Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
513 PM EDT Wednesday Aug 20 2014
weak low pressure will move north of the area tonight and Thursday.
Another low pressure system will move south of the area Thursday
night through early Saturday. High pressure will build in from the
north later Friday, then remain for the weekend and into early next
Near term /until 6 am Thursday morning/...
a short wave trough ahead of a main upper-level trough dropping down
across the Great Lakes region will lift east-northeastward through
tonight. The initial line of showers and thunderstorms with this
feature continues to weaken and fragment as it enters our far
western zones. This should continue as it encounters a more stable
airmass with an eastward extent and also less moisture. There is
some airmass recovery occurring to the west of the line and an
analysis showed deeper moisture farther to the west. While some
showers /perhaps a rumble of thunder/ should make their way to the
east tonight especially across portions of eastern Pennsylvania and
northern New Jersey, they should be weaker. We will monitor radar
trends and adjust the probability of precipitation accordingly. In addition, some
thunderstorms are developing near Washington District of Columbia however this in
within an area of higher instability.
Otherwise, enough moisture and the leftover debris clouds should
result in more cloudiness through the night especially east and south
where the sky has cleared thus far. The hourly grids were tweaked
based on the latest observations and then the lamp/lav guidance was
blended in to help assist with trends.
Short term /6 am Thursday morning through 6 PM Thursday/...
Thursday...another short wave in the west-northwest flow over southern New
York state should redevelop heavy convection during the afternoon over
east PA...possibly extending into west New Jersey and the Maryland East Shore closer to the
convergence of the surface low and inverted trough extending northward from
the vicinity of dca. Precipitable water values are generally forecast around
1.5-1.75 inches, so some showers/storms could produce a period of
moderate to heavy rainfall. Isolated small hail not impossible as
tt near 50 in area of maximum instability in New Jersey (near the Delaware
Forecast basis: probability of precipitation were blended NCEP MOS probability of precipitation with the 09z sref and
that gives the best chance for some needed rain to east PA. Otherwise a 50
50 blend of 12z/20 NCEP MOS except blended rgem sky with NAM sky
and GFS MOS guide.
Near or slightly above normal temperatures.
Long term /Thursday night through Wednesday/...
the long term forecast starts off with rain chances, before a drying
out period sets in across the area.
The weak areas of low pressure to the north (thu night and
friday) and the south (friday through saturday) will force US to keep
low chance probability of precipitation or slight chance probability of precipitation for those periods. The systems do
not look strong enough to produce any heavy rains however. Dry
weather is expected for Sunday into early next week. High pressure
will build in from the north/northeast allowing dry air to
overspread the area.
Temperatures through the long range will start near normal
Friday...before dropping to below normal for the weekend and next
Monday. Readings will rebound back to near normal next Tuesday and
then possibly go above normal Wednesday.
Aviation /21z Wednesday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...VFR ceilings at or above 4000 feet spreading from west to
east. Some showers should be around mainly north and west of kphl.
Light southerly winds. There could be some localized MVFR ceilings
with fog toward daybreak.
Thursday...generally VFR ceilings. Some showers and thunderstorms
are expected to occur especially farther inland, which may lower
ceilings and visibilities to briefly IFR. Southerly winds generally
Thursday night through Saturday...mostly VFR. Showers with lower
conditions are possible.
Sat night through Monday...mostly VFR.
no marine related headlines through Thursday.
East-southeast winds between 5-15 knots.
Thursday night through Friday night...sub Small Craft Advisory conditions west/ scattered showers.
Sat through Monday...low end Small Craft Advisory seas expected on the ocean. Mostly fair weather.