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Area forecast discussion 
National Weather Service Mount Holly New Jersey
417 am EST Thursday Jan 29 2015

Synopsis...
high pressure overhead this morning will move offshore late in the
afternoon. Low pressure will move across New York tonight and then
across the New England waters Friday night. It will send an Arctic
front across our area early Friday. High pressure will build in for
most of the weekend. A low pressure system is expected to move just
south of the area Sunday night through Monday night. High pressure
will build back in for the middle of next week.

&&

Near term /until 6 PM this evening/...
surface high pressure was centered between the East Coast and the
Appalachians. There has been a fairly large temperature spread across the
area. Temperatures have dropped into the single digits in the sheltered
valleys of NE PA and northwest New Jersey where the high is directly overhead and
winds were calm. There is enough of a pressure gradient farther
south and east for a light northwest wind to keep temperatures steady in the upper
teens/lower 20s across the Delmarva, far southeast PA and S New Jersey. However,
these areas have a chance to cool several more degrees through daybreak
as the high builds toward the coast.

The high will move offshore in the afternoon while an area of low
pressure that is currently over the Midwest tracks eastward toward
the Middle-Atlantic States late in the day. After a sunny start to the
morning, high and middle clouds ahead of this system will overspread
our area later this morning and lower/thicken during the afternoon.

There is good model agreement regarding the time of arrival for the
precipitation late this afternoon in our far western zones (mpo-rdg-mqs-esn
roughly between 4 PM and 6 pm). Note that we did speed up the onset
an hour or two earlier as models often are too slow with the leading
warm air advection band. Thermal profiles support ptype starting out as snow in PA,
snow/ice pellets in NE Maryland/far north Delaware-Maryland-Virginia and rain/ice pellets toward Queen Anne's and
Talbot.

&&

Short term /6 PM this evening through 6 am Friday/...
low pressure will move through the eastern Great Lakes this evening.
The initial shield of precipitation that is expected to be entering our far
western zones by the start of the period will spread eastward during
the early and middle evening as a leading shortwave trough aloft swings
through. Ptype from philly and points northward will be all snow. A
warm nose aloft is forecast to cause snow to mix with sleet in the
northern Delaware-Maryland-Virginia and the southern most locations in New Jersey. Warmer surface
temperatures will likely result in mainly rain across southern Delaware and
adjacent Maryland zones.

Probability of precipitation and snowfall amounts are highest along and north of the I-78
corridor, where synoptic lift will be greatest and less transitory
closer to the surface low. Forecast snowfall amounts with this event
are around 1-2 for these areas. There is certainly a possibility for
locally higher amounts up to 3 inches mainly across the higher
elevations in northeast PA and northwest New Jersey but not expecting it to
be widespread enough to warrant a Winter Weather Advisory.

The majority of the snow is expected to move out of the area by
midnight. However, some light snow may linger overnight in northeast
PA and northern New Jersey.

We are not anticipating temperatures to fall much during the overnight with
cloud cover blanketing the area and a southwest wind ahead of a cold
front.

&&

Long term /Friday through Wednesday/...
Friday...the Arctic front and low pressure north of the region will
be moving away. Scattered snows across the northern areas just after 12z
will remain into the morning before diminishing. Cold and windy
conditions developing with temperatures not changing much...remaining in
the low 30s north and middle 30s south. Temperatures may begin to fall during
the afternoon as the cold air advection increases. Winds gusting to
25 to 35 miles per hour at times. Wind chills in the single digits over the southern
Poconos...teens across the northern third of the area and low 20s
elsewhere.

Friday night through Sun morning...high pressure remains across the area.
A dry forecast but bitter cold temperatures continue Sat with some moderation
Sunday. Highs Sat mostly teens (north) and low 20s (south) wind
chills mostly single digits early with sub zero far north. A wind
chill flag may be needed. Wind chills in the teens across the
Delaware-Maryland-Virginia and southern New Jersey.

Sun afternoon through Monday...another low pressure system will affect
much of the area. After more disorganized solutions for the system
with the 12z Wednesday models...the 00z Thursday op models have again swung
back to wetter solutions for our area. GFS...moves low pressure from
the Carolinas up off the Delaware-Maryland-Virginia then just east of 40/70 Monday. A
decent swath of moderate quantitative precipitation forecast (mostly snow) to much of the forecast
area. Ec...weaker low pressure moves from the Carolinas up well east
of the 40/70 mark with slower deepening. Still some snow to the
area...but much lighter and the higher totals are across the
Delaware-Maryland-Virginia and southern New Jersey. CMC...much closer...stronger and very wet.
Areas S/east of I-95 would change to rain Monday with the CMC solution.

There can be a tendency for a northward track bias with systems when
a strong high is north/northwest of the system. The GFS/CMC models
may be displaying this...so we have gone with the wpc numbers for
now and offered the high chance/low likely probability of precipitation for these period. Not
much of a change from previous forecast. With this written...an
increasing chance for an accumulating snow for Sun night Monday for the
southern/eastern parts of the County Warning Area. We will make mention of this in the severe weather potential statement
and ask users to continue to follow this system over the next few
days. Models have yet to lock on to a solution...but may be
beginning to settle...with at least more agreement than this time
last night.

Monday night through Wednesday...more high pressure with cold temperatures Tuesday and a
bit warmer Wednesday. A mostly dry forecast for this period.

&&

Aviation /09z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

VFR this morning and first part of the afternoon. Expect a band of snow to
reach the western terminals late in the day (rdg around 22z and Abe
23z). Visibilities will likely lower to IFR quickly after onset of snow.
Snow moves eastward toward the I-95 terminals between 00z-02z. This
will be a quick moving system, so only expecting a brief, 3-6 hour,
period of snow. Sleet may mix in at ilg/miv/Acy but confidence in
precipitation making it to Acy is relatively low for this close to the
event. Snow may linger out toward Abe-ridge after midnight.

Winds will be light this morning, becoming southerly this afternoon/evening and
southwesterly overnight 5-10 knots.

Outlook...
Friday through Sun morning...VFR expected. Gusty winds Friday.
Sun afternoon through Monday...lowering ceilings. Snow with MVFR/IFR possible.

&&

Marine...
light winds today with high pressure overhead. The high shifts
offshore tonight and southwest winds increase. Small Craft Advisory was issued for
the coastal zones, which starts at 11 PM and continues through the
overnight. Waves will build to near 5 feet during the overnight.

Outlook...
Sat through sun...gale warnings issued. Winds and seas subside back
to Small Craft Advisory conditions Sunday. Freezing spray expected.
Sun night...sub-sca conditions.
Monday through Tuesday...Small Craft Advisory conditions. Winds/seas subside Tuesday afternoon.
Tuesday night through Wednesday...Small Craft Advisory seas possible.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory from 11 PM this evening to 6 am EST
Friday for anz450>455.
Gale Warning from 6 am Friday to 6 am EST Saturday for anz430-
431-450>455.

&&

$$
Synopsis...O'Hara
near term...Klein
short term...Klein
long term...O'Hara
aviation...Klein/O'Hara
marine...Klein/O'Hara

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