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857
FXUS61 KPHI 191948
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
348 PM EDT Sat May 19 2018

.SYNOPSIS...
A warm front will continue lifting northward through our region
this evening. A cold front approaching from the northwest is
forecast to arrive late on Sunday. The boundary is anticipated
to stall to our south on Monday. Weak low pressure is expected
to move from the eastern Great Lakes to New England on Tuesday
and Tuesday night and it should pull another cold front through
our region early on Wednesday. The front is forecast to stall to
our south as weak high pressure influences our weather on
Thursday and Friday. The boundary may return northward as a warm
front next weekend.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of mid afternoon, the persistent pattern we`ve been in
continues. Low pressure centered to our west near Michigan with
a warm front extending eastward from it across the Delmarva.
This boundary is separating warm and very humid air with dew
points near 70 from a much cooler airmass to the north. Deep
layer southerly flow continues east of the aformentioned low and
around a high in the western Atlantic as it continues to pump
rich moisture northward with PWATs near 2.0 inches. This
moisture interacting with the front is leading to periods of
heavy rainfall over the Delmarva with the latest batch moving in
and showing some signs of training as it`s oriented in a south-
north axis...the same as the cell motion. As such, we`ve
extending the Flood Watch for southern NJ and the Delmarva to 9
pm but have removed SE PA zones where the threat for flooding
has diminished.

As we head through the late afternoon into this evening, big
concern will be watching rain/showers continuing to move north
and potentially producing continuing periods of heavy rainfall
with embedded thunder possible with amounts of a half inch to an
inch or more possible within a brief period. Area of greatest
concern again looks to be the Delmarva especially from Talbot
and Caroline Counties in Maryland into Kent Co. Delaware and
points north...especially since these areas so such much rain
Friday. Urban and small stream flooding will the most likely
type of flooding but flash flooding will also be possible. The
good news is, is that as we head through this evening, warm
front will continue to lift northward through the area and this
along with the loss of diurnal heating will lead to rain/showers
diminishing...becoming lighter and more scattered across the
area in the warm sector. Concern will then shift to areas of
patchy fog and drizzle that may form in the increasingly muggy
airmass as it advects in. In fact, as this airmass moves in,
much of the area will continue to warm into this evening and
then see temperatures hold fairly steady in the 60s or even rise
overnight along with increasing dew points. Late at night, a
cold front will begin to approach from the north and west along
with some shortwave energy in the upper levels and this may tend
to increase the chances for showers and even some isolated
thunder mainly N/W of I-95.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
For Sunday, area will be firmly in the warm sector to start the
day as low pressure moves northeast through Quebec. Don`t
really expect any sun though as low levels will remain quite
saturated in southerly flow and there will continue to be some
showers, mist, and drizzle around. Heading into the late morning
through the afternoon, the cold front will push south with
time...reaching the I-95 corridor by mid afternoon and southern
NJ across the Delmarva by evening. This front will be the focal
point for more scattered showers and storms to
develop...especially during the afternoon from the I-95 corridor
S/E. Some good news is the the mid and upper levels will be
drying out and the upper forcing will be shifting off to the
east. This may tend to limit the coverage of showers and storms
but nevertheless, PWATs will still be quite high (1.7+ inches)
and with the saturated ground any showers/storms will be a
concern for additional hydro issues...mainly of the urban and
small stream variety. Temperatures will be much warmer as there
will also be some sun developing by afternoon...highs will be
mainly in the upper 70s to low 80s except cooler in the far
north across the southern Poconos. Dew points will also be in
the upper 60s ahead of the front so it will feel very humid
until the front clears the area by tomorrow night.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
The long-term forecast period will begin with a mid level
trough over eastern Canada and the northeastern states on Sunday
night. The feature is expected to progress slowly eastward
during the course of the week. A ridge is anticipated to build
overhead from the west on Friday and Saturday.

Conditions are expected to remain in flux during the first half
of the work week. Dry air is forecast to push down from the
north for Monday in the wake of a frontal boundary. However, the
boundary and moisture should build back to the north on Monday
night and Tuesday. We will keep the forecast rain-free for
Sunday night and most of Monday, then we will indicate a chance
of showers and an increasing potential for thunderstorms from
Monday night into Tuesday.

Weak low pressure is forecast to pass to our north on Tuesday
night and it should pull a cold front through our area early on
Wednesday. We will keep a chance of showers and thunderstorms
for Tuesday night in advance of the front.

A more substantial shot of dry air is expected for the second
half of the work week. We are not anticipating any precipitation
from Wednesday through Friday as the frontal boundary stalls
well to our south and as ridging begins to build overhead from
the west.

The forecast for Saturday could go either way at this point. We
will not mention any precipitation at this time. However, with
a southerly flow becoming established and with the mid level
ridge axis moving to our east, we may eventually need to
introduce a chance of afternoon showers and thunderstorms.

Temperatures for the period from Sunday night through Saturday
are expected to be typical for this time of the year with highs
mainly in the 70s and lower 80s, and lows in the 50s and 60s.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...There may be some brief improvement to MVFR into
early this afternoon, especially from PHL southward, before a
return to IFR or lower Cigs by the overnight. Visbys will also
be reduced to at least MVFR due to patchy fog, mist, lingering
scattered showers, and drizzle. Winds veer to SE into this
evening and eventually SW overnight and continue to be around
5-10 knots. Also, LLWS will likely be an issue for
KMIV/KACY/KTTN and possibly for remaining sites to the N/W but
confidence a bit lower here.

Sunday...IFR restrictions continue into the morning before
improvement to MVFR by around midday and eventually VFR for most
sites by 18z. Some showers with the risk of thunder will be
around, especially in the afternoon, and this could cause
additional brief restrictions. Winds becoming west at generally
10-15 knots with gusts to around 20 knots.

OUTLOOK...
Sunday night and Monday...Mainly VFR. Some late night and early
morning visibility restrictions are possible.

Monday night through Tuesday night...A chance of showers and
thunderstorms. Conditions varying between VFR and MVFR. Brief
periods of IFR may occur in precipitation.

Wednesday through Thursday...Mainly VFR. Some late night and
early morning visibility restrictions are possible.

&&

.MARINE...
A Small Craft Advisory remains in effect. While winds continue
to see a lull in many areas expect them to increase again by
later this evening through tonight. Also, there will be some
showers around tonight along with patchy fog, especially for the
northern waters, and this may lead to reduced visibilities.

For Sunday, SCA conditions continue over the ocean waters as SW
winds gust up to 25 knots and seas will be around 5 ft.
Conditions should be below SCA levels over the Delaware Bay.
There will be some scattered showers around with the chance of
thunderstorms, especially in the afternoon.

OUTLOOK...
Sunday night...A Small Craft Advisory is in effect until 10:00
PM Sunday for our ocean waters to allow wave heights to fall
below 5 feet. West wind around 10 knots becoming north.

Monday through Thursday...No marine headlines are anticipated.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Flood Watch until 9 PM EDT this evening for NJZ016>027.
DE...Flood Watch until 9 PM EDT this evening for DEZ001>004.
MD...Flood Watch until 9 PM EDT this evening for MDZ008-012-015-019-
     020.
MARINE...Small Craft Advisory until 10 PM EDT Sunday for ANZ450>455.
     Small Craft Advisory until 6 AM EDT Sunday for ANZ430-431.

&&

$$

Synopsis...Iovino
Near Term...Fitzsimmons
Short Term...Fitzsimmons
Long Term...Iovino
Aviation...Fitzsimmons/Iovino
Marine...Fitzsimmons/Iovino