Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 140852
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
352 AM EST Sat Jan 14 2017

.SYNOPSIS...
An inverted trough associated with low pressure over the southeast
states will persist near our region through Saturday. High pressure
over the Mississippi Valley will move into our area on Sunday and
offshore on Monday. Low pressure traversing the Great Lakes sends a
warm front through our region on Tuesday, followed by a cold front
on Wednesday. An area of high pressure is expected to settle over
the Appalachians Thursday into Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pressure to the north will move off the New england coast this
afternoon. Meanwhile, weak low pressure and a warm front will be
south of the area. This weak low and front will try to send some
warmer humid air over cooler air at the sfc. A mix of precipitation
is expected today, but the later starting times (compared to
earlier fcsts) tend to lead us to believe that snow/sleet are
favored across the north and sleet and some rain over Delmarva.
There is still the possibility for some freezing rain, but the
amounts will be very limited and probably restricted to the wrn most
areas of the forecast area. We have decided to issue a Winter
weather advisory for a small glazing potential at this time for
Chester, Cecil and Kent MD. It`s possible that the area could be
expanded later. The confidence in p-types is rather limited. The
good thing is that with the system being rather weak is that amounts
will be light. Snow accumulations will probably only be an inch or
so. Roads may become a bit slippery later today, so be prepared for
some slower travel across the area.  Temperatures today will reach
the low 30s over the far north and close to 40 over srn Delaware.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
The system from the near term will be advancing across the area this
evening and it should more offshore tonight. Pops will decrease this
evening, but low clouds will remain thru the night. Temperatures will
drop into the upper teens/ low 20s over the north and upper 20s/low
30s south. Winds will shift to NW tonight behind the low which will
be offshore. The winter weather advisory will be up thru midnight,
but may be taken down earlier if the threat for freezing rain is
done by then.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
The mid-level flow features a shortwave moving southward along the
west coast of the U.S. this weekend, lifting a closed low northeast
out of the four corners into early next week. Meanwhile, a complex
northern stream features several shortwaves near the U.S./Canadian
border. The streams remain largely separate with little in the way
of phasing, with the development of a slow moving storm system over
the Mississippi Valley early next week, moving slowly eastward thru
mid-week.

This storm system will lift a warm front northward through our area
on Tuesday, followed by a cold front on Wednesday. These features
will be the primary focus for precipitation during this time frame,
including the potential for a wintry mix Monday night into Tuesday
morning, and heavy downpours with the frontal passage on Wednesday.
There is uncertainty with regard to the timing and extent of wintry
precip, although the models have come into better agreement on the
timing of the cold frontal passage.

A relatively warm period is in store with daily average temperatures
above normal during the Sunday thru Friday time frame. Indications
are not quite as warm as this past week, thanks to additional mid-
latitude blocking over Atlantic Canada, which will suppress heights
somewhat. With the anomalous warm pattern over the past week, NWP
guidance was biased cold. Given a somewhat similar pattern, went
above guidance, especially Tuesday and Wednesday in advance of a
cold front.

Fair weather is expected Sunday into Monday with an increasingly
anticyclonic flow aloft building in high pressure at the surface.
We expect ideal radiational cooling conditions Sunday night with
high pressure directly overhead. As a result, went several degrees
below guidance at the typically colder locations outside of the I-95
corridor. With the approach of a warm front Monday night into
Tuesday, an overrunning regime will setup over the region.

The lift is fairly weak and dry air at the surface will discourage
precip initially. Model soundings already indicate a significant
above freezing layer aloft (warm nose) which will favor more sleet
over snow, with a changeover to freezing rain. With the lack of warm
air advection in the boundary layer and a dry air mass in place, we
favored colder model 2-meter temperatures. There is still a lot of
uncertainty in terms of the amount of precipitation that can be
generated, as well as a dominant p-type, if any. At this time, the
area most favored for wintry precip would be northwest of the NJ
Turnpike/I-95. Stay tuned.

Patchy fog is also possible Tuesday and especially Tuesday night,
mainly northwest of the NJ Turnpike/I-95. A fairly robust short-wave
will move accompany the cold frontal passage on Wednesday. Expect
some heavier downpours as a result, although the front will be
progressive enough to limit rainfall amounts only to around a half
an inch. In addition, lapse rates approach 6.5 C/Km, along with weak
ML CAPE and Showalter values falling to near zero. As a result,
cannot rule out some thunder across the region. Fair weather is
expected to return for Thursday.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

While clouds will be increasing across the area this morning, VFR
conditions are expected for much of the day. Winds will mostly be
from the NE to E this morning before becoming somewhat variable and
light for the rest of the day. Clouds will lower this afternoon with
the approach of a disturbance and MVFR conditions are expected by
late afternoon. Light snow possibly mixed with sleet will occur
across the area south of KRDG-KTTN. IFR conditions and lower vsbys
also south of KRDG-KTTN this evening. Confid in precip types not the
best, but amounts will be light. Precip will end this evening, but
cigs/vsbys in fog will be slow to improve overnight.

OUTLOOK...
VFR conditions expected across all the terminals Sunday and Monday.
With the approach of a warm front Monday night into Tuesday, there
is a strong signal for widespread MVFR conditions during the day on
Tuesday continuing into Wednesday. IFR conditions are also possible
at times, especially Tuesday night.

&&

.MARINE...
Strong high pressure to the north will move offshore today while a
disturbance moves by to the south. The pressure gradient will favor
N to NE winds this morning, before winds veer to E then SE by
afternoon. Winds should continue to veer to SW then W tonight. Winds
speeds will be around 10-12 knots early today then decrease a little
this afternoon. Winds and seas will remain below SCA criteria thru
the period. Light snow/rain expected this afternoon and evening.

OUTLOOK...
Tranquil conditions across the waters Sunday into Monday with high
pressure overhead. A southerly flow will setup over the waters on
Monday night into Tuesday in advance of a cold front. Wind gusts may
reach Small Craft Advisory criteria Tuesday night into Wednesday. In
addition, seas will approach 5 FT.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 7 AM this morning to midnight EST
     tonight for PAZ101-102.
NJ...None.
DE...None.
MD...Winter Weather Advisory from 7 AM this morning to midnight EST
     tonight for MDZ008-012.
MARINE...None.

&&

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



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