Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 202354
Area Forecast Discussion
National Weather Service Mount Holly NJ
754 PM EDT SAT AUG 20 2016
An area of high pressure centered over the northwestern Atlantic
Ocean will continue to nose down the toward the mid-Atlantic region
tonight. A strong cold front will approach from west Sunday morning
before moving through the area Sunday afternoon and evening. High
pressure builds in from the Midwest Monday before settling over the
region through midweek. The high will move offshore late in the week
while the next cold front approaches from the northwest.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Shower and tstm activity has decreased but a few remain and should
do so for the next several hours. We will just keep the small chc
or slgt chc wording through the evening, before everything
dissipates.It will be warm and humid overnight with lows only
dropping into the upper 60s/low 70s. patchy fog is possible too,
like last night.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
The cold front will approach from the west and chcs for showers and
tstms will increase from w to e thru the day. SPC has maintained a
marginal risk for severe weather for our area. Wind fields will be
strengthening thru the day, but overall the parameters for severe
weather are not overly terrific. We will still have downpours and
gusty winds possible however. The front will probably be across the
Delaware River area by early evening. High temperatures Sunday will
again be in the upper 80s to low 90s.
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
A large-scale trough will approach from our west Sunday nigh with
the forecast area positioned near the base of trough. There has been
a modest trend evident in the model guidance toward a more
progressive system with the upper trough not quite as amplified and
negatively-tilted as what was once seen in the model runs from 1-2
days ago. At the surface, the cold front is expected to quickly move
through the area during the evening and off the coast around
midnight. Note, the models are in very good agreement with the fropa
timing, contributing to higher confidence in the forecast.
The Sunday night system already has an established deep connection
of tropical moisture from the Pacific and Gulf of Mexico as seen on
the latest GPS/ satellite-derived total blended PWAT imagery. PWATs
are forecast to peak between 2.25-2.50 inches over the area as this
well-defined atmosphere river reaches the Eastern seaboard and taps
into additional moisture from the Atlantic. Ongoing showers and
storms ahead of the cold front will certainly have the potential to
contain very high rainfall rates. However, with the best dynamics
(e.g., greatest height falls, DPVA, and low-level jet streak) from
this system skirting to our north through the Northeast states and a
fast eastward progression of the frontal boundary, the setup for
widespread heavy rainfall and flash flooding is not optimal. Based
on the expected fropa timing, a brief window for localized heavy
rainfall and perhaps isolated flash flooding should quickly shift
from the Delaware Valley very early in the evening (through sunset)
to the coastal plain during the mid evening. The bulk of the
precipitation will likely move off the coast before midnight.
A tight pressure gradient (particularly for this time of year) is
expected over the area on Monday as high pressure over the Midwest
builds in promptly behind the front. Northwest winds could be a bit
breezy during the day with the potential for 20-25 mph gusts as a
result. You will certainly notice the change in airmass with much
cooler and drier conditions post frontal with highs only in the 70s
(low to mid 80s) west (east) of the fall line on Monday.
An extended stretch of tranquil weather with comfortable summer
temperatures will continue into midweek with a large area of high
pressure in control. A gradual warming trend can be expected
Wednesday and Thursday as southerly return flow develops when the
center of the high moves offshore but temperatures still remain
below 90 degrees.
The next chance of precipitation looks to be Friday when a cold
front will likely approach from the northwest. We will see at least
one hotter day with highs near 90 on Friday. However, the front may
struggle to completely make it through the area Friday night into
Saturday due to strong downstream blocking on the northern periphery
of a large anticyclone over the Southeast U.S. This would favor a
continuation of above normal temperatures into the weekend but
excessive heat is not expected.
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
A continuation of VFR conditions is expected the rest of today and
most of the evening. There will be plenty of daytime Cu across most
areas with CIGS and possible sct showers over ern NJ and favored
topographical areas across the srn Poconos. Winds will be mostly
from the E or SE at 5 to 10 mph through the evening.
Conditions will likely deteriorate somewhat tonight since the
onshore flow has been in place for awhile and the lower atmosphere
is moistening up. Some of the guidance points to both abundant low
clouds and fog overnight. We have bought on to this to some extent,
but an not completely confident in total IFR conditions tonight. We
have forecasted some light fog and sct low clouds in many areas
after midnight. An increasing srly flow in the lower atmosphere Sun
morning could favor low clouds instead of fog.
Sunday...Mostly VFR with sct showers. Increasing srly winds. Sct
showers and tstms possible later in the afternoon.
Sunday night...Temporary flight restrictions likely in the evening
with showers and thunderstorms moving through the area. The models
are in remarkably good agreement showing a broken line of convection
ahead of a cold front that progresses steadily eastward through the
I-95 terminals early in the evening and then MIV/ACY terminals
around or just after sunset. The line may be accompanied by a brief
period of gusty winds and poor visibility in torrential downpours.
Improving to VFR later in the evening and overnight as winds shift
to northwesterly behind the cold front.
Monday through Wednesday...Predominately VFR. Northwest wind gusts
to around 20 kt during the day Monday. Light winds are expected thru
the rest of the period.
Wednesday night through Thursday night...Some potential for low
clouds or fog to develop late Wednesday night and/or Thursday night
as southerly return flow draws tropical moisture into the area. Low
confidence this far out in time. South-southeast winds 10-15 kt.
A decent onshore flow continues across the waters this afternoon
with wind speeds now around 10-12 knots and seas on the ocean
generally around 2 ft. This should continue tonight with high
pressure remaining NE of the waters and a cold front approaching
from the west. Isolated showers will continue across the waters
through the early evening. Sunday, winds will become more srly and
speeds will remain around 10 to 15 knots. An increasing chc for
showers and tstms as the front draws closer.
Sunday night...A cold front will cross the area. A broken line of
showers and storms may form ahead of the front and pass through
the waters during the evening. These storms may contain locally
Monday and Monday night...Northwest winds pick up behind a cold
front early in the morning. A SCA was issued starting 5 AM Monday
morning for the coastal Atlantic waters and Delaware Bay for gusts
to near 25 kt. Seas will also increase to 4-5 ft in our coastal
waters and 2-3 ft in the Delaware Bay. The SCA ends late Monday
morning for all but our northern most coastal zones adjacent to
Monmouth and Ocean Counties. The pressure gradient will be stronger
over these northern areas, which will allow for gusts near 25 kt to
continue into the afternoon.
Tuesday through Thursday...Winds and seas below SCA thresholds.
The rip current risk is low today.
The probable risk for the development of dangerous rip currents
on Sunday is low but may approach moderate in the afternoon with
a strengthening southerly flow.
The monthly average for Philadelphia continues to head for a top 5
warmest August on record. The period of record dates back to
1874. As we go through this exercise every day, the projected
value continues increasing. If in fact the current projections
continue close to being on track, we would have our warmest
August on record.
Tomorrow we`ll try to look at ILG, ACY and ABE to gain a broader
Meanwhile, later this evening we`ll update the seasonal 90F or
MARINE...Small Craft Advisory from 5 AM to 11 AM EDT Monday for ANZ430-
Small Craft Advisory from 5 AM to 6 PM EDT Monday for ANZ450-