Scientific Forecaster Discussion
fxus61 kphi 180223
Area forecast discussion
National Weather Service Mount Holly New Jersey
923 PM EST sun Nov 17 2019
a coastal low will migrate from off the Carolina coast
northeastward tonight as high pressure exits the northeast. The
low will begin to accelerate Monday, reaching the Canadian
Maritimes by Tuesday. A weak wave of low pressure will cross the
region Wednesday before moving offshore Thursday as a ridge of
high pressure builds into the region. Another area of low pressure
and cold front are likely to move through the region by the end
of the week.
Near term /until 6 am Monday morning/...
920 PM update...precip at this hour still remains spotty and
mostly confined to areas near the coast. However there were some
flurries reported earlier this evening at Mount Pocono and also
in northwest New Jersey. So still think mostly light, spotty precip will tend
to increase from east to west through tonight but that it won't
amount to much. Only change with the forecast was to raise
temperatures slightly through tonight and this also resulted in
some minor changes to the weather grids for areas near freezing.
Overall though, not a significant change so no real change to
the Winter Weather Advisory that remains in effect.
Previous discussion...at the surface, high pressure to our
northeast is moving into the Canadian Maritimes while a coastal
low offshore of the Carolinas is slowly making its way north-
northeastward. Lower clouds associated with this system have
overspread the area today and some light drizzle has been
observed along the New Jersey and southern Delaware coasts. This drizzle may
transition to light rain along the New Jersey coast this evening as weak
isentropic lift occurs on the northern flank of the approaching
low. Generally expect that overnight precipitation amounts will
range from nothing measurable (particularly inland locations)
to a few hundredths near the coast.
There will be the potential for some freezing drizzle- light
freezing rain tonight into Monday morning over the Poconos and northwest
New Jersey. Due to the low quantitative precipitation forecast and shallow precipitation growth zone, any
ice accumulations in this area are expected to be quite light
(anywhere from a glaze to a few hundredths), but even this very
small amount could cause problems on untreated surfaces.
Consequently going Winter Weather Advisory covers this potential. It
is also possible that precipitation does not reach this far inland
until late enough Monday morning that temperatures will have warmed
Short term /6 am Monday morning through 6 PM Monday/...
the surface low will begin to accelerate northward tomorrow in
response to an approaching mid-lvl trough, and the low should be
more or less parallel to the area by late-morning/early afternoon.
Low clouds should remain entrenched over the area during the day,
and periods of light rain are likely. In general the pop & quantitative precipitation forecast
forecast remains uncertain as although there will be several sources
of lift, these for the most part will be weak (at least during the
day on monday). First we will have the potential for continued wrap-
around precipitation over primarily northern portions of the area,
while further south lift will begin to increase Monday afternoon in
response to the approaching mid-lvl vort/ speed Max. Additionally
the GFS and to some extent the hrw suite want to develop a low-lvl
reflection and associated confluence zone ahead of the mid-lvl wave
Monday afternoon which would result in a more focused zone of
precipitation (the ec is slower progressing this feature northward,
while the NAM is weakest).
Kept high temperatures similar to the previous forecast (e.G. On the
lower side of guidance) as persistent cloud cover and periods of
precipitation should not allow US to efficiently mix down the warmer
airmass aloft. Consequently expect low to mid 40s for most of the
area, with some upper 30s in the far north. If the precipitation is
more spotty than currently forecast, could see some locations in
southern New Jersey and Delmarva reach the upper 40s to even lower 50s.
Long term /Monday night through Sunday/...
a quite progressive pattern takes shape for the remainder of the
week and into next weekend with several vorticity maxima ejecting
out of the Canadian rockies into the eastern U.S. And a pair or
short wave troughs likely to traverse the Continental U.S. Through next
The 12z model runs continue to suggest a potent shortwave trough
will cross the Great Lakes within the polar jet, increasing negative
tilt as it does so. As the ocean/coastal storm accelerates off to
the northeast out of the mid-Atlantic, precipitation looks to
quickly fill in on the Lee side of the alleghenies into our
region as the vort Max approaches the region. This looks to
enhance upward forcing, with a likely substantial, though
somewhat narrow band of precipitation forming in a southeast to
northwest orientation. An investigation into model soundings
suggests an accumulating snow is becoming more likely in the
Poconos. Totals of course will be highly dependent on where this
precipitation forms and its intensity. There is the potential
for some stronger snow rates, so the forecast snowfall totals
here may end up being a little low. Wouldn't be surprised if
they end up increasing slightly with the following forecast. The
NAM nest is perhaps the most vigorous with the snowfall,
suggesting a few hours with rates of 1 in/hr may occur, yielding
2-4 inches across the Pocono plateau. Other guidance hasn't
quite bought on yet, with the GFS and Canadian solutions showing
only a slushy accumulation under an inch. This may be underdone
if the changeover occurs early enough Monday night with high
Irregardless, precipitation looks to start as rain Monday night,
changing over to a mix of rain, snow, and sleet, and eventually over
to all snow across the southern Poconos as precipitation rates
increase and the atmospheric column cools. This may extend into
Sussex County, NJ, though snowfall totals would be less than an inch
at most. As of now, snowfall totals look to range from a little
over an inch across the Pocono plateau to a couple tenths of an
inch from northwest New Jersey and perhaps a dusting into the northern
portion of the Lehigh Valley. Elsewhere, temperatures look to
be too warm to preclude any snowfall accumulation with lows
Monday night in the low to mid 30s.
Tuesday afternoon through Thursday continues to look fairly quiet,
though a weak perturbation could bring some cloud cover Wednesday,
but moisture looks limited enough that only some snow showers look
to form to our north. Highs should range from the low 40s across the
Poconos and northern New Jersey to the low 50s across Delmarva.
