Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
706 am EST Sat Jan 31 2015
low pressure will depart eastern New England and give way
to high pressure approaching from the Ohio Valley today. This high
pressure will move to the Middle-Atlantic States tonight and then
offshore on Sunday. By Sunday night, low pressure will move into the
Ohio Valley then will track into our region on Monday. Another area
of high pressure will move into the region Tuesday and Wednesday
with low pressure tracking just offshore for the later half of the
Near term /until 6 PM this evening/...
6 am update...winds continue to decrease across the region, so
have let the Wind Advisory expire. Still could be one or two gusts
near 40 miles per hour for coastal locations (especially those at the mouth
of the Delaware bay), but not enough confidence to extend the Wind
Advisory at this time.
As for the Wind Chill Advisory, Mount Pocono is still reaching
criteria so will keep the Wind Chill Advisory going for now.
Previous near term discussion...with the surface high propagating
east, pressure gradient across the region will decrease, and with
that, winds will slowly subside but remain out of the northwest.
With the continued northwesterly flow, will see cold air advection
through the day so temperatures will be quite low, even for late
January. Highs today should be 15 to 20 degrees below normal and
15 to 20 degrees less than yesterday/S highs. Subtle short wave
ridging in the middle and upper levels along with dry air still in
place in the boundary layer, should help to keep skies mostly
sunny, although current satellite imagery shows a middle layer cloud
deck (around 4000 feet agl) which could advect over the region from
the northwest through the day.
Short term /6 PM this evening through 6 am Sunday/...
as the surface low shifts even further east, pulling away from the
coast, winds in our region will shift to westerly, but will
generally be near or below 10kt. Despite the light winds, the slight
downslope, along with increasing middle and high level clouds should
help to at least somewhat limit radiational cooling overnight.
Therefore, lows tonight, while still slightly below normal, should
be 5 to 10 degrees higher than lows last night. Towards the early
morning hours on Sunday, the cold front should begin to approach the
region from the northwest. However, at this point, expect it to
remain northwest of the region through the early morning hours.
Long term /Sunday through Friday/...
sunday: looks to be fairly quiet day with high pressure moving
offshore. This will bring southerly flow and a moderating trend to
the region. Stayed close to met and mav which are a few degrees
warmer than modeled NAM/European model (ecmwf) two meter temperatures which seem to
Sunday night through Monday night:
* winter storm potential for at least the northern half of the region*
Low pressure will track into the Ohio Valley by Sunday night and
toward our region on Monday. This low pressure system will track
along a cold front moving in from the northwest. However, southerly
flow will continue to the south of this cold front allowing for warm
enough temperatures to where mixed precipitation or rain are more
likely than snow south of the low track as the front stalls over
the region. The past few model cycle runs a shortwave which
develops the low pressure system has come into the National upper
air network. This increases forecaster confidence to some degree.
The shortwave has also trended stronger and sharper which in turn
has shifted the track of the low further north over the past few
model cycles. The UKMET, NAM and sref have been the more amplified
while the European model (ecmwf) is most south of the models with deeper low level
Plenty of moisture is drawn north and rung out along the frontal
boundary with the potential for periods of moderate and heavy
precipitation. Went close to mav guidance on temperatures
throughout the storm. The NAM seems to warm at this juncture and
the European model (ecmwf) to cool. Stayed close to wpc on quantitative precipitation forecast and also used the
sref for the front end Sunday evening.
Periods of snow develop for most of the region with rain in the
Delaware-Maryland-Virginia around 00z Monday. This gradually transitions to rain for
Philadelphia metropolitan and a wintry mix just northwest of
Philadelphia. Further north snow, moderate to heavy at times
continues for the overnight and Monday morning hours. A very sharp
cutoff is likely with snow accumulations to occur based on the very slow
movement of the changeover line north. Accumulations range from an
inch or two in phl to six to ten inches in the Lehigh Valley and
even close to a foot for the Poconos. Where this cutoff sets up
will be determined on the eventual location of the front and the
low track. Any shifts in track could alter amounts with future
forecast updates. A Winter Storm Watch has been issued for the Lehigh
Valley into northern New Jersey and the Poconos for moderate to high
confidence in snowfall over six inches for the Sunday night and
Tuesday and wednesday: behind the system, a pretty potent blast of
cold comes into the region by Tuesday. 925 and 850 mb both will be
well below -10c coupled with strong northwesterly winds. This
quickly modifies by Wednesday ahead of another cold frontal boundary
with a return to southerly winds. Snowcover leads to greater
uncertainty in temperatures. Overall thinking is European model (ecmwf)/ mex MOS
and ensemble guidance may be a touch to warm Tuesday then to cool
Wednesday night through Friday night: potential exists for an area
of low pressure to develop in the Gulf of Mexico and track northeast
along the cold front which passes through Wednesday night. Limited
time to focus on this period but left in chance of snow Thursday
into Friday. The European model (ecmwf) is furthest east with the GFS, CMC and
UKMET hinting at this threat.
Aviation /12z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Generally VFR conditions are expected through the taf period. A middle
level cloud deck around 4000 feet above ground level could advect in from the
northwest through the day time hours. There is a small chance that
as it does, the ceiling could lower to MVFR at kabe, but that is too
unlikely to include in the taf at this time.
Northwest winds will begin to decrease after 12z. By late this
afternoon, winds should be near 10kt with few gusts. After 00z,
expect the light winds to shift to westerly through the evening
Sunday: VFR, increasing clouds.
Sunday night and monday: MVFR and IFR ceilings in rain and snow.
Mainly snow for krdg, kttn and kabe with mainly rain at other taf
Monday night through wednesday: VFR, northwest wind gusts around
25 knots Monday night.
although winds will slowly subside after sunrise this morning, but
may not drop below gale conditions until late this afternoon. Once
gusts do drop below gales, a Small Craft Advisory may be needed through at least the
evening hours as winds and seas continue to slowly fall.
Sunday and Sunday night: sub Small Craft Advisory seas and winds with seas building
toward sunrise Monday.
Monday through tuesday: Small Craft Advisory seas through Tuesday morning and northwest
Small Craft Advisory wind gusts late Monday afternoon and night.
Tuesday night and wednesday: sub Small Craft Advisory seas and winds.
water levels have come up on the Upper Bay, but low tide is still
occuring on tidal portions of the Delaware River. Winds should
begin to subside after sunrise.
PA...Winter Storm Watch from Sunday evening through Monday
afternoon for paz054-055-060>062.
Wind Chill Advisory until 11 am EST this morning for paz054-
New Jersey...Winter Storm Watch from Sunday evening through Monday
afternoon for njz001-007>010.
Wind Chill Advisory until 11 am EST this morning for njz001.
Marine...freezing spray advisory until 6 PM EST this evening for anz430-
Gale Warning until 6 PM EST this evening for anz430-431-