Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
946 PM EST Friday Mar 6 2015
Arctic high pressure settles to our south tonight and Saturday and
gradually weakens. A weak low pressure system will then track to our
north Saturday night into Sunday, pulling a weak cold front across
our region. Low pressure should develop along this front to our
southwest late Monday, then track to our south Tuesday. High pressure
should then build into the region Wednesday through Friday,
however a weak front may slide by late Wednesday.
Near term /until 6 am Saturday morning/...
high pressure was centered along the middle-Atlantic coast this
evening. Aside from some thin cirrus, skies are clear. The airmass
has been able to radiate effectively in some locations like
miv,Ged and 12n where the winds are calm and temperatures are already in
the single digits to lower teens. Meanwhile other spots that have
a 5 miles per hour wind has kept temperatures from dropping much since sunset.
Updated min temperatures based on the latest temperature trends and taking into
account climatology/terrain. Overall, went a few degrees cooler
than the mav and met outside of phl. Some records are possible
tonight across the region, please see the climate section.
Short term /6 am Saturday morning through 6 PM Saturday/...
a cold front will approach the region late in the day Saturday.
Middle to high level clouds will be on the increase from west to east
during the afternoon. Soundings look fairly dry across the region
for measurable precipitation. The GFS and rgem indicate the
potential for some non measurable precipitation in the late
afternoon across the Poconos and northern New Jersey. Have added
some scattered flurries to the forecast in those areas. Some wind
gusts from 15-20 miles per hour may be possible in the afternoon as well.
Long term /Saturday night through Friday/...
the overall synoptic setup is comprised of an upper-level trough
from the Midwest to the northeast and middle Atlantic. This should
eventually weaken as energy ejects across the Southern Plains late
in the weekend and early next week, with a ridge building off the
southeastern U.S. Coast. This results in the upper-level flow
turning more zonal for much of next week. The aforementioned energy
into the Southern Plains though should result in a surface low
tracking to our south with perhaps overrunning precipitation getting
into at least a portion of our County Warning Area Tuesday. We used a model blend
for Saturday night through Monday, then went with the 12z wpc
guidance thereafter. We then made some adjustments after additional
collaboration with our neighboring offices.
For Saturday night and Sunday...a weak short wave tracks to our
north with a weak cold front moving through Saturday night. This
feature looks moisture starved with much of the lift to our north
and also confined to the Great Lakes area. Some warm air advection occurs ahead of
this feature, then cold air advection aloft is forecast to occur Sunday behind the
weak cold front. While there will be some increase in clouds, this
looks more pronounced across the northern zones with even the
potential for some lower clouds for a time. We maintained more
cloudiness across the northern areas, with slight chance probability of precipitation
/northwest/ for a few snow showers Saturday night /the airmass
may remain dry or the forcing weak enough to not allow precipitation
to occur/. Overall, any quantitative precipitation forecast would be rather light.
For Monday...high pressure at the surface is forecast to be over our
area, however a short wave aloft should generally glance our County Warning Area. At
the surface, this is reflected by a weak cold front that is more
pronounced to our north. There is some weak warm air advection forecast to occur
ahead of this feature, however based on the quick motion and also
limited moisture available spells for a dry system sliding by. We
once again placed some higher cloud cover across the north closer to
the actual short wave.
For Tuesday and Wednesday...high pressure should shift to our east
and southeast as ridging builds off the southeastern U.S. Coast. As
this occurs, the flow backs some allowing the warm air advection to increase some
through Tuesday. This will focus a warm front to our north with our
boundary layer warming. This should allow for noticeably milder air
to overspread the area with each day getting a bit warmer. The
stronger flow in the northern stream is forecast to shift northward,
which drives storms farther to our north. As a result, low pressure
should track well to our north helping to pull warmer air into our
County Warning Area. There should be a frontal boundary stalled however to our south
on the northwest edging of the building ridge. A short wave sliding
east across the southern states should allow for low pressure to
develop and track along the aforementioned boundary. The strength of
the southeastern U.S. Ridge may then allow this low to track farther
north and push the overrunning precipitation shield to cover at
least a portion of our County Warning Area Tuesday. We are anticipating this to be
rain if it were to occur given a moderating airmass. We favored the
wpc probability of precipitation which increases the slight chance and chance probability of precipitation a bit and
farther northward. High pressure builds in Wednesday, although a
cold front may be approaching from the northwest.
For Thursday and Friday...the Wednesday front should wash out or
shift to our east Thursday. Some ridging building across the plains
should force surface high pressure north of the Great Lakes
southeastward into the middle Atlantic. This should bring some cooling
to the area, with highs Thursday about 5 degrees colder than
Wednesday. This high should be overhead to start Friday, then start
to ease off to the east.
Aviation /03z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
VFR conditions expected tonight and Saturday. Mostly clear tonight
with winds shifting from northwest to west through the early evening
under 10 knots. A general increase in middle and high level clouds
throughout the day tomorrow ahead a cold front. Some wind gusts from
15-20 knots are possible around 18z Saturday with moderate
confidence for these gusts.
Saturday night and Sunday...some MVFR ceilings possible especially
from about kttn to kabe northward. Otherwise, VFR with some
increase in clouds for a time.
Tuesday and Wednesday...VFR, however a period of MVFR/IFR conditions
possible especially from about the kphl metropolitan on southward Tuesday
with a chance of some rain.
seas will continue to decrease to around 2-3 feet for tonight on the
ocean with lower seas closer to 1-2 feet on the Bay. Northwest winds
will shift to west this evening with top gusts Saturday afternoon
from 15-20 knots.
Saturday night and Sunday...a west-southwest flow increases some for
a time as a weak front arrives, however overall the conditions
should be below Small Craft Advisory criteria.
Monday...overall, conditions below Small Craft Advisory criteria as
high pressure moves across the area.
Tuesday and Wednesday...low pressure is forecast to track to our
south, however if it favors a more northward track then winds may
increase enough to advisory levels for a time mainly Tuesday.
for reference, below are the record low temperatures for Saturday,
Acy...10 in 1890
phl....9 in 1960
ilg...11 in 1960
Abe....1 in 1960
ttn....7 in 1890
Ged....3 in 1960
ridge...10 in 1989
mpo..-18 in 1911