Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
944 PM EDT Tuesday Jun 2 2015
a frontal boundary will stall south of the area through Friday.
Meanwhile, high pressure will pass to our north tonight and
Wednesday before moving off the New England coast late in the week.
A cold front will progress southward through the area Friday night
into Saturday. Another area of high pressure will build into the
region Saturday night before moving offshore Sunday. A warm front
moving into the area Monday will be followed by the passage of a
cold front on Tuesday.
Near term /until 6 am Wednesday morning/...
the slow moving front well to the south continues to aid in
transporting moisture across the Delaware-Maryland-Virginia and southern New Jersey this evening.
Another batch of steady rains appears to be heading across the
Chesapeake Bay and will affect the Delaware-Maryland-Virginia and southeast PA over the
next several hours. Probability of precipitation in these areas were raised and kept
categorical for several more hours. Dryer air is also advancing
southward across the southern Poconos and northern Lehigh Valley. The radar
shows little precipitation in these areas. It will remain mostly cloudy
overnight. Patchy fog and low clouds will prevail in most areas.
Temperatures/winds generally look OK for the update.
Short term /6 am Wednesday morning through 6 PM Wednesday/...
low clouds, drizzle and light rain showers will still be in
place through most of the day. These conditions will hang on longest
across the Delmarva, closest the front. Some breaks in the clouds
may occur later in the day the further north you go. This will likely
lead to an unusual temperature spread across the region with the
highest readings in the upper 60's across the north where more solar
radiation can come come through and cooler temperatures across the
Delaware-Maryland-Virginia. Philadelphia metropolitan could actually go either way, took a
middle approach between the cooler, wetter further north NAM and the
drier, warmer European model (ecmwf) for the Philadelphia metropolitan. Quantitative precipitation forecast should be light
under 1/10th of an inch.
Long term /Wednesday night through Tuesday/...
the cutoff low over the southern Appalachians Wednesday night is
forecast to become an open wave as it moves eastward toward the
Carolinas through Thursday night. The surface reflection of this
low will be marked by an inverted trough along the southeast
coast. This trough is expected to extend northeastward to 50
miles or so off the Delaware-Maryland-Virginia coast. This surface trough, which is
associated with an old frontal boundary that moved through the
area earlier in the week, is expected to remain nearly stationary
to our south and east. Meanwhile, the forecast area will remain
stuck in a hybrid cold-air damming (cad) like setup to the
northwest of this boundary. Although the center of the high will
be moving off the New England coast (which is not an ideal cad
position), The Pocket of colder air near the surface will be
reinforced by east-northeast flow off the Atlantic waters and by
diabatic cooling. This setup will prolonged our stretch of
seasonably cool, cloudy and damp conditions into Friday morning.
Highest coverage of showers are expected Wednesday night/Thursday
morning in conjunction with the low-level trough lifting northward
through the northern Middle-Atlantic States. Probability of precipitation were increased to
likely for a majority of the forecast area during this time.
The upper low and inverted surface trough will move farther off the
East Coast Friday afternoon and night. We will lose the onshore flow
as winds back out of the north and even become light/variable at the
surface. The temperature forecast for Friday is tricky as the difference
this time of year between highs in the low 70s vs low 80s can be as
little as an hour or two of sunshine. Official forecast sides closer
to the warmer maximum temperature guidance given the opportunity for breaks in
the clouds Friday afternoon.
A cold front is forecast to weaken as it drops southward into the
area Friday night and Saturday. Coverage of showers should be low
(20-30 pops) during this time since forcing for ascent appears to be
limited with this system. The operational GFS and several of its
gefs members have even trended dry with the frontal passage with the latest
12z run. High pressure quickly builds in from the north behind the
The center of the high will start to move the New England coast on
Sunday. Kept the forecast dry for Sunday as there should be enough
subsidence underneath the ridge to cap deeper convection from
Southerly return around the western periphery of the offshore high
and ahead of a cold front approaching from the west will strengthen
along the eastern Seaboard, resulting in a warming trend early next
week. The Heart of the warmer air is expected to arrive after a warm
front lifts northeastward through the area during the day Monday.
There will also be a chance for showers and storms Monday and
Aviation /02z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
We have gone along with the guidance which mostly shows IFR
conditions across most areas overnight. Showers/fog and low clouds
over all areas...except no precipitation krdg/kabe. Visibilities will slowly
improve Wednesday morning...followed by ceilings later. Earliest improvement
north/west with timing to VFR during the afternoon for the del valley
Wednesday night through Friday morning...ceilings expected to lower from
south to north to MVFR Wednesday night and Thursday morning in conjunction with
the arrival of rain showers and strengthening onshore flow. IFR ceilings may
develop, especially at Acy (where the influence of the marine layer
is greatest). Sref probabilities for ceilings below 1 kft at 12z Thursday are
around 33 percent. Even if ceilings briefly improve Thursday afternoon, they
are expected to lower again Thursday night. MVFR ceilings inland and IFR ceilings
closer to the coast is the most likely outcome.
Friday afternoon through Sunday...MVFR ceilings expected to improve to
VFR Friday afternoon. Predominately VFR through the weekend though
there will be a chance of showers.
continuing with the Small Craft Advisory on the coastal zones as seas remain near or
or over five feet. Seas will likely be close or over five feet
through Wednesday. Northeast wind gusts will increase to between 25
and 30 knots tonight and continue through Wednesday. Wavewatch may
end up a foot low with seas in this period due to onshore flow which
has been reflected in this forecast.
Wednesday night and Thursday....east winds 15-20 knots with a
occasional gusts to 25 knots in our coastal Atlantic waters Wednesday
night while seas are predicted to remain around 4-6 feet. Had enough
support from guidance to extend the Small Craft Advisory into Wednesday night.
Easterly winds will subside Thursday but seas will still remain
elevated to near Small Craft Advisory threshold of 5 feet.
Thursday night through Sunday...winds should remain below Small Craft Advisory
criteria. Seas should generally be below Small Craft Advisory criteria too although
it may increase to 4 to perhaps near 5 feet at times this weekend.
due to the continued northeast wind and today's full moon, we
will carry a moderate risk of rip currents through this evening.
A moderate risk will most likely continue into tomorrow.
Marine...Small Craft Advisory until 6 am EDT Thursday for anz430-431-