Area Forecast Discussion
Issued by NWS Burlington, VT-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 171944
Area Forecast Discussion
National Weather Service Burlington VT
344 PM EDT Mon Oct 17 2016
Skies will range from partly sunny to mostly cloudy across the
north country today. Clouds will be on the increase late this
afternoon and tonight as a strong warm front lifts northeast
across the North Country, bringing showers and a possible rumble
of thunder. Well above normal temperatures and breezy conditions
for Tuesday precede a cold frontal passage on Tuesday night. Above
normal temperatures continue into midweek, with the weather
pattern turning more unsettled late this week.
.NEAR TERM /THROUGH TUESDAY/...
As of 146 PM EDT Monday...The cloud cover has slowly thinned out
across the northern Champlain Valley and northern Vermont. However as
mentioned with the previous update the clear skies will quickly
give way to increasing cloud cover building from the southwest as
a warm front advances towards the North Country. Otherwise the
forecast is in good shape with no changes needed.
Previous discussion from 638 AM EDT
Monday...Issued an early update for two purposes: to add patchy
fog in the forecast into mid-morning and to get temperatures
better in line. METARs and reports from spotters indicate that fog
has been dense in isolated spots this morning. While the trend is
for improvement, it will likely continue to impact the morning
commute before lifting as the cold front - and its associated
increase in north winds and dry air advection - begin to lift out
areas of mist or fog into the mid- morning hours. For more
specific details, see the Special Weather Statement issued
Other than that, the other main update was to adjust the hourly
temperatures generally up a few degrees into the next few hours.
The cold front still is slowly making its way out of Quebec and as
such, houry temperatures have generally been several degrees
warmer than conveyed in the grids. So I made some changes to try
to get those better in line. Otherwise, the forecast for the rest
of the day still looks on track.
Previous near-term discussion issued at 400 AM Monday follows...
We start the first day of the workweek off cloudy across southern
Vermont. However much of the rest of the North Country is stuck in
areas of radiational fog/mist due to skies having cleared,
relatively high dewpoints for late October and wet ground from
yesterday`s rainfall. Still awaiting the actual cold front which
is located along the US/Canada border at this point. The fog/mist
should be temporary as once this boundary slips southward across
our area, north winds and dry air advection should lift the fog.
However, it may restrict visibilities into the morning commute.
Morning commuters should drive with a little extra caution in
areas of fog this morning. Front will continue to sag southward
through today, while areas to the south see prevailing overcast
begin to erode by the afternoon hours. So, expect to see variable
cloud cover today, greatest to the south with more sun to the
north. Highs today are pretty tough to pin down given the cold
advection to the north and the cloud cover to the south. I`ve
shown temperatures being pretty uniform, give or take a couple
degrees, as areas that receive more sunshine also are cooler this
morning at 925 mb than the cloudier areas in southern Vermont.
I`ve shown highs ranging from the upper 50s across northern
Vermont to the lower 60s in southern Vermont and the St. Lawrence
For tonight: Clouds should increase from southwest to northeast
from rather strong isentropic ascent owing to an approaching warm
front tied to a low pressure that will pass well to our northwest.
A number of forecast models both global and higher-resolution CAMs
generally agree on precipitation timing between about 00z through
10z and primarily across our northern and western counties.
Strongest warm thermal advection between 925-700 mb takes place
during that period of time, driven by a low-level jet of 35-45 kts
as progged by the BTV-4km WRF. There are also indications from the
00z NAM and BTV-4km of elevated instability (Showalter values as
low as -2) as the front lifts northeast. So, PoPs increase into
the the high-Likely range across the northern half of the CWA,
with lower slight/low Chance range across southern VT further
removed from the stronger lift. While rain is the predominant
weather, I`ve included isolated thunder as well from the St.
