Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 290954
Area Forecast Discussion
National Weather Service Mount Holly NJ
554 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/...
-- Changed Discussion --Sunday...there is some question on how far south the front will
reach before stalling. The general trend with the 00Z models was
to bring the front further south (possibly entirely south of our
forecast area). Where the front stalls will have implications
for both high temperatures Sunday as well as precip chances. As
mentioned by the previous shift, the GFS appears to be
overestimating the precip north of the front given relatively
dry air in the cool sector. Therefore, focused the PoPs through
this period on Delmarva closer to the front. The front is
expected to return north as a warm front either late in the day
tomorrow or tomorrow night.
Monday...With the cold front still over the Ohio Valley, 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
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.
Tuesday and Wednesday...in the wake of the cold front,
temperatures will be about 5 to 10 degrees lower, with highs
generally in the 60s and 70s. Models have trended faster with
the dry air advection behind the front, so I trimmed back on
the PoPs on Tuesday. It is looking mostly dry both days.
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.
-- End Changed Discussion --
.AVIATION /10Z 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.
-- Changed Discussion --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.
Sunday...winds and seas are expected to be below SCA criteria.
Monday and Monday night...building seas and increasing winds are
expected by Monday morning. Southerly gusts near or above 30 KT
are possible Monday evening.
Tuesday and Wednesday...winds will shift to southwesterly and
then westerly behind a cold front expected early Tuesday. Gusts
on Tuesday may linger near 25 kt. Elevated seas may linger into
-- End Changed Discussion --
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.