Scientific Forecaster Discussion
fxus61 kbtv 261044
Area forecast discussion
National Weather Service Burlington Vermont
issued by National Weather Service Albany New York
644 am EDT Tue Sep 26 2017
strong high pressure at the surface and aloft will continue to
provide unseasonably warm, record setting temperatures for the
region today through Wednesday. A cold front will move across
northern New York and upstate Vermont Wednesday night with some
isolated to scattered showers and isolated thunderstorms. A much
cooler air mass will return, as more seasonable weather is expected
behind this front from Thursday through the upcoming weekend.
Near term /until 6 am Wednesday/...
as of 644 am EDT Tuesday...high pressure remains in control early
this morning with mostly clear/partly cloudy skies and light to calm
winds, as radiative mist and fog continues to slowly dissipate
across the forecast area based on the GOES-16 fog product and the
latest local observations. The fog has been locally dense in parts
of the Champlain Valley, eastern Vermont near the CT valley, portions of
the St Lawrence Valley, and the favored climo locations in the
northern Adirondacks such as Saranac Lake. The mist/fog should burn
off between 7-10 am with the strong subsidence from the high and
sunshine. Some cirrus has increased across the region well in
advance of the cold front over S-central Quebec and the central and
northern Great Lakes region, as well as along the northern periphery
of the mid and upper level ridge. The cirrus is thin and should not
hold temps down too much.
Another hot, record breaking day is expected with h850 temps still
running a few Standard deviations above normal according to the
latest 00z gefs with actual h850 temps in the +18c to +19c range.
High temps should be fairly similar to yesterday and maybe a degree
or two cooler with a few-sct cumulus and the scattered cirrus
around. Overall, mostly sunny conditions should be prevail with the
cumulus mainly along the western spine of the central and northern
greens and over the Adirondacks. Highs will be in the upper 80s to
lower 90s in the valleys especially the St Lawrence and Champlain
valleys and 70s to mid 80s over the elevated terrain. Sfc dewpts
will still be in the 60s and it will be very humid outside. We will
re-run the Special Weather Statement with the heat indices in the lower 90s. They fall
just short of the 2nd day with heat indices in the mid 90s for a
possible advisory for N-cntrl Vermont. Please see the climo section below
with the records that may be broken.
Expecting a similar night to this morning with the sfc high
weakening, and the mid level ridging flattening aloft. Some locally
patchy dense fog may form in the valleys. We are expecting some
high clouds to move in from the west ahead of the cold front over
the eastern Great Lakes region and southeast Canada towards
daybreak. Lows will be in the mid 50s to mid 60s. It will be the
last mild night.
Short term /6 am Wednesday through Thursday night/...
as of 430 am EDT Tuesday...Maria drifts close to the mid-Atlantic
coast then starts to make the turn to the east to northeast. Mid
and upper level heights continue to fall over upstate New York into
western New England during the day with low pressure moving into
north-central Quebec and a cold front approaching the region. The
increasing clouds should hold temps down a bit west of the Champlain
Valley with upper 70s to mid 80s in the valley areas, and upper 60s
to upper 70s over the higher terrain. Some upper 80s are possible
in the Champlain Valley and near btv /possibly some isolated 90f
reading/, with generally 80-85f readings in the other valley
locations, and 70s to around 80f over the mtns. Some record temps
are possible again at several sites.
There is modest convergence with the front and some small amounts of
sfc based instability in the 250-750 j/kg range based on the latest
GFS. We have placed slight to low chances of showers in the
afternoon with a slight chc of thunderstorms.
We will continue the previous btv discussion highlighting heat
While these temps are considered sub advisory(<95 f), they are
not to be taken lightly especially given the time of year. Based
on the forecast and current records, its expected that records will
fall at many sites by 2-5 degrees. Prolonged exposure outside
combined with strenuous activity can lead to heat related injuries.
Please take caution, stay hydrated and take frequent breaks during
any outdoor activities. This will be the fourth consecutive day with
90+ degree heat indexes during the afternoon.
Wednesday night into Thursday...fairly good agreement with the
latest deterministic guidance that the front will clear the forecast
area between 06z-12z/Thu. We did keep a few lingering showers over
nrn-cntrl Vermont. Total rainfall from this front will likely be less
than a tenth of an inch unless some convection occurs. Cold
advection occurs in the wake of the front with h850 temps falling to
+2c to +10c from the St Lawrence River valley southeast across
central Vermont. Lows will fall into the 40s to lower 50s. Cool and
breezy conditions are expected on Thursday with sunshine mixing with
clouds, as a sfc high noses in from the southeast Ontario. Highs
will trend back to normal readings with mid 60s to around 70f in the
valley areas, and 50s to lower 60s over the higher terrain.
Thu night...a short-wave moving through the upper level trough over
S-central Canada, the Great Lakes region and into the northeast will
approach the forecast area. Mostly clear conditions early will give
way to increasing clouds especially over northern New York. The short-
wave and its associated cold front looks to impact portions of the
local area on Fri. It should remain dry Thursday night with lows in the
30s to around 40f. There could be some patchy frost with lower to
mid 30s in the northern Adirondacks.
Long term /Friday through Monday/...
persistence was used predominately in the long term with the one
change being the short-wave diving south and east of the region
during the day. The limited low-level moisture will hold the
chances of showers mainly in the slight chance category on Friday
mainly west of the Champlain Valley. From the Champlain Valley
eastward we have kept it dry.
A slight chc of showers was kept in Fri night into Saturday with the
mid and upper level trough passage, but overall this could end of
dry again which has been the trend the past few weeks. A large
ridge of high pressure builds in late Saturday into Monday with fair
and dry weather with seasonable temps. Some patchy frost may be
possible in the sheltered valleys within the higher terrain on the
Aviation /11z Tuesday through Saturday/...
high pressure at the surface and aloft will be over the region today
into tonight. A cold front will approach from the west tomorrow.
The locally dense fog and low stratus with IFR/LIFR/vlifr conditions
at kmss, kslk, and kmpv will gradually dissipate between 12z-14z
with the strong subsidence with the ridge and abundant sunshine. The
fog may linger the longest at kmpv. VFR conditions will prevail at
kbtv, krut and kpbg this morning.
VFR conditions will dominate from the late morning through the
afternoon at all the taf sites with some sct-bkn cirrus and a few-
sct cumulus clouds. The clouds will thin towards sunset with some
lingering scattered cirrus.
Some locally dense fog will be possible once again tonight,
especially after 06z at kslk, kmpv and possibly kmss. Conditions may
lower to LIFR/vlifr at these locations. Some brief MVFR conditions
maybe possible at krut after 08z.
The winds will be from the southeast to southwest at 6 kts or less
during the late morning through the afternoon, and will be light to
Wednesday: VFR. Chance rain showers.
Wednesday night: VFR. Chance rain showers.
Thursday: VFR. No sig weather.
Thursday night: VFR. No sig weather.
Friday-saturday: VFR. Slight chance rain showers.
record high temperatures and year recorded for the period
through Wednesday Sep 27
Day Burlington Massena Montpelier
9/26 84 / 1934 82 / 1970 83 / 2007
9/27 83 / 1920 82 / 2003 80 / 2007
day Burlington Massena Montpelier St Johnsbury
9/24 91 88 85 89* (tied)
9/25 92 91 88 91