Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
619 PM EDT Sat Oct 25 2014
a strong upper level disturbance will drop southeast across the
region tonight into Sunday accompanied by some showers and higher
Summit snow showers. Precipitation tapers off by Sunday night with
high pressure returning for Monday and Tuesday with generally dry
weather and moderating temperatures.
Near term /until 7 am Sunday morning/...
as of 612 PM EDT Saturday...updated the forecast to include
isolated thunderstorms across northern New York through 01z. National
lightning detection network showing a few cloud-to-ground/S in strongly
difluent region across St. Lawrence and Franklin New York counties. This
is occurring in left exit region of 130-150 knots 300mb jet...and
strong middle-upper troposhperhic height falls. Associated upward vertical velocity is
making best use of very minimal cape present (generally 100 j/kg
or less per Storm Prediction Center mesoanalysis). Otherwise...given strength of
upward motion and dynamics associated with progressive shortwave
trough...did bump up the quantitative precipitation forecast a bit as well and indicated 90-100
probability of precipitation for a period of 1-3 hours as best forcing works on through
from west to east. Generally looking at 0.10-0.30" rainfall
As flow trends west/northwesterly aloft later tonight...freezing
levels will drop to around 3000 feet or so with precipitation mixing
with or changing to snow at The Summit level or slightly below.
Lows from the upper 30s to middle 40s below the 2000 feet level. May
see a dusting to an inch of snow by daybreak across the higher
summits. Elsewhere...generally dry with a brief sprinkle or two
possible. The orographically favored west-northwest slopes of the
Adirondacks and central to northern Green Mountains will have the
best chance of seeing any additional measuarable rainfall after
Early morning lows generally 39-44f at elevations below 1000 feet.
Short term /7 am Sunday morning through Monday night/...
as of 345 PM EDT Saturday...for Sunday into Sunday evening we
remain under the influence of the upper low with cyclonic
northwest flow aloft resulting in plenty of clouds and the
continued chance for showers with snow showers over the summits.
Flow will become blocked over time such that shower coverage will
become increasingly confined to the northern mountains where some
light additional snowfall still possible above around 2500 feet.
High temperatures will only be in the middle 40s to lower 50s with
lows Sunday night in the middle 30s to around 40.
Improving conditions during Monday as upper low moves away from
region up through Canadian Maritimes. This allows for upper level
ridging over the Great Lakes to build into the northeast along
with weak surface ridge as well. The result will be diminished
northwest flow. Still some lingering clouds...especially over the
north Central/Northeast Vermont where a sprinkle will remain
possible during the first half of Monday across the higher
terrain. Temperatures near seasonal levels with highs in the upper 40s to
middle 50s. Some clouds Monday night as ridge moves east of the area
late. Lows will be in the middle 30s to lower 40s.
Long term /Tuesday through Saturday/...
as of 315 PM EDT Saturday...extended period starts off with area
under vertically stacked ridge from surface up through 500 mb.
Ridge shifts east during the day Tuesday with southerly flow
developing ahead of next low. 850 mb temperatures maximum out around +12c
during the day Tuesday. Bumped up maximum forecasts a bit, but 850
temperatures could support temperatures even warmer than the 60s already
forecast...will need to watch to see if trend persists.
Timing for cold frontal passage late Tuesday night/early Wednesday
morning still on track. GFS and European model (ecmwf) in good agreement with
narrow band of showers right along the front...for a quick hit of
rainfall at frontal passage. Low level winds turn more westerly/northwest to
begin cold air advection in earnest. Temperatures trend downward
through rest of extended period to near seasonal normals. With
west to northwest flow and low level humidity will get some terrain
influenced rain and/or snow showers lingering mainly over the
Late in the extended towards Saturday models bring deep trough
into the eastern US with cut off low slowly moving through the
region. Models differ with this feature as GFS keeps it more
progressive and moving east in northern stream...while European model (ecmwf)
digs it further south. European model (ecmwf) has trended toward GFS solution
between 00 and 12z runs...and given this trend putting more weight
on the GFS for Friday into Saturday. Probability of precipitation come up to chance
category late Friday and continue into Saturday. Precipitation type to
start off as rain on Friday then as temperatures cool Friday night
change to snow during overnight hours.
Aviation /22z Saturday through Thursday/...
through 18z Sunday...VFR through the rest of the
afternoon...although band of rain approaching along cold front.
Forecast to reach St. Lawrence Valley 19z...Champlain Valley
21-22z and then into eastern Vermont. Upstream observation and radar
indicate visible to remain VFR in precipitation. After precipitation/frontal passage
moisture trapped below frontal inversion with MVFR ceilings. Winds
shift to southwest this afternoon then west after 00z. Overnight
into Sunday terrain induced rain shower/SW will be over the mountains but
generally away from taf sites so did not include tafs.
Outlook 18z Sunday through Thursday...
12z Sunday - 12z Monday...a mix of MVFR and VFR associated with a
second round of valley rain showers and mountain snow showers
behind an exiting front on northwest flow.
12z Monday - 06z Wednesday...VFR under building high pressure.
06z Wednesday - 00z Thursday...VFR with some areas of MVFR in
rain showers as a cold front moves through the region.
00z Thursday-00z Friday...MVFR ceilings in northwest flow and
scattered rain or snow showers over higher terrain.