Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
403 PM EDT Tuesday Jul 7 2015
a trough of low pressure to our south will move eastward very slowly
this evening, as a cold frontal boundary slowly makes its way
towards our region. The trough to our south will merge with this
frontal boundary on Thursday, stalling the front over our area.
Several areas of low pressure will move along the frontal boundary
on Thursday and Friday. High pressure will briefly move into the
region for the weekend, before a warm frontal boundary moves to our
north on Monday. A trough looks to persist over our area through
most of next week, as a result of a dominant ridge over the
Near term /until 6 am Wednesday morning/...
a short wave trough was passing overhead in the middle level flow this
afternoon. The feature was helping to enhance the scattered shower
activity in our region. Mixed level cape values were peaking in the
1000 to 1500 j/kg range at middle afternoon in eastern Pennsylvania and
in northern and central New Jersey. A bit of drying aloft in the
southwesterly flow along with the gradual loss of daytime heating
should cause the cape values to decrease slowly during the late
afternoon and early evening hours. The middle level trough should pass
to our northeast and east early this evening and it will likely take
the last of the showers and isolated thunderstorms with it at that
We are anticipating a mostly clear sky from about sunset until
shortly after midnight, then clouds ahead of an approaching frontal
boundary should begin to spread over our region from the northwest
It will remain humid tonight with minimum temperatures forecast to
range from the upper 60s to the middle 70s.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
a frontal boundary is forecast to extend from the Catskills across
northeastern Pennsylvania to around Pittsburgh early on Wednesday
morning. The boundary is expected to sink slowly into our
northwestern counties as the day progresses. Meanwhile, a surface
trough is anticipated to develop to the Lee of the Appalachians in
the southwesterly flow.
The convection that was over the eastern Great Lakes and the lower
Ohio River valley this afternoon should reach our region on
Wednesday. As a result, we will indicate an increasing chance of
showers and thunderstorms from northwest to southeast.
The model guidance is suggesting only marginal instability for
Wednesday. However, precipitable water values will likely increase
to 2 inches or more. As a result, we will continue to mention the
possibility of locally heavy rainfall.
Maximum temperatures on Wednesday are anticipated to be mainly in the
80s with some upper 70s in the far north and some lower 90s in the
Long term /Wednesday night through Tuesday/...
hemispheric wave guidance shows deep southwesterly flow across the
eastern half of the U.S. At the start of the longterm period. By the
weekend the wavelength across the contiguous U.S. Becomes longer
allowing the southeast ridging to retrograde towards the central
U.S. This sets up a pseudo-high latitude Omega block, with our
region on the periphery of an East Coast trough. This pattern looks
to remain in place, while lifting and weakening a bit, going into
next work week, adding to our daily chances for showers and
Thursday - Friday night...the slow sagging cold front that begins to
cross the region on Wednesday looks to make it as far south as
Delaware-Maryland-Virginia on Thursday and remain nearly in place through Friday.
Multiple waves move along this boundary as it presses southward
adding to the increased chances for scattered showers and embedded
thunder. Guidance tries to advect in more instability from the south
on Thursday ahead of the front but the timing doesn't look like it
overlaps the frontal passage. That being said precipitable waters will still be
well above normal, possibly 2+ inches giving US more localized
flooding issues...same as it ever was. We continue with the heavy
rain wording in the forecast Thursday night into Friday morning, but
confine it to our northern half...better lift/dynamics and some
elevated instability to work with. After what could be a Great Lakes
mesoscale convective system passage Friday morning across our north, the front continues to
sag southward during the day with isolated showers and thunderstorms
possible across Delaware-Maryland-Virginia...drying out behind the front across the
north. It should be noted that ffg across the northern zones is
running quite low with a lot of areas only needing 1.5 inches in an
hour to cause issues...something to watch.
Saturday...the aforementioned front should be farther to our south
this weekend while large scale subsidence takes over...the longwave
ridging retrograding all the while. We still expect Saturday to be
rain free but there could be lingering middle-level energy moving by to
our southwest that may touch off a few isolated to scattered showers
in our extreme southwest zones...have time to better define these
chances if any.
Sunday - Tuesday...warm front passage, from what was once the cold
front earlier in the period, moves back towards the north on Sunday
night into Monday. Cold front then nears from the northwest late
on Monday into Tuesday as troughing takes back over again.
Northwest flow aloft looks to prevail as central U.S. Ridging
amplifies. This may send several shortwaves through the region
from late Monday Onward...northern plains mesoscale convective system season.
Aviation /20z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
The scattered showers and isolated thunderstorms in our region this
afternoon should pull away to our northeast this evening. We have
the mention of precipitation in the tafs for kabe and kttn until
Mainly VFR conditions are expected for tonight. The sky is forecast
to be mainly clear before midnight with an increase in VFR clouds
from the northwest late tonight.
A slow moving frontal boundary will approach from the northwest on
Wednesday. MVFR ceilings along with scattered showers and
thunderstorms are expected to reach krdg and kabe in the morning.
The lowering conditions and precipitation should reach our remaining
six taf sites in the afternoon.
A southwesterly wind around 10 knots this afternoon should drop to 4
to 8 knots for tonight. A west southwest wind around 5 to 10 knots
is expected for Wednesday.
Thursday...potential MVFR and IFR restrictions in showers and
thunderstorms, highest chances each afternoon and evening. West-
southwest wind gusts at or under 20 knots.
Friday - Saturday night...VFR. Winds at or under 10 knots, mainly
Sunday...mostly VFR. Some scattered showers and embedded thunder
weak high pressure will influence the coastal waters of New Jersey
and Delaware for tonight and early Wednesday. A slow moving frontal
boundary is forecast to approach from the northwest on Wednesday
afternoon. A south to southwest wind around 10 to 15 knots is
anticipated. Speeds may increase to 15 to 20 knots for a time
tonight on our ocean waters.
Wave heights on our ocean waters should favor the 2 to 4 foot range
for tonight and Wednesday. Waves are expected to be 2 feet or less
on Delaware Bay.
Sub-Small Craft Advisory winds and seas expected. Any wind gusts look to remain
below 20 knots, more northerly through Saturday night. Seas
around four feet on Wednesday and Thursday. The highest chance of
thunderstorms is Wednesday afternoon and evening then again later