Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
624 PM EDT sun Mar 29 2015
a cold front is expected tomorrow. On its heals will be a fast
moving low pressure system which should sweep through the area late
Tuesday. High pressure will build into the region for Wednesday and
move offshore on Thursday. The next cold front will come late in the
Near term /until 6 am Monday morning/...
surface ridging crests to our south and east later this evening
as the winds across our region back further towards the south-
southwest. An positive flux in moisture is expected to occur
tonight as the return flow and 40 knot low-level jet moves in
overhead, though we do have a relative minimum starting point with
our surface dewpoints.
A weak cold front will push toward the region late tonight and
cross most of the area by later Monday morning. Not much moisture
with this front and dewpoints were still in the single digits in most
areas through late Sunday afternoon. However...models are
indicating up to a tenth of an inch of precipitation over our
southern flank...and a few hundreds in the north. Normally this
would not be newsworthy, but with clear skies and lighter winds
into the overnight hours...temperatures are expected to drop below
freezing north and west of Philadelphia. Any precipitation that
falls during the late overnight hours (4 am to 7 am)could be in
the from of mainly light snow showers...especially north of I-78.
The snow grids have been adjusted accordingly. No impact is
expected...and any accumulation would be on grassy surfaces in
the higher elevations. The changeover back to light rain should
occur within an hour or so after sunrise Monday morning...assuming
enough moisture is available at the point in time.
Short term /6 am Monday morning through 6 PM Monday/...
the front will clear the region by late morning helping to pull any
lingering moisture off to our east...rather quickly. Drying and
warming trend is expected for Monday as we maintain the southwest-
west surface flow. Temperatures should be able to climb back to
average, if not above once we start to clear some of the stratocu
out of the region. Went with the warmer mav guidance.
Long term /Monday night through Sunday/...
still considerable uncertainty with this forecast especially as
the split flow pattern continues for much of the week.
Tuesday and Wednesday...the big question through this period will
be the track of the fast moving clipper system Tuesday into
Tuesday night. Most models bring the center of the surface low
across Delaware-Maryland-Virginia and southern NJ, with the exception of the NAM,
which takes a northern track, bringing the center of the low
across northern New Jersey. With more model agreement on the southern
track, forecast favors the southern track, keeping higher probability of precipitation
across the south and favoring the colder guidance for highs on
Tuesday. By Wednesday, a surface high moves in for a brief
Thursday through Saturday...this continues to be the most
uncertain period of the forecast. The GFS and European model (ecmwf) continue to
show vast differences in the timing and track of a pair of lows.
The first low over the Hudson Bay region late in the work week.
The question will be if and when the associated cold front will
track as far south as our region. The second low the GFS shows
developing over the southern High Plains by Thursday night and
sliding east just south of region through Saturday, keeping a
stationary front south of US through this time. The European model (ecmwf) on the
other hand...shows the low filling and essentially disappearing
by Friday. Given the uncertainty, stayed close to the previous
forecast. However, at this point, am concerned that the European model (ecmwf) may
be underestimating Lee side cyclogenesis. With both solutions
though, the end result is that it will be cooler (40s and 50s)
for the weekend.
Aviation /22z Sunday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy, and surrounding areas.
Tonight...VFR. Clear skies prevail through the evening hours as high
pressure crests over the region. The winds will continue to back
towards the west-southwest this evening before becoming southerly
late tonight. This is ahead of a cold front passage Monday morning.
Monday...mostly VFR. The cold front will cross the region Monday
morning and could produce a brief period of rain/snow at the
terminals. Coverage looks spotty and was not confident enough to add
precipitation to the tafs, though farther south into the Delaware-Maryland-Virginia
has the better chances. Right behind the front the winds veer
towards the southwest a bit and increase with some gusts into the
low-20s. Brief MVFR ceilings are possible right behind the front,
otherwise broken-overcast 5000ft deck should persist through much of the
afternoon before scattering out.
Tuesday...ceilings and visibilities decreasing to MVFR, possibly
IFR, with incoming rain. Snow possible in higher terrain.
Wednesday...mostly VFR conditions.
Thursday and Friday...mostly VFR, chance for rain and slight chance
for thunderstorms and rain. With precipitation, MVFR conditions possible.
tonight - Monday...sub-sca expected across the waters through the
late evening hours. Then winds back towards the south-southwest and
the seas begin to increase again. The pressure gradient tightens
with some enhanced mixing and gusts close to 30 knots right around a
cold front passage. Winds veer towards the west-southwest behind the
front and continue to gust for a period. The gusts on the Bay and
ocean should drop by Monday evening while the seas remain somewhat
elevated along the oceanfront. Small Craft Advisory is good from 6z tonight to 6z
Tuesday...once waves decrease below 5 feet early Tuesday morning,
winds and seas should remain below Small Craft Advisory criteria for the rest of
Tuesday night and Wednesday...winds should remain below Small Craft Advisory
criteria unless the low is stronger than forecast. Seas will be
dependent on the wind forecast but at this point are generally
expected to remain near or below 5 feet.
Thursday and Friday...southerly and southwesterly winds will
likely increase above 25 knots for at least part of this period. Seas
will likely increase above Small Craft Advisory criteria as well.
Marine...Small Craft Advisory from 2 am Monday to 2 am EDT Tuesday for
Small Craft Advisory from 2 am to 6 PM EDT Monday for anz430-