Scientific Forecaster Discussion
fxus61 kphi 122039
Area forecast discussion
National Weather Service Mount Holly New Jersey
339 PM EST Tue Nov 12 2019
Arctic high pressure will build into the region through Wednesday,
bringing an unseasonably cold air mass. The area of high pressure
will shift offshore on Thursday. A cold front will move through
Friday night and into Saturday. High pressure should then build back
in later Saturday and Sunday. An ocean storm is likely to develop
off the southeast coast over the weekend, but is currently expected
to remain mainly to the southeast of the mid-Atlantic.
Near term /until 6 am Wednesday morning/...
an interesting rain/snow event winding down across the region with
radars showing the steady echos moving east across Delmarva and extreme
S New Jersey. The colder air charged across the region earlier, a bit faster
than modeled. This combined with a subtle upper short wave created a bit
more snow across srn New Jersey and Delaware than earlier expected. A few hours of
snow with 3/4 to 2sm visibilities were reported in many areas, but the
accums were only a trace. This is first snow of the season for many
parts of the region including the philly Metro areas (as measured at
phl) and The Mount Holly, New Jersey National Weather Service.
Going into tonight, high pressure well to the west will begin to
push into the area with a decrease in clouds expected. Winds will
remain gusty overnight and temperatures will remain well below
normal. Lows will reach around 10 across the far north and teens
most other areas. Lows for Delmarva and coastal waters the lows will
be closer to 20 degrees. Wind chills will be 10 to 15 degrees cooler
than the air temps lows, so teens and single digits fairly common.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
high pressure across WV early will move towards New Jersey during the day.
Fair weather with mostly sunny skies are expected. Some CI/cs clouds
will spill in from the northwest during the afternoon. Cold. Morning lows
in the teens and low 20s will rebound back to the low/mid 30s in
most areas. The north/west most areas may remain in the 20s however. Winds
will be from the northwest at mostly around 10 mph, but little gusty into
Long term /Wednesday night through Tuesday/...
summary...very cold air lingers into Thursday morning. The air mass
moderates some Thursday and especially Friday before cooling takes
place Saturday. Milder air looks to arrive for early next week,
however a storm system looks to be lurking offshore.
Synoptic overview...a strong upper-level trough lifts out of the
east Wednesday with the mid level flow turning more zonal, then a
short wave trough from the Midwest to the central Mississippi Valley
pivots eastward Wednesday night and Thursday. This feature slides
across the east later Friday as a closed low amplifies and shifts
southward some across eastern Canada. The latter shifts across the
northeast into Saturday with a ridge building across portions of the
western Atlantic, however a cutoff low looks to develop off the
southeast coast over the weekend and into early next week. A surface
low tied to this is forecast to slowly track northeastward into
early next week.
For Wednesday night through Friday...another very cold night is
likely Wednesday night thanks to clear skies and light winds even as
the air mass starts to slowly moderate. Some additional record lows
are possible. Some warming Thursday afternoon as high pressure
shifts off to the east and flow turns southerly. A short wave trough
is forecast to slide eastward from the Great Lakes region Thursday
to New England Thursday night, with a clipper system at the surface
tagging along with it. This will toss a weak cold front across our
area Friday night. The main warm air advection and therefore lift is
focused well to our north therefore no precipitation is expected
with it as of now. However, energy diving across the southern states
Thursday is forecast to close off as is nears the southeast coast.
This will induce surface low pressure development along a lingering
baroclinic zone. Some energy and forcing ahead of this feature may
try and produce some light precipitation late Thursday night into
Friday across southeastern New Jersey and portions of Delmarva. This
is less certain given weaker forcing this far north, with the main
focus farther south closer to the closed low and developing surface
low. For now, kept some low pops in for portions of the
aforementioned area. The thermal profiles should be warming enough
for mainly rain, although this may have to battle some lingering mid
to low level dry air before dew points recover more. Given enough
warm air advection, most places should warm into the lower 50s
Friday afternoon despite some increase in cloud cover.
For Saturday through Monday...the evolution of northern and southern
stream energy becomes a bit more uncertain, however overall strong
high pressure slides by to our north while a closed low near the
southeast coast Saturday drives surface low development. The
forecast challenge is the timing and also the question of how much
protection does our area get from the surface high as it gradually
departs. Our region may get brushed by the storm as it tracks
northeastward across the western Atlantic, however a gusty
northeasterly wind (especially closer to the coast) looks certain
given the pressure gradient forecast. We will continue with some
slight chance to low chance pops given the uncertainty especially
later Sunday through Monday. The airmass should moderate during the
weekend and early next week, however this could be tempered some by
the strengthening onshore flow, if more precipitation ends up
occurring and if the system is even slower in moving further
Aviation /21z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of today... precipitation has ended across most of the area,
and conditions have returned to mainly VFR levels. This trend is
expected to continue. Northwest winds will also continue, sustained
at 10 to 15 kt with gusts up to 25 kt.
Tonight... VFR. Northwest wind around 10 kt with gusts to 20 kt
possible mainly before midnight.
Wednesday... VFR. Northwest wind 10 to 15 kt becoming northerly and
decreasing in the late afternoon.
Wednesday night-Thursday...VFR, however MVFR ceilings are possible
late at night mainly at Acy and miv. Light and variable winds
through Thursday morning becoming southerly or south-southwesterly
around 5 knots, then light and variable again Thursday night.
Friday and Saturday...mainly VFR ceilings, with MVFR possible Friday
especially at miv and Acy. West to northwest winds 5 to 10 knots
Friday turning northerly Friday night, then northeast 10 to 15 knots
Saturday. Moderate confidence.
we will continue with the Gale Warning on the waters into the
overnight period with a good shot of cold air arriving and decent
mixing over the relatively warmer waters. Gusts between 35 and 40
knots are expected. The gusts will begin to diminish late, but
perhaps a bit after the original gale was set to expire, so I added
a few hours onto the end. A Small Craft Advisory is expected after the gale
comes down. Except for some showers across the srn waters early,
fair weather expected overnight. Cold.
Arctic air pours across the entire area by later today and sticks
around into Thursday. This may lead to some record lows.
Here are the record low temperatures for Wednesday and thursday:
Climate sitenov 13
allentown18 in 1996
Atlantic city22 in 2001, 1996, and 1995
atl. City Marina 24 in 1920
georgetown21 in 1986
mount pocono12 in 1911
philadelphia24 in 1986
reading21 in 1976
Trenton 23 in 1920, 1911
wilmington18 in 1911
Climate sitenov 14
allentown17 in 1986
Atlantic city15 in 1986
atl. City Marina 23 in 1874
georgetown22 in 1986, 1950
Mount Pocono 5 in 1905
philadelphia19 in 1986
reading16 in 1986
Trenton 20 in 1905
Wilmington 20 in 1986, 1911
Marine...Gale Warning until 11 am EST Wednesday for anz430-431-450>455.