Scientific Forecaster Discussion
fxus61 kphi 201418
Area forecast discussion
National Weather Service Mount Holly New Jersey
1018 am EDT Fri Apr 20 2018
high pressure will build in from the west today and remain in the
area through the weekend before sliding offshore on Monday. Low
pressure developing over the southeastern United States will move up
the mid Atlantic coast, affecting our area through the mid week
Near term /until 6 PM this evening/...
Low pressure was located near the Canadian Maritimes this morning
while high pressure was centered over the Midwest states. A
relatively tight gradient in between both systems has resulted in a
breezy start to the day with northwest winds 15-20 mph gusting 25-30
mph. Winds will relax ever-so-slightly this afternoon owing the
presence of a weak surface trough over the area.
Cold-air advection stratocu originating from Lake Ontario continues
to break apart downstream past the Poconos owing to downsloping flow
and mid-level subsidence in wake of the exiting mid-level trough.
However, a cumulus field should be present through the afternoon with
strong boundary-layer mixing underneath the subsidence inversion.
High temperatures today in the 40s in the southern Poconos and far
northwestern New Jersey and low to mid 50s elsewhere are close to what climo
would be for March 20th but generally 10-15 degrees below normal for
Short term /6 PM this evening through 6 am Saturday/...
the center of the surface high is forecast to slide into the eastern
Great Lakes region and the upper Ohio River valley tonight. We are
anticipating a mostly clear sky with perhaps an increase in cirrus
late tonight. The northwest wind is expected to diminish to less
than 10 mph.
We continue to issue frost and freeze products only for locations
from the counties of Berks, Montgomery, lower Bucks, Mercer and
Middlesex southward. We will begin frost and freeze products for
much of the remainder of our forecast area next week. Based on the
anticipated low temperatures for tonight (mostly in the 30s) and the
decreasing wind, we may need to put some areas under a frost
advisory. Another freeze warning is possible for the same locations
as the current one. We will look at the next full suite of guidance
before making a final decision during the day.
Long term /Saturday through Thursday/...
Saturday through Monday...
Surface high pressure will build over the region through this period
along with an associated upper level ridge. This will bring fair
weather with sunshine and gradually warming temperatures.
Forecast models are in excellent agreement with this scenario
so a high confidence forecast for this period.
In terms of the day to day specifics, each day will feature plenty
of sunshine but there will still be a bit a northwest breeze Saturday near
10 mph with highs generally in the upper 50s to low 60s (except
cooler in the southern poconos). This is still a little cool for
this time of year. However winds will be lighter for Sunday and
Monday with temperatures warming a couple degrees each day so by
Monday, highs will be well into the 60s for much of the region. Lows
each day will be chilly due to the clear skies and light
winds...generally in the 30s with western and northern zones in the
County Warning Area likely dipping to near or below freezing.
Tuesday through Thursday...
Overall, no major changes to this part of the forecast as general
thinking remains the same. A low pressure system will move across
the Mississippi Valley and into the southeastern United States early
next week. As the low pushes towards the coast, it starts to move
northward towards the mid-Atlantic states. While the forecast models
agree that there is some form of a coastal low that develops and
impacts our area, there are still differences regarding timing and
evolution that lead to a relatively low confidence forecast at this
time. The system will bear watching as it will have good moisture
associated with it and the potential for some heavy rain will exist.
Strong onshore flow could also bring some coastal flooding concerns
and will also need to be monitored. Still a long way out and plenty
of time to see how the models come together on this system over the
Aviation /14z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR with predominately few to sct cumulus with bases 4-6 kft
above ground level. Northwest winds 10-20 kt with gusts to 25 kt, weakening a bit mid
to late afternoon.
Tonight...VFR with a mostly clear sky. Northwest wind diminishing to
less than 10 knots.
Saturday...VFR conditions with northwest winds around 10 knots. High
Sunday...VFR conditions with light winds. High confidence.
Monday...VFR conditions expected along with continuing light winds.
Tuesday...mainly VFR conditions expected. East to southeast winds
around 10 to 15 knots. Increasing cloudiness through the day.
today and tonight...northwest winds have weakened slightly this
morning but widespread gusts of 20-25 kt are still occurring as
of 10 am. Seas are currently around 5 ft. The 2 PM expiration
time for the current Small Craft Advisory still looks reasonable as the
diminishing trend for winds and seas will continue through the
rest of the day.
Friday night through Monday....sub-advisory conditions are expected
on the the area waters.
Tuesday...winds and seas increase in advance of an approaching
coastal low with Small Craft Advisory conditions likely be late day.
we are expecting a northwest wind of 10 to 15 mph with gusts of 20
to 25 mph for today. Relative humidity values are forecast to drop
around 30 percent in much of northeastern Maryland, Delaware, New
Jersey and southeastern Pennsylvania. We will be coordinating with
our fire weather partners later this morning regarding fuel
moisture levels to determine if any additional fire weather
products need to be issued for today.
Marine...Small Craft Advisory until 2 PM EDT this afternoon for anz430-