Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
927 PM EDT Tuesday Sep 2 2014
a cold front will cross the region late tonight into Wednesday
morning. High pressure will build into the area from the west and
persist through Friday. Another cold front will cross the region
on Saturday and then stall to the south of our area. High pressure
will build across the Great Lakes region and then slide across to
the north of the region early next week.
Near term /until 6 am Wednesday morning/...
at 9 PM, surface cold front over central New York and central PA stretches
southwestward into southwest PA (fropa through pittsburgh). Despite the
best wind field aloft and dynamics from the front and upper trough
staying to the northwest of the cwa, convection over the Delaware/chesepeake
Bay regions has been more robust as it moved into an increasingly
unstable and moist pre-frontal airmass. These showers and storms
have accordingly been able to be maintained after sunset and have
been locally strong to severe at times, but eventually the loss of
daytime heating will lead to a weakening trend as these storms move
farther east late this evening. Probability of precipitation have been updated based on
recent radar trends.
The cold front will reach the the Poconos late this evening before
moving southeast through southeast PA and central/northwest New Jersey
overnight. Expect the last of the showers to be exiting the New Jersey and
Delaware coasts between midnight and 3 am. The front may not pass through
Acy-dov-Ged until the morning. Official forecast is slightly warmer
than guidance for min temperatures tonight with the progression of the
front has been a bit slower than previously forecast and with the
cold air advection behind of the front being weak.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
as mentioned previously, there won't be a large difference in the
temperatures Post frontal (highs will generally be in the 80s across
the region). However, what the front will be bringing is considerable dry
air advection. Dew points into the upper 50s and lower 60s across
the region by tomorrow afternoon. Thus, while heat index values have
been about 5 degrees above air temperature today, by tomorrow, heat
index values will be right at the air temperatures.
Long term /Wednesday night through Tuesday/...
Wednesday night through Friday...high pressure dominates our weather
through the end of the week as it shifts just to tour south and east
late Wednesday through Friday. This will keep US in a more south to
southwesterly flow and in return we will continue to see an increase
in moisture across the region. Temperatures will continue to mimic
more of middle Summer as opposed to late Summer and we will see maximum
temperatures reach into the upper 80s to around 90 on both Thursday and
Saturday...the high shifts further offshore and we will be awaiting
the passage of a cold front through the day. The front appears to be
slow moving and may take all day to cross from the northwestern
portions of the area and then through the southern most points. We
will likely see a pre-frontal trough develop across the area and
this will likely help serve as a focus for any pre-frontal
convection and showers. Saturday will be the last day of this heat
wave as cooler air behind the front will drop temperatures quite a bit.
Sunday...the front is slow enough that we may not see it clear the
Delaware-Maryland-Virginia area until Sunday morning. As the front pushes south, the
question will be, where will the front stall? Current model guidance
indicates that the front will have enough of a push to get south of
our area, which should allow for some cooler and drier air to
infiltrate our region. The slow nature of the front will allow for
showers to continue, especially further south, into Sunday. As the
front pushes further south, any lingering showers should end from
north to south. With high pressure building into the Great Lakes
area and the stalled boundary to our south, we will be in a more
easterly flow regime with mostly cloudy skies. This will allow US to
be cooler across the area. Temperatures will only make it into the
70s through the region and it will truly feel like fall out there.
Monday through Tuesday...the boundary remains stalled to our south
but as we head into Monday, a wave develops along it and it starts
to move a bit. It currently looks like the wave helps move the
front slightly north and then to the east, keeping the main
boundary to our south. Cooler temperatures will continue on Monday
and Tuesday with highs into the middle to upper 70s, with some lower
80s possible as skies clear out and we start to see more sunshine.
Aviation /01z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
At 01z...second round of strong storms currently moving through ilg.
These storms will gradually weaken as it moves eastward into miv
and Acy between 02z-03z. Heavy downpours will lead to brief MVFR/IFR
visibility restrictions during this time. Lightning and gusty winds are
also possible at those taf sites. Elsewhere, scattered rain showers possible
through about midnight EDT, but aviation impacts should generally be
Not expecting a sharp wind shift with the cold front overnight,
but southwesterly winds 5-10 knots ahead of the front will gradually shift out
of the west and northwest between 06-12z. There is a small risk of br
development but with dry air advection behind the front, think
this is unlikely.
VFR on Wednesday with northwest winds 5-10 knots.
Wednesday night through Friday... mainly VFR conditions expected.
Some fog is possible which may cause MVFR/IFR conditions on Thursday
and Friday mornings.
Saturday through Sunday...mainly VFR conditions expected with
MVFR/IFR conditions possible in showers and thunderstorms.
seas are expected to remain below Small Craft Advisory criteria
through tomorrow. Gusty winds will be possible in the vicinity of
any thunderstorms late this evening. A wind shift to northwesterly
winds is expected with a cold front that will move through late
tonight in the northern waters and Wednesday morning in the
southern waters. However, wind gusts should remain well below
20kt even with the front.
Wednesday night through Sunday...sub-advisory conditions are
expected. Some stronger gusts and higher waves are possible in
showers and thunderstorms, mainly in the Saturday/Sunday timeframe.