Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 240127
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
927 PM EDT Tue Apr 23 2019

.SYNOPSIS...
A cold front extended from the eastern Great Lakes to the
middle Mississippi River Valley this evening. The front will
progress to the southeast and it should pass through our region
late tonight. High pressure is expected to follow for Wednesday
into Thursday. Low pressure is forecast to move from the Great
Lakes to the northeastern states on Thursday night and Friday.
The low is anticipated to pull a cold front through our region
late on Friday. The weather pattern is expected to remain
progressive with another weak low and cold front following a
similar path on Sunday. High pressure and a warm front are
anticipated early in the new week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As advertised, sprinkles and showers are moving through the
forecast area. A few observations are showing the light
precipitation, but visibilities are not being affected. The
weather grids were adjusted this evening to reflect a quicker
arrival by a few hours. Albeit light, the showers were much more
extensive earlier this afternoon than any hi-res model
depicted. The coverage has diminished the last few hours. Some
lighting is still occurring to the west of Reading. Grids across
our far western zones do have thunder mentioned.

Previous discussion...
A very warm, but not humid, afternoon in progress across much
of the area (cooler along the coast due to a sea breeze.

An upper-level trough will continue to progress eastward from
the Great Lakes and adjacent Canada tonight and near New England
toward daybreak. This will drive surface low pressure well to
our north, however its associated cold front will cross our
region late tonight and early Wednesday morning. Clouds will be
on the increase ahead of the cold front, especially for the
northern and central areas.

The main short wave energy associated with the trough tracks
well to our north, however the model guidance indicates that the
tailend of a short wave moves across our northern and western
areas by the midnight hour. This will be accompanied by a 40-50
knot mid level jet streak while a low-level jet develops from
about the I-95 corridor on eastward this evening before quickly
shifting offshore. While the main lift tracks to our north, some
ascent from warm air advection and the aforementioned low to
mid level jets should allow for some showers. A mesoanalysis
this afternoon shows a narrow corridor of weak instability in
the Ohio Valley northeastward into western to near central
Pennsylvania. There is some lightning occurring in western
Pennsylvania near the leading edge of the greater instability.

Much of the guidance focuses some showers across mostly the
western to northern areas by later this evening, with a
weakening or dissipating trend farther south and east. There is
not much in the way of instability forecast especially given
only modest moisture and therefore thunder should be limited
(kept a mention west of I-95 this evening). Maintained the
highest PoPs in the northwest areas, then these drop off in the
wee hours of the morning as the front shifts east. Along and in
the wake of the cold front, an increase in a west to northwest
breeze should occur very late tonight.

Low temperatures are mainly a MOS/continuity blend and it will
be a mild night ahead of the cold front.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
A compact upper-level low is forecast to slowly move across
northern New England during Wednesday. Surface low pressure tied
to it will also slowly shift eastward, and its associated cold
front is expected to be off our coasts by the start of the day.

Cyclonic flow aloft will turn more zonal by the end of the day
as the aforementioned trough slips eastward. Weak surface high
pressure will be approaching from the west, however a tightened
pressure gradient will be present across our area. The forecast
soundings indicated a lot of dry air in place therefore plenty
of sunshine should be present. These soundings also show deeper
mixing occurring as the boundary layer warms (increasing
breeze), and while cold air advection is occurring it is not all
that robust. Therefore while it will be cooler compared to
today, it will still be on the mild side. An offshore wind
component will keep much of the coastal areas warmer as well.
Highs are mainly a model consensus/continuity blend.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
The mid level pattern is forecast to remain quite progressive
during the period from Wednesday night through Tuesday. Weather
systems are expected to move quickly across our region.

The first weather system that is anticipated to affect our
region is a weak area of high pressure. Its center should move
from the Great Lakes on Wednesday to the waters off New Jersey
and Delaware on Thursday.

Surface low pressure is forecast to drift from the upper Ohio
River Valley on Thursday to New England on Friday. Another low
is expected to lift northeastward from the lower Mississippi
River Valley on Thursday and it should phase with the northern
low on Friday. As a result, we are anticipating showers from
Thursday night into Friday. We will mention a chance of thunder
during the afternoon and evening hours on Friday as marginal
instability develops. The low and its associated cold front are
forecast to pass off the coast on Friday night, allowing dry air
to build into our region from the northwest for Saturday.

The progressive nature of the pattern begins to result in some
substantial differences in the model output from Sunday onward.
As a result, there is low confidence in the forecast details for
Sunday, Monday and Tuesday. We will mention a slight or low
chance of showers for Sunday and Tuesday with dry weather
anticipated for Monday based on current and recent model trends.

Forecast temperatures for the period from Wednesday night
through Tuesday are typical for late April.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of this afternoon...VFR. West-southwest to southwest winds
around 10 knots. A sea breeze is expected at ACY around 22z and
potentially at MIV near 00z, therefore the winds will become
more from the south. The timing of how far inland the sea breeze
may reach is less certain, however a bay/river breeze bay turn
the winds more from the south at ILG and PHL.

Tonight...VFR ceilings for a time. Some showers are expected,
with the greatest chance at ABE and RDG where a VCSH is carried.
A couple of thunderstorms cannot be ruled out mainly west of
PHL, however this is less certain. Any showers or a storm can
result in brief MVFR/IFR conditions. Southwesterly winds near 10
knots, becoming west to northwest after about 06z.

Wednesday...VFR. West-northwest winds 10-15 knots with gusts to
around 20 knots.

OUTLOOK...

Wednesday night...Mainly VFR. Variable wind 6 knots or less.

Thursday...Mainly VFR. Variable wind 6 knots or less becoming
southwest to south 5 to 10 knots.

Thursday night...VFR lowering to MVFR and IFR with showers
developing. Variable wind 6 knots or less.

Friday...MVFR and IFR in showers. A chance of thunder in the
afternoon. Southwest wind increasing around 10 knots.

Friday night...MVFR and IFR in the evening with a chance of
showers and thunderstorms. Conditions improving to VFR
overnight. Southwest wind around 10 knots becoming northwest.

Saturday...Mainly VFR. Northwest wind 10 to 15 knots.

Saturday night...Mainly VFR. Variable wind 6 knots or less.

Sunday...Mainly VFR. Southwest wind 5 to 10 knots.

&&

.MARINE...
The conditions are anticipated to remain below Small Craft
Advisory criteria through Wednesday. A southerly wind however
will increase some tonight for a time ahead of a cold front and
as a low-level jet moves through, however mixing overall should
be limited given a much warmer airmass in place. Seas will build
some as well and seas to near 5 feet are possible overnight
near 20NM.

OUTLOOK...

Wednesday night through Sunday...No marine headlines are
anticipated.

&&

.EQUIPMENT...
Update...KDIX has returned to service.

Update...The transmitter that drives the Allentown NWR All
Hazards Radio continues to be serviced. Our broadcast will be
off the air until further notice.

Previous discussion...
The KDIX radar remains out of service. Technicians continue to
work on installing the replacement parts. Surrounding radars
include, KDOX, KOKX, KLWX, KCCX, KBGM and TPHL.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Iovino
Near Term...Gorse/Kruzdlo
Short Term...Gorse
Long Term...Iovino
Aviation...Gorse/Iovino
Marine...Gorse/Iovino
Equipment...Kruzdlo


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