Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
758 PM EDT Friday Aug 1 2014
a coastal front and several weak areas of low pressure will affect
the weather tonight into the weekend. High pressure will build in
for early next week. A cold front will approach and cross the area
next Tuesday and Wednesday.
Near term /until 6 am Saturday morning/...
isolated to scattered showers with some embedded thunderstorms will
continue to slowly advance northward across our region, associated
with a shortwave trough/vorticity maximum passing overhead. Coverage of
showers will continue to be scattered at best through this evening.
We have kept a mention of thunder through the middle to late evening
hours across the forecast area as there will be some limited
instability. With the latest update did increase probability of precipitation and quantitative precipitation forecast
across the Lehigh Valley to account for the highest concentration
of storms through the remainder of the evening. Temperatures and
dewpoints were also adjusted based on the latest 21-22z metar observation
and the lav guidance for the next several hours.
Likely probability of precipitation are then in place for continued showers, mainly after
midnight, for the eastern half of the County Warning Area from about the Delaware
valley and the Delaware-Maryland-Virginia eastward through central and southern New Jersey.
This second and more widespread wave of showers will be associated
with another shortwave/vorticity maximum passing over the region around the
06z time- frame. In addition, model guidance also shows an
inverted surface trough and possible weak low pressure developing
along a frontal boundary edging closer to the East Coast from the
Atlantic by around 12z Saturday. Precipitable waters increase, especially for
our eastern zones through the 06z to 12z time- frame, and we have
kept the idea of moderate to perhaps heavy showers leading up to
daybreak Saturday. There still continues to be some model
differences with respect to the axis of heaviest rainfall through
the overnight and into Saturday, as the GFS and European model (ecmwf) keep most of
the heavier precipitation offshore or mainly over our eastern zones, with
the NAM showing some heavier precipitation across much of the County Warning Area between
06z and 18z Saturday. As such, confidence is a little below
average with respect to coverage and timing of moderate to heavier
For overnight temperatures, we mostly took a met/mav MOS blend with
continuity across the region. Minimum temperatures are mainly
expected to be in the 60s across the forecast area with overcast
conditions and an increase in showers.
Short term /6 am Saturday morning through 6 PM Saturday/...
the previously mentioned upper shortwave/vorticity maximum along with weak
surface low pressure along an East Coast frontal boundary will lead
to enhanced moderate to perhaps heavy rainfall at times, especially
through the first half of Saturday and into the early afternoon.
Also as mentioned in the near term, there continues to be
differences between the ECMWF, GFS, and NAM with respect to the axis
of heaviest rainfall. Overall, we took a general compromise between
model solutions and focused the heaviest rain and highest probability of precipitation over
our eastern zones and offshore. This looks to be more of a heavy
rain event, with only isolated thunder, and for now, we kept the
mention of thunder out of most areas. With regards to temperatures,
we leaned more toward the mav MOS guidance, as the met guidance
overall looked a bit on the cool side. That being said, it will be a
below average day temperature-wise, with most locations only topping
out in the middle to upper 70s with mainly overcast conditions, rain,
and a continued east to northeast flow.
Long term /Saturday night through Friday/...
a continuation of the humid and unsettled pattern for Sat night
through Sunday night as a weakening 500 mb trough and coastal front
remain across the area. Occasional showers and scattered thunderstorms with downpours
will be across the area. Temperatures will remain below normal
with the abundant clouds and showers. Scattered showers early Monday
then improving conditions with weak high pressure building in.
Monday night through Tuesday night will be a mostly dry period with weak
high pressure affecting the weather. Temperatures will rebound
back to near normal for the period. A cold front will approach
from the north/west later Tuesday.
Scattered thunderstorms are expected next Wednesday as the cold front crosses the
area. The upper flow becomes more zonal...leading to quicker
weather changes later next week. Fair weather Thursday...then another
system with showers possible next Friday. Temperatures near to above
normal middle/late next week.
Aviation /00z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Any thunderstorms near the taf sites have diminished this evening,
so took out any tempo groups. We await the arrival of the next system
from the southeast which will bring gradually lowering ceilings
and some showers/rain after midnight. This rain is likely to last
to around 16-18z ending from west to east. During this timeframe
MVFR ceilings are likely at times along with some MVFR
visibilities. The coverage of showers and lower ceilings is more
uncertain at kabe and krdg so a lower scattered cloud deck was included in
the taf where there is a higher chance ceilings are more
predominately MVFR to VFR. Steadier rain is expected at kmiv and
kacy so ceilings may lower to threshold of MVFR/IFR for a few
hours. Some variability in the winds is expected this evening
before a more easterly direction overnight and then a gradual
transition to southerly winds on Saturday.
Sat night through Monday...scattered showers and thunderstorms may create localized
Monday night through Wednesday...mostly VFR.
overall, sub-advisory conditions are expected for the coastal waters
and Delaware Bay through tonight and Saturday. Winds are expected to
remain mainly below 20 knots, with seas mostly in the 2 to 3 foot
range. A southeasterly flow this evening will gradually become more
east-northeast into Saturday.
Sat night through Wednesday...overall, winds and seas will remain below Small Craft Advisory
conditions. Scattered thunderstorms may create localized higher winds and seas
there will be a moderate risk of rip currents along the New Jersey shore