Scientific Forecaster Discussion
fxus61 kphi 182339
Area forecast discussion
National Weather Service Mount Holly New Jersey
639 PM EST Sat Nov 18 2017
low pressure over the Ohio Valley will lift to the north and
east and into southeast Canada tonight, and then a strong cold
front will move across the region Sunday morning. High pressure
then builds in from the west and moves off the mid-Atlantic on
Tuesday. A cold front moves through the region Wednesday night.
Low pressure develops along that front and may impact the region
on Thursday. High pressure returns on Friday, followed by low
pressure passing north of the area on Saturday.
Near term /until 6 am Sunday morning/...
update: a few adjustments to hourly temps (upward) across
Delmarva and southeast New Jersey. Pops also adjusted according to recent radar
trends. Other showers will arrive over the area later this
evening ahead of the approaching cold front. Winds are slow to
increase this evening, so far.
An area of low pressure will move across the eastern Great
Lakes region and toward the northeast tonight. A strong cold
front associated with this low will approach the area overnight
tonight and toward Sunday morning. Southwest flow aloft will
continue across the area, with several short wave/vorticity
impulses moving across the area. A couple rounds of showers are
expected tonight across the are. The first will exit the are
this evening as the initial short wave moves past the area. Then
a brief dry period may occur for a time this evening. However,
a second short wave will approach the area around/after
midnight, leading to a second round of showers. Finally, as the
cold front approaches, the final round of showers will move into
the area toward daybreak Sunday. There is not much instability,
although the front and short wave/vorticity impulse are fairly
potent. So it would not be surprising to see an isolated
lightning strike or rumble of thunder, but the chances are
pretty small so we did not include them in the forecast. Precipitable water
values continue to be forecast to reach 1.00-1.25 inches, so
there could be some moderate, to occasionally heavy rainfall at
Another concern overnight is the increasing winds. Winds will
be increasing through the night and wind gusts of 25-35 mph are
possible through the night. It will likely not be gusty
everywhere overnight as mixing will not be very deep everywhere
during the night time period. However, as any showers move
through, and as the cold front approaches, gusts have a better
chance of mixing down. Winds have the potential to gust to
around 50 mph as the front moves through around daybreak, so we
have issued a Wind Advisory across the area.
Short term /6 am Sunday morning through 6 PM Sunday/...
the cold front pushes through the area around and shortly after
daybreak Sunday, and the rain showers will be ending as the
front moves through. The main concern for the daylight hours
Sunday will be the winds. Right as the front moves through, a
surge of wind is possible to occur, then the winds could
continue to gust 45-50 mph through the morning and into the
early afternoon hours. Therefore the Wind Advisory will continue
into the afternoon hours Sunday across the entire area.
Long term /Sunday night through Saturday/...
strong northwest flow continues night as low pressure lifts into
eastern Canada and high pressure builds into the Tennessee Valley and
Gulf Coast states. Winds will gust to 25-30 mph in the evening,
and will gradually diminish after midnight Sunday night. Though
precip will be over for the vast majority of the forecast area,
some lake effect snow streamers may make it into the Pocono
Mountains, and could result in some spots picking up 1/4" snow.
Cold night in store with lows dropping into the 20s for the
Poconos and northwest NJ, otherwise in the low 30s for the Lehigh
Valley, southern NJ, and the Delmarva. Wind chills will range
from the teens up north to around 30.
High pressure just north of the Gulf Coast will build east on
Monday, and will gradually move off the mid-Atlantic coast on
Tuesday. Chilly conditions on Monday with highs in the 30s up
north and in the 40s elsewhere will moderate back into the 50s
to near 60 on Tuesday as return flow sets up.
From there, low pressure develops off the southeast U.S. Coast
and lifts to the north along the coast as a cold front
approaches from the west. That front passes through the region
Tuesday night or Wednesday. Confidence is low for this
timeframe, as there is uncertainty with how far west that low
will track and how much precip will fall. For now, will follow a
blend of guidance and carry chance pops Tuesday night-
High pressure builds in from the west on Thursday, but models
are indicating another coastal low passing south and east of the
area during this time, and depending on how close it tracks,
more precip is possible for the area. Will carry slight chance
pops for southeast portions of the forecast area, but it will
take a couple of days or so before the details are ironed out
with this potential low.
Dry conditions on tap for Friday.
Low pressure passes north of the area Saturday and drags a cold
front through the region. Some snow is possible up north Friday
night, and then precip changes to rain on Saturday.
Aviation /00z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR conditions are in place across the area this
afternoon and evening. Temporary near MVFR conditions are
possible as showers move across the area late this afternoon,
but should remain VFR through most of the evening. As showers
increase overnight, conditions are expected to lower to MVFR.
This is especially true as a cold front moves across the area
around daybreak Sunday.
Winds will increase through the night, and could gust 15-25
knots for much the night, then increase after midnight, and
especially through daybreak as the cold front moves through to
around 25-35 knots.
Sunday...MVFR conditions are expected right around daybreak as
the showers move through the area, then a return to VFR is
expected through the morning hours into the afternoon. Winds are
expected to be gusting 30-40 knots through much of the day.
Sunday night...VFR. Some flurries possible at krdg/kabe. Northwest
winds 15- 20 knots with gusts up to 30 kt, diminishing to 10-15 knots
late. High confidence.
Monday through Tuesday...VFR. West winds 10-15 knots on Monday
become S 5-10 knots Monday night, and then 10-15 knots with gusts up
to 20 knots on Tuesday. High confidence.
Tuesday night through Thursday...potential for rain Tuesday
night/Wednesday, then again on Thursday with sub-VFR conditions.
Low confidence forecast.
a Gale Warning is in effect for all areas through Sunday night.
The Delaware Bay does not begin until 1 am, but the Gale
Warning for the Atlantic coastal waters is already in effect.
Sunday night...northwest gales continue Sunday night, but may end just
after midnight on Delaware Bay.
Monday through Monday night...northwest winds gusting to 25 knots on the
ocean waters, along with 4-6 ft seas.
Tuesday through Tuesday night...SW winds 15-20 knots with 25-30 knots
gusts on the ocean; SW winds gusting to 25 knots on Delaware Bay. Winds
diminish after midnight Tuesday night.
Wednesday...winds and seas subside to sub-Small Craft Advisory conditions.
Thursday...low confidence forecast with the potential for Small Craft Advisory
conditions on the ocean.
there is a potential for blow out tides on Sunday, especially
in the Delaware Bay and the tidal portion of the Delaware River,
where strong west-northwest winds will effectively drain water out of the
Bay. The low tide Sunday afternoon/evening seems to be the most
susceptible for low water concerns that could impact navigation
in the area.
PA...Wind Advisory from 5 am to 4 PM EST Sunday for paz054-055-
New Jersey...Wind Advisory from 5 am to 4 PM EST Sunday for njz001-007>010-
Delaware...Wind Advisory from 5 am to 4 PM EST Sunday for dez001>004.
Maryland...Wind Advisory from 5 am to 4 PM EST Sunday for mdz008-012-015-
Marine...Gale Warning until 5 am EST Monday for anz450>455.
Gale Warning from 1 am Sunday to 5 am EST Monday for anz430-