong flow remaining in place for much of Sunday, the gradual
warming aloft should allow for less mixing overall (not as steep
low-level lapse rates). While breezy conditions are expected
Sunday, the peak gusts are expected to be less than Saturday.
A short wave then amplifies the trough starting Sunday night as a
secondary cold front moves through. The moisture looks to be
limited with this feature despite a strong short wave, however the
guidance shows a tightening thermal gradient near our northern
zones ahead of and with this feature. This should drive a band of
frontogenetic forcing leading to some showers. The coverage and
placement of these showers varies some in the guidance, given the
track of the aforementioned short wave. We will keep some low pops
across the northern areas for now later Sunday night into early
Monday. It will be chilly to Cold Saturday night, then some
moderation on Sunday ahead of the next cold front.
For Monday and Tuesday...an upper-level trough dominates the east
for much of this timeframe, although it is forecast to shift east
during Tuesday. This will result in cyclonic flow of cool to
chilly air across the area. To start off Monday, an initial short
wave that starts the trough amplification moves through and this
may result in some showers early up north. Otherwise, the boundary
layer should become well mixed during the daylight hours with
plenty of drying above the inversion. This should result in less
clouds but at least some stratocumulus should occur especially on
Monday. It looks to be breezy once again especially during peak
heating as the forecast soundings show deeper mixing occurring
with 25-30 knots of wind to mix down. There is a frost or freeze
potential for some areas Tuesday night especially as the winds
For Wednesday through Friday...as the trough continues to shift
east of our area Wednesday, another trough gradually moves from
the Midwest to the Great Lakes. High pressure briefly over our
area Wednesday will shift offshore. A return flow sets up in its
wake, allowing warm air advection to occur up the Ohio Valley and
into our area especially starting Thursday. This will allow a
developing warm front to our southwest to move into our area
Thursday night then slowly advance northward Friday. The timing
and placement of this warm front will have an affect on cloud
cover and any precipitation. As of now, the main forcing may
remain to our west and therefore the pops were kept on the low
side later Thursday and Friday.
Aviation /02z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
MVFR ceilings are expected to prevail overnight as additional
showers develop and move into our region from the south. Ceilings
are forecast to lift into the VFR range for Saturday with a
continuing chance of showers, mainly in the morning. The cloud
cover should begin to lessen during the course of the afternoon.
The wind will settle into the northwest for tonight with speeds
increasing to around 15 to 20 knots gusting near 30 knots. A brisk
west northwest wind will continue on Saturday with speeds around
20 knots gusting near 35 knots. The wind speeds are forecast to
begin subsiding gradually late in the day.
Saturday night and Sunday...VFR overall. Northwesterly winds
15-20 knots with gusts to 30 knots early are expected to diminish
some during Saturday night, then turn gusty again Sunday (not as
strong as saturday). A secondary cold front arrives Sunday night,
with some showers possible mainly near and north of kabe to kttn.
Monday and Tuesday...VFR overall. Northwesterly wind gusts up to
30 knots especially Monday in the wake of a cold front, then
diminishing winds at night.
Wednesday...VFR with high pressure in place, resulting in
northwest winds less than 10 knots.
additional showers will impact the waters as the winds shift to
Winds will increase to 15-20 knots with 20-30 knots gusts, and then
strengthen even more on Saturday. As a result, a Gale Warning is
Winds increase to 20-30 knots with 35-45 knots gusts on the waters on
deep mixing within a colder airmass will allow for gale force
gusts Saturday night and Sunday. These are expected to diminish
first for Delaware Bay, then from south to north for the Atlantic
coastal waters during Sunday. We did not make any changes to the
ending times of the Gale Warning. The conditions are then expected
to be to Small Craft Advisory levels Sunday night into Tuesday in
the wake of a cold front. The conditions are anticipated to drop
below advisory criteria Tuesday night and Wednesday as high
Marine...Gale Warning until noon EDT Sunday for anz452>455.
Gale Warning until 6 PM EDT Sunday for anz450-451.
Gale Warning until 2 am EDT Sunday for anz430-431.