Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kphi 131140 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
640 am EST Wed Nov 13 2019

Synopsis...
Arctic high pressure will build across our region later today into
tonight, then it shifts offshore during Thursday. A cold front will
move through later Friday, then high pressure builds into our area
from the northwest and north later Saturday and Sunday. An ocean
storm develops off the southeast coast Friday night and slowly moves
northeastward over the weekend with it currently looking to remain
to the south and east of our region, then another storm may develop
off the Carolina coast early next week.

&&

Near term /until 6 PM this evening/...
temperature this morning are in the teens and lower 20s, and northwest
winds will generally range from 10-15 mph. As a result, the
wind chill will range from zero to 10 below in the southern
Poconos to the single digits across southeast Pennsylvania and
most of New Jersey to the teens in Delmarva.

High pressure over the Midwest will build east today, and will
be centered just east of the Appalachians by late afternoon. 850
mb temps will range from -17c across the southern Poconos to
-12c to -13c in Delmarva. Quite cold for this time of the year
with highs in the upper 20s to lower 30s in the southern Poconos
and far northern New Jersey, and otherwise in the mid to upper
30s.

&&

Short term /6 PM this evening through 6 am Thursday/...
the center of the high will lift northeast over New Jersey early
this evening, and will move into the Gulf of Maine by daybreak
Thursday. Winds go light and variable, and some high clouds will
begin to move in from the west.

In terms of temperatures, overnight lows may night be quite as
straightforward as it seems they should be. Still quite cold, but
with high pressure lifting to the north, there will be warm air advection in the
mid levels of the atmosphere. 850 mb temps will rise to -7c in the
southern Poconos to around 0c in Delmarva. However, with clear skies
and nearly calm winds, at least prior to midnight, strong
radiational cooling is possible for The Pine Barrens of New Jersey,
the southern Poconos, and portions of southeast Pennsylvania.

Will go with a consensus blend of guidance, and will lower by a
couple of degrees or so. Lows will generally be in the low to mid
teens for most of the region, in the low to mid 20s for the urban
corridor from Philadelphia to Wilmington and in Delmarva.

Should those clouds build in from the west, temperatures should hold
steady, or even rise a bit.

&&

Long term /Thursday through Tuesday/...
summary...very cold with potentially some record lows to start
Thursday, then some moderation of the air mass Thursday
afternoon and especially Friday. A colder air mass then arrives
for Saturday into Sunday before milder air should overtake our
area early next week. A couple of storm systems however look to
track offshore over the weekend and through early next week.

Synoptic overview...a positively tilted upper-level trough from the
Great Lakes to the Central Plains Thursday will shift eastward into
Friday. The northern part of this feature looks to get absorbed into
a much stronger trough/closed low sliding southeastward from near
Hudson Bay Canada. Meanwhile, energy within a southern stream is
forecast to close off across the Gulf Coast states Friday then it
gradually shifts off the southeast coast over the weekend. This
system aloft is forecast to develop surface low pressure off the
southeast coast late Friday and it slowly shifts northeastward over
the weekend into early next week. An upstream system should kick the
lead short wave along but reinforce the surface boundary along the
Gulf Stream. This however may develop another surface low off the
North Carolina coast, as it also lifts northeastward in advance of
an amplifying upper-level trough.

For Thursday and Friday...after a very cold start Thursday morning,
some recovery occurs Thursday afternoon with weak warm air advection
(southerly flow) and as high pressure shifts off to the northeast
and east. A short wave trough is forecast to slide eastward from the
Great Lakes region Thursday to New England Thursday night, with a
clipper system at the surface tagging along with it. This will toss
a weak cold front across our area mainly Friday night. The main warm
air advection and therefore lift is focused well to our north
therefore no precipitation is expected with it as of now. However,
energy diving across the southern states Thursday is forecast to
close off as is nears the southeast coast. This will induce surface
low pressure development along a lingering baroclinic zone. Some
energy and forcing ahead of this feature may try to produce some
light showers Thursday night into Friday across southeastern New
Jersey and portions of Delmarva. This may be focused near a zone of
increasing warm air advection, a low-level jet and some convergence
near 850 mb. This is less certain though given weaker forcing this
far north, with the main focus farther south closer to the closed
low and developing surface low. For now, kept some slight chance to
chance pops in for portions of the aforementioned area. The thermal
profiles should be warming enough for mainly rain, although this may
have to battle some lingering mid to low level dry air. Given enough
warm air advection, most places should warm to around 50f Friday
afternoon despite more cloud cover.

