Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
410 am EDT Wednesday Aug 5 2015
the cold front pushing south and east of the area will stall to our
south while high pressure tries to build in from the west into
Thursday. An area of low pressure will develop along the boundary to
our south Thursday into Thursday night, then slowly move off the
North Carolina coast late Friday into Saturday. The low is then
forecast to move northward over the western Atlantic, while high
pressure tries to nose down into our area from the northeast over
the weekend. Another frontal boundary is expected in the early to
middle part of next week.
Near term /until 6 PM this evening/...
a cold front has pushed just south and east of the area early this
morning. Convection along and ahead of the front has accordingly
moved offshore. The front was rather diffuse with the temperature
and dewpoint gradient separated 50-100 miles behind (i.E., North) of
the pressure trough/wind shift. Patchy fog may develop toward
daybreak in southern New Jersey and the Delmarva, where the ground is wet
from last night's storms and dewpoints are still in the upper 60s
and low 70s, but middle-level clouds should help to limit the extent of
The front will stall just to our south and east today while high
pressure builds in from the Great Lakes/Midwest regions. West-northwest winds
will increase this afternoon in response to a tightening pressure
gradient between these two systems. Gusts to 20 miles per hour should be common
during the middle and late afternoon.
A vorticity maximum associated with the passage of the upper trough is
forecast to pass through our northern zones late this afternoon. There
is limited moisture with this system, so opted to keep probability of precipitation below 20
percent but added isolated/scattered sprinkles along and north of I-78.
Maximum temperatures in northeast PA and northwest New Jersey should be near climatology
(upper 70s in the Poconos/middle 80s in the Lehigh Valley and northwest nj).
However, with the cooler air lagging behind the front, expect maximum
temperatures to be 3-6 degrees above normal in phila and locations to the
south and east (upper 80s and low 90s). If the forecast high of 91f
for phl is realized today, it would extend the stretch of 90-degree
days to 9 consecutive days for the city.
Short term /6 PM this evening through 6 am Thursday/...
high pressure continues to build in from the Great Lakes tonight.
Winds will veer out of the north-northwest in association with the pressure
surge but should overall be light enough to not impede radiational
cooling much. Therefore, weighted the temperature forecast on the cooler
side of guidance under mainly clear skies and light winds. Min temperatures
range from the low 50s in the Poconos to upper 60s in phila and
along the coast. Fog potential will be low due to a dry airmass in
Long term /Thursday through Tuesday/...
Thursday into Thursday night, an area of low pressure will be
developing along the stalled frontal boundary to our south.
Meanwhile, a couple of short wave/vorticity impulses will be making
their way across the area from late Thursday into late Friday. This
should lead to some rainfall for at least the southern portions of
the forecast area which will be closer to the surface low. Areas
farther north away from the low may not see any rainfall as models
are keeping the majority of the rain further south. So we've lowered
probability of precipitation some across much of the area.
The low is forecast to drift into the western Atlantic into the
weekend while high pressure tries to nose down into our area from the
north. With drier air expected to filter in and no significant short
wave/vorticity disturbances aloft, we expect a dry forecast into
Models have slowed down the arrival of the next frontal system and
associated precipitation. Before they were bringing it in as early
as Monday, but now they are bringing an area of low pressure and
associated rainfall through the Ohio River valley Monday into
Tuesday, and into our area late Tuesday into Wednesday. Due to the
uncertainty, we've kept a chance of rainfall for Monday into
Wednesday, although it will likely not rain the entire period.
Aviation /08z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Mainly MVFR visibilities in fog at miv and Acy through about 12z, where the
ground is wet from earlier rainfall. Added a short tempo group at
miv for IFR visibilities in denser fog for a couple of hours just before
sunrise. Confidence not particularly high though with middle-level
clouds around. Otherwise, VFR today and tonight for the terminals.
West-northwest winds will increase this afternoon when gusts of 15-20 knots are
expected. Winds will diminish toward sunset.
Thursday night-Friday night...MVFR/IFR conditions possible across
southern areas with rain possible. Generally VFR across the north.
Saturday-Sunday...generally VFR. MVFR conditions possible along the
coastal areas. Northeast winds with gusts 15-25 knots, especially
along the coast during the day Saturday and Sunday.
Small Craft Advisory cancelled for the coastal Atlantic marine zones as winds have
subsided to under 20 knots and seas are below 5 feet. No marine hazards
expected today and tonight.
Thursday-Thursday night...sub-Small Craft Advisory conditions
Friday-Friday night...winds and seas increase and approach Small
Craft Advisory levels, possible exceeded advisory levels late Friday
Saturday-Saturday night...winds and seas expected to remain above
Small Craft Advisory levels through Saturday. Winds expected to drop
below advisory levels Saturday night, but seas remain elevated.
Sunday...winds remain below advisory levels, however seas are
forecast to remain above advisory levels.
yesterday 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 today, 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