Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
954 am EDT Tuesday Sep 30 2014
a low pressure system and weak front will affect the weather today
and tonight. High pressure will build in Wednesday and remain through
Friday. A strong cold front will cross the region Friday night into
early Saturday. High pressure will build across the area Saturday
night into early Monday. Low pressure will approach for later
Monday and into next Tuesday.
Near term /until 6 PM this evening/...
at middle morning, visibility issues were continuing to improve
across portions of eastern PA, but there were still some leftover
patches of fog, especially around the Lehigh Valley. We expect
continued improvement through and beyond 14z. Otherwise, the
remaining sprinkles across portions of southern New Jersey continue to
wane at middle morning as an upper shortwave moves offshore. Today's
maximum temperatures look on track, but we did adjust hourly temperatures and
dewpoints through this afternoon to account for current trends and
Rest of today...between short waves it should be quiet through
early afternoon with some sunshine visibility at times through the
clouds. Afternoon heating develops small showers northwest of i95 which
probably have a tendency to drift west. If there is to be any
thunder this far east...it should be confined to the far western
edge of our forecast area western Berks into the Poconos. The European model (ecmwf)
suggests temperatures may run 1-2f warmer than our forecast...especially east Maryland.
Overall: temperatures about 7f warmer than normal and the entire month of
September should average about 1.5 degrees above normal most areas.
Forecast was based on a 50 50 blend of the 00z/30 GFS/NAM MOS
Short term /6 PM this evening through 6 am Wednesday/...
tonight...cool pool aloft slides eastward across the region with 500mb
temperatures near -15-16c. Bands of showers may be occurring with subtle
lift from both weak but deep Ely moist winds north of i78 and the
backdoor cool front convergence zone driven by the strengthening
NE flow NE of the backdoor cf.
Additionally fog is likely to develop in the cooler bl air NE of
the frontal boundary.
Temperatures about 10f warmer than normal.
Forecast was based on a 50 50 blend of the 00z/30 GFS/NAM MOS
Long term /Wednesday through Monday/...
the last of the upper low and weak surface low will be exiting the
area Wednesday. There will still be enough residual low level
moisture to produce some scattered showers...mostly during the first
part of the day. We have retained the chance probability of precipitation from earlier. The
probability of precipitation decrease during the afternoon from west to east. Temperatures Wednesday
near or a bit above normal...mostly low/middle 70s.
Wednesday night through Friday morning...mostly dry weather during this period
as high pressure builds across the area. Partly to mostly sunny
daytime periods and mostly clear overnights. Temperatures
again...near or a bit above normal.
Friday afternoon through Saturday...a strong cold front will cross the
area Friday night into early Sat. The models have been rather
consistent with a 6 hour or so window of quantitative precipitation forecast centered around Friday
evening. We have upper the probability of precipitation to likely for the evening period
with the extra confid in multiple/consistent trends. Probabilities
for thunder look low at this point so we will hold on that...some
gusty winds will accompany the frontal passage however. Temperatures will drop back
to below normal Sat with decent cold advection expected after
Sat night through Monday...another dry period expected with high
pressure building in, temperatures will be below normal
Sunday...but back to near normal Monday. Lows both Sat and sun
nights will feature low 40s north ranging to the low 50s over the
Delaware-Maryland-Virginia and metropolitan Philadelphia.
Aviation /14z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Continued improvement with regards to ceilings/visibilities for our western
taf sites krdg/kabe is expected through middle morning.
Otherwise for the rest of today...sct- broken clouds at or above 5000 feet for
all sites with a possible shower vicinity krdg/kabe late in the day.
Light south wind turning E, remaining under 10 knots.
Tonight...wind becoming NE at 5-15 knots and a deck of IFR St/fog should
develop southwestward from Long Island behind the backdoor cold front
currently moving SW from southern New England. Chance of showers...mainly
north of kphl.
Wednesday...mostly VFR. Scattered showers with short periods of MVFR
conditions possible. East/NE winds with gusts up to 15 knots.
Thursday...morning fog with local lower cigs/vsbys...then mostly
VFR. North wind gust 15 knots...becoming NE late.
Friday...VFR ceilings except possible MVFR conditions in St/fog early Friday
morning and then again Friday night in showers near a cold front.
East-southeast wind becoming S or SW late at night.
Saturday...a few morning showers east...then VFR conditions
no headlines at this time.
Today...light winds and seas at or below 3 feet today with the S-SW wind
turning to the east or northeast.
Tonight...NE winds increasing with gusts to 22 knots late and seas
building to near 4 feet by sunrise Wednesday. Capped seas at 4 feet
through 8am Wednesday as I believe the GFS ww3 guidance is too
soon too high.
Wednesday through Wednesday night: NE flow with building winds and seas and Small Craft Advisory
criteria expected along the nnj coast and then possibly southward
to the entire Atlantic coast later Wednesday or Wednesday night.
Delaware Bay may not see wind gusts above 22 knots with any Small Craft Advisory
headline there not likely. Have held off on issuing any formal
headlines on this forecast update as conditions will just meet
lower end Small Craft Advisory criteria and confidence is not yet high.
Thursday...small chance of a continuing Small Craft Advisory flag seas on the
Atlantic waters from NE swells generated by an offshore low.
Conditions may drop below Small Craft Advisory criteria late.
Friday...south winds increasing and building seas. Small Craft Advisory conditions
a good bet by afternoon. Showers with gusty winds late.
Saturday...Small Craft Advisory conditions early with scattered showers...then winds and seas