Scientific Forecaster Discussion
fxus61 kphi 150824
Area forecast discussion
National Weather Service Mount Holly New Jersey
324 am EST Fri Nov 15 2019
a cold front will cross our area tonight, then strong high pressure
across the Great Lakes will build to our north Saturday and Sunday.
Low pressure develops off the southeast coast Friday, then slowly
moves east northeastward over the weekend. This storm tracks well
offshore of our area Sunday night and Monday. Another storm may
track northeastward off the Carolina coast around Wednesday followed
by high pressure arriving on Thursday.
Near term /until 6 PM this evening/...
the base of an upper trough will work its way through the region
later today. Meanwhile, a cold front remains along the Atlantic
Seaboard, just offshore. Some waves of light precip will slide along
that boundary this morning, producing mainly light rain across
portions of Delmarva and southeast New Jersey. Depending on how far
west that precip spread, some of the more interior locations may be
cold enough to support a brief period of light rain mixed with light
snow through daybreak or so.
Warm air advection will be underway today. Although temperatures will be warmer
than Thursday, they will still be some 5 degrees or so below normal
levels, topping off in the upper 40s to lower 50s.
By this afternoon, there may be a sharp cutoff between sunny skies
across the northern two-thirds of the forecast area and cloudy skies
across southern Delmarva and extreme southeast New Jersey due to
weak high pressure building in from the north and low pressure
approaching from the south.
Short term /6 PM this evening through 6 am Saturday/...
high pressure builds in from the west and will situate itself north
of Lake Erie and Lake Ontario by daybreak Saturday. Meanwhile,
developing low pressure off the southeast U.S. Coast will lift along
the coast to just off the Carolina coast by daybreak Saturday. In
terms of sensible weather, the high to the north should keep the
precip well south of Delmarva. Northeast flow develops between these
two systems, and weak cold air advection will result in lows in the teens and 20s
for most of the region, and in the lower 30s in southern
Long term /Saturday through Thursday/...
summary...colder air surges into the region Saturday and Sunday
(much drier air also for much of the area). Strong winds probable
along the coast Saturday and Sunday with chilly conditions lingering
into Monday as an ocean storm tracks by well offshore. The
temperatures should moderate some Tuesday through Thursday.
Synoptic overview...as a closed low exits the Canadian Maritimes
region Saturday, another closed low shifts off the southeast coast.
The latter shifts east and northeastward Saturday and Sunday, taking
surface low pressure with it (the storm tracks well offshore of our
area Sunday night and monday). A strong surface high moving across
New England wedges southwestward into the mid-Atlantic, slowing the
initial forward motion of the ocean storm. Lots of energy dropping
into the plains and Gulf Coast regions will carve out a larger
trough during the second half of the weekend and early next week.
Strong short wave energy into the base of this trough may develop
another ocean storm off the Carolina coast Tuesday and Wednesday
before it also takes a similar track to the east-northeast.
For Saturday...our region will be caught between two systems. The
first one is strong surface high pressure sliding eastward from
Ontario/Quebec Canada which gradually wedges itself down into the
northern mid-Atlantic. The second one is low pressure off the
southeast coast. The latter looks slow to move as the closed low
becomes positioned above the surface low Saturday night. However,
the pressure gradient between these two systems will continue to
tighten across our region and this will result in a gusty
northeasterly wind. The sustained winds look to be in the 10-25 mph
range, however gusts 25-35 mph are expected with the highest gusts
closer to the coast where peak gusts to around 40 mph are possible.
The southern New Jersey coast to the Delaware beaches could have
some wind gusts near 50 mph later Saturday, and a Wind Advisory may
be needed. The surface high to our north will also be responsible
for delivering much colder air back into our area and also much
drier air from the north and northeast. This is expected to halt the
northward advancement of a rain shield. The presence of subsidence
and much drier air should result in a good amount of sunshine,
although more clouds especially the mid level variety should develop
across portions of our southern areas. Overall, a rather chilly and
gusty day to start the weekend.
