Area Forecast Discussion
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FXUS61 KPHI 290753
Area Forecast Discussion
National Weather Service Mount Holly NJ
353 AM EDT Sat Apr 29 2017
A cold front is expected to slide south into our region tonight
before stalling over Delmarva and south Jersey. The front is
expected to return north as a warm front late tomorrow. Another cold
front is expected on Monday night as an area of low pressure moves
into the Great Lakes region. This low will drift northeast through
eastern Canada through mid week. Another low pressure system will
lift out of the lower Mississippi Valley towards the Mid Atlantic by
late in the week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An area of showers continues to develop along an old weakening
frontal boundary that remains stalled out across the area early this
morning as a strong short wave/vorticity impulse moves across the
area. There is enough lift to interact with the elevated
instability to create some scattered thunderstorms as well.
While we do not expect any severe weather to occur, any
thunderstorms that do develop will produce a period of heavy
rainfall, frequent lightning, and locally gusty winds. Some
small hail may also be possible.
This first round of showers and thunderstorms will move to the east
and offshore around or shortly after sunrise as the first short wave
passes to our east. Then we should have a break in
shower/thunderstorm activity, before another round of showers and
thunderstorms move into the area later this morning into the the
noon hour as a second short wave/vorticity impulse moves across the
area. This area should weaken move to our east as the second short
wave passes to the east.
Then yet another round of showers and thunderstorms is possible by
late this afternoon into this evening as a backdoor cold front moves
into the area and another short wave slides across the area as well.
This batch of showers and thunderstorms will have more surface based
instability to tap into and less of a cap. So it could be possible
that an isolated severe thunderstorm could develop late today.
Temperatures today will warm quite significantly and come withing a
couple of degrees for some areas. GED is the one site that is
actually forecast to reach a record.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
The backdoor cold front will continue to push through the area this
evening and overnight. The round of showers and thunderstorms
mentioned for the late afternoon and evening will slide east and
move offshore during the evening hours as the short
wave/vorticity impulse associated with it moves to our east as
As the front sinks to our south, a northeast-east flow will develop
across the area. There could be some light fog develop overnight,
but we do not expect much if any dense fog at this time as winds
will remain around 5-10 mph through the night and dewpoints are
expected to drop enough behind the front that RH values do not reach
high enough for widespread fog for most places.
With the front near the area, it is possible that some
isolated/scattered showers may develop overnight through daybreak
Sunday north of the frontal boundary.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
The polar jet remains displaced well to our north in Canada, with an
active southern stream across the conus thru the period. A southern
stream closed low ejects northeast out of the four corners region on
Sunday and through the Great Lakes on Tuesday. A broader long wave
trough then sets up on Wednesday, extending from Atlantic Canada to
the Colorado Rockies. There is general model agreement that this
feature slowly progresses eastward, as a cutoff low develops across
the southeast states. Overall, this will maintain a southwest flow
regime with temperatures at or above normal. The two primary focuses
for precipitation will be with a cold frontal passage Monday night,
then within the overrunning area ahead of the southern stream cutoff
low from Thursday into Friday.
Some residual convection is possible through at least midnight on
Saturday night across Delmarva and southern NJ, as a cold front
moves slowly through this area, and stalls over central Delmarva
through Sunday. The GFS appears to be overdone with QPF north of
this boundary through Sunday, and have discounted it, given the
drier surface air to the north and slight ridging aloft as well. The
NAM and ECMWF are much drier, and the forecast reflects this, with
Delmarva the exception. As the boundary stalls, we expect renewed
showers and thunderstorms on Sunday. The high temperature forecast
will be challenging on Sunday, with a maritime air mass within the
easterly flow north of the front, while portions of Delmarva remains
south of the front within the warm sector. We expect low-70s to low-
80s across Delmarva, with low-60s to low-70s across the remainder of
the region. The exception will be some of the NJ barrier islands,
where highs will not make it out of the 50s!
The boundary is then expected to lift northward as a warm front on
Sunday night. There is not much support for precip, so PoPs were
kept in the slight chance category. Expect temperatures to remain
steady or rise overnight. With the cold front still over the Ohio
Valley on Monday, expect a mostly sunny and dry day. A brisk south-
west flow will develop, with wind gusts up to around 30 MPH in
the afternoon. Temperatures will be well above normal, with
highs in the low-mid 80s across the urban corridor. With the
cold frontal passage Monday night, showers and thunderstorms are
likely. While the timing is not ideal for severe weather and
instability is limited, the wind field is strong and
Precipitable Water values approach 2.0 inches, so gusty winds
and heavy downpours are likely with any thunderstorms, the
primary focus being northwest of the NJ Turnpike/I-95.
