Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
938 PM EDT Thursday Aug 27 2015
high pressure will settle across our region overnight and Friday,
then move offshore during the weekend. A weakening cool front is
forecast to arrive late Sunday into Monday, then high pressure
builds in for Monday into Tuesday. A weak system may slide across
our area Tuesday, as high pressure continues to build nearby into
Near term /until 6 am Friday morning/...
high pressure was centered over Lake Erie and vicinity this
evening. The high will drift eastward overnight.
The last of the stratocumulus will continue to dissipate with a
mainly clear sky anticipated. A light northwest to north surface
flow is expected. Temperatures should drop into the 5os and lower
Short term /6 am Friday morning through 6 PM Friday/...
the high pressure system will ease across our County Warning Area. The transition
to warmer and more humid weather slowly starts on Friday. Still
another spectacular late August day. The predicted convective
temperatures are not suppose to be reached until the afternoon and
with less of an antecedent moisture pool between 925mb and 850mb
forecasting less cumulus than today. The 250mb jet will be farther to
the southeast, so no jet stream cirrus problems. Air mass
modification by late in the afternoon suggests a 1-3f bump in maximum
temperatures from today. This is much closer to NAM MOS than the cooler
GFS MOS where the stat guidance parts ways on Friday.
Overall light wind pattern with the sea and Bay breeze making
more of an inland advance than the past two days late in the
Long term /Friday night through Thursday/...
the synoptic setup is comprised of a ridge east of the Carolinas
with an initial zonal flow across the northeast and middle Atlantic
regions. A short wave trough is forecast to be traversing the
Midwest and Great Lakes regions Saturday and Sunday, however this
feature may end up weakening as it gets to the northeast with the
western Atlantic ridge building west and north some. The leftovers
of the short wave trough slides across our area Tuesday and
Wednesday, then an upper-level ridge expands across the Ohio
Valley and Great Lakes region eastward through Thursday. We used a
model blend for Friday night into Sunday, then the 12z wpc
guidance thereafter. Some adjustments were then made following
additional collaboration with our neighboring offices.
For Friday night...a ridge centered to our southeast will allow
surface high pressure to be over our area. This will be assisted
by a short wave trough moving across the Midwest and upper Great
Lakes, although there is some variations within the model guidance
on the amplitude of this feature. Overall, continued quiet weather
for our area during this time is anticipated.
For Saturday and Sunday...a short wave trough is forecast to be
sliding across the Great Lakes region during this time, however it
may end up weakening as it approaches the northeast. Some model
guidance maintains this feature as it approaches Sunday night and
especially beyond, however with the western Atlantic ridge tending
to build some and even expand a bit westward, this feature should
not have much in the way of an impact on our weather especially
since it looks to approach slowly. The possible fly in the
ointment may be late Sunday as come convection upstream within the
lingering upper-level weakness could spill into our northwest
zones. A southerly flow of warmer air is expected to occur each
day with at least some increase in the dew points as well. The
latter should be more noticeable during Sunday as the southern
flow is more established then, although the moisture return does
not appear to be substantial.
For Monday and Tuesday...as a trough migrates across the Pacific
northwest, downstream ridging is expected to occur. The model
guidance shows a higher amplitude ridge occurring during this time
frame with the axis mainly to our west. Some model guidance has
been showing the weakening short wave trough migrating overhead
during this time. There still could be some convection that
develops with daytime heating within a moistening air mass,
however there does not appear to be any pronounced large scale
forcing mechanism. Therefore, we went with a dry forecast.
Otherwise, very warm to hot and humid for much of the area. The
flow looks light enough to allow for afternoon sea breeze
For Wednesday and Thursday...a similar synoptic setup during this
time frame as well with ridging generally holding. This keeps high
pressure at the surface close by, with a blocking type pattern in
place. Tropical cyclone Erika may be lurking off the southeastern
U.S. Coast, however there is a lot of uncertainty. There are some
hints in the guidance that a trough slides across the northeast
Thursday before the ridge builds again, however it looks weak and
bypasses the tropical system. Some guidance brings the tropical
system farther north, however that would be into the ridge
overall. The trough out west will assist in the downstream ridge
placement and strength, therefore more uncertainty with the flow
across the east. For the latest forecast information on tropical
cyclone Erika, visit the National hurricane centers web site.
Other than a rather low chance for diurnally driven convection, no
real organized triggers appear to be present at this time for rain chances
which the area needs. The very warm and humid conditions should
persist for much of the area, with perhaps some relaxation if the
aforementioned trough is able to knock The Heights/temperatures
down some for a time.
Aviation /02z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
VFR conditions are expected through the taf period with a mainly
A light northwest to north wind overnight into Friday morning
should back toward the west and southwest on Friday afternoon. The
sea breeze front may reach kacy on Friday afternoon.
Friday night and Saturday...VFR. Light southwesterly winds at
night, increasing up to 10 knots during the day Saturday.
Sunday...a chance of local fog early, otherwise VFR. A few
showers and thunderstorms may develop in the afternoon and evening
well to our west and northwest.
Monday and Tuesday...a chance of local fog each morning,
otherwise mainly VFR. There could be a shower or thunderstorm
around especially Tuesday afternoon.
no marine hazards expected tonight and Friday.
Overnight, the generally northerly gradient wind around the
surface high is predicted to return.
On Friday, with the surface high passing across the marine
waters, wind speeds will become lighter with more variability in
direction as the morning and early afternoon progress. Then a
light east to southeast circulation around the surface high should
develop. This will likely also start working its way into Delaware
Friday night through Tuesday, high pressure generally dominates
the weather with lighter flow. A southerly flow however should
increase some at times, especially during the afternoon and
evening hours particularly nearshore with the development of
sea/Bay breezes. Overall, the conditions are anticipated to remain
below Small Craft Advisory criteria.