Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1015 PM EDT Friday Oct 31 2014
an upper level disturbance over the central Great Lakes will
translate into the central Appalachians and contribute to the
development of a surface low pressure system off the East Coast late
tonight. This low pressure area is expected to track northeastward
and pass southeast of Cape Cod late Saturday...and move across the
Gulf of Maine and Canadian Maritimes on Sunday. The north country
will see just some fringe effects of this system...amounting to some
light rain showers Saturday with light rain or snow showers
Saturday night into Sunday. The offshore low will create gusty
north winds...especially Saturday night into Sunday. Drier weather
returns with high pressure Monday and Tuesday. Temperatures will
be near to slightly below normal through Monday.
Near term /until 7 am Saturday morning/...
as of 1015 PM EDT Friday...forecast generally holding up well. I
did raise mins up by a degree or so based on current temperatures in the
upper 30s to middle 40s and on the degree of cloud cover across the
north country. Low-levels still remain too dry for any appreciable
precipitation for the northern and western half of the County Warning Area...so
going dry forecast for these areas looks good. Starting to see
some light precipitation slowly spreading northward into interior Massachusetts.
Dewpoints in southern Vermont are slightly higher in the middle/upper 30s
and more conducive to light showers...but not occurring until the
pre-dawn hours. This is already reflected in the forecast with
slight chance probability of precipitation for southeast Vermont. Aside from populating with
latest observational data...no other changes were made.
Short term /7 am Saturday morning through Sunday night/...
as of 322 PM EDT Friday...surface low pressure developing well east of
the Delaware-Maryland-Virginia peninsula during the daylight hours Saturday morning
will deepen as it moves northeastward to near or just southeast of the 40n
70w benchmark by late afternoon Saturday. Skies will generally be
overcast across the north country...but otherwise we/ll only
experience fringe precipitation affects from this system. Models
are in good agreement with just some light rain/high elevation
snow shower activity affecting the Adirondacks eastward across
Vermont...and mostly not until the afternoon hours. Probability of precipitation range
from 30-40 percent and any measurable precipitation should only be
a few hundreths of an inch of rainfall (or a dusting of snow at
the summits) through early Saturday evening. Highs on Saturday
will range from the low-middle 40s in most locations...and 32-34f at
the summits above 3000 feet.
The surface low tracks northeastward through the Gulf of Maine Saturday night
with an increasing northerly pressure gradient and associated north
winds. Most locations will see north winds of 10-15 miles per hour through the
overnight period. Could see a few rain or snow showers around during
Saturday night into Sunday morning...with potential for an inch or
so across the higher terrain and little to no accumulation most over
locations. If low track is a bit further west (similar to 12z
gfs)...a dusting to 1" is possible across eastern Vermont valleys during
Saturday night. Low temperatures will be relatively uniform given
cloudy/windy environment...with lows in the upper 20s to lower 30s in
Brisk north winds are also expected to continue on Sunday with
development of steep low-level lapse rates with development of
partly sunny conditions. Combined with moderately strong pressure
gradient...will see sustained winds of 15-25 miles per hour much of the
day...with some gusts to 30-35 miles per hour possible. A few snow showers
remain possible mainly across northestern Vermont as surface low departs northeastward
across the Canadian Maritimes. Highs on Sunday will be chilly and
generally in the upper 30s to lower 40s. Clearing skies and
diminishing winds for Sunday night as drier air moves into the
region from the northwest. Looking for lows generally in the middle to
upper 20s for most locations.
Long term /Monday through Friday/...
as of 310 PM EDT Friday...12z guidance suite continues to be
fairly consistent with 00z runs and among the GFS/Euro members --
at least through Wednesday. Deviations get larger for Thursday and
Friday. Overall the forecast hasn't changed much. Looks pretty
quiet Monday & Tuesday and then getting unsettled for the rest of
the week. Daily specifics below...
the weekend storm will be far to the east, with much drier air
advecting in. Pressure gradient will be slowly relaxing as high
pressure ridge builds in from the west, but still enough to make
for a semi-breezy day -- perhaps some gusts upwards of 20mph.