The post-frontal air mass will remain moist on Tuesday, with a
surface trough traversing the region under a cyclonic flow aloft.
Expect considerable cloudiness and a continued chance of showers,
especially during the afternoon, and northwest of the NJ Turnpike/
I95. It should be too stable for any thunder but winds may gust up
to around 30 MPH. Much cooler compared to Monday, but high temps
still at or slightly above normal. For Wednesday, slight ridging
builds in aloft and the column is dry, so fair weather is expected.
Unsettled weather during the Thursday and Friday time frame. A broad
trough to our west will maintain a southwest flow aloft, along with
moisture of Gulf of Mexico origins moving up the eastern
seaboard, within an overrunning regime. Heavy rainfall is
certainly possible, with WPC guidance indicating the potential
for 1-2 inches across our region, but there is still inherent
uncertainty given it`s Day 6-7. Stay tuned.
.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Showers and thunderstorms are moving across the area early this
morning and will affect all TAF sites. With the showers, a period of
heavy rain will cause a reduction in VSBYS and possibly CIGS. These
showers and thunderstorms will move east of the area after sunrise,
then another round of showers, possible thunderstorms, could affect
the TAF sites later this morning. Another round of showers and
thunderstorms is more likely later this afternoon which has a better
chance of being stronger storms with reductions to conditions.
Outside of the showers and thunderstorms, VFR conditions will
prevail through the daytime hours. However, as a backdoor cold front
sinks through the area later this evening and overnight, we expect
lower clouds and light fog to develop. At this time, we only
expect conditions to lower to MVFR, but there is the possibility
that conditions could lower to IFR overnight.
Winds are variable at many locations, but are generally out of the
southeast to south for most places where there is any direction.
Winds will increase out of the southwest this morning, before
becoming west then northwest through the day and into the afternoon
and evening. Winds could gust 15-20 knots for a period this
afternoon as well. Behind the frontal passage, winds will become
northeast this evening and overnight.
Sunday...Mostly VFR conditions expected.
Sunday night...MVFR or IFR conditions are possible with low clouds
Monday...Mostly VFR conditions are expected although MVFR conditions
are possible with any showers or thunderstorms.
Monday night...Widespread MVFR or IFR conditions with thunderstorms
likely. An abrupt wind shift to westerly is expected with a cold
front Monday night.
Tuesday and Wednesday...Mostly VFR conditions expected.
Conditions on the coastal waters are expected to remain below Small
Craft Advisory levels through today and tonight. Even though there
are some strong winds above the surface, there is a strong inversion
which will keep those winds fro mixing to the surface. However,
winds could gust around 20 knots and seas could reach 4 feet at
times through the day.
There is a chance of showers and thunderstorms across the waters.
Any thunderstorms will contain frequent lightning and may cause
strong gusty winds.
SCA likely Monday through Tuesday. Southerly winds increase Monday,
with gusts up to 30 knots continuing into Monday night. Winds will
become northwest by Tuesday morning, with renewed gusts around 25
knots possible. Seas building to the 5-7 Ft range on Monday, and
then 7-9 FT Monday night, decreasing to around 5 FT late Tuesday.
Seas may remain elevated into Tuesday night on the ocean, which
would necessitate the extension of any Small craft Advisories.
Record high temps listed today where it is forecast to be
within 2 degrees of record.
TTN 88- 1974 & 1888
**Record or number 2 warmest April on record expected**
Presuming our forecast temps these last 2 days of April are
accurate, we are assured of a top 2 warmest April on record in
much of our forecast area. Sunday is probably the critical day
for determining record or not.
Below: April projected within the top April average temps, the
normal for April and the period of record (POR).
This includes Friday`s (28th) high and low temperatures through
Sundays max temps may occur at 1 am and the min temps Sunday
PHL normal 54.0 POR 1874
59.5 2017 Projected warmest ever: still could slip .2 degrees.
ABE normal 49.9 POR 1922
56.9 projecting record and almost cant miss a record.
ACY normal 51.7 POR 1874
57.6 projecting record and almost cant miss.