Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180533

Area Forecast Discussion
National Weather Service Mount Holly NJ
1233 AM EST Thu Jan 18 2018

Low pressure with its attendant frontal system will move off
the East Coast tonight. High pressure will build across the Gulf
coast through the end of the week, then offshore over the
weekend, bringing fair weather to the mid- Atlantic region. Low
pressure is forecast to develop over the central U.S. on Monday.
This low will move northeast through the Great Lakes Monday
night into Tuesday, pulling a cold front across the mid-
Atlantic area on Tuesday.


Quiet weather on tap through the overnight. Skies continue to
clear out, and winds for most of the area will diminish to less
than 5 mph. The exception will be along the southeast NJ coast
and into the Delmarva, where NW winds range from 10-15 mph with
gusts up to 20 mph.

For areas where winds are light, the combination of clear
skies, light winds, and new snow on ground will allow for
radiational cooling and temperatures will drop off

Will adjust hourly temperature grids going through the early
morning hours. Will also drop overnight lows by a few degrees
across the Poconos and Lehigh Valley.


On the heels of the low, a mid level short wave ridge is
expected to propagate over the region through the day tomorrow
resulting in mostly sunny conditions. At the surface, the
pressure gradient is expected to increase for a period tomorrow
as the surface high builds in. As a result, could see some gusty
conditions, but on land, not expecting gusts above 25 mph.

Temperature wise, we will still have cold air advection with the
northwesterly flow. As a result, expect highs to be from the mid 20s
to near 40 across the region, or about 5 degrees below normal.


The extended forecast will feature somewhat above normal
temperatures (for a change) and generally fair weather at least
through this weekend. A fairly strong frontal passage with
associated low pressure and precipitation is expected sometime
on Tuesday of next week.

By Thursday night the low pressure aloft now over the southern
Appalachians will be well offshore. A fast-moving shortwv trof
will swing across New England but should have little effect on
sensible weather over the mid-Atlantic region. Thereafter
through the weekend zonal flow aloft will prevail across the
north-central and northeast US. Meanwhile a large area of high
pressure centered along the GlfMex coast will gradually shift
east and off the southeast US coast by Sunday. Westerly flow
around the northern periphery of this high will help maintain
fair weather with a trend toward moderating temps, especially
starting Saturday.

A fairly deep trof aloft is forecast to move into the western US
over the weekend and into the central GrtPlns by Monday. In
response surface low pressure should develop over the Plains and
move eastward into the GrtLks by Tuesday. The associated cold
front should move through NJ and vicinity roughly in the Tuesday
morning time frame, although the latest ECMWF looks a bit
slower. Increasing SW low-level flow ahead of the low/front will
result in increasing moisture starting Sunday night. At that
time the forecast includes slight chance PoPs well north of PHL,
with the possibility of some freezing rain or drizzle,
depending on the degree of overnight surface cooling.

Forecast PoPs increase from chance on Monday to likely Monday
night with the approaching cold front. Depending on how quickly
cold air moves in, there could be some changeover to snow in the
Poconos late Monday night. Due to timing uncertainty, the
forecast maintains some chance for precip through Tuesday,
mainly in the morning. Forecast max temps for Tue are still
above freezing (and above normal) but cold advection aloft could
produce snow showers well N/W of PHL.

The air mass behind the front is not terribly cold and forecast
max temps for Wednesday look to be still slightly above normal.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Overnight...VFR conditions. After 09-10Z, wind speeds at 2000
feet will will increase to around 40 kt with light surface
winds. Will add a LLWS group to the 06z TAFs. High confidence.

Thursday...VFR/SKC. NW winds 10-15 KT with gusts up to 20 KT,
except for KPHL/KACY, where gusts up to 25 KT are possible.


Friday through Sunday...VFR conditions expected. West to
southwest winds, generally less than 10 kt. High confidence.

Monday...Mainly VFR conditions but occasional MVFR possible in
scattered showers.


Expect the highest winds, and most widespread Small Craft
Advisory conditions to occur late through mid morning Thursday.
Gusts near or above 25 kt are likely to continue through the
rest of Thursday. Therefore, have continued the SCA as is for

Small chance a short fuse Gale Warning may be needed for the De
Waters and lower De Bay in the 08-14z/18 time frame. Sct gusts
35 kt.


Thursday night...Will extend SCA on ocean to 1AM Friday for
continued 25 KT gusts. Otherwise, conditions expected to drop
below advisory levels.

Friday-Sunday...Conditions expected to remain below advisory levels,
but winds may periodically gust around 20 knots.

Monday...Increasing south winds with gusts possibly approaching
SCA levels late in the day.


The NOAA All-hazards weather radio transmitter in Sudlersville
has returned to service with the correction of earlier phone
line issues. RDG temp has rts.


MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ450>455.
     Small Craft Advisory until 10 AM EST this morning for ANZ430-


Near Term...Drag/Johnson/MPS
Short Term...Johnson
Long Term...AMC
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