Guidance all similar, so a blend looks the best way to go. Should
be little in the way of cloudiness and even less in the way of any
threat of rain/snow (so 0% pop is good). 925mb temperatures start
off chilly (-5c or so) but slowly warm toward -1c by the
afternoon. What that means at the surface are temperatures only in
the low 40s (upper 30s higher elevations).
flow starts to turn southwest as the ridge axis moves over and
east of here. As winds turn southwest, we should start to see some
middle clouds associated with warm air advection start to move in
from the west late at night. Temperatures will be the tricky
part. Think coldest readings will be across the Northeast Kingdom
with low/middle 20s expected with more time with clear conditions.
However, if the arrival time of the clouds is a few hours
different, it could mean lows could be colder or warmer. Bottom
line, went a bit on the colder side of guidance, but things are
warmer air continues to move in. 925mb temperatures rise to 8c by
late in the day. This would support temperatures into the 60s
under perfect conditions, but clouds and even some rain showers
will keep that from happening. 50s (though a bit above normal)
will do it. During the day a front slowly sags toward the region
from the northwest, however the southwest flow aloft means that
ultimately the front will pull up stationary and start to
dissipate in place. Showers will be focused along and ahead of
the front. So low chances in the St Lawrence Valley during the
day, but by Tuesday night the front will be close enough so
clouds/showers will be more widespread. Have continued the idea of
best chances of showers being across northern/western section with
probability of precipitation around 60% there but trending down to <30% in southeast
sections of Vermont. Good support for the models for this sort of
orientation of rain chances thanks to a stalled front just
north/west of here. Clouds/showers will keep temperatures from
falling much. Lots of 40s and a few upper 30s.
looks like a somewhat dreary couple of days. Southwest flow with
embedded weak shortwaves is in place. With the stalled front,
we'll see spotty areas of light rain break out as the weak
disturbances pass through. Temperatures won't vary much. Stuck
with a model blend, but even that may be too warm during the day
and too cool at night. Basically low 50s in the day, 40s at night.
models diverge more by this point. Both the GFS and European model (ecmwf) say we
will have the upper trough amplify some and cause surface
cyclogenesis. Differences are with where this all happens. GFS is
farther west with trough and cyclogenesis and slower with the
pattern evolution. It would keep US in a warmer environment with
scattered rain showers Thursday night transitioning to snow
showers by Friday afternoon as the trough passes by and colder air
comes in. 12z European model (ecmwf) has all of this happening quickly Thursday
night such that colder air is moving in by Friday morning
resulting in a more chance of white stuff, even at low elevations.
As a comparison, GFS has 850mb temperatures of about 0c as of 12z
Friday -- meanwhile the European model (ecmwf) is already down to -8 to -10c at
that same time.
This far out, just stuck with a model blend which results in some
light snow at elevations above roughly 2000ft and rain showers
below that as highs on Friday are only in the 40s.
I'm sure this forecast will change several more times between now
and then. That's just the way things work....
Aviation /02z Saturday through Wednesday/...
through 00z Sunday...VFR ceilings exist over the area tonight and
will do so through about 12z...then ceilings will lower into the
MVFR category. There may be some light rain or snow showers
especially after 16z...but no obstruction to visibility is
expected. Winds will be variable under 10 knots tonight...then
increase from the north into the 10 to 20 knot range after 12z.
Outlook 00z Sunday through Wednesday...
00z sun-00z Mon: varying between VFR and MVFR with a few
rain/snow showers around. Northerly surface winds will be gusting
in the 25-35kt range on Sunday.
00z Monday-12z Tue: VFR
12z Tuesday onward: MVFR conditions developing with scattered showers
and lower ceilings.
as of 1030 am EDT Friday...the kcxx-88d Doppler radar in
Colchester Vermont is out of service at this time. Electronics
technicians have checked the radar and found a problem with high
voltage arcing. Electronics technicians are at the radar site this
morning attempting repairs. Owing to the complex nature of the
problem...it appears the earliest return to service will be
sometime on Saturday.
equipment...weather forecast office btv