Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 211805
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
105 PM EST Mon Jan 21 2019

.SYNOPSIS...
Deep low pressure will remain across the Canadian Maritimes today
while arctic high pressure builds towards the area. The high will
crest over the area Tuesday before heading out to sea. Low pressure
will move into the upper Great Lakes region Wednesday and then down
the Saint Lawrence Valley Thursday. Its associated fronts will affect
the Middle Atlantic region both days. More high pressure will follow
for Friday and Saturday. A coastal storm may affect our weather next
Sunday and Monday.
&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1 PM Update...We have allowed the Wind Chill Advisory to expire
and converted the Wind Chill Warning for Carbon and Monroe to an
advisory and extended it to 6 AM Tuesday.


920 AM Update...No major changes to the forecast with this
update...just some minor adjustments to hourly temperature and
sky cover grids based on latest obs and trends.

Previous Discussion: Bundle up! Today is the day we get the
full effect of the cold front that moved through yesterday. In
the wake of the cold front that moved through yesterday,
temperatures will be about 20 to 25 degrees below normal, with
highs today around 30 degrees lower than Sunday`s highs.

As for winds, the pressure gradient will remain quite strong through
the day. However, pressure rises will be decreasing, and with it the
isallobaric component of the wind. Therefore, will continue with a
wind advisory only over the eastern coastal plains and portions of
Delmarva. Further northwest, have kept the forecast just below wind
advisory criteria for now, but will be watching this closely through
the morning.

The combination of these temperatures and winds will mean very low
wind chills. Many locations will not see wind chills above 0 through
the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Pressure gradient finally begins to relax this evening, and with it,
we should see winds drop off significantly. Even so, with
temperatures in the single digits and winds still in the 10 to 20
mph range overnight, some locations could reach wind chill advisory
criteria for a second night in a row. The areas most at risk for
this are the southern Poconos and northwestern NJ. For now though,
will hold off on issuing a second wind chill advisory until the
current one expires.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
The arctic high pressure that has brought the cold temperatures will
be centered across the region Tuesday morning with the coldest air
already have passed thru the area. Gentle warm advection will begin
Tuesday with highs still below normal, but more than 10 degrees
milder than Monday. Winds chills will still be very cold in the
morning, but moderate by day`s end. Fair weather is expected Tue
and Tue night with increasing clouds Tue night. Temperatures Tue
night will remain steady or slowly climb.

Precipitation will arrive across the area Wednesday as low pressure
moves into the upper Great Lakes area and its associated fronts
approach. By in large, precipitation will be rain for most areas.
The exception will be Wed morning and possibly into the early
afternoon  where some mixed precip could occur for for the areas N/W
of the Delaware Valley. Right now, we are calling for some light ice
accums across the southern Poconos and northern NJ, but the forecast
for precip type and amounts is rather low confid attm. We could
end up adding some snow for the Poconos in future fcsts, but at
this time only a light accum would be expected. Any small delay
in arrival time would limit any mixed precip even occurring. We
will have a better handle on this p-type issue later today or
tonight. Warm air will continue to overspread all areas later
Wed, so all rain is expected Wed afternoon and into Thursday. A
cold front will cross later Thu ending the precip, but bringing
in cooler temperatures again. We will continue with the likely
and categorical pops. QPF will again be in the 1 to 2 inch
range for the Wed-Thu period.

Mostly fair weather is expected from Thu night into the first half
of the weekend. More cold air will arrive behind the departing
system for Fri/Sat. This cold air will not be the deep arctic chill
that we are presently experiencing however. Readings will be 5 or so
degrees below normal Fri and perhaps 10-12 degrees below normal for
Saturday. Another short spell of cold air with moderating temps
and a renewed chc for precipitation for next Sunday and into
Monday. The latest 00Z models are showing varying solutions, not
surprising. So mostly chc pops in the fcst for now. The EC/CMC
are showing a coastal system for this period while the GFS
pushes the energy offshore with no development.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR conditions. Gusty northwest winds continue with gusts up
to 40 kt possible at times at KACY and KMIV. At other TAF sites,
gusts up to 35 kt are possible.

Tonight...VFR conditions Northwest winds should be gradually
diminishing to near or below 20 kt.

Outlook...

Tue/Tue night...VFR. Increasing clouds Tue night. Light winds.

Wed/Wed night/Thu...Sub-VFR with lowering CIGS and rain with
some snow N/W Wed morning. South winds around 10 knots.

Thu night...Improving conditions. Chance for snow N/W rain S/E.

Fri...Mostly VFR expected.

&&

.MARINE...
Gale force gusts are expected to continue at least into this
evening. Through the evening we should see winds begin to decrease
and by late this evening, winds may be below gale force on the
Delaware Bay. On the Atlantic coastal waters, gale force gusts are
likely to continue for much of the night.

Another concern is freezing spray, in fact the first significant
freezing spray event of the season. Moderate freezing spray has
already developed. On the upper Delaware Bay, heavy freezing spray
has already developed, where the freezing spray advisory has been
upgraded to a warning. It is possible that localized heavy freezing
spray will occur in other locations through the day. However, at
this point, it is unlikely it will be widespread. Therefore,
continued with a freezing spray advisory on the rest of the waters.
Freezing spray is likely to continue at least as long as gales
continue.

Finally, our last marine concern today into tonight is the potential
for low water levels. Thanks to the full moon today and the strong
off shore flow, water levels at the time of low tide will be much
lower than normal. At this point, the area with the biggest risk of
reaching at least 2 feet below MLLW is the Delaware Bay, where a low
water advisory has been issued. On the Atlantic coastal waters,
although we will be below MLLW at the time of low tide, it looks
like we should stay just above criteria, so will hold off on a low
water advisory at this time. On the tidal Delaware River, it could
also get close, but will hold off for now, until we see how tidal
forecasts verify on the Delaware Bay.

Outlook..
Lowering winds and seas with high pressure for Tue and Tue
night. Fair weather expected.

Wed-Fri...SCA conditions expected much of the time. Rain Wed-
Thu. Fair Thu night and Fri.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Chill Advisory until 6 AM EST Tuesday for PAZ054-055.
NJ...Wind Advisory until 6 PM EST this evening for NJZ012>014-
     020>027.
DE...Wind Advisory until 6 PM EST this evening for DEZ002>004.
MD...Wind Advisory until 6 PM EST this evening for MDZ015-019-020.
MARINE...Freezing Spray Advisory until 4 AM EST Tuesday for ANZ450>455.
     Gale Warning until 4 AM EST Tuesday for ANZ450>455.
     Heavy Freezing Spray Warning until midnight EST tonight for
     ANZ430.
     Low Water Advisory until 10 PM EST this evening for ANZ430-431.
     Gale Warning until midnight EST tonight for ANZ430-431.
     Freezing Spray Advisory until midnight EST tonight for ANZ431.

&&

$$
Synopsis...O`Hara
Near Term...Fitzsimmons/Johnson
Short Term...Johnson
Long Term...O`Hara
Aviation...Johnson/O`Hara
Marine...Johnson/O`Hara


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