Another system still looks to affect the region late in the week,
though there is less agreement in its overall structure with the GFS
portraying a more positively oriented trough that is less vertically
stacked and the ec showing a more neutrally oriented trough with a
trailing/cut-off low settling over the four corner's region. Thus,
the European model (ecmwf) pushes the cold front through the mid-Atlantic a little
faster with clearing occuring by Friday night, yet the GFS still
positions the cold front to our west at this time and doesn't take
the front through our region until Saturday morning. Went with a
general chance to slight chance for showers Friday into Saturday
morning until further agreement is made. Highs Friday look to be in
the 40s and 50s then staying in the 40s Saturday behind the front.
The next concern will be what transpires with the four corner's low.
The ec develops a stronger surface low that attempts to merge with
the northern stream as a clipper-type shortwave ejects from Alberta.
This solutions paints more substantial precipitation across the mid-
Atlantic Sunday night into Monday, while the GFS places both
features a quarter to a half wavelength ahead, keeping the merger
over the open Atlantic, rendering mostly dry weather for our region,
save for a few snow showers across the Poconos. This will also be a
feature to watch over the coming days. Either way, highs Sunday will
range from the low 40s to the low 50s.
Aviation /03z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
This afternoon/tonight...primarily MVFR ceilings will prevail, with IFR
possible at miv and Acy. Some drizzle or light rain will be possible
particularly at miv and Acy. Northeasterly winds 10-15 kts, with
gusts 20-25kts before sunset. High confidence.
Monday... generally low-end MVFR (with potentially periods of ifr)
conditions prevailing with periods of rain possible at all
terminals. Winds shift more northerly then northwesterly in the
afternoon, with speeds generally around 10 kts (and coming down in
the afternoon). High confidence in winds, moderate confidence in
Monday night...MVFR cigs eventually turning VFR as rain moves out of
the region. Westerly winds generally from 5 to 10 knots. A few gusts
to 20 knots possible at Acy. Moderate confidence in winds and
Tuesday...generally VFR with westerly winds from 5 to 10 knots.
Moderate confidence overall.
Wednesday...generally VFR with northwesterly winds from 5 to 10
knots and gusts to 15 knots. Wing gusts to 20 knots possible at
Acy. Moderate confidence overall.
Thursday...generally VFR with westerly to southwesterly winds from 5
to 10 knots. Moderate confidence overall.
today/tonight... northeasterly wind gusts in the 35kt range will
continue into tonight, with gusts likely dipping below gale-force by
early Monday morning. Seas generally remaining 10-12 ft along the
Monday... northerly wind gusts in the 25-30 kt range, Monday
morning should dip below 25 kts by Monday afternoon and seas will
slowly come down into the 8-10 ft range by Monday afternoon.
Monday night...westerly winds from 10 to 15 knots and gusts to 20
knots, however, advisory-level seas from 5 to 8 feet will persist
through the night.
Tuesday...sub-sca conditions expected with westerly winds from 5 to
10 knots. Seas from 4 to 6 feet in the morning will drop to 2 to 4
feet in the afternoon.
Wednesday...sub-sca conditions in the morning may approach Small Craft Advisory
conditions by the afternoon with northwest winds from 10 to 20 knots
and gusts nearing 25 knots. Seas from 2 to 4 feet.
Thursday...generally sub-Small Craft Advisory conditions expected with southwesterly
winds from 10 to 15 knots turning southwesterly from 10 to 15 knots
with gusts to 20 knots. Seas building from 1 to 3 feet.
coastal flooding is expected to occur for the next two high-tide
cycles, through the day Monday, across coastal sections of New Jersey
and Delaware. The second high tide will be the higher of the two.
Through the night last night and through the day today, models have
trended downward with anomolies and resultant high-tide levels, likely
owing to weaker onshore winds and the fact that the coastal low itself
is still southeast of Cape Hatteras.
Though moderate flooding is still expected to occur on the Atlantic
coast of southern New Jersey and Delaware, it looks like it will be
more spotty along Raritan Bay and the adjacent Atlantic coast of
Monmouth County. Nevertheless, we still think the threat is high enough
here to warrant a continuation of the coastal Flood Warning for now.
Both Perth Amboy and Sandy Hook are still within a few tenths of a foot
from moderate flooding tomorrow afternoon. We have at least another 12
hours to access both model and observed trends before making
adjustments to headlines.
Bottom line...widespread minor tidal flooding is expected up and down
the New Jersey and Delaware coasts, and at the moment, the threat of a
more widespread moderate event lies south of Barnegat Bay.
The coastal flood advisory still looks good for the upper portion of
Delaware Bay (coastal sections of New Castle and Salem counties).
We still cannot rule out minor flooding on the tidal Delaware River on
Monday evening and the Eastern Shore of Chesapeake Bay Monday night.
There was some concern that we would see minor flooding across the
tidal Delaware River and portions of the Eastern Shore of Maryland
tonight. With the lower anomolies, that is no longer expected.
PA...Winter Weather Advisory until 10 am EST Monday for paz054-055.
New Jersey...Winter Weather Advisory until 10 am EST Monday for njz001-007-
Coastal Flood Warning until 5 PM EST Monday for njz012>014-
Coastal flood advisory until 4 PM EST Monday for njz016.
Delaware...coastal Flood Warning until 5 PM EST Monday for dez002>004.
Coastal flood advisory until 4 PM EST Monday for dez001.
Marine...Gale Warning until 6 am EST Monday for anz431-450>455.
Small Craft Advisory until 6 am EST Monday for anz430.