Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
405 PM EDT Monday may 4 2015
high pressure in the west central Atlantic through tonight. A cold
front sags slowly south across the area Tuesday afternoon and night.
High pressure follows over the Middle Atlantic States Wednesday and
Thursday, edging offshore Friday through the weekend. This occurs
while low pressure meanders along the southeast United States coast
later this week into the weekend.
Near term /through Tuesday/...
surface high pressure will continue to get squeezed farther south
tonight as a cold front approaches from the north. Dry conditions
are expected overnight, although cloud cover will increase through
the night. Some showers may begin to approach our far northwestern
areas toward daybreak as the front get closer to the area. Gusty
winds this afternoon should diminish/drop off around or shortly
after sunset, although a steady southwest breeze around 5 to 10 miles per hour
may remain for most areas overnight.
Short term /Tuesday night through 6 PM Tuesday/...
a cold front is forecast to move in from the west Tuesday morning,
and slowly progress eastward through the day. Precipitable water values will
increase to around 1.0-1.5 inches as the front sags across the area,
and with an increase in moisture and warm temperatures, there is
some instability forecast with cape values approaching 500-1000
j/kg, Li values go slightly negative, and total total values
approach 50. So as the front moves through the area, and a short
wave/vorticity pulse approaches the area during the afternoon
scattered showers are expected to increase in coverage, along with
isolated thunderstorms. Even though there is instability, there is
not a lot of shear forecast. Actually the strongest shear builds in
behind the front. Still, with any thunderstorms, there could be
heavy rain, along with gusty winds as we should end up with an
Long term /Tuesday night through Monday/...
500 mb: above normal heights will prevail over much of the northeast
USA this 6 day period. We just need to monitor the possible eventual
influence of a coastal southeast USA low pressure system, which
might leak some moisture northward into our area next weekend.
Temperatures: calendar day average above normal through the
period. Relatively modest positive 5 degree departures Wednesday
and Thursday, then almost 10 degrees above Friday and possibly
more than 10 degrees above normal each day Saturday through
Forecast basis: unless otherwise noted, generally a 50 50 blend
12z/4 GFS/NAM MOS guidance Tuesday night - Wednesday night, 12z/4
mex MOS Thursday and Thursday night, then the 1521z/4 wpc gridded
elements of maximum/min temp, 12 hour pop, 6 hour dewpoint-sky-wind
from Friday through Monday.
Tuesday night...scattered showers/isolated tstms, mainly south two
thirds with the cold front passage. Above normal minimum temperatures. Confidence:
Wednesday...considerable cloudiness. A small chance of lingering
showers over the southwest portion of the forecast area. Easterly
flow in between the high centered to our north and the lingering
frontal boundary to our south will produce cooler east or NE
winds...possibly gusty to 20 miles per hour. No matter, maximum temperatures should
remain at or above normal except possibly right along the Atlantic
Ocean which should be chilly. Confidence: average or below average
regarding the maximum temperatures and whether there might be patches of
lingering showers. It could run cooler than currently posted in
the phi forecast.
Thursday-Sunday...Bermuda high pressure will extend back toward the
northern middle-Atlantic region late in the week and this weekend. A
closed low is forecast to develop along the southeast coast late
this week. The low is not expected to move much through the
weekend since it developed underneath the large-scale ridge where
there is minimal steering flow. This will allow the forecast area
to remain mainly dry through the weekend. However, we could see
weakly-forced convection drift eastward into the Poconos during
Sunday. Positive temperature departures should increase as we move
into the weekend. Morning fog and stratus could become part of
the reality this weekend.
Next Monday...rather warm and humid ahead of an approaching cold
front. Chance of showers and thunderstorms.
Aviation /20z Monday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
VFR conditions are forecast through tonight and into Tuesday. A cold
front is expected to slowly move across the area Tuesday, with
scattered showers developing and increasing in coverage during the
afternoon, along with a few thunderstorms possible. We have kept
thunderstorms out of the forecast for now, but we have introduced
showers for the afternoon. If showers and/or thunderstorms are heavy
enough, they could briefly reduce ceilings/vsbys, but we will wait to
include restrictions until confidence of occurrence/timing is higher.
Gusty southwest winds remain this afternoon, with gusts
diminishing/dropping off around or shortly after sunset. A steady
southwest breeze around 5-10 knots may remain for many areas
overnight. Winds will become more west-northwest behind the front
Tuesday night...predominately VFR. Visibility/ceiling restrictions possible
during the night from scattered showers and isolated storms. Restrictions would
be localized/temporary. Light wind. Confidence: average
Wednesday..VFR ceilings. A small chance of showers. A gusty east or NE wind
of 15-20 knots during the day. Confidence: average
Wednesday night through Friday...VFR and light south-southeast winds
with high pressure in control. Confidence: average (normally above
average but don't like the modeled closed low not too far to our
Saturday...possible morning IFR figure/stratus otherwise VFR during
the afternoon. Maximum gust 15 knots during the afternoon. Confidence:
sub-Small Craft Advisory conditions continue to be forecast tonight
through Tuesday. Winds are expected to gust in the low 20s, but
should remain below advisory levels. The strongest winds would be
expected on our northern waters. Seas should remain 3-4 feet. Seas
may approach 5 feet overnight into Tuesday morning, but we think it
would be farther offshore than our coastal waters.
Tuesday night...southwesterly winds ahead of a cold front should shift north behind
the front during the night. Isolated thunderstorms may move over the waters
during the evening. At this time no marine headline anticipated
though seas may eventually reach 5 feet in the southern New Jersey or Delaware
waters. Marginal confidence for meeting Small Craft Advisory hazardous seas
criteria and no headline at this time.
Wednesday through Saturday...winds and seas below Small Craft Advisory criteria.
red flag warning remains in place through the early evening as
relative humidity values have dropped into the low 20s and winds
continue to gust around 20-25 miles per hour. Humidity values should rebound
overnight as temperatures cool. Also, wind gusts should diminish by
sunset as well.
our phone system was changed last week and we're still short
several public phone lines. Results: frequent busy signals for
those trying to access our forecasts via the phone. We're not sure
when this problem will be resolved. We apologize for this difficulty
accessing our products via the phone.
PA...red flag warning until 8 PM EDT this evening for paz054-055-
New Jersey...red flag warning until 8 PM EDT this evening for njz001-
long term...drag 405