Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
336 PM EDT Friday Aug 29 2014
surface high pressure moving across the region this afternoon and
evening will provide the north country with another pleasant night
tonight. Warmer and more humid weather will return for the weekend
as it slides east of the region and south to southwest flow
develops. Saturday should be rain free...but showers and
thunderstorms are likely by Sunday as a system moves in from the
west. Above normal temperatures...with highs in the upper 70s and
low 80s...and the chances for scattered showers and
thunderstorms...will continue into next week.
Near term /until 8 am Saturday morning/...
as of 335 PM EDT Friday...pleasant night expected for tonight as
the surface ridge of high pressure centered over the region this
afternoon shifts eastward this evening and overnight. Will begin
to see southerly return flow develop overnight as well as an
increase in high clouds from the west. Temperatures should fall
quite rapidly in the evening but then level out as the clouds and
low level flow increase. Lows generally in the 50s for
most...around 60 near Lake Champlain...with some upper 40s in the
normally colder locations in the Adirondacks and Northeast
Short term /8 am Saturday morning through Sunday night/...
as of 335 PM EDT Friday...southwest flow intensifes on Saturday around
the amplifying Southeast Ridge with warm air advection
continuing. Should be a pretty nice day with filtered sunshine
through a deck of high clouds. Not expecting much in the way of
shower/thunderstorm development with little to no cape and a
capped atmosphere. Will see a gradual increase in humidity
throughout the day as dew points creep back up to near 60 by late
in the day. Highs should reach from the middle 70s to low
80s...warmest in the Saint Lawrence and Champlain valleys.
The warmest air aloft moves overhead Saturday night with strong low
level southwest flow. The upper trough will be approaching from the
west and precipitable water values increase to near 1.8" by morning.
Thus will be looking at chances for showers increasing from west to
east overnight. Most of Vermont should remain dry through daybreak.
Could see a few rumbles of thunder as well with some elevated
instability. Lows won't fall much overnight...generally upper 50s to
upper 60s...and near 70 along Lake Champlain.
The trough continues its advancement towards the region on Sunday
and a surface boundary will be off to the north. Expecting a mostly
cloudy and relatively muggy day with temperatures in the upper 70s
to around 80 and dew points well into the 60s. Widespread showers
and scattered thunderstorms are expected as well throughout the day.
With precipitable water values close to 2" and warm cloud depths in
excess of 12000 feet...there is the likelihood of localized heavy
rainfall. Not anticipating much in the way of flooding however
outside of localized ponding on roads and in poor drainage areas.
Could also be a few stronger thunderstorms in southern Vermont with
fairly robust wind field (0-6km shear of 40 knots)...however
instability will be limited given widespread nature of showers. Best
chances will be further south in greater instability.
The weakening trough and vorticity maximum will move across the region Sunday
night with the frontal boundary remaining off to the north so some
lingering rain showers are possible through the night. Otherwise a
mild and muggy night in store with lows in the 60s to again near 70
along Lake Champlain.
Long term /Monday through Friday/...
as of 325 PM EDT Friday...no big modifications made to the
forecasts after review of the 12z guidance. The Holiday weekend
will end on a mostly dry note, with showers/T-storms returning for
Tuesday before a mostly quiet Wednesday to Friday timeframe. Above
normal temperatures for much of the week, but trending toward
normal by the end of the week.
For those that want more details, just keep reading for the daily specifics:
Monday: the system from Sunday moves east, and in it's wake middle-
level drying and shortwave ridging comes in. Still a warm
atmosphere (850mb temperatures up around 14-15c) and with
dewpoints still in the 60s, we will generate surface based
instability which should result in a few showers, perhaps a rogue
T-storm. Generally looking at 20-40% pops, with the higher chances
favoring the higher terrain. Should be a good deal of sun around,
and low 80s looks to be a good bet, though there is the potential
of it ending up even a few degrees warmer if we have fewer
Tuesday: another fast moving shortwave will cut across the region
during the day. It will be accompanied by a band of showers and
T-storms. Not looking for any strong storms or heavy rain. 12z GFS
and Euro are similar in the timing, so entering northern New York
during the late morning, Vermont by late afternoon/early evening
and then out of Vermont by late evening. Though models are similar
in timing at this point, so far in the future things are bound to
change. So about all I did was to show a little bump up in probability of precipitation
for the afternoon vs morning. 850mb temperatures warm up a degree
or two, and with no clouds we would be looking at middle to upper
80s. However with the uncertainty of cloud cover and shower
timing, I stuck pretty close to the model blend for temperatures
so it's around 80 for northern New York and lower to spot middle 80s
Wednesday: weak surface high pressure builds in and flow aloft
turns more northwest. So it should be dry. The European model (ecmwf) for days has
been saying this. The GFS now says it too, but yesterday said
"wet". As I did yesterday, i'm leaning more toward the Euro
because of it's consistency. 850mb temperatures still fairly warm (12-14c),
but cooler than Tuesday. With plenty of sun, we should be able to
achieve maximum warmth which will be the upper 70s to lower 80s.
Dewpoints will also be dropping.
Thursday & friday: as been the case for days, the models are
diverging at the day 6 mark. I will stick with the Euro for it's
better run to run consistency. GFS says showers for late Thursday,
while the Euro is dry. The Euro continues to indicate that it's
really Friday where a weak front will slide into the region. So
with that, kept probability of precipitation below 15% for Thursday and then a token
20-25% for Friday due to all the uncertainty