NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 14, 2:19 PM EST, 1 hour 5 minutes earlier.
Area forecast discussion, Sep 14, 2:19 PM EST, 1 hour 5 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
319 PM EDT WED SEP 14 2016
.SYNOPSIS...
A cold front will cross the entire area tonight, then high pressure
builds in for Thursday into Friday. This high moves offshore later
Friday and Saturday, then another cold front moves through late
Sunday night and Monday. High pressure then builds in for Tuesday
and Wednesday.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The cold front as of 3 PM was just NW of our region across NE PA
back towards central PA. A rather robust line of showers and
thunderstorms has developed along the front across NE PA, but as
this line reaches our region, there is a cap in place that will
likely inhibit widespread coverage. In addition, the front is not
likely to arrive before sunset for much of our region, further
limiting widespread rain potential. Therefore, made few changes to
the PoPs beyond the first few hours.
Once the front sweeps through the region, skies should clear out
pretty quickly. This, combined with the cold and dry air advection
should enhance nocturnal cooling, with low generally in the 50s for
most of the area, upper 40 for the Poconos and NW NJ, and lower 60s
for Delmarva and far SE NJ.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
In the wake of the cold front, a surface high will slide east across
the NE U.S. In the upper levels, a short wave ridge will build to
our west. As a result, expect tranquil weather and clearing skies.
Here's something we haven't had the opportunity to say much this
month: temperatures tomorrow should be below normal for much of the
region, with highs generally in the 70s.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
The synoptic setup is comprised of a trough in the Northeast that
quickly shifts offshore Thursday night into Friday. A ridge then
builds across the East Coast Friday and Saturday before shifting
offshore. The pattern looks progressive therefore another trough
migrating across the Midwest and Great Lakes Saturday and Sunday
will push a cold front across our area later Sunday night and
Monday. A strong upper-level trough is forecast to track across
Canada Monday through Wednesday, however this feature may end up
tracking north of our area due to enough ridging that holds to our
south. We used a model blend Thursday night into Saturday, then
blended the 12z WPC Guidance into continuity thereafter. Some
adjustments were then made following additional collaboration with
our neighboring offices.
For Thursday night and Friday...As a trough quickly shifts east of
New England, a ridge will build across the East. This will allow
high pressure across New England to shift offshore through Friday.
This will maintain an onshore flow across the area along with cooler
conditions. The airmass should remain dry enough to prevent low
clouds from developing despite an inversion developing Thursday
night, especially since the main moisture return is forecast to
remain to our west and southwest.
For Saturday through Monday...High pressure shifts farther offshore
as an upper-level ridge exits the East Coast. This occurs as the
flow looks to be progressive with a trough migrating across the
Midwest and Great Lakes region. This will drive a cold front
eastward, however much of the energy may track well to our north
along with low pressure. This should slow the forward progress of
the surface cold front for a time, which now may not arrive until
later Sunday night and Monday. Prior to this though, a warm front
working northeastward up the Ohio Valley to start Saturday should
lift into northern New England by early Sunday morning. This places
our area within the warm sector, with even a pre-frontal trough
potentially developing by later Saturday.
Some convection should arrive later Saturday particularly with the
pre-frontal trough. There should then be a band of convection with
the front as it moves across the Great Lakes and upper Ohio Valley,
and some of this may arrive into our northwestern zones Sunday
afternoon. While this may be the primary forcing, some convection
may redevelop near the pre-frontal trough Sunday afternoon and
evening. The cold front should then be moving offshore by later
Monday, ending any convective threat. Given some uncertainty on the
convective coverage with the cold front especially with a more zonal
flow aloft, we held the POPs no higher than chance. Much of our area
needs the rain however.
For Tuesday and Wednesday...Some guidance wants to hang the cold
front up for a time Tuesday, which could allow for lingering
convection mainly across the southern areas. This front may be
weakening though as much of the energy peels well off to the north
and east, therefore we leaned closer to WPC which shows the front
well to our south and east Tuesday. As this occurs, high pressure
builds in through Wednesday from the west.
