Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kphi 190126 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
826 PM EST Mon Nov 18 2019

Synopsis...
a coastal low pressure system will continue to move off the
middle Atlantic coast this evening and head towards the Canadian
Maritimes. A weak wave of low pressure will cross the region Wednesday
before moving offshore Thursday with high pressure building in behind
it. Heading into the end of the work week another low pressure system
will begin to move through the region.

&&

Near term /through Tuesday/...
not much has changed from earlier, a band of showers formed
across New Jersey and extended up into southeast New York about as expected. More
showers associated with the upper short wave are pivoting in
from Maryland attm. As the shortwave approaches, dynamic lift ahead
of this feature will provide the primary impetus for precipitation
this evening/overnight, and this lift (e.G. Dcva) is expected
to be more potent and deeper then the isentropic lift that has
generated the drizzle so far today. Consequently expect
precipitation to increase in intensity through the evening as
this feature pivots in, and analysis of 1000-850 streamlines
would also hint at the development of a sfc. Wave/confluence
zone over more or less the center of the forecast area.



Still expect that the heaviest precipitation will occur near
and north of this feature (roughly north of of a ttn-Abe line)
as it and the lagging mid-lvl wave pivot northeastward
overnight. Expect general quantitative precipitation forecast in this zone to range from about 2
tenths, to potentially as high as half an inch in northwest New Jersey. Some
lighter rain on the order of trace-few hundredths will be
possible elsewhere.

Regarding the potential for frozen precipitation, guidance thermal
profiles would favor a mostly rain event, particularly given the
warmth of the saturated layer. Can't totally rule out some initial zl-
freezing rain in some of the higher elevation areas of northwest New Jersey/Poconos but given
the fact that sfc. Dewpoints (and thus wetbulbs) are currently
several degrees above freezing think initial precip should be
predominantly "plain rain". On the tail end of the system the column
will be cooling, so a change to snow in the higher elevations of the
Poconos and northwest New Jersey is possible. However synoptic subsidence behind
the mid-lvl wave should keep accums below an inch (and largely in
the trace-half inch range). It is always a concern that in these
events (e.G quantitative precipitation forecast > 0.25 inches, and forecast temperatures in the mid
30s) unexpected accumulating snowfall can occur due to dynamic
cooling, but at this point guidance seems to point to a primarily
rain event.

&&

Short term /Tuesday night through 6 PM Tuesday/...
Tuesday should be much quieter weather-wise in the wake of the first
mid-lvl wave. A relatively dry westerly flow will prevail over the
area, and although a secondary/weaker low will pass offshore it
should not impact the area. Cloud cover will generally be less than
the last couple days although there may be some residual low clouds
in the morning, and then in the afternoon some high clouds should
spread from S-north ahead of the next shortwave. High temperatures will
generally be in the low-mid 50s and this combined with weaker winds
should make it feel more pleasant than the brisk NE flow of the past
weekend.

&&

Long term /Tuesday night through Monday/...
progressive is the name of the game in the extended forecast into
this weekend.

Summary...a weak disturbance will cross the region Wednesday as the
coastal storm complex continues to exit the region and enters the
Canadian Maritimes. Meanwhile into Thursday, a stronger storm system
will begin to evolve as cyclogenesis takes place across the Great
Plains, developing a mature Colorado low. This storm system will be
the next feature to watch by the end of the workweek as it pushes
across the Great Lakes and drags a cold front toward the mid-
Atlantic and northeast Friday into Saturday. High pressure will
begin to build eastward in its wake, leading to a quiet start to the
workweek next week.

A weak disturbance will skirt out of the Great Lakes and into the
mid-Atlantic Wednesday as an upper-level jet digs southward.
Moisture will be limited through the region, thus only a few clouds
are expected, save for a snow shower or two in the Poconos and
points north. Highs will be just a tad below average in the 40s to
low 50s for this time of year.

Quiet weather Thursday through early Friday as high pressure builds
across the region. A warm front will transition northward through
the region Thursday ahead of the developing extratropical cyclone
across the plains. Therefore, highs will moderate a few degrees each
day reaching the upper 50s to near 60 across Delmarva by Friday.

