Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kphi 241601 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
1101 am EST Tue Jan 24 2017

Synopsis...
the coastal low will lift northeast, passing east of Cape Cod
this evening. A ridge builds over our region briefly tomorrow. A
cold front passes southeastward off the mid Atlantic coast
Thursday followed by a second cold front moving through our
region late in the weekend.

&&

Near term /until 6 PM this evening/...
the coastal low located off the New Jersey coast will continue
to drift east northeastward through today. The mid-level low
located off the Delmarva coast will continue to move east
northeastward as well. Several vorticity impulses will Circle
around the trough aloft, while low-mid level moisture will
continue to wrap around the backside of the surface low. This
will keep periods of showers moving back across much of the are
through the day.

Several ASOS stations across southern New Jersey have at times
reported -sn mixing in this morning, but with their temperatures
being 35-38 and dewpoints being 34-36, it's hard to believe
this is actually snow and not ASOS having a hard time
determining what to call the -ra or -dz that is actually
falling. If there is any potential for sleet or snow to mix in
with any rain/drizzle, it would be for areas along and north of
I-78. Further north across the higher elevations of
Carbon/Monroe, Pennsylvania and Sussex, New Jersey where
temperatures will remain below freezing through today, there
could continue to be some light freezing rain or drizzle.
Therefore we've kept the Winter Weather Advisory in place.

Northwest winds will remain gusty at times today with gusts
20-30 mph. The strongest winds continue to be expected across
southern and coastal New Jersey, southeast Pennsylvania, and
most of the Delmarva.

&&

Short term /6 PM this evening through 6 am Wednesday/...
as the coastal low begins to move into the open Atlantic east of
Cape Cod, northwest flow becomes established across the region
overnight. The column will dry rapidly as this occurs shutting
any remaining precipitation down quickly. Antecedent overcast
conditions will likely scour out rapidly after dark. Winds
should continue to diminish but will likely be elevated enough
to prevent ideal radiational cooling. Temperatures will cool to
the mid 20s in the southern Poconos to the mid to upper 30s near
the coast.

&&

Long term /Wednesday through Monday/...
Wednesday...for a brief period a short wave ridge will build
over our region. Thus, expect dry weather through the day. As
the low level ridge axis shifts east of our region through the
later half of the day, we should see some warm air advection.

Thursday...the warm air advection will be short lived however,
as the models generally sped up the timing of the cold front,
which is now expected to sweep off shore by mid day Thursday.
Any opportunity for precipitation should be brief, generally
along or just ahead of the front, but even that is somewhat
uncertain.

Friday through Monday...northwest flow pattern develops keeping
the cold air in place. In addition, a second cold front could
arrive in the region late in the weekend. In addition to cold
air advection, these northwest flow patterns also tend to result
in dry air advection, so at this point do not expect much in the
way of precipitation except possibly in the southern Poconos,
where some lake effect snow showers could sneak down into the
region.

&&

Aviation /15z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

Generally MVFR ceilings are expected through the day and into this
evening, except across central and southern New Jersey where
IFR ceilings could continue with clouds wrapping around the coastal
low. Periods of showers and drizzle will also wrap around the
low and affect the area through today as well until the low
slowly pulls away late this afternoon and evening. Visibilities in the
rain/drizzle will vary from MVFR to IFR in a few locations.
Conditions are expected to return to VFR later this evening and
overnight but may deteriorate back to MVFR after midnight and
toward daybreak Wednesday, especially for kabe/krdg.

Northwest winds generally 10-15 kts with occasional gusts 20 to 25
kts are expected through the day and into tonight. Gusts may
periodically drop in and out through tonight.

Outlook...
Wednesday...mostly VFR conditions expected.

Wednesday night and Thursday...small chance of showers which
could lower conditions to MVFR. Gusty westerly winds behind a
cold front.

Friday and Saturday...mostly VFR conditions expected.

&&

Marine...
the Gale Warning was continued across the northern Atlantic
coastal waters where it previously was, and has now been issued
for the rest of the Atlantic coastal waters and lower Delaware
Bay through 1 am tonight. While winds will be below gale force
for the next several hours, gusts are expected to increase back
to gale force late this afternoon and into this evening as
winds above the surface and low-level mixing increases.

Outlook... Wednesday...winds should diminish below Small Craft Advisory criteria
by mid day. Once they do so, sub Small Craft Advisory conditions are expected
for the remainder of the day.

Thursday through Friday...west wind gusts 25-30 knots possible and
seas could build above 5 feet.

Saturday...west wind gusts near or above 25 knots possible.

&&

Tides/coastal flooding...
the coastal Flood Warning was allowed to expire at 11 am as tide
levels have crested and will continue to fall through this
afternoon. There may continue to be high water levels for
another hour along the Back Bay areas causing some minor
flooding.

Based on the forecast guidance and the expected north-northwest
winds, we are not anticipating any additional coastal flooding
with the next high tide cycle this afternoon and evening.

&&

Phi watches/warnings/advisories...
PA...Winter Weather Advisory until 6 PM EST this evening for paz054-
055.
New Jersey...Winter Weather Advisory until 6 PM EST this evening for njz001.
Delaware...none.
Maryland...none.
Marine...Gale Warning until 1 am EST Wednesday for anz431-450>455.
Small Craft Advisory until 1 am EST Wednesday for anz430.

&&

$$
Synopsis...Johnson
near term...cms/Robertson

National Weather Service Glossary of Abbreviations