For Saturday through Tuesday...the model guidance is in pretty good
agreement with the large scale features during this time frame.
There are two features of note, both of which slide across the
southern states. An initial closed low exits off the southeast coast
later in the weekend then may open up some as it lifts east-
northeast and takes surface low pressure with it. While the bulk of
this system should remain far enough offshore to keep much of the
precipitation out of our area, some rain cannot be ruled on at some
point over the weekend. Our area though may remain protected enough
from surface high pressure that may maintain itself near northern
New England with an extension southwestward. This however will
result in a tight pressure gradient as surface low pressure tracks
offshore, and therefore a gusty northeasterly wind is expected
especially closer to the coast. This surface high will result in
another shot of cold air Saturday into Sunday, then some moderating
occurs next week however the onshore flow will probably offset this
some especially closer to the coast and if thicker cloud cover and
some rain occurs. A secondary strong piece of energy may induce
another surface low off the Carolina coast during early next week
and that will also track northeastward ahead of a much more
amplified upper-level trough. While the guidance agrees with the
overall setup, the details are less certain and therefore generally
blended the 00z wpc guidance in with continuity.

&&

Aviation /12z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Today...VFR/skc. Northwest wind 10 to 15 kt with gusts to 20 kt,
diminishing to less than 10 kt in the late afternoon.

Tonight...VFR. Northwest winds less than 10 kt, becoming lgt/vrb.

Outlook...
Thursday...VFR ceilings lower, with perhaps a period of MVFR
ceilings at night mainly at Acy and miv. A few rain showers possible
near Acy and miv at night. Light and variable winds in the morning
becoming southerly around 5 knots, then light and variable again at
night. Moderate confidence, however low confidence regarding any
MVFR ceilings.

Friday and Saturday...mainly VFR ceilings. Light and variable winds
becoming northwest around 10 knots during Friday then turning
northerly Friday night, then northeast 10-15 knots with gusts to
around 25 knots Saturday (strongest at acy). Moderate confidence.

Sunday...areas of MVFR ceilings possible especially closer to the
coast with a chance of some rain. Northeast winds 10-15 knots with
gusts to around 25 knots (strongest at Acy to miv). Low confidence.

&&

Marine...
although there are a few lingering gale force gusts on the
ocean waters, gales are coming to an end. Will convert Gale
Warning to Small Craft Advisory for the rest of the day. For
Delaware Bay, will convert Gale Warning to a Small Craft
Advisory for 25-30 kt gusts, and that will run into early
afternoon. Dry weather on tap. Quite cold, with a chance of
freezing spray this morning.

Outlook...
Thursday and Friday...the conditions are anticipated to be below
Small Craft Advisory criteria much of the time, however winds
increase Friday night with an advisory probable (gusts could near
gale force closer to daybreak saturday).

Saturday and Sunday...a period of northeast gale force wind gusts
are possible with rough seas.

&&

Climate...
Arctic air in place into Thursday, and this will lead to some
additional record low temperatures. Several climate sites tied
or broke their record low temperature for November 12th just
before midnight.

Here are the record low temperatures for today and thursday:

Climate sitenov 13
------------ ------
allentown18 in 1996
Atlantic city22 in 2001, 1996, and 1995
atl. City Marina 24 in 1920
georgetown21 in 1996
mount pocono12 in 1911
philadelphia24 in 1996
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

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory until 4 PM EST this afternoon for
anz450>455.
Small Craft Advisory until 1 PM EST this afternoon for anz430-
431.

&&

$$
Synopsis...gorse
near term...mps

National Weather Service Glossary of Abbreviations