There is still some disagreement over the evolution of said system,
but at the very least, global model guidance appears to agree that
the primary low will move out of Ontario and Quebec and into the
Canadian maritime provinces into Saturday morning, drawing a cold
front through the Great Lakes and into the region sometime Friday
night and into Saturday morning. The tail end of this system still
remains somewhat of a mystery as both the GFS and ec form a
stretched pv feature from the Southern Plains into the northeast,
then developing another surface low as this energy ejects into the
southeast Saturday into Sunday. The big question is how far north
and fast does this system evolve? If it develops more quickly, as
the ec solution suggests, another widespread precip event may be in
store for Saturday night and Sunday. On the other hand, the GFS
suppresses the southern fringe of this pv feature and keeps the
evolving feature south of the mid-Atlantic and into the Carolinas. A
clipper-like feature, as noted in yesterday's discussion, is also of
interest in case these features emerge. This appears less likely
given this morning's model runs. Cooler weather returns behind the
main cold front with highs generally in the 40s across the County Warning Area
Saturday and Sunday.

Monday looks fairy quiet as high pressure begins to build across the
southeast. A weak mid-level wave looks to travel through the long-
wave trough as the aforementioned evolving low shifts offshore, but
this is not expected to noticeable affect the weather at this point.
Highs should reach into the mid to upper 40s across the region,
maybe reaching 50 across Delaware and Maryland.

&&

Aviation /01z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Tonight through Tuesday morning... mostly MVFR, with rain expected
roughly Acy-phl-Abe and northward. Some periods of VFR possible at
ridge/ilg with IFR cigs possible generally north of phl. Winds
generally 5 kts or less and favoring a westerly component if not
variable.

Tuesday... some initial MVFR cigs/vsbys may linger into Tuesday
morning although expect recovery to VFR by 15z at all sites. Winds
generally west/west-northwest around 5-10 kts. High confidence.

Outlook...

Wednesday...generally VFR with northwest winds from 5 to 10 knots
and gusts up to 20 knots.

Thursday...VFR with westerly winds around 5 knots with gusts
to 10 knots turning southerly in the evening.

Friday...restrictions possible as rain showers enter the region
ahead of a cold front. Westerly winds from 10 to 15 knots and gusts
to 20 knots.

Saturday...restrictions possible in the morning as a cold front
exits the region and moves offshore, bringing rain showers with it.
West-northwesterly winds from 5 to 10 knots and gusts to 15
knots.

&&

Marine...
Delaware bay: winds and waves are expected to stay below Small Craft
Advisory conditions tonight and Tuesday.

Delaware bay: winds and waves are expected to stay below Small Craft
Advisory conditions tonight and Tuesday.

New Jersey and Delaware Atlantic coastal waters: winds and seas will
continue to gradually diminish. However, seas will stay elevated
above 5 feet through Tuesday morning, before finally dropping below
Small Craft Advisory criteria Tuesday afternoon.

Outlook...

Wednesday...sub-sca conditions in the morning will give way to
possible advisory-level gusts past 25 knots out of the northwest in
the afternoon and evening. Seas building from 2 to 4 feet.

Thursday...sub-sca conditions expected with westerly winds around 10
knots and gusts to 15 knots. Seas from 1 to 3 feet.

Friday...sub-sca conditions in the morning may give way to advisory-
level southerly winds as gust may approach 25 to 30 knots in the
afternoon and evening ahead of a cold front. Seas building to 3 to 5
feet.

Saturday...Small Craft Advisory conditions possible in the morning with northwesterly
winds gusting from 25 to 30 knots. Winds should die off behind the
cold front and drop below advisory criteria to 10 to 15 knots with
gusts from 15 to 20 knots in the afternoon. Seas ranging from 4 to 6
feet in the morning to 2 to 4 feet in the afternoon.

&&

Tides/coastal flooding...
now that winds are shifting offshore, tidal departures should
continue lower, and the high tide cycle that just passed should
be the last of concern as tidal levels are lowering back below
minor flood levels. The next astronomical high tide is lower
than the previous cycles, and by the next cycle, departures will
be even lower. The are two exceptions where levels remain above
the advisory-minor flood level. This is Barnegat Bay, to the
north of Barnegat Inlet, and its tidal tributaries as well as
Little Assawoman Bay. We will have a coastal flood statement for
these areas until tidal levels lower.

For Chesapeake Bay, Claiborne may get close to or just barely reach
minor flood levels, but they are not expected to reach advisory-
minor levels.

For the tidal Delaware River, points should either remain just below
or just barely reach minor flood levels, but they are not expected
to reach advisory-minor levels.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory until 2 PM EST Tuesday for anz450>455.

&&

$$
Synopsis...Davis
near term...Carr/po
short term...Carr

National Weather Service Glossary of Abbreviations