Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
933 am EST sun Dec 21 2014
high pressure centered over Quebec today will drift eastward and
it should reach Atlantic Canada on Monday. Weak low pressure is
forecast to develop off the Carolina coast on Monday before moving
slowly northeastward and dissipating off the Delaware-Maryland-Virginia peninsula on
Tuesday. Low pressure is expected to develop around the central
Gulf Coast region on Tuesday. The low should strengthen as it
lifts northward and across the eastern Great Lakes on Wednesday
night. The low is anticipated to pull a warm front through our
region on Wednesday, followed by a cold front late on Wednesday
night. High pressure is expected to follow from the southwest for
Thursday and Friday. Another cold front from the west is forecast
to arrive on Saturday.
Near term /until 6 PM this evening/...
the center of a 1030 mb surface high was analyzed over eastern
Canada at 14z this morning. This broad area of high pressure
encompasses most of the eastern Seaboard. The pressure gradient
and resultant winds will be light over the middle-Atlantic region
today under this setup.
Stratocu still holding strong over northeast PA and northern New Jersey this
morning, where higher moisture in association with a passing
shortwave trough to our northeast remains trapped below the
subsidence inversion at around 900 mb. The Delaware-Maryland-Virginia is positioned in
the right entrance region of middle-level jet streak, resulting in
overcast middle clouds in our southern zones. However, there is a
band of clearing evident on the latest visible satellite imagery
in the middle part of the County Warning Area that is developing over southeast
PA, including philly and adjacent central/southern New Jersey middle
morning. The clearing should expand south and eastward thruout the
day as the jet streak progresses off the coast, although the
heating will lead to development of scattered stratocu. Clouds
should be slower to erode over northeast PA and northwest New Jersey through
midday, but some sun is anticipated later in the afternoon.
Only made minor adjustments to the maximum temperature forecast based off
changes made to the sky grids. Maximum temperatures range from the lower 30s in
the Poconos to around 40f in philly, southern New Jersey and the Delaware-Maryland-Virginia.
Short term /6 PM this evening through 6 am Monday/...
the high pressure begins to retreat some overnight tonight, but
our area will still remain on the southern fringe. Any partial
clearing that occurred during the day will continue into the
evening, but high level cloud cover may begin to develop and
spread back into the area overnight as a weak short wave lifts
through the area. We are not expecting any precipitation overnight
as there is a lack of significant vertical moisture.
Low temperatures are a blend of mav/met MOS and mosguide which
were all in pretty good agreement.
Long term /Monday through Saturday/...
a middle level ridge axis should be to our east on Monday. An
impulse traveling in the middle level flow is expected to pass
overhead on Monday afternoon. Moisture is forecast to spread into
our region from the south at that time. We have mentioned a chance
of rain arriving from south to north from the late morning into
the afternoon hours. The forecast temperature profiles suggest
that the boundary layer will be able to support all rain even up
north where the chance for precipitation is the lowest in our
Surface high pressure is forecast to be located over Atlantic
Canada from Monday into Tuesday. A ridge axis is expected to nose
southwestward along the Lee of the Appalachians at that time with
an inverted trough developing off the coast. Weak low pressure is
anticipated to develop on the trough off the Carolina coast on
Monday. The feature is forecast to remain weak as it drifts
northeastward reaching the waters off the Delaware-Maryland-Virginia peninsula
before dissipating on Tuesday.
Meanwhile, a deep middle level trough is expected to dig over the
middle part of the country on Monday and Tuesday as the ridge over
the western North Atlantic becomes more pronounced. The pattern
will result in the development of strong warm advection over our
region from Tuesday into Tuesday night.
The pattern should keep our region overcast with a chance of rain
from Monday night into Tuesday with the probability of
precipitation increasing to likely for Tuesday night. It continues
to appear as though there may be pockets of below freezing
temperatures in the Poconos and in far northern New Jersey from
Monday night into Tuesday morning to possibly result in some
localized light freezing rain.
Surface low pressure is anticipated to develop around the central
Gulf Coast region on Tuesday in response to the deep middle level
trough. The low is forecast to strengthen as it moves northward on
Wednesday and across the eastern Great Lakes on Wednesday night.
The system should have an opportunity to tap into Gulf moisture
and it will bring the potential for some moderate to heavy
rainfall to our region from late Tuesday night into early
Wednesday night. The consensus of the models continues to suggest
representative rainfall amounts up to an inch to an inch and a
half in our region during the middle week period.
The low is expected to pull a warm front through our region on
Wednesday with temperatures forecast to rise into the 50s and
lower 60s. A strong cold front is forecast to follow late on
Wednesday night with temperatures dropping back into the upper 30s
and lower 40s by daybreak on Thursday. The probability of
precipitation decreases rapidly late on Wednesday night as dry air
is expected to begin building into our region from the west and
southwest. Conditions are anticipated to become quite breezy in
the wake of the cold front for Christmas day. A west wind around
15 to 20 miles per hour is forecast with gusts near 30 miles per hour. Temperatures
should return to seasonable levels for Thursday, Friday and
Ridging is forecast to develop at the surface and aloft for
Thursday night into Friday with dry weather anticipated.
A middle level short wave is expected to approach from the west
along with an associated surface cold front. The front is forecast
to pass through our region on Saturday. The system is forecast to
be fast moving and it should not have much of an opportunity to
tap into a moisture source. As a result, we will not forecast any
precipitation with the front at this time.
Aviation /15z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
VFR today. Clearing has already occurred across philly area
terminals this morning while Abe remains overcast just above 3000 feet.
Expect scattered ceilings around 3 kft this afternoon for all terminals. Winds
will be light (below 10 kt). Winds will become light and
variable/calm once again tonight.
Monday...mainly VFR with a chance of light rain spreading
northward into our region.
Monday night and Tuesday...conditions possibly lowering into the
MVFR category with a chance of light rain.
Tuesday night...MVFR and IFR conditions anticipated with rain
Wednesday and Wednesday night...MVFR and IFR conditions with rain
likely. The rain may be heavy at times.
Thursday...conditions improving to VFR with a gusty west wind.
sub-Small Craft Advisory conditions will remain today into
tonight as high pressure from the north will continue to affect
Monday and Monday night...no marine headlines are anticipated.
Tuesday and Tuesday night...wave heights on our ocean waters may
build to 5 feet in a developing onshore flow.
Wednesday...southerly wind gusts in excess of 25 knots are
expected. Wave heights on our ocean waters may build to 6 to 9
Wednesday night...a south wind becoming west. Wind gusts in
excess of 25 knots are expected. Wave heights on our ocean waters
may be to 6 to 9 feet.
Thursday...westerly wind gusts in excess of 25 knots are
expected. Wave heights on our ocean waters may be to 5 to 7 feet.