For Sunday and Monday...the center of strong surface high pressure
will gradually shift out of northern New England and into the
Canadian Maritimes, however a wedge will linger into the northern
mid-Atlantic states into Monday. A closed low off the Carolina coast
with an associated surface low will track east and northeastward
during this time frame. Much of Sunday may be dry across much of the
area, however increasing warm air and moisture advection to the
north of the surface low will moisten the column and provide some
lift. This may result in some light rain/drizzle especially closer
to the coast Sunday afternoon, then as the influence from an
incoming upper-level trough arrives from the west some rain may get
pulled inland Sunday night and Monday. This will especially be true
as the surface low slides well offshore of our area Monday. While
there will be deeper moisture along the coast, a much drier air mass
looks to hang on longer as one GOES westward across our forecast
area. This should limit the inland extent of the precipitation,
however if it can manage to get farther inland then the drier air
and evaporative cooling could result in precipitation types other
than plain rain. This is highly uncertain given the setup, therefore
did more of a broad brush of rain or snow for now. Increased the
pops some Sunday with low likelies now along the coastal counties.
The wind may be the main story with this system given the pronounced
pressure gradient north and west of the surface low. This will
lessen some Monday, however Sunday northeasterly winds should gust
40 to perhaps 50 mph along the coast with these speeds dropping off
as one GOES inland. It is possible that a Wind Advisory may be
needed along the coast, especially from southern New Jersey to
southern Delaware where the tightest pressure gradient is forecast
along with the longest fetch off the ocean. The combination of lots
of clouds and strong onshore flow will keep temperatures on the
chilly side. See The Tides section below regarding the coastal
For Tuesday through Thursday...an upper-level trough swings across
the east during Tuesday with a weak surface low tracking across the
Great Lakes. The main surface cold front may remain far back to our
northwest as high pressure builds in from the southwest late
Wednesday into Thursday, then the cold front approaches from the
west Thursday night. Overall, no significant changes were made to
this time frame.
Aviation /09z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...occasional MVFR ceilings at kmiv/kacy this morning, along with waves
of light rain with minimal visibility restrictions. VFR after 12z at
kmiv/kacy, and VFR otherwise at the rest of the terminals. Northwest winds
less than 10 kt.
Tonight...VFR. North winds less than 10 kt, becoming northeast 10-15
Saturday and Sunday...VFR ceilings especially Sunday. Some MVFR
ceilings and some rain are possible Sunday particularly at Acy and
miv. Northeast winds 10-20 knots with gusts 25-35 knots. The
strongest winds should be at Acy. Low confidence regarding sub-VFR
conditions and rain.
Monday and Tuesday...some rain from an ocean storm could result in
sub-VFR conditions at times. Northeast to north winds diminishing to
10 knots or less Monday, then becoming mostly light and variable
Monday night and Tuesday. Low confidence on the extent of any rain
and thus sub-VFR conditions.
sub-Small Craft Advisory conditions today. Northeast winds increase to 15-20 kt with
25-30 kt gusts tonight. Will hoist a Small Craft Advisory on Delaware Bay for the
tonight period. For the ocean, although Small Craft Advisory conditions develop late
this evening, gales will develop well after midnight. Will issue a
Gale Warning starting in the pre-dawn hours of Saturday morning.
Saturday and Sunday...northeasterly gale force wind gusts are
expected for most areas. A Gale Warning has been issued for all
areas except the upper Delaware Bay through Saturday night. This
warning will probably need to be extended into much of Sunday.
However, some guidance is a bit weaker across the northern New
Jersey Atlantic coastal waters. Given that it is close and to avoid
confusion with a warning next to a watch, opted to upgraded all of
the New Jersey zones to a warning. A Small Craft Advisory is in
effect for the upper Delaware Bay. Seas will be rather rough.
Monday and Tuesday...the winds diminish Monday with a more notable
decrease Monday night and Tuesday. Seas will remain elevated before
subsiding late, therefore a Small Craft Advisory will be needed for
much of the area during most of this time frame.
northeast winds over the weekend will gust to around 40 mph along
the coast due to a strong coastal storm to our south. The long fetch
will result in a piling up of water along the coast with minor
coastal flooding occurring in areas along the New Jersey and
Delaware coasts and Delaware Bay by Sunday afternoons high tide
cycle. It is possible some locations reach moderate flooding Sunday
especially from Atlantic City southward to the Delaware Atlantic
coast and perhaps up Delaware Bay. This is still a few days away so
confidence is not high in the details especially regarding the tidal
surge above the minor advisory level criteria.
Marine...Gale Warning from 3 am Saturday to 6 am EST Sunday for
Small Craft Advisory from 11 PM this evening to 6 am EST
Sunday for anz430.
Small Craft Advisory from 11 PM this evening to 6 am EST
Saturday for anz431.
Gale Warning from 6 am Saturday to 6 am EST Sunday for anz431.