Scientific Forecaster Discussion
fxus61 kphi 192329
Area forecast discussion
National Weather Service Mount Holly New Jersey
729 PM EDT Sat Oct 19 2019
high pressure will continue to move offshore through the overnight.
Meanwhile, Post-tropical storm Nestor will skirt to our south
tomorrow, moving offshore into the open Atlantic. High pressure
builds into our region for a brief period before a cold front
approaches from the west Tuesday evening. High pressure brings a
return to mild and pleasant weather to end the week with another low
pressure center and cold front potentially moving into the mid-
Atlantic by next Saturday.
Near term /until 6 am Sunday morning/...
high will shift further east as Post-tropical storm Nestor crosses
through the Carolinas. For most of our region the only impacts we
will see overnight will be increasing clouds, though the leading
edge of the rain could nudge into Delmarva around dawn.
Given the increasing clouds and the winds shifting to onshore flow,
do not expect as efficient radiational cooling tonight as what we
saw this morning. The one possible exception is in the southern
Poconos and northwest New Jersey which will be the last to see clouds and
wind shift. However, the growing season has ended for Carbon,
Monroe, Sussex, and Warren counties which would be the most likely
to have frost. Therefore, no frost advisories or freeze warnings are
anticipated for tonight.
Short term /6 am Sunday morning through Sunday night/...
Nestor is expected to cross off shore of the Carolinas, leaving our
region on the northwestern fringe of the precipitation shield. NAM
continues to depict a track much closer to the coast than any other
guidance. Therefore, continued to favor a non-NAM blend for the
Sunday/Sunday night period.
Even ignoring the NAM, there continues to be a wide spread both
among models and with run to run consistency on the extent and
amount of rain across our region. In contrast to the 00z runs, most
of the synoptic models trended further east with the edge of the
precip shield. There was also a trend towards a later start time,
which seems reasonable considering where dewpoints are now; it may
take some time to get the boundary layer close enough to saturation
before we will see precip at the surface. I made minor adjustments
to the pops based on these trends, but hesitated to make any
significant adjustments given the poor run-to-run consistency.
As for the amount of rain, have gone with a middle of the Road
solution for qpf, with amounts of 1 -1.5 inches for Delmarva and southeast
NJ, less than an inch elsewhere. Model solutions range from less
than one half inch across the entire region to widespread 1 to 3
inches on the coastal plains. Given that the system has already lost
its tropical characteristics, and the relatively brief window of
opportunity for rain with this system, it doesn't appear a favorable
set up for widespread heavy rain.
Rain should quickly end tomorrow evening as the center of the system
continues to progress further off shore. Overnight winds will shift
to northerly and clouds will gradually clear. However, there isn't
expected to be any significant dry air advection before then, so
lows will likely be limited by how low dewpoints are by Sunday
evening - likely in the 40s and 50s across the region.
Long term /Monday through Saturday/...
overview...a progressive pattern will persist through the upcoming
week with a persistent trough across the western U.S. And ridging to
the east. A series of shortwave perturbations will attempt to nudge
this trough eastward, facing difficulty in eroding the ridge across
the East Coast.
High pressure will work its way across our area Monday as
a cold front moves toward the area Tuesday. This front will clear
the area by Wednesday, though the occluding low associated with it
will remain anchored across Ontario. A zonal mid-level flow pattern
will take place through the middle portion of the week, with a
surface high building across the eastern U.S. Through the early
portion of Friday. An amplified trough is forecast to dig through
the middle of the country, leading to the formation of a new surface
low across the Gulf Coast by Friday. This low looks to quickly cut
northward toward the eastern Great Lakes by Saturday along a cold
front as the associated trough remains in a positive orientation.
A brief respite Monday as high pressure builds into the region in a
north-south fashion. Breezy winds associated with Nestor will begin
to relax as the system moves off the east, away from our area.
Milder afternoon temps will spread across the region, with
widespread mid to upper 60s.
The western trough begins to lift north and east by Tuesday, as
surface low lifts across the Great Lakes. This low will push a cold
front across our area as it begins to fill and occlude Tuesday. The
motion of the front will continue to decelerate as the parent
surface low continues to weaken. There are indications that a new
surface low may begin to form along this front just offshore along
the New England coast, which warrants watching. As of now, the front
looks to clear our area, with high pressure leading to clearing
conditions by Wednesday evening.
