Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1031 am EST Sat Jan 31 2015
strong low pressure will continue to track into the Canadian
Maritimes, meanwhile high pressure will gradually build into our
area from the Ohio Valley into tonight. This high will then move
offshore late tonight and 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 week.
Near term /until 6 PM this evening/...
strong low pressure will continue to move into the Canadian
Maritimes today. Meanwhile, high pressure centered across the
southeastern states extends into the eastern Great Lakes. This
feature will gradually build eastward through this afternoon, and as
a result the pressure gradient will relax. This will allow the gusty
winds to gradually diminish through the afternoon from west to east.
An Arctic airmass remains in place today, and with the gusty winds
the added wind chill effect will be noticeable. The gusty winds have
been producing some blowing and drifting snow mainly across our far
northwest zones, and this mention was continue a bit longer.
It appears that the lowest wind chill values are tied to the highest
terrain, with other areas below criteria. Given this and based on
the winds diminishing through the afternoon, the Wind Chill Advisory
for our far northwest zones was cancelled.
No major changes were made to the going forecast, other than to
adjust the current conditions based on the observations and then the
lamp/lav guidance was used to help assist through the afternoon.
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
Monday period. The watch has been expanded to include upper Bucks
and Montgomery counties based on the forecast snow amounts,
although there could be more mixing/icing here. This will be looked at
closer with the afternoon forecast issuance.
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 /16z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Rest of today...VFR. Northwest winds 15-20 knots with gusts
up to 30 knots, diminishing by late afternoon.
Tonight...VFR, with some increase in clouds especially for kabe and
krdg. West-northwest winds quickly diminishing to around 5 knots
early, then locally becoming southwesterly.
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 through midday, they may not
drop below gale force 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. Moderate freezing
spray will continue through this afternoon, with an advisory in
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.
PA...Winter Storm Watch from Sunday evening through Monday
afternoon for paz054-055-060>062-103-105.
New Jersey...Winter Storm Watch from Sunday evening through Monday
afternoon for njz001-007>010.
Marine...freezing spray advisory until 6 PM EST this evening for anz430-
Gale Warning until 6 PM EST this evening for anz430-431-