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211
FXUS61 KPHI 141317
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
917 AM EDT Mon Oct 14 2019

.SYNOPSIS...
A weak cold front will move across the area today. High pressure
will build in tonight and remain nearby through Tuesday. Two weather
systems will approach on Wednesday, one a low pressure tracking out
of the Great Lakes and the other a wave of moisture coming out of
the Gulf States. These two systems will phase into a powerful storm
that will impact the region Wednesday and Wednesday night. The storm
will move away on Thursday with blustery conditions lingering. High
pressure will build in for the end of the week and next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

930 update: Previous forecast is in good shape, the stratus is
clearing from W-E and should be more or less off the coast
within the next couple hours. Although some locally dense fog
has developed behind this clearing line in Chester and Cecil
counties this should also dissipate shortly with insolation
increasing (and its eastward spread should also be halted by
the warmer/drier conditions in the I-95 corridor).

Previous discussion:

The front and weak area of low pressure that caused the rain
showers across the SE areas last night will continue to move
offshore early this morning. In its wake, low clouds and areas
of fog have developed across many areas. Patchy drizzle is also
being observed in a few areas. This low level moisture will
diminish this morning as high pressure begins to work its way
towards the area. The clouds will thin out across the NW areas
first, then across the coastal plain later this morning. The
afternoon will be mostly sunny in all areas.

High temperatures today should reach the low/mid 70s in many areas
with some upper 60s across the far N/W. Winds will be mostly west to
southwest at 5 to 10 mph.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
A weak cold front will cross the area this evening before high
pressure arrives from the W tonight. Clear skies and cool
temperatures are expected. Lows will drop into the upper 30s/low 40s
across the north and into the mid/upper 40s for Delmarva and srn NJ.
Winds will be from the NW to N around 5 mph overnight. A little
patchy valley fog is possible.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Overview...

No significant changes in thinking for the coming week. We start on
Tuesday beneath an area of high pressure which will yield a pleasant
fall day. The one weather system in the long term will impact us on
Wednesday and into early Thursday. Guidance continues to indicate
the potential for a strong but quick moving storm system to impact
us during that time. By the end of the week and next weekend, we
revert back to a pattern we saw a lot of in August and September.
That is, one of East Coast ridging and surface high pressure which
should grace us with a lengthy stretch of dry and warmer than normal
weather once the midweek storm departs.

Dailies...

Tuesday-Tuesday night... Surface high pressure will be almost
directly overhead for most of Tuesday, before starting to shift off
to the east late. We see some weak CAA during the day thanks to a
trough to the north, so highs will be a little cooler than Monday,
mainly in the mid to upper 60s. Dry conditions, plenty of sun, and
light winds expected. Lowered mins a couple degrees Tuesday night as
believe we may fall rather quickly early in the night while we still
have partly to mostly clear skies.

Wednesday-Wednesday night... The most active part of the week, as
two weather systems approach and phase into what should become a
powerful storm. Dynamically, it is an impressive setup at mid and
upper levels, and guidance has been consistent for several days in
the overall evolution of events, with only minor differences in
timing and the tracks of the northern and southern stream pieces.
The northern stream frontal system over the Great Lakes should
eventually be absorbed by the developing low along the wave of
moisture coming up from the south. Main question will be just how
much rain we get, which will depend on the tracks of the features
and the timing of their phasing. As previous forecaster noted, most
of our rain will be due to warm advection and low level FGEN on
Wednesday afternoon and evening. Given the dynamics, a period of
steady moderate rain appears probable. Not especially confident on
QPF and did not change the previous forecast too much; expecting
near an inch of rain but there will be some local variations. The
overnight runs of the EC and the GEM both show much higher totals
with widespread amounts over two inches. The southern stream wave
coming out of the Gulf states certainly has plenty of moisture with
it, so if that wave tracks a little farther north like those models
show then we could end up with heavier rain. We will dry out
Wednesday night, though the theme in the 0z guidance overnight was
to delay both precip arrival and departure by a few hours. Lows
falling back into the mid to upper 40s as NW flow kicks in, though
if the slower trend continues may have to adjust mins up.

Thursday-Thursday night... The upper level pattern is progressive,
so the Wednesday storm system will pull away into the maritimes on
Thursday. Dry conditions will return though cannot rule out some
cold advection showers to the northwest. As the low pressure
intensifies to our north, high pressure will be building in behind
it, and that will set up a sharp pressure gradient on Thursday.
Gusty northwest winds are expected. In fact, some BUFKIT profiles
suggest we have a chance at advisory level gusts, and we would
probably be a little lenient on criteria in this case given fully
leafed trees. Strong CAA behind the departing low will lead to a
chilly day with highs struggling to crack 60 and a cooler feel due
to the wind. 850mb temperatures dip to near 0C just about
everywhere. While the overnight will also be on the cool side, we
should avoid too much of a tumble thanks to the winds, which will be
diminishing but still steady overnight.

Friday-Sunday... Guidance agrees on an expansive ridge developing
over the East, something we saw a lot of in the late summer and
early fall. The result will be several days of dry weather with
temperatures steadily moderating after the Thursday chill. We should
be back in the low 70s by late in the weekend or early next week.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...Low clouds and areas of fog (mostly IFR) early this morning
then improvement to VFR after 12Z/13Z West and 14Z/15Z south/east.
Winds will become W to NW and increase to 5 to 10 knots for much of
the day.

Tonight...High pressure will move overhead so VFR expected with
light winds. The dry airmass should preclude widespread fog
formation. A little across the rural areas possible. We`ll not put
it in the tafs attm with low confid of it occurring.

Outlook...

Tuesday-Tuesday night... VFR. Light and variable wind Tuesday
becoming light southeasterly overnight. High confidence.

Wednesday-Wednesday night... Initially VFR on Wednesday morning, but
conditions deteriorating during the late morning and especially
afternoon and evening. MVFR/IFR likely. Winds will be increasing and
also erratic in direction. Initially southeasterly winds should turn
southerly then southwesterly during the afternoon. A sharp shift to
west-northwest is likely during the evening. Gusts of 20 to 25 kt
are possible by evening. LLWS may be a concern Wednesday afternoon
and evening as well. Conditions should gradually return to
VFR later in the night, especially after 6z. Moderate confidence.

Thursday-Thursday night... Mainly VFR. Windy, with west-northwest
winds of 15 to 20 kt potentially gusting over 30 kt during the day
Thursday. Northwest winds will diminish Thursday evening and
especially overnight. High confidence.

Friday... VFR. NW winds around 10 kt with gusts up to 20 kt. High
confidence.

&&

.MARINE...
Low pressure that was across the waters Sunday evening will continue
to move away today. A weak cold front will cross the waters this
evening before high pressure approaches from the west later tonight.
Winds and seas will remain below SCA conditions thru the period.
There may be some fog across the waters this morning, but then fair
weather is expected this afternoon and tonight. Winds will shift to
W/SW later today, then shift to NW behind the front tonight.

Outlook...

Tuesday-Tuesday night... Sub-SCA conditions expected. Seas 2 to 3
ft. Light and variable winds becoming southeasterly at 10 to 15 kt
overnight.

Wednesday-Friday... Marine headlines are likely most of this period
due to a storm system. Winds and seas likely build to SCA levels
Wednesday morning or early afternoon. West-northwesterly gales
appear likely Wednesday night and Thursday. Seas building 4 to 7 ft.
Gales subsiding to SCA levels Thursday night with seas also
diminishing. By Friday morning, conditions should subside to sub-SCA
levels though gusts around 20 kt remain possible.

&&

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

&&

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