Lawrence Valley, northern Champlain Valley of NY/VT and
northern/central VT given the negative showalter indices. It
should be more of an exception than the rule, however. Rainfall
amounts range from a few hundreths in southern Vermont up to a
third of an inch along the northern border counties. Temperatures
tonight are also challenging as the potential for cooler temps in
shallow northeast drainage flow in the St. Lawrence Valley amidst
strong warm advection aloft and overcast. Given the clouds, temps
should be slow to cool and likely rise after midnight. Lows range
from the low to mid 40s across the Northeast Kingdom and northern
St. Lawrence Valley, to the middle 50s in southern Vermont.
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --As of 344 PM EDT Monday...A weakening cold front will move
through the region Tuesday night. Models showing QPF falling about
as the front moves through the region Tuesday night. Thus, have
stayed with just chance pops for Tuesday night. A weak ridge of
high pressure will build east from the Great Lakes on Wednesday
and will remain over the region through Wednesday night. Models
showing some differences for late Wednesday night, with the NAM
and ECMWF trying to bring some showers into the region after 06Z
Thursday, while the GFS model is dry. Will stick with the dry GFS
and keep a dry forecast for Wednesday night, with just increasing
cloud cover late Wednesday night.
-- End Changed Discussion --
.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --As of 344 PM EDT Monday...ECMWF and GFS models showing some
timing differences on Thursday with the ECMWF faster than the GFS
in bringing rain into the region on Thursday. Models show a
digging upper trough over the Mississippi valley which will
transport plenty of moisture northeast into the region from the
Ohio valley and the lower Mississippi valley on Thursday and
Friday. The cold front associated with this will be slow to move
eastward, as both the ECMWF and GFS models showing a hybrid
subtropical low over the western Atlantic that will drift slowly
northward Thursday and Friday. This low will slow the eastward
progression of the front on Thursday and Friday. Have gone with
likely pops for rain on Thursday and Friday. Models showing some
timing differences on Saturday with the ECMWF much more
progressive than the GFS with less QPF on Saturday, while the GFS
model is slower and suggesting a wetter day and more QPF across
the region on Saturday. Have stuck with the superblend pops from
Saturday through Monday, given the model timing differences. Model
guidance showing colder air aloft will move into the region
Saturday night and Sunday, as an upper trough moves through the
region. The higher summits of the Adirondacks and Green Mountains
will likely see some snow showers Saturday night and Sunday.
-- End Changed Discussion --
.AVIATION /19Z Monday THROUGH Saturday/...
Through 18Z Tuesday...VFR expected to trend towards MVFR as a
warm front moves into the area. The mostly clear skies this
afternoon will give way to an MVFR cloud deck as clouds advance
into the North Country this afternoon. Showers will begin in
earnest over northern New York between 22-00z however confidence
in measurable precip is limited to just MSS with this update so
elsewhere I mentioned the precip chances at VCSH. Upstream
observations are indicating thunder is possible through the early
evening and overnight hours but have not chosen to include in the
TAF for MSS/SLK with this update.
A strong low level jet 30-40kts will develop overnight over the
Saint Lawrence Valley and with northeasterly drainage flow expect
low level wind shear to be prominent at MSS from 08-14Z. Expect
veering winds with the warm front gradually trending southeast
6-10 kts overnight and early morning. By mid morning tomorrow the
low level jet will have moved over most of the North Country and
winds across the Saint Lawrence and Champlain Valleys will become
very gusty. Expect southerly wind gusts of 20-30kts developing at
SLK/MSS/BTV between 13-16z with sustain winds of 15-20kts.
Outlook 18Z Tuesday through Saturday...
18z Tuesday - 00z Wednesday: Early MVFR improves to VFR. Gusty
south/southwest winds possible at MSS and BTV.
00z Wednesday - 12z Wednesday: VFR deteriorates to MVFR with
showers along a cold front.
12z Wednesday - 00z Thursday: VFR under weak high pressure.
00z Thursday through Friday: Trending MVFR by 00z Thursday with
MVFR to IFR at times through parts of Friday as steady rain