Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 290119

Area Forecast Discussion
National Weather Service Mount Holly NJ
919 PM EDT SAT MAY 28 2016

A Bermuda high will maintain very warm weather with generally
southwest winds over our area through Monday. Low pressure
associated with Tropical Storm Bonnie should remain well to our
south. However, moisture from this system will be drawn northward
Sunday into Monday. High pressure will build in Tuesday through
Thursday, then a frontal system is forecast to approach from the
west late in the week.


High pressure anchored well off the Mid Atlantic coast will continue
to dominate our weather through tonight.

With the loss of day time heating, earlier convection has
dissipated, so removed mention of showers through the remainder
of the evening. Clear to partly cloudy through the night with the
potential for local fog to develop. This may have the most
opportunity where earlier rainfall occurred across the far
northern areas. Otherwise, it will be a warm night.

The temperature and dew point grids were adjusted based on the
latest obs, then the lamp/lav guidance was blended in. The pops have
been adjusted based on radar trends.


Sunday will start out dry, but moisture associated with Tropical
Storm Bonnie will move northward during the day. Across the southern
areas, showers could move in late morning to early afternoon, but
most areas will hold off until later in the afternoon. The northern
areas may remain dry through the balance of the day. Once the
showers start, some locally heavy rain may occur given increasing PW
values especially across the Delmarva. Given the idea of some more
cloudiness, temperatures are forecast to be a bit cooler.


It looks like the most significant weather will be occurring at
the beginning of the long term period, i.e., Sunday night into
Monday. At that time rather deep moisture, PWAT up to 2 inches,
from Tropical Storm Bonnie is forecast to move across the area
with widespread showers and T-storms. Although CAPE and UVV seem
to be rather limited, believe some areas could see 1 to 2 inches,
depending on how the convection sets up. Locally higher amounts
are possible. Heaviest rain should occur overnight Sun night into
Mon morning, then shift SE and gradually decrease through
afternoon and evening of Memorial Day.

The pattern changes some from Mon into Tue/Wed as the upper trof
currently over the central US lifts NE and suppresses the East
Coast upper ridge. This results in more westerly winds and drier
air. However, some remnants of the tropical circulation are
forecast to remain invof east NC through mid-week and could
result in some showers well S of PHL. This is rather uncertain and
is not strongly represented in the PoP/Wx grids.

Surface high pressure is forecast to build SE out of Canada and
across New England by Wed. This will result in onshore flow with
slightly cooler (but near normal) daytime temps and somewhat higher
RH. Another shortwave trof and associated frontal system is forecast
to approach the area on Fri/Sat. The latest GFS and ECMWF are
somewhat similar with this feature although the GFS is a bit more
amplified. The forecast reflects increased chance for showers and
diurnal T-storms for this time.


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

Tonight...Mostly VFR conditions expected through 06Z. After 06Z,
fog should develop at most terminals overnight resulting in MVFR
visibilities. It is possible local IFR occurs, however confidence
is not high. Southerly winds diminishing to 5 knots or less.

Sunday...MVFR/IFR visibilities to start for some terminals due to
fog, otherwise mainly VFR. Clouds increase from south to north as
moisture from Tropical Storm Bonnie moves northward, with ceilings
nearing MVFR toward evening for some areas. While some showers or
thunderstorms should develop especially in the afternoon, these may
be mainly west and south of KPHL. South to southwest winds up to 10
knots, although turning south-southeast at KACY, KILG and KMIV.

Sunday Night and Monday...MVFR to IFR conditions are likely in
low clouds, fog, and +SHRA. Sustained winds mostly under 10 kt.

Tuesday through Thursday...Mainly VFR conditions. Sustained winds
mostly under 10 kt, with some daytime gusts 10 to 15 kt.


No marine headlines are anticipated during the near and short
term periods.

Sub-SCA conditions are expected through early to mid-week. Some
reduced VSBYs are possible in rain and fog Sun night through Mon


There is some potential for heavy rain and localized flooding from
Sunday night through Monday. This is due to an influx of tropical
moisture from Tropical Storm Bonnie. PWATs are forecast to be near 2
inches, well above normal for late May. Depending on how the heavier
showers and t-storms set up, some locations could receive 2 inches
or more of rainfall. This may result in localized flooding. The
potential for heavy rain was added to the forecast.




Near Term...Gorse/Johnson
Short Term...Gorse/Nierenberg
Long Term...AMC
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