Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kphi 170940 

Area forecast discussion
National Weather Service Mount Holly New Jersey
440 am EST sun Nov 17 2019

high pressure will migrate from New England today to the northern
Atlantic by Monday night. An ocean low will drift northeastward off
the Carolina coast today before accelerating northeastward to the
Canadian Maritimes by Tuesday morning. High pressure will build into
the eastern U.S. Wednesday and Thursday. A cold front is anticipated
to move through the region near the end of the week.


Near term /until 6 PM this evening/...
the coastal low has started to deepen overnight and will gradually
intensify through the day today as it lifts to the north and east.
Light streamer showers on northern extent of the low are already
starting to spread into southern New Jersey and the Delmarva but
given dewpoint depressions are 5-10 degrees I think most of the
light rain is evaporating before it reaches the ground. The rain
will eventually start pushing north this afternoon over the Jersey
Shore and we'll see minor accumulations of a couple of tenths or so
right along the coastline.

Winds will remain similar, if not stronger than today with gusty
northeast winds from 25 to 30 mph possible, and higher gusts from 45
to 50 mph in the Wind Advisory areas near and along the coast. With
highs in the low to mid 40s, this will lead to another chilly day,
especially once the rain begins.


Short term /6 PM this evening through 6 PM Monday/...
heading into the overnight hours Sunday night we'll see the precip
start to push further inland. As this happens, expect some freezing
drizzle to be on the leading edge of the precip shield. I dont
expect significant amounts of ice as the precip should be quite
light but for the southern Poconos we could see a few hundredths as a
light glaze on untreated surfaces. There wouldn't be enough to cause
power outages and for treated surfaces I expect minor to no impacts.
Nonetheless, a light glaze certainly could impact the southern
Poconos and so we've gone ahead and issued a Winter Weather Advisory
for freezing rain through early Monday morning.

Monday is a tricky day because as the low starts to pull east and
north, cold air will be wrapping in from the west. We could start at
the higher elevation sites in the Poconos see the rain switching
over in the late afternoon from rain to a mix and then snow heading
into the evening. Its certainly Worth watching as the namnest and ec
are starting to give indications that the precip will hold on longer
and perhaps a fair bit cold leading to a quick thump of snow. We
aren't quite ready yet to go all in on that as the forecast but its
in the realm of possible outcomes.

Temperatures Sunday night will be in the 30s with areas east of i95
above freezing and areas west generally below freezing. Mondays
highs should in the mid 30s to mid 40s along the coast.


Long term /Monday night through Saturday/...
main focus of the medium-range forecast was the intensifying vort
Max moving through the region Monday night and resultant potential
of wintry weather in the northern County Warning Area.

The 00z operational model suite has trended slower and stronger with
a northern-stream system moving through the northeast Monday night.
As the shortwave trough acquires an increasingly negative tilt, the
ocean storm will race north-northeast from offshore New England to
the Canadian Maritimes Monday night and Tuesday. Meanwhile,
immediately downstream of the vort Max (vicinity of the central
Appalachians at 00z tuesday), very strong lift will be generated via
a combination of differential cyclonic vorticity advection and
residual warm advection aloft on the west/southwest (wraparound)
side of the departing surface low. A band of precipitation will
break out in this favored area (likely eastern PA and nj), lifting
northeastward as the vort Max surges that direction via a 60-80+ kt
500-mb jet streak.

Residual warm air aloft will likely allow for liquid precipitation
to fall initially, and the question is what the surface temperatures
will be in the Poconos and vicinity. The colder operational models
are near freezing (and even these tend to bias too warm in this
area), so it is looking increasingly likely that there will be some
freezing precipitation during the evening hours near/north of the I-
80 corridor. A quick transition to snow (via the strong lift in the
column) is expected before the precipitation shuts off via cold/dry
advection surging into the area from the west/southwest. Given the
very strong lift expected, precipitation may be at least briefly
heavy during this transition. The 00z NAM nest (along with the high-
quantitative precipitation forecast look to the 00z ecmwf) promotes concern that there will be a
window of opportunity (albeit brief) for some heavy snow rates as
the precipitation transition occurs. The 00z GFS/CMC hint at this
potential as well, but the 00z NAM looks paltry in comparison. This
will need to be watched closely during the next couple of model
cycles to determine if a stronger consensus is reached and if the
more aggressive output seen tonight is what consensus will
eventually show.

For now, main changes to the forecast were to bump pops considerably
in eastern PA and New Jersey Monday night and to hasten the transition to
snow in the northwest County Warning Area. May need to extend pops into Tuesday
morning if the slowing trend continues with the operational models,
but did not bite quite yet (especially given the fairly rapid shut-
off of the precipitation expected).

The Tuesday afternoon through Thursday period looks quiet, with high
pressure building into the eastern U.S. Expect temperatures near
seasonal averages, as the source region of the building high is
fairly warm. Models are showing a northwest-flow vort Max moving
through on Wednesday, which will speed up the winds a bit and may
bring some showers to areas upstream. Cannot rule out the
possibility of a stray shower in the Poconos, but would like to see
a stronger signal of this in the models before adding pops.

