Scientific Forecaster Discussion
fxus61 kphi 231943
Area forecast discussion
National Weather Service Mount Holly New Jersey
343 PM EDT Mon Sep 23 2019
a cold front will cross the region tonight. High pressure returns
Tuesday and Wednesday, followed by another cold front Thursday into
Thursday night. High pressure builds in on Friday. Another cold
front may approach the region this weekend.
Near term /until 6 am Tuesday morning/...
another hot, humid, well above normal day temperature wise today
ahead of an approaching cold front. A weak surface trough remains
across the area this afternoon while the first of a couple of short
waves/vorticity impulses moves across the area. This has helped keep
an area of showers progressing toward our area through the
afternoon, which may hold together into portions of eastern
Pennsylvania before dissipating. The same cannot be said about
showers that are expected to develop ahead of the approaching cold
front. The front will continue to progress eastward across
Pennsylvania and make its way into our area around sunset.
Instability will remain in place across the area ahead of the front,
while the short wave/vorticity impulse aloft approaches as well.
Cape values are not significantly strong, maxing out around 500-
1,000 j/kg this afternoon, but shear values increase to 35-40 knots
underneath 40-45 knots of mid-level flow. This could help lead to
isolated thunderstorms, which one or two may become strong to
severe, hence Storm Prediction Center has a small portion of Carbon and Monroe under a
marginal risk for severe weather late this afternoon and evening.
The showers and thunderstorms will continue to progress eastward
across the area, eventually moving offshore during the overnight
period as the front moves offshore as well.. a brief period of
moderate to heavy rain may also be possible due to precipitable water values
approaching 1.75 inches.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
the low pressure that will be pulling the cold front across the area
Monday night will slowly drift offshore of Maine through the day
Tuesday while high pressure builds across the Ohio River valley and
southern/central Appalachians. This will keep a northwest flow
across the area on Tuesday, which could become gusty around 15-25
mph at times through the day. While cloud cover will likely increase
through the day, precipitation is not expected to reach our area at
this time. Temperatures Tuesday will be cooler than Monday, but will
remain a few degrees above normal.
Long term /Tuesday night through Monday/...
overview...with the exception of two potential cold fronts (one on
Thursday and one Saturday into sunday), the relatively quiet weather
pattern is expected to continue through the next week.
Wednesday and Thursday...surface high is expected to progress east,
going off shore by Wednesday night ahead of the next cold front
which should arrive later Thursday into Thursday night. As mentioned
by the previous shift, this looks to be mostly a dry frontal passage
as the best synoptic scale lift should stay well north of the
Friday...southeasterly onshore flow develops which should help to
keep temperatures closer to normal. Highs are expected to be
slightly above normal, ranging from the upper 60s to near 80.
Saturday and Sunday...another cold front could approach the area
Saturday into Sunday. There is some question though with how far
south this front will get before stalling. Some models have the
front stalling along the New York/PA state line, while others show the
front progressing all the way through the region Saturday night. If
it does progress through our region, then the chance for rain could
increase. For now though, given the uncertainty, have kept pops at
20 percent or less.
Monday...the pattern on Monday will be highly dependent on where and
if the weekend front stalls. It is possible if the front stalls, we
could see the front progress from the northeast as a backdoor
Aviation /20z Monday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...showers will move across the area through this evening and
the first half of the overnight period. Mostly VFR conditions are
expected, except where heavier showers occur which is expected
mainly at Abe and ridge. There is a slight chance for thunderstorms,
however, the chance remains too small to include in the taf at this
time. Southwest winds 5-10 knots may gust 15-20 knots at times this
afternoon into this evening. Winds shift to west then northwest
overnight behind a cold front.
Tuesday...VFR conditions will persist through Tuesday. Northwest
winds 5-10 knots early, increase to 10-15 knots with gusts 15-20
Wednesday through Thursday...mostly VFR conditions are expected.
Winds are expected to be mostly southwesterly or northwesterly at 15
kt or less.
Friday and Saturday...mostly VFR conditions are expected. There is a
chance for low clouds and/or fog late Friday night into Saturday
morning which could lower conditions to MVFR or even IFR. Winds will
be shifting to southeasterly and speeds should be 5 to 15 kt through
tonight...a Small Craft Advisory will remain this evening across the
Atlantic Ocean coastal waters as seas will remain near 5 feet and
winds gust around 25 knots. Winds and seas are expected to lower
below advisory levels later tonight.
Tuesday...winds are expected to remain below 25 knots on Tuesday
while seas are expected to remain around 4 feet or less. It is
possible seas may reach 5 feet, but we are not confident enough in
this occuring to extend the advisory into Tuesday.
Wednesday through Friday...seas should subside Wednesday morning,
winds and seas should stay below Small Craft Advisory criteria through this period.
Friday night and Saturday...seas could once again build above 5 feet
through this period.
A high risk of rip currents remains this afternoon and evening
due to southerly winds 10-15 knots, and seas 4-5 feet with a
5-10 second period, occasionally reaching 15 seconds.
With seas 3-4 feet, a period of 10-12 seconds, and
an offshore wind of 10-15 knots, the rip current risk on Tuesday
will be at least moderate.
New Jersey...high rip current risk until 10 PM EDT this evening for njz014-
Delaware...high rip current risk until 10 PM EDT this evening for dez004.
Marine...Small Craft Advisory until 2 am EDT Tuesday for anz450>455.