Scientific Forecaster Discussion
fxus61 kphi 102050
Area forecast discussion
National Weather Service Mount Holly New Jersey
350 PM EST Tue Dec 10 2019
A cold front will push through the area this afternoon/evening
as low pressure passes to our northeast. Strong high pressure
will build in from the west Wednesday night into Thursday and
then move offshore Thursday night. A low pressure system will
move through the southeastern states and into the mid-Atlantic
late Friday into Saturday. The low will quickly move off to the
northeast allowing high pressure to briefly build into the
region for the start of the new week, before another storm
system approaches from the south late Monday into Tuesday.
Near term /through midnight/...
An upper level jet streak is now positioned to our north with rain
showers forecast to continue developing into the overnight. At the
surface, a cold front is making its way toward eastern PA and will
cross the forecast area through the evening hours and will be
offshore by midnight. There will be an enhancement in the
precipitation as the front itself moves through this evening so i've
kept likely to categorical pops in the forecast.
Temperatures have warmed well into the 50s and low 60s across the
area thanks to warm air advection in the wake of a warm front now
located well to our north. As the front passes, winds will shift
westerly and temps/dewpoints will being to drop quickly into the 40s
Short term /12 am Wednesday through 6 PM Wednesday/...
In the wake of the cold frontal passage, another quick shot of light
to moderate precipitation is forecast to develop. This is in
response to a shortwave trough ejecting northeastward from the
Tennessee Valley along with an area of frontogenesis developing
behind the exiting cold front. Hi-res guidance develops a modest
band of precip across the forecast area a few hours after midnight,
then the band will persist and move offshore by around 10 am. As
cold air advection continues overnight, rain will mix with and
change to all snow from northwest to southeast from midnight to
about daybreak area wide. Some sleet is also possible across
Delmarva and southern New Jersey where the warm nose persists a bit longer.
The heaviest snowfall will be before daybreak on Tuesday north/west
of I-95. This is the area where confidence is highest on
accumulating snowfall since temperatures will be colder. However,
less quantitative precipitation forecast is forecast in these areas so many areas may end up with
less than an inch. For the I-95 corridor, the heaviest snowfall is
forecast to fall from about 4-7am. Farther south across southern and
coastal New Jersey as well as Delmarva, snowfall will end by around 10-11
With antecedent conditions being quite warm, we do expect there to
be very poor efficiency in accumulating any snow, especially on
roads. Most of the snow will only stick to grassy and elevated
surfaces where it can fall quickly enough and temps can cool to near
freezing. Therefore, we aren't expecting any significant travel
issues, however there may be some slushy spots on roads causing them
to become slippery.
As far as total snow accumulations, we're expecting a coating around
an inch or so for most areas, with less than an inch across Delmarva
and extreme southern New Jersey. Farther north and east, isolated areas up
to 2" are possible. This is mainly confined to areas that will be
colder at the onset of snow and areas that will receive snow for
longer as the band of precip is moving offshore. The highest
uncertainty for snow amounts is across Monmouth and ocean counties
where banding and moderate snow may persist longer potentially
leading to higher totals.
Morning low temperatures will likely occur while snow is falling and
will be within a degree or two of the freezing mark. Skies will
clear quickly in the wake of the departing band of precip as much
drier air advects in from the west. Temperatures will then rise into
the upper 30s to near 40 degrees by the afternoon hours with
westerly winds around 10 mph, so whatever snow does fall will likely
be all melted by the end of the day.
Long term /Wednesday night through Tuesday/...
Summary: cold and dry Thursday, then cloudy and a bit warmer
with a chance of showers Friday, with heavier rainfall expected Friday
night into Saturday morning. Largely dry weather Sunday into
Monday before another storm system approaches from the south
late Monday into Tuesday.
Thursday: strong (1040 mb) high pressure builds in from the
west with cold and dry conditions prevailing. Although it will
be mostly sunny highs will only reach the 20s in the Poconos and
generally mid 30s elsewhere. Guidance has become more bullish
on bringing in some lower cloud cover Thursday night so nudged
mins a couple degrees to account for this possibility.
Friday: the high will move into the Gulf of Maine and towards
the Canadian Maritimes on Friday, with east to southeast flow
developing behind the it. Temperatures warm back up to near and
slightly above normal levels on (e.G. From the upper 30s in the
Poconos to lower 50s in delmarva).
Some showers will be possible during the daytime hours on Friday
as lead shortwave energy & an ul jet streak combine with
isentropic upglide. Generally expect these to remain relatively
light and be mostly rain (although a period of mix will be
possible in the far north).
