Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
840 PM EDT Tuesday Aug 4 2015
a cold frontal boundary will continue moving southeast through
the region tonight. High pressure will then build eastward into
the region for the middle part of the week. By Thursday night, low
pressure will advance northeast toward the region then exit off
the New England coast by early Saturday. High pressure will build
eastward into the region on Sunday with another cold frontal
passage for the early part of next week.
Near term /until 6 am Wednesday morning/...
dry air will continue to build into eastern Pennsylvania and
northern and central New Jersey from the west tonight. Dew point
readings should remain mostly in the 50s in those locations under
a partly cloudy sky.
A frontal boundary is forecast to remain across northeastern
Maryland, Delaware and southern New Jersey overnight. Showers and
thunderstorms were continuing to spread into that area from the
west this evening. Most of the guidance suggests that the area of
showers and thunderstorms will continue to affect the southern
part of our forecast area before moving off the coast after
midnight. The convection is associated with an impulse traveling
in the middle level flow as well as the surface front. The potential
for gusty winds with the thunderstorms appears to have diminished,
so we have removed that possibility from the forecast.
Minimum temperatures in our region should range from the upper
50s in the far north to around 70 in the south. The wind will
favor the west and southwest and speeds will likely decrease to 8
miles per hour or less after dark.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
the weak cold front will continue to push off the coast tomorrow
allowing surface high pressure to begin building late in the day.
A nice day shaping up overall with expected temperatures not that
far off from seasonal norms and comfortable dew points in the middle
50s to lower 60s. The region will see a good amount sunshine and a
bit of a breeze in the afternoon.
Long term /Wednesday night through Tuesday/...
Wednesday night and thursday:
High pressure will move west to east across the region in this
period with a somewhat cooler air mass in the region compared to
recent days. An increase in high clouds is likely as the next low
pressure system develops in the Ohio Valley Thursday with a few
showers/rumbles of thunder as well possible by sunset. Not much
spread overall in this period on most elements with the model and
their respective ensembles. 925 mb temperatures close to 20c still
suggest high temperatures will be in the middle 80's on average.
Thursday night through saturday:
A very complicated picture on the evolution of various features
in this period with a wide range in modeled solutions still on The
Table. Some potential exists for a heavy rain event Thursday night
through Friday night. Low pressure is expected to develop in the
Ohio Valley on Thursday with moisture overrunning a warm front
triggering showers and thunderstorms along it. Modeling is having
a poor time with the exact details on this convection. As a
result, feedback is occurring on some model runs with regards to
further development of the convection. Model consensus has the low
pressure traveling eastward along the front to our south with
overrunning rain to the north of the boundary and a strong/severe
storm threat well south of the region. This low then turns
northeast off the coast. The gefs and the 12z GFS are more
suppressed and faster, while the 00z European model (ecmwf) had a Nor'easter look
to it (2-4 inches of rain and a windy, cool day) and was a lot
slower. Right now these look like the goal posts. A considerable
spread appears in the sref and the gefs as well, with the European model (ecmwf)
ensemble mean a less aggressive suggestion than it's 00z
Our forecast will take The Middle Ground approach which was
represented by the 12z CMC, 12z UKMET and the 12z NAM/European model (ecmwf) which
have recently found middle ground today. This brings the
steadiest/ heaviest rains from phl southward with a sharp cutoff
further north for Thursday night through Friday night. Areas that
see clouds and decent rain Friday may stay in the 60's/70's, don't
want to go to low on temperatures at this point. If conditions are more
on the dry side then we would see highs into the 80's. With this
picture, conditions do clear out for the weekend. Quantitative precipitation forecast forecast for
this event has the highest amounts 1-2 inches across the Delaware-Maryland-Virginia
with amounts around an inch for philly and very little rain in the
Saturday night through tuesday:
High pressure will build back into the region late in the
weekend. Another frontal boundary brings a chance of showers and
storms and muggier/warmer weather on Monday and Tuesday. Wpc
guidance was primarily used in this period. However high
temperatures were increased Sunday and Monday based on the modeled
925 mb temperatures.
Aviation /01z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Dry air will continue to build into the northern part of our
region during tonight and Wednesday. As a result, we will carry a
VFR forecast for krdg, kabe, kttn, kpne, kphl and kilg through the
taf period. However, showers and thunderstorms are forecast to
pass nearby to the south and southeast of kilg, kphl and kpne
tonight mainly before 0600z. We have carried a vcsh for now to
cover the situation.
A frontal boundary will remain near kmiv and kacy into tonight so
we have mentioned the potential for thunderstorms in those tafs
until about 0600z. There may be some MVFR fog at kmiv and kacy
during the late night and early morning period, especially if they
do receive a fair amount of rainfall. Conditions at both locations
will improve to VFR for Wednesday with dry air arriving from the
Westerly winds should be 8 knots or less for tonight. A west
northwest wind around 8 to 12 knots is expected for Wednesday
along with gusts into the lower 20s.
Wednesday night and thursday: VFR, westerly wind gusts 10-15
knots becoming lighter and variable throughout the night and on
Thursday night through Friday night: MVFR/IFR conditions in rain
with highest chance for restrictions for kphl/kacy/kilg and kmiv.
East to northeast wind gusts around 20 knots, highest Friday
Saturday through Sunday night: VFR. Winds under 10 knots, 15-20
knot possible east of kphl Saturday afternoon.
we did not change any headlines this afternoon. We'll keep the
Small Craft Advisory going through much of night on the ocean waters. No headlines
are up for Delaware Bay.
We received a high quality National oceanic and atmospheric administration-19 sea surface temperature map from
Rutgers this afternoon with little cloud cover obstruction. The
image clearly shows the upwelling along the nearshore waters. This
could be the very reason only the offshore buoys were lit up with
25 kts and 4 to 6 foot seas. This colder water could of
strengthened the inversion right along the coast.
For tomorrow, winds will continue to subside, but swells will
take a bit longer to respond. No headlines are expected.
Seas and northeasterly winds increasing Thursday night and
Friday, reaching Small Craft Advisory criteria by Friday afternoon. Wave heights
likely around five feet through Saturday night with some
intermittent 25 knot gusts. Seas and waves falling below Small Craft Advisory
criteria by Sunday.
today was philadelphia's 8th consecutive day of 90 or higher (as
measured at Philadelphia international airport). It's been a
relatively easy going 8 day streak of 90 degree discomfort...the
most difficult being the 29th and 30th when heat indices topped
out in the upper 90s.
If the temperature nudges 90 at Philadelphia tomorrow, the 9 day
streak would be the longest here since the 12 consecutive day
stretch that ended July 9 2012.
As it stands now, the current 8 day streak ranks 21st to 34th
longest. It began July 28th.
The mean number of 90 or higher days in a year in the period of
record dating back to 1874 is 21. This year we've had 22 so far (1
in may, 7 in June, 10 in July and 4 so far in august). If you
recall the Summer of 2010, there were 55 days of 90 or higher in
The longest consecutive day streak of 90 or higher in Philadelphia
was 18 days ending August 15 1988.
Then 17 ending August 5 1995
13 ending September 5 1953
Marine...Small Craft Advisory until 5 am EDT Wednesday for anz450>455.