Scientific Forecaster Discussion
fxus61 kphi 121755
Area forecast discussion
National Weather Service Mount Holly New Jersey
1255 PM EST Tue Nov 12 2019
an Arctic front will cross our region this morning, then high
pressure builds in during Wednesday before shifting offshore
Thursday. A cold front moves through Friday night with high pressure
building in from the northwest Saturday into Sunday. Meanwhile, low
pressure develops off the southeast coast Saturday then it tracks
northeastward across the western Atlantic over the weekend and early
Near term /until 6 PM this evening/...
considering the latest radar trends and hints in the hi-res
models it seemed prudent to issue an early afternoon update to
include a little more snow across srn New Jersey and adjacent Delaware. The
cold air has arrived a bit quicker and temps have been running
cooler than expected. Meanwhile, a weak wave along the front has
shown itself by a slowing of the back edge of precip across srn
New Jersey and Delmarva. Some enhancement in the echos has also
developed. We expect that any snow that is seen on the ground
will only be across grassy areas with the pavement being
initially too warm.
Northwest winds 15 to 25 mph with gusts to 25 mph are still
expected. Wind chills will drop into the teens by evening with
single digits across the north/west areas.
Short term /6 PM this evening through 6 am Wednesday/...
Arctic high pressure builds in from the north and west tonight.
Northwest winds this evening will continue to average 15-20 mph
with gusts to 25 mph, diminishing a bit after midnight, then to
5-10 mph prior to daybreak Wednesday.
A frigid air mass with the potential for record breaking low
temperatures will be in place tonight with lows ranging from
10-15 in the southern Poconos and far northern New Jersey, and
otherwise in the teens and low 20s. Minimum wind chills tonight
will range from zero to five below in the far northern zones,
and in the single digits to low teens otherwise.
Long term /Wednesday through Monday/...
summary...very cold to even potentially record cold to start
Wednesday (and thursday) with a little warming during the day, then
the airmass 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...as a strong upper-level trough exits the northeast,
the center of Arctic high pressure builds over our area during the
afternoon and at night. This will result in a very cold day with
even record cold possible to start the day, then temperatures only
warming into the 30s for most during the afternoon. The strongest
breeze should be during the first half of the day, with wind chill
values starting out in the 5-10 degree range (down to zero or just
below in the poconos). The airmass is forecast to be very dry, given
its Arctic source, and with surface high pressure building in during
the course of the day the winds will ease up. While some flurries or
even an isolated snow shower is possible early across mostly the
Poconos, this should end quickly due to the very dry air along with
increasing subsidence. As the surface high slides right over our
area in the evening before shifting more to our northeast overnight,
a very cold night is in store due to light/calm winds, limited cloud
cover and a very dry airmass. This could result in some temperatures
dropping to near record territory.
For Thursday and Friday...a very cold start Thursday with even some
record lows possible, then some warming in the afternoon. 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 a surface low. The forecast
challenge is the timing and also 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 some 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 away.
Aviation /18z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of today... precipitation is ending from west to east across
the area. For Acy and miv, light snow or sleet remains possible
through mid to late afternoon. Elsewhere, dry weather has returned
but conditions may fluctuate between MVFR and VFR for a time during
the early to mid afternoon. A trend towards VFR is expected later
this afternoon and this evening. Northwest winds will 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...VFR. Northwest winds 10-15 knots, then becoming light
and variable at night. High confidence.
Thursday...VFR, however MVFR ceilings are possible late at night
mainly at Acy and miv. Light and variable winds becoming southerly
around 5 knots, then light and variable at night. Moderate
Friday and Saturday...mainly VFR ceilings. West to northwest winds 5-
10 knots Friday turning northerly Friday night, then northeast 5-15
knots Saturday. Low confidence.
this afternoon...gales gusts occurring across the waters attm
and it should continue with decent cold air advection expected
to promote excellent mixing this afternoon. G35 to 40 kts
expected during the period.
Tonight...gale force winds for most of the night, diminishing
to 15- 20 kt with gusts up to 30 kt by daybreak Wednesday. Ocean
seas 4-6 feet, and waves on Delaware Bay 2-4 feet.
Wednesday...the conditions are anticipated to be dropping below
Small Craft Advisory criteria by the early afternoon, then continue
to subside at night.
Thursday and Friday...the conditions are anticipated to be below
Small Craft Advisory criteria much of the time, however winds
increase Friday night and an advisory may be needed.
Saturday...Small Craft Advisory anticipated. Northeast winds are
forecast to gust to 30 knots, however a period of gale force gusts
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 6 am EST Wednesday for anz430-431-450>455.