Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
340 am EST Thursday Dec 18 2014
low pressure system has pushed off into the Canadian
Maritimes...however trough remains overhead and some snow showers
can still be expected from this on Thursday. Weak high pressure
will start to build in this evening. Some ocean effect snow may be
possible Sunday into Monday due to weak onshore flow. A weak
coastal low will likely strengthen and pass by to our west
Tuesday and may spread light precipitation into New England. An intense
low pressure system will most likely develop off to our west on
Wednesday and possibly bring heavy rain and strong winds Wednesday
and into Christmas morning.
Near term /until 6 PM this evening/...
a surface low pressure now moving into Nova Scotia with upper
level low pressure spinning over the northeast. The most vigorous
short wave energy is to our south and offshore... as well as to
our NE. This will keep any significant banding just out of the
forecast area and thus snowfall amounts should stay within Winter
Weather Advisory criteria. The advisories continue through 1 PM
for 3-6" of snow. Northern sections and especially portions of
Somerset will have the highest accumulations.
Showers will taper off around midday with the passage of a surface
trough. Upslope showers are expected to linger along the whites
and the western Maine mountains but snowfall accumulations will be
very light as dry air filters in aloft. Moderate cold air
advection as well as a tight pressure gradient will allow northwest
winds behind the surface trough to gust to near 30ph at times.
Temperatures range from the lower to middle 30s north to lower 40s
Short term /6 PM this evening through 6 PM Friday/...
colder air dams along the high terrain tonight with teens north
and lower to middle 20s south. The boundary layer decouples and
allows winds to decrease quite a bit overnight. The downsloping
winds will begin to scour clouds out over the coastal plain
Drier and colder air continues to filter in Friday with the
departure of the upper low. Looking at a dry...cool and somewhat
gusty Friday with clouds clearing out over the coastal plain and
then eventually over the mountains. There may be enough moisture
left to squeeze out a few stray snowflakes over the highest
peaks... but little else.
Long term /Friday night through Wednesday/...
start off with high pressure over the region which should bring
fair weather into the beginning of next week. The pattern will
then significantly change from zonal flow to highly amplified as a
deep long wave trough digs over the central U.S. The weak coastal
low that the GFS was showing last night for Sunday into Monday is
now completely removed from the 00z run. The Canadian still
develops this weak system out of the southern stream...but it is
now way too far east to pose much of a threat to our area. If we
see any light snow by the end of the weekend it will be due to
onshore flow and some ocean effect snow showers.
Models are now in decent agreement that another southern stream
system will move south of New England on Tuesday. Still
confidence is low at this time. The operational Euro/Gem/GFS are
showing this system passing to our south and east...however timing
issues on when the low passes and how far north any light precipitation
makes it into New England is still up in the air. 00z Euro is also
the furthest east with this system...bringing very little if any
moisture into New England.
After this system passes our focus then shifts to the long wave
trough starting to materialize Tuesday in the central U.S. Models
are in good agreement with 500 mb closed low forming in the upper
Midwest. Trough tilts negative by Wednesday morning and vigorous
shortwave rotates around it...developing a deep low pressure at
the surface. As it stands right now...we end up in the warm sector
with a deep moisture fetch from the Gulf of Mexico and Atlantic.
Euro ensembles/gefs/and Gem ensembles all are in good agreement
with this scenario. However...there is some concern on how
negatively amplified the 500mb trough becomes...with the 00z Euro
now showing the trough tilting further east...forming the surface
low closer to Delaware-Maryland-Virginia and tracking right up the Hudson Valley
and then into northern New England. Although this is still a warm
track for US...if it were to continue this trend and form the low
further south and east off the coast...then of course the forecast
will significantly change. Also...just caught the 00z Euro
ensemble and a small handful of the 50 members are also showing
For now though it appears we will not be looking at snow...but
even so this system has potential for major impacts in our area.
With the westerly track...precipitable waters are looking to be in the 1.1 to
1.2 range...which is more than 2 Standard deviations above normal
for this time of year. Will have to monitor the potential for very
heavy rainfall and possible flooding as we start to get
closer...but a lot can still change over the next 6 days. The
potential for high winds will also exist with tight southeasterly
gradient...this will be especially true along the coast and higher
Confidence remains low at this time as far as timing and track of
this system...but confidence is growing that we will see precipitation in
the form of rain and not snow as models have now been fairly consistent
in showing a western track over the past several runs...will
continue to have to keep a close eye on this over the days ahead
due to the possible strength of this system.
Aviation /08z Thursday through Monday/...
short term...scattered snow showers this morning will continue
through early afternoon causing mainly MVFR ceilings with some
lower visibilities. We should see improvement to VFR by this
afternoon with northwest gusting into the lower 20s at times. Winds
decrease after the boundary layer decouples after dark.
Long term...VFR conditions can be expected through the weekend.
There is a chance for MVFR conditions along the coast due to ocean
effect snow early Sunday night through Monday morning
short term...winds are on the low side at the moment but should
pick back up with the passage of a surface trough and renewed cold
air advection. Mixing will bring wind gusts into the 20-30 knots
range by middle morning. Seas are currently marginal but should drop
below 5 feet today.
Long term...no flags expected at least through Tuesday. Then a
weak coastal low may bring borderline Small Craft Advisory conditions on Tuesday
afternoon. A significant storm will develop midweek and depending
on the track of this system...storm force winds may be possible.
ME...Winter Weather Advisory until 1 PM EST this afternoon for
New Hampshire...Winter Weather Advisory until 1 PM EST this afternoon for
Marine...Small Craft Advisory until 4 am EST Friday for anz150>154.