&&
.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Mostly VFR conditions are expected through the TAF period. The one
exception is if any showers and thunderstorms move over a TAF site
(the highest risk for this is KABE through 03Z), in which case brief
IFR visibilities are possible.
As the cold front pushes through our region between now and 04Z,
expect an abrupt shift to northwesterly winds and breezy conditions
are possible for the first few hours behind the front. Overnight,
winds are expected to back from northwesterly to northerly to
northeasterly by tomorrow morning, but should remain light
(generally less than 10 kts).
OUTLOOK...
Thursday night through Saturday...Other than some possible localized
fog early each morning especially Saturday, VFR overall. Winds
becoming light and variable Thursday night, then southeast 5-10
knots Friday before shifting to the south Saturday. A few showers
and thunderstorms may move in Saturday night especially north and
west of PHL.
Sunday and Monday...Some showers and thunderstorms should move
though ahead of and with a cold front. The actual front moves
through late Sunday night and Monday. VFR except during any showers
and thunderstorms. A wind shift to the west and northwest occurs
behind the front during Monday.
&&
.MARINE...
A cold front will push over the waters late this evening. With the
front, expect an abrupt shift to northwesterly winds and an increase
in wind speeds. Wind gusts near or above 25 kts are expected on the
ocean waters. Therefore, the SCA conditions for the coastal waters
from late this evening through mid day tomorrow. It's possible there
may be a few gusts near 25 KT on the Delaware Bay immediately
following the frontal passage this evening, but confidence is too
low to issue a SCA at this time.
Winds should drop off late tomorrow morning, however, if seas on the
coastal waters stay near 5 ft, the SCA may need to be extended.
Otherwise, expect winds and seas to gradually decrease through the
remainder of the day.
OUTLOOK...
High pressure shifts off the New England coast Friday, allowing a
northeast to east wind to become southeast Friday. A cold front
moves through Monday with south-southwest winds ahead of it, which
should increase some Sunday, however at this time it appears that
the conditions remain below Small Craft Advisory criteria.
RIP CURRENTS...
There is a low risk for the development of dangerous rip currents
along the coasts of New Jersey and Delaware through this evening.
The probable risk for the development of dangerous rip currents on
Thursday is moderate due to the expected northeast wind at 10 to 20
MPH.
&&
.TIDES/COASTAL FLOODING...
A prolonged period of onshore flow is expected to commence Wednesday
night and last thru Friday night. In fact, Northeast winds may gust
20 to 25 mph tonight into Thursday. Astronomical tides will also
be running higher due to Friday's Full Moon. The combination of
prolonged onshore flow and higher astronomical tides will result
in elevated water levels along the coast. The Thursday evening
high tide may be the most problematic, given the occurrence of the
peak astronomical tide coinciding with the strongest onshore flow.
At this time, we are forecasting that water levels should get
close, but fall just short of advisory issuance criteria. However
we will continue to watch closely especially with the next two
high tide tidal departures.
&&
.CLIMATE...
Near record high temperatures occurred today. Here are the observed
highs as of 230 PM. Trenton set a new record high and Atlantic City
and Wilmington tied their record highs for the day.
Location Observed High Record High
as of 230 PM EDT
Mount Pocono PA 81 83 (1976)
Allentown PA 90 91 (1931, 2008)
Reading PA 91 92 (1915, 1931, 2008)
Philadelphia PA 91 92 (1995)
Trenton NJ 92 91 (1915, 2008)
Atlantic City NJ 92 92 (1981)
Wilmington DE 92 92 (1915)
Georgetown DE 91 93 (1962, 2008)
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from midnight tonight to noon EDT
Thursday for ANZ450>455.
&&
Synopsis...Gorse
Near Term...Johnson
Short Term...Johnson
Long Term...Gorse
Aviation...Gorse/Johnson
Marine...Gorse/Johnson
Tides/Coastal Flooding...Johnson
Climate...Johnson