Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
914 PM EDT sun Sep 21 2014
low pressure off the middle-Atlantic coast will move northeastward and
away from the region through tonight. Meanwhile, a cold front over
the Ohio Valley this afternoon will move through our area tonight.
A large area of high pressure builds in from the Midwest early in
the week. The high is expected to park over the northeast states
through the remainder of the week.
Near term /until 6 am Monday morning/...
a cold front was approaching from the west an a broken area of showers with
a few embedded lightning strikes was evident on radar. It appears
to be holding together at it moves eastward. The hrrr indicates at
least some portion of the precipitation will survive into the eastern
portions of our County Warning Area. So have upped the probability of precipitation into NJ, but not all
the way to the CST just yet. Still think with loss of daytime
heating and not much dynamics to work with there could be some
weakening with time. Winds will shift to wrly/nwrly behind the
front. Drier air will overspread the area by morning. Lows will
dip into the low.Middle 50s north/west to the upper 50s/low 60s
Short term /6 am Monday morning through 6 PM Monday/...
a pleasant fall-like day is expected across the region Monday as
cool and drier air continues to build over the area. A gusty west/northwest
wind will be in place early and continue through the afternoon. Winds
gusts of 20 to 25 miles per hour are expected. High temperatures Monday will be
mostly in the upper 60s/low 70s across the area...with the northern most
areas only having highs in the upper 50s (mount pocono) to the middle
60s. Dew points mostly in the low/middle 40s.
Long term /Monday night through Sunday/...
expansive area of high pressure over the Midwest will build eastward
into middle-Atlantic region states Monday night and Tuesday. Meanwhile,
a southern piece of energy associated with the upper low that is
currently over the Great Lakes region is forecast to lag behind the
main upper trough and potentially develop into a closed low over the
southeast states. A cold air advection regime will become established over our
region during this time under northwest flow. Minimal cloud cover
and below normal temperatures are expected. Temperatures Monday night may dip into
the upper 30s in the Poconos but the northwest winds overnight should
preclude any frost from forming. With 800 mb temperatures in the single digits,
maximum temperatures on Tuesday will struggle to reach 70f.
High pressure will retreat northeastward into New England Tuesday
night and remain anchored there through the end of the week.
Forecast uncertainty decreases during the second half of the week as
models have had a difficult time coming to agreement regarding what
happens with the above mentioned disturbance over the southeast
states. Over the past few days, the European model (ecmwf) and Gem continue to
advertise a stronger disturbance drifting up the middle-Atlantic coast
late in the week, which would bring rain to southern portions of the
area Thursday and possibly into Friday. Meanwhile, the operational
GFS and just about all of its gefs members (including the latest 12z
run) has been persistent in suppressing the disturbance far enough
to the south and east to keep US dry. This has a low predictability
pattern written all over it given the weak steering flow the low
will encounter underneath the upper ridge. Opted to closely follow
the latest wpc guidance, which preferred an in-between scenario
using the 00z European model (ecmwf) ensemble mean. Forecast was rather conservative
with slight chance probability of precipitation confined to the Delaware-Maryland-Virginia and southern New Jersey.
Regardless of which solution pans out, the setup of high pressure to
our northeast and low pressure to our south will result in
persistent flow off the Atlantic Ocean, seasonably cool temperatures and
increasing cloud cover.
The coastal disturbance is forecast to move offshore by the weekend
while high pressure builds back into the area. Strengthening
subsidence from the high overhead would yield a warming trend with
highs potentially near 80f both days this weekend.
Aviation /01z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
VFR conds are generally expected. However, there is a broken line of
showers moving across eastern PA at this time. This line could briefly drop
ceilings/visibilities into the MVFR or even IFR range. Still some uncertainty
as to how far east this precipitation will get. Have added some brief
rain showers/MVFR at kphl...kpne and kttn.
Behind the front winds will shift to wrly/nwrly and skies will
become mostly clear. Monday...VFR with a gusty west-northwest wind through the day.
Monday night through Tuesday night...VFR under mainly sky clear and
light northwest winds.
Wednesday and Wednesday night...onshore flow develops. Expect
stratocu to increase as marine layer draws inland. Some potential
for MVFR ceilings especially closer to the coast.
Thursday and Friday...lower than normal forecast confidence as
lopres over the southeast states drifts northward. Sub-VFR
conditions and light rain could occur (particularly southern
terminals) if the low tracks far enough north, which is still
uncertain at this time.
winds are beginning to switch around to northwest behind the departing low
offshore. The winds will remain mostly around 10 kts and then switch
more southwesterly this evening...before a cold front crosses the waters
overnight. Winds behind the front will shift wrly...then nwrly and
increase to 10 to 20 kts with some gusts around 25 kts. Seas on the
ocean will build to around 5 feet overnight. We have issued a Small Craft Advisory flag
for the ocean waters and lower del Bay to cover the expected
conditions. Winds/seas will begin to subside by around noon
Monday...so we will set the expiration time to that for now...its
possible it may need to be extended a few hours however.
Monday night...breezy northwest flow continues as hipres builds into the
waters. Capped winds around 20 kt, but still some potential for a
Small Craft Advisory if the pressure gradient winds up being a tad stronger than
indicated by the latest guidance.
Tuesday and Tuesday night...northwest winds diminish Tuesday before
shifting out of the NE Tuesday night.
Wednesday and Wednesday night...NE winds strengthen to near Small Craft Advisory
criteria on Wednesday. In response to the flow, seas are forecast to
build to around 5 feet by Wednesday night.
Thursday through Friday...four to six feet seas may continue through
Thursday night or Friday despite a weaker onshore flow. Small Craft Advisory may be
a moderate risk of rip currents is being forecast for Monday.
Marine...Small Craft Advisory from midnight tonight to noon EDT Monday