Next system moves in late this week, with somewhat better agreement
on timing of the cold front among the GFS, CMC, and European model (ecmwf). Also
apparent is that the stronger lift with the front will be well to
the north of the area, with a trend toward fairly scant coverage of
precipitation in our area. Best timing appears to be Thursday night
and Friday, when pops are highest. Downstream of the front, decent
warm/moist advection should warm temperatures to well above seasonal
averages. As a result, most precipitation should be rain for the
County Warning Area. Overall, looks like a fairly low-impact system for the region.

Thereafter, things may get more interesting, as an ejecting low from
the Desert Southwest may phase with northern-stream troughing to
develop a strong surface wave/low by late next weekend into early
next week in the eastern U.S. Will need to watch this pattern
evolution closely.


Aviation /10z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Rest of tonight...VFR will slowly drop to MVFR shortly after day
break as clouds move in from the the south and east.Northeast winds
from 10 to 15 knots. Occasional gusts between 20 to 25 kts will be
through the overnight with gusts to 30 knots along the immediate
coast. High confidence in the winds, medium confidence in cigs.

Sunday...expect widespread MVFR ceilings. Strong northeasterly winds
from 10 to 15 knots and gusts to 25 knots. Stronger winds from 20 to
30 knots and gusts to 40 knots likely near and along the immediate
coast. Light rain will move into the region but confidence only
allows for inclusion of vcsh at Atlantic City as of taf issuances.
High confidence in winds, medium confidence regarding cigs and
precipitation timing.

Sunday night...MVFR with possible IFR conditions as rain falls
across some of the region, with highest chances at miv and Acy.
Winds remain gusty 20-30 knots, shifting from northeast early to
northerly by Monday am. Moderate confidence in flight categories,
high confidence in winds.


Monday...some improvement expected with continued periods of light
rain and possible sub-VFR ceilings. Northwest winds around 10 kts,
with gusts to 20 kts possible at kacy. Moderate confidence in
ceilings, high confidence in winds.

Monday night...restrictions possible with light rain (possibly a
wintry mix north of the terminals). Light west to northwest winds.
Moderate confidence in precipitation/restrictions; high confidence
in winds.

Tuesday through Wednesday night...mainly VFR with west to northwest
winds generally 5 to 15 kt. Higher gusts possible, especially on
Wednesday. High confidence.

Thursday...mainly VFR with winds becoming southwest up to 10 kt or
so. High confidence.


winds have diminished somewhat overnight and are mostly at advisory
levels on the Atlantic waters and Delaware Bay at this time.
However, as the ocean storm to our south slowly intensifies today,
expecting another surge of stronger winds by this afternoon. Gusts
are expected to approach 40 kt by afternoon, especially off the
southern New Jersey and Delaware coasts. Gusts to gale-force are
expected to continue through this evening before slowly diminishing
overnight. The Gale Warning expires at 6 am Monday and will need to
be replaced by a Small Craft Advisory once the gales end.

Advisory conditions will continue on the Atlantic waters through
Monday, even as winds diminish below criteria by afternoon, as seas
will be quite elevated. Seas of 8 to 13 feet are expected on the
Atlantic waters today and tonight, only slowly diminishing on Monday
(and remaining well above 5 feet). For Delaware Bay, advisory
conditions should end Monday morning.


Monday night and Tuesday morning...seas above 5 feet are expected on
the Atlantic waters.

Tuesday afternoon through Wednesday morning...sub-advisory
winds/seas expected.

Wednesday afternoon and night...northwest winds may approach
advisory criteria.

Thursday...sub-advisory winds/seas expected.


Tides/coastal flooding...
deep low pressure off the southeast and middle Atlantic coasts combined
with high pressure to our north will maintain a strong northeast wind
along the shores of Delaware and New Jersey through Sunday night. The
expected onshore flow will affect five consecutive high tide cycles and
should result in another lengthy period with the threat of tidal
flooding, similar to what occurred back around the 10th through 12th of

We have issued a coastal Flood Warning for moderate flooding on Sunday
and Monday for tidal areas of Delaware and New Jersey. While locations
up and down the Delaware and New Jersey coasts could see moderate
flooding, widespread moderate flooding is most likely to occur from
about Barnegat Inlet south. The daytime high tides will be the higher
of the two daily high tides.

As we get closer to Sunday and Monday, a coastal flood advisory
may be issued for the tidal part of the Delaware River.

Also, minor flooding is possible up into the upper part of Chesapeake
Bay on Sunday and Monday evenings, so an advisory may also become
necessary along the upper Eastern Shore as well.

The strong and persistent onshore wind will likely result in
significant beach erosion along the coasts of New Jersey and


Phi watches/warnings/advisories...
PA...Winter Weather Advisory from midnight tonight to 10 am EST
Monday for paz054-055.
New Jersey...Winter Weather Advisory from midnight tonight to 10 am EST
Monday for njz001-007-008.
Coastal Flood Warning from 8 am this morning to 5 PM EST
Monday for njz012>014-020>027.
Wind Advisory until 6 PM EST this evening for njz024-025.
Coastal flood advisory from 11 am this morning to 4 PM EST
Monday for njz016.
Delaware...coastal Flood Warning from 8 am this morning to 5 PM EST
Monday for dez002>004.
Wind Advisory until 6 PM EST this evening for dez004.
Coastal flood advisory from 11 am this morning to 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.



National Weather Service Glossary of Abbreviations