Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180419
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1119 PM EST Tue Jan 17 2017

.SYNOPSIS...
Low pressure forming near the New Jersey coast will intensify
eastward to the south of Cape Cod Wednesday. High pressure then
builds across the Eastern Seaboard Thursday. Weak low pressure
will pass through the region this weekend, and then a much larger
and stronger system will impact the area early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Overnight...light freezing rain and drizzle persists at or above
1000 feet in northern monroe and northern Sussex counties.
Otherwise patches of showers drizzle and fog will be occuring in
our forecast area. North to northeast wind PA and northern half
of Nj while low pressure forms near the s NJ coast with light
southwest winds Delmarva and s NJ turning northwest overnight.

Wednesday...Mostly cloudy with scattered showers through early
afternoon (drizzle north as well) as a sharp trough aloft passes
southeast through the mid Atlantic states. Cool north but becoming
milder south during the afternoon as skies brighten a bit toward
sunset. North winds near and northwest of I78 while a northwest
wind becomes gusty 20-25 MPH during the afternoon s NJ and Philly
area southward through the Delmarva. Max temps 5 to 10F warmer
than normal north and around 10 warmer than normal south.

&&

.SHORT TERM /WEDNESDAY NIGHT/...
Clearing south though it may remain mostly cloudy north. Temps 10
to 15 degrees above normal. Northwest wind.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Overview: The long term period will feature a series of low
pressure systems that will bring unsettled weather to much of the
Northeast and Mid-Atlantic. This period also features a jet stream
that will keep the Arctic air bottled up to the north. Although a
series of storm systems will impact the area during this time,
they do not have origins from the Arctic, so any cold air that
funnels into the Northeast and Mid-Atlantic will generally return
temperatures closer to normal. With deep S-SW flow that will
dominate the time frame due to a Bermuda high that will set up
over the western Atlantic, temperatures will run well above
normal, with high temperatures generally 10 degrees above normal,
for this time of the year.

Although a bit beyond the time frame for this forecast period,
the Climate Prediction Center 6-10 day outlook starting on Monday
indicates a high probability, 60-70% for NJ and Delmarva and
70-80% for SE PA and the Poconos, of above normal temperatures
next week.

The high will continue to slowly press east on Thursday, and will
be nearly overhead along the East Coast late Thursday night, and
then will move offshore on Friday. Skies clear out during the day
Thursday, and generally expecting mild conditions with highs in
the low to mid 40s across the Poconos, and in the low to mid 50s
across the rest of NJ, SE PA, and into the Delmarva.

The next system is rather weak and disorganized, and is almost
falling apart as it tracks from the Southern Plains and into the
Great Lakes and OH Valley. Nonetheless, a weak warm front
approaches on Friday afternoon, and some light precip will develop
over extreme SW portions of the CWA, generally across SE PA, the
Delmarva, and southern NJ in the afternoon, and then light precip
spreads to the north and east Friday night as that system lifts
northeast through the region. High pressure briefly builds through
the region on Saturday, but moves offshore by Sunday as a weak
cold front passes through. Conditions should generally be dry, but
cannot rule out a few passing showers.

Things get interesting for the start of the new work week. A
trough moves into the Western U.S. early in the weekend, and then
a strong closed H5 low moves into the Southern Plains/Gulf Coast
states on Sunday, where a storm system become more organized and
developed. This system will lift to the north and east, towards
the TN/OH Valleys, Sunday night and Monday, and will slowly work
its way through the East Coast Monday through Tuesday. Latest
GFS/ECMWF in decent agreement with the overall setup, so feel
reasonably confident going with high-end likely PoPs for Sunday
night through Monday night, with western portions of the CWA
bumped up to low-end categorical. With strong onshore flow ahead
of this system, can expect abundant low-level moisture to spread
into the region. GFS indicating PWATs around 1.5" during this
time, so can expect locally heavy rain from time to time. In
addition, GFS indicating an environment with CAPE (less than 100
J/kg) and 850-700MB wind speed 60-65 KT. Cannot rule out a rumble
of thunder Monday afternoon, especially south of I-76, but given
that it is mid-late January, may be a bit too far to include a
mention of thunder on Day 7. But will keep an eye out on it.

Lower confidence in the forecast by Tuesday. Models indicating
secondary low will develop off the Mid-Atlantic coast, and it
remains to be seen how that will impact the Northeast/Mid-
Atlantic. Will carry chance PoPs for most of the region, with
higher PoPs along the coast.

Monday looks to be the warmest, but wettest, day of the period
with highs ranging from the 40s across the Poconos to near 60 in
the Delmarva. Otherwise, as mentioned above, temperatures will be
warm.

&&

.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Overnight...IFR conditions with patches of LIFR in stratus/fog/drizzle
and scattered showers overnight. Light north - northeast wind except
vcnty KACY and KMIV where nearly calm or light southwest wind
turns northwest.

Wednesday...IFR conditions at sunrise will gradually improve to
MVFR cigs during midday with vsby improving to VFR as north to
northwest winds gradually increase with northwest gusts vcnty
KACY, KPHL, KMIV and KILG of 20-25 kt during the afternoon.
Scattered morning showers/drizzle will end early afternoon.

Wednesday night...Probably VFR sct-bkn aoa 3500 ft. Light
northwest wind.

OUTLOOK...

Thursday through Friday morning...VFR. Wind speeds should be 10
KT or less during this time.

Friday afternoon through Friday night...Sub-VFR conditions in
-RA.

Saturday through Sunday. Mainly VFR. Few passing showers with
brief sub-VFR conditions possible.

&&

.MARINE...
Short period of SCA northwest wind headline anticipated to be
issued 330 am Wednesday for the S NJ and De coasts.


OUTLOOK...
Thursday through Sunday...Sub-SCA conditions expected. Few
passing showers possible on Friday/Friday night.

Sunday night through Monday night...Easterly flow 20-30 KT. SCA
conditions likely, with gale force winds possible on Monday,
mainly on the ocean waters. Rain, possibly heavy at times.
Isolated thunderstorms possible Monday afternoon.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Freezing Rain Advisory until 7 AM EST Wednesday for PAZ055.
NJ...Freezing Rain Advisory until 7 AM EST Wednesday for NJZ001.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...MPS
Near Term...CMS/Drag  1118
Short Term...Drag/Iovino 1118
Long Term...MPS
Aviation...CMS/Drag/Iovino/MPS 1118
Marine...Drag/Iovino/MPS 1118



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