Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
546 PM EDT Thursday Aug 25 2016

a weak cold front moves across the region on Friday, and then
remains nearly stationary just south of the region through the
weekend. High pressure builds to the north this weekend and then
moves off the New England coast on Monday. Another high settles
over the area into the middle of the new week, but a series of
weak disturbances will pass through the region during this time.


Near term /until 6 am Friday morning/...
530 PM update...made some minor adjustments to the hourly
pops/weather grids thru tonight. Except for northern NJ, kept
pops below 20 percent and replaced showers with a brief period of
sprinkles. Additionally, showers were introduced into the forecast
for late tonight in northeast PA and northern New Jersey as an area of
convection that is currently developing late this afternoon near
Lake Erie progresses eastward toward the Poconos. Showers will
likely be falling apart as it advances downstream into an
increasingly stable airmass that resides over the forecast area.
Accordingly, the shower coverage should be isolated and rainfall
amounts light.

Previous discussion...
showers have not been very persistent this afternoon thanks to
the limited instability and synoptic scale subsidence from the
building upper level ridge. Expect this trend to continue through
the evening hours, so have only a slight chance from the i95
Corridor North westward.

Once we lose diurnal mixing, winds should decouple (with the
possible exception of right along the coast), leading to generally
light winds, but remaining out of the south or southwest.

With the light winds and ample low level moisture, could see
patchy fog develop, primarily in more rural locations after


Short term /6 am Friday morning through 6 PM Friday/...
latest models trended faster with the weak cold front. GFS is the
most progressive, showing the cold front arriving at the i95
corridor by 15z. Given the upper level ridge and strength of the
low level southwesterly flow ahead of the front, this appears to
be too fast. Still, did speed up the timing slightly (closer to
the nam), with the front now arriving at the i95 corridor near
18z. Given the faster arrival of the front, expect heat index
values will fall short of heat advisory conditions (though we may
not see significant cold air advection just behind the front,
expect there will be some dry air advection through the day).

As with today, do not expect much in the way of precipitation
primarily because of subsidence and limited instability.


Long term /Friday night through Thursday/...
cold front continues to push south of the region Friday night.
Behind that front, high pressure builds into the Great Lakes
region and will slowly track east through the weekend. Northerly
flow ahead of the high will usher a much dryer airmass into the
region on Saturday with surface dewpoints falling from the upper
60s to near 70 Friday evening to the upper 50s to around 60 by
Saturday afternoon. High temps will only be a few degrees cooler
compared to Friday, but conditions will feel more comfortable due
to the lower humidity levels.

The center of the high will pass over central New York/PA Saturday
night, and then moves off the New England coast on Sunday. Return
flow sets up behind the departing high, and returns flow sets up
with surface dewpoints creeping back up into the mid and upper
60s, making it a bit more humid compared to Saturday.

Cold front then approaches on Monday and slowly passes through
the region on Tuesday. Isolated showers and thunderstorms are
possible Monday afternoon and evening, and then there is a better
chance for showers and thunderstorms on Tuesday with the passage
of the front. There currently is not much upper level support, so
will keep pops capped at low end chance for now. Thereafter,
surface high pressure settles over the Great Lakes and Ohio Valley
into the middle of the week. However, a series of weak upper level
shortwaves and vort maxes will pass through the region, touching
off isolated to scattered showers and thunderstorms during that
time. Will go no higher than low chance for pops.

Temperatures will continue to run several degrees above normal
through the middle of next week, but should as hot as Friday.


Aviation /22z Thursday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

Mostly VFR conditions are expected through 06z. There may be
isolated showers from the i95 corridor west through this time, but
if any develop, coverage is too limited to mention in the tafs.
Additionally, an MVFR ceiling is present across northwestern
portions of the area (including kabe earlier), but this should be
transient for most locations, and should dissipate by sunset.

After 06z, fog may develop at some taf sites (primarily our more
rural taf sites including krdg, kabe, and kmiv). Any fog should
dissipate shortly after 12z. There is a small chance (too small to
mention in the tafs at this time) that MVFR ceilings could move in
behind the cold front tomorrow.


Friday night through Sunday night...VFR. Light north winds will
become NE on Saturday afternoon, and then will become southeast on

Monday through Tuesday...mainly VFR. Isolated to scattered
showers and thunderstorms possible.


gusts at or above 20 kt will continue through the overnight
hours, but are expected to stay below Small Craft Advisory criteria at this time.
By tomorrow, winds should begin to decrease.


Friday night through Tuesday...high pressure passes well north of
the waters this weekend. A cold front approaches on Monday and
slowly passes across the waters through Tuesday. Sub-Small Craft
Advisory conditions expected to continue across the waters.

For today...the risk for the formation of dangerous rip currents
is moderate for the New Jersey shore. The risk is currently low
for the Delaware beaches.

The probable risk for the formation of dangerous rip currents
Friday and Saturday is low at this time.

Sunday through Wednesday...model ensemble guidance on every
successive cycle continues to send 2-4 ft long period (15 to 17
second) east southeast swell into our waters from the central
Atlantic - Gaston. It could be even higher but we're taking the
conservative approach at this time from this distant offshore
hurricane. This is all dependent on size, strength and track but
there is little doubt that swells will build here...just how much
is the question. Swimming and wading dangers will probably
increase. For now we're anticipating a moderate or greater risk
for Monday through Wednesday and possibly starting Sunday.


Phi watches/warnings/advisories...
New Jersey...none.


near term...Johnson/Klein
short term...Johnson
long term...mps

National Weather Service Glossary of Abbreviations