Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
922 PM EST Wednesday Dec 4 2013
high pressure off the East Coast will move further offshore tonight
and Thursday. A cold front will cross the region Thursday night and
Friday, with another area of high pressure building in from the
northwest Saturday into Sunday. A warm front is expected to lift
north Sunday night into Monday morning, followed by another cold
front late Monday. High pressure will then build in from the west
through the middle part of next week.
Near term /until 6 am Thursday morning/...
a strong area of low pressure will move northward through the Great
Lakes region and into Canada tonight. An associated weak warm front
will move northward into our area overnight along with a weak
middle-level shortwave. With plenty of low-level moisture around the
region, there may be some light rain or drizzle that develops and
moves through the region overnight toward Thursday morning.
There will continue to be warming through the low and middle levels of
the atmosphere and in turn, temperatures will remain quite mild.
With pretty good cloud cover overnight, we will not be radiating all
that well, which will also keep US on the warmer side.
In addition, as the warm front moves through, more warm air will be
pushed into the area. This will allow for rising temperatures
overnight, with the lows occurring before midnight in most
locations. Expect low temperatures to be in the 40s across the
Once again just adjusted cloud cover and temps, but also removed
probability of precipitation in the near term to account for the fact that there is
nothing on radar at this time. Lowered probability of precipitation through about 06z as well.
Short term /6 am Thursday morning through 6 PM Thursday/...
the aforementioned warm front will push north of the region by
late morning. Light winds will start to pick up just a bit from
the south southwest. Precipitation will continue mainly across the
northern half of the cwa, spreading to the south toward the
evening as a cold front approaches from the west.
Warm air will continue to remain over the region in the southwest
flow with unseasonably high temperatures forecast. We are not
expecting any records to occur as the records are anomalously high
for this date in December. Regardless, expect high temperatures to
reach well into the upper 50s to middle 60s across the region.
Long term /Thursday night through Wednesday/...
the middle-to-upper level pattern during the extended portion of the
forecast period fluctuates between ridging in the east to a more
zonal pattern, then back to ridging, then back to zonal, and the
temperature pattern will mimic this pattern (warmer than normal,
slightly below normal, warmer than normal, below normal). Given
this pattern, the storm track won't stray far from the middle-Atlantic
region, so as precipitation moves through from time to time, some of
it will fall in the frozen form, especially north of the I-95
corridor. As always, the devil is in the details, and this far out,
those details are subject to change as time moves closer to the
actual events. However, the 12z GFS is fairly similar to its earlier
run, so at least for now there is some consistency to grab on to. The
breakdown is as follows:
Thursday night through Friday night...wet. The cold front assd with a deep low
moving through central and eastern Canada will cross the area Friday morning.
A weak area of low pressure will move along it Friday night/early Sat
only adding to precipitation chances. Temperatures will be mild Thursday
night...but then begin dropping behind the front Friday. Lows will fall
back below freezing by Sat morning over much of the northern/western areas.
Precipitation will probably end as snow across the far northern/western areas. A light
accumulate of snow is possible by Sat morning across the higher
elevations...especially in the far north. Amounts are expected to be
well below advisory criteria.
Sat through Sun morning... a short break in the wet weather as high
pressure noses into the area. Cold. Highs back a few degrees below
normal Sat and 3-5 degrees colder on sun. Highs across the southern
areas mostly in the low/middle 40s Sat and close to 40 on sun. Readings
5-7 degrees colder across the northern areas.
Sun afternoon through Tuesday morning...a warm front lifts north with more
precipitation overspreading the area on sun. Temperatures initially cold enough
for frozen/freezing precipitation. Once again some chance for accums across the
western/northern areas. Temperatures should then warm overnight and all precipitation
changes back to rain by Monday. Quantitative precipitation forecast 0.2 to 0.5 possible.
Tuesday afternoon/night...improving conditions...cold. Lows mostly on
the 20s with teens far north and low 30s phl metropolitan.
Wednesday...continued cold as high pressure builds in from the west.
Aviation /02z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Conds ranged from VFR to MVFR across the area and a downward trend
is expected as we progress through the night. Not much confidence on
timing and exactly how low things get, but IFR is anticipated and
LIFR is psbl, but will everywhere reach these thresholds at the
Winds are light across the region and will continue to remain light
through this evening and overnight. Bases around 3000-4000 feet will
start to lower this afternoon to MVFR levels and then continue to
lower through the overnight period to IFR, with some locations
dropping down to LIFR by Thursday morning. Ceilings will lift a
little bit toward Thursday afternoon and winds will increase out of
the south southwest with speeds around 10 knots or less. While the
winds will help to promote a little bit of mixing, confidence is
presently low that ceilings will lift enough to become VFR for the
Plenty of low level moisture will across the region and as a
shortwave and weak warm front move into the area, we may see some
light rain and/or drizzle overnight through Thursday late morning.
Thursday through Sat morning...low ceilings/visibilities expected much of the time.
Periods of rain which may change to snow before ending early Sat,
especially the northern taf sites.
Sat afternoon through Sun morning...mostly VFR.
Sun afternoon...deteriorating cigs/vsbys. Periods of snow sleet
Sun night through Monday...mainly IFR conditions as a warm front lifts
north through the region. Precipitation changes to rain...then back
to a frozen form later Monday.
sub advisory conditions are expected through Thursday.
Winds remain fairly light across the areas waters with seas
remaining around 3 feet or less. Winds and seas will start to
increase as we head into Thursday night in advance of an
approaching cold front.
Small Craft Advisory flag will probably be needed by Thursday night for increasing
winds/seas. Winds/seas may remain Small Craft Advisory criteria into the weekend.