Friday night/Saturday... a period of moderate rainfall is
expected as a strengthening coastal low moves in from the south.
Lift provided by the system's warm (potentially occluded) front,
and the exit region of the curved ul jet will combine with
precipitable waters around 1.25 inches to create a potential for some locally
heavy rainfall Friday night/Saturday morning. Right now most
guidance is hinting at totals in the 1-1.5 inch range although
some ensemble members show the potential for even higher
amounts. If the higher end scenarios were to verify there could
be some Hydro concerns, but this will become more clear in the
Some additional precipitation (still mostly rain) is possible
Saturday afternoon/night as northern branch energy interacts
with the system's cold front.
Sunday/Monday... some light precipitation will be possible
Sunday morning as a last piece of shortwave energy pivots
through although there isn't much moisture left to work with.
Otherwise high pressure will build in more or less overhead by
Monday. Temperatures will generally be in the mid 40s to lower
50s on Sunday, before cooling off 5-10 degrees behind the dry
cold front on Monday.
Monday night/Tuesday... the next storm system (of southern
stream origin) will likely impact the area in this time frame
although timing discrepancies exist (the Canadian is the
fastest, the GFS intermediate, and the ec the slowest). There
are also significant differences in the low's track and
thermodynamic profiles. Since it is so far out went with a pure
rain/snow forecast this package, but depending upon the low's
track and how entrenched the antecedent cold air is, there is
certainly some potential for mixed precipitation (the Canadian
in particular is keying in on this). This system will certainly
bear watching over the next few days.
Aviation /20z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Late afternoon...a cold front will be approaching from the west late
this afternoon. Ahead of the front lower ceilings and some visibility
restrictions with -shra and br. SW winds around 10 to 15 knots early
will become wrly after the front passes. Showers will diminish after
Tonight... some improving conditions early but then a trend towards
decreasing ceilings and visibilities around and after midnight with more -ra
early then -sn/-ra after 08z/09z. The amounts of -sn and how it will
affect visibilities is probably the main fcst challenge with the 18z tafs.
For now, mostly MVFR conditions are expected, but included some IFR
late for kilg/kmiv/kacy with a band of snow shown developing on some
fcst models. Confid in this period is moderate (at best) lower southeast
and higher northwest. Winds mostly northwest at 10 to 15 knots overnight.
Wednesday... poor conditions in the morning with MVFR or possibly
IFR conditions early (12z) before improving back to VFR by
around 15z/16z. The improving conditions will arrive across the wrn
sites (krdg/kabe) earlier and kacy/kmiv a bit later. Drier air
arriving will cause ceilings to diminish with good visibilities after any early
precip ends. Winds will become gusty from the west or northwest with g20 knots
possible by afternoon.
Wed night thru Thu night...VFR expected. Winds mostly under 10
Fri...VFR early then lower ceilings and visibilities with rain and fog late.
Fri night thru Sat night...lower ceilings/visibilities with rain and fog. Gusty
Sunday...VFR expected. Gusty winds.
the Small Craft Advisory was extended through the end of the short
term period (and into the long term period). Waves of 4-5 feet are
possible through much of the day Wednesday despite winds forecast to
be below criteria during the day. There will be a surge of westerly
winds overnight tonight with gusts of 20-25 kts. Winds will diminish
toward daybreak then another stronger surge of wind is forecast to
develop Wednesday evening with westerly winds gusting 25-30 kts.
Wednesday night/Thursday...W/NW wind gusts over 25 kts are
expected to persist into Wednesday night before dropping below
criteria by Thursday morning. Seas initially 3-4 ft are expected
to decrease to 2-3 ft by late Thursday.
Friday...increasing easterly winds and building seas expected,
especially later in the day, but expected to remain below Small
Craft Advisory conditions through the daytime hours. East winds
around 10 to 15 knots with gusts around 20 knots and seas
around 2 to 4 feet.
Friday night through Saturday...east winds will continue to increase
Friday evening and gusts are expected to approach 25 knots
by Saturday morning while seas build to over 5 ft by Saturday
morning. Winds will then turn to south and then west on
Saturday. An Small Craft Advisory will likely be needed in this period.
Saturday night through Sunday... westerly wind gusts likely
increase above 25 kts in this period and may even approach gale
force on Sunday. Seas will be initially 5-7 ft and potentially
decrease to around 5 ft by the end of the period.
Marine...Small Craft Advisory until 4 am EST Wednesday for anz450>455.