High pressure will build behind the front leading to pleasant Fall
weather through much of the day Friday. Mild highs in the mid to
upper 60s will persist across the County Warning Area.
A rather amplified trough will eject out of the inner-mountain west
by Saturday, quickly developing a surface low out of the Gulf of
Mexico, which will zip northward toward the Great Lakes along a cold
front Saturday. This system will bring the next widespread rainfall
to the area Friday night through the day Saturday. Lower confidence
in high temperatures at this point with the timing of the rainfall
and position of the front as it moves into our region. At this
point, mid 60s ahead of the front and mid 50s behind it seem
Aviation /00z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...VFR conditions should continue for most if not all of the
night. Ceilings will gradually lower overnight, and could be as low
as 5000 ft, especially at ilg and miv, by 12z, but should remain
VFR. Rain is expected to nudge closer to the region, but should stay
south of the taf sites through 12z. Winds may be light and variable
for much of the night, but we should start to see light
southeasterly flow develop where it has not already. However, speeds
should remain very light at only around 5 kt. Moderate confidence on
the flight category remaining VFR at ilg and miv. High confidence
Sunday...expect conditions, primarily ceilings, to lower from VFR to
MVFR, for the Delaware valley taf sites (kphl, kilg, kpne, and kttn)
and coastal sites (kmiv and kacy) between 14 and 18z along with the
start of -ra from south to north. At this point, do not expect much
in the way of visibility restrictions, though periods of 3 to 5sm
are possible with some heavier rain. There is potential for IFR
conditions to develop in the afternoon and evening especially at Acy
and miv. There is also a low chance for at least intermittent IFR
conditions as far north as phl tomorrow afternoon, but should stay
mostly MVFR. At kabe and krdg, the forecast is also a bit more
uncertain, as these sites could be on the edge of the rain. They may
stay VFR through the day, but a period of MVFR looks more likely.
Expect easterly winds shifting to northeasterly through the day.
Wind speeds will be 5 to 15 kt, except at kmiv and kacy where wind
speeds of 10 to 20 kt are possible. High confidence on the overall
pattern, but moderate confidence on the timing and extent of flight
Sunday night...flight category should quickly improve to VFR as rain
clears out of the region between 21 and 03z. Winds should stay
northeasterly through 06z, but will be mostly northerly after 06z.
However, wind speeds should diminish below 10 kt. High
Monday...VFR through the early evening before
higher clouds move in. Ceiling reductions to MVFR through Monday
night. Northeast to east winds 10 to 15 knots, becoming
southeast at night. High confidence during the day; low
confidence at night.
Tuesday...MVFR/IFR conditions spread across the region through the
day with showers, then conditions should quickly improve to VFR
during the night. Moderate to high confidence on conditions below
VFR, but low confidence on the timing of flight category changes.
Easterly to southeasterly winds around 10 knots, shifting to
westerly at night.
Wednesday...mostly VFR. Westerly winds of 5-15 knots. Moderate
Thursday...VFR across the region with southwesterly winds 5 to
tonight, winds and seas should stay below Small Craft Advisory
criteria. Starting tomorrow morning, easterly winds will increase,
starting with the Delaware coastal waters and expanding northward.
Gales are expected for the Delaware coastal waters Sunday afternoon
and evening. For the New Jersey coastal waters and the lower
Delaware Bay, wind gusts up to 30 kt are possible Sunday afternoon
and evening. Seas on the coastal waters will subsequently increase
as well. At this point, wind gusts on the upper Delaware Bay are
expected to stay just below Small Craft Advisory criteria.
Monday...Small Craft Advisory conditions likely to persist with seas remaining
elevated from 5 to 7 feet. Winds begin to lessen to an extent from
10 to 20 knots out of the northeast.
Tuesday...conditions generally falling below Small Craft Advisory criteria with
easterly winds turning southerly from 10 to 15 knots and seas
dropping below 5 feet for the Delaware Bay and most of each of the
Wednesday...sub-sca conditions likely with westerly winds from 15 to
20 knots and seas from 1 to 3 feet.
Thursday...sub-sca conditions likely with southwesterly winds from
10 to 15 knots and seas from 1 to 3 feet.
Marine...Small Craft Advisory from 2 PM Sunday to 8 am EDT Monday for
Small Craft Advisory from 6 PM Sunday to 8 am EDT Monday for
Gale Warning from 2 PM Sunday to midnight EDT Sunday night for
Small Craft Advisory from 2 PM Sunday to 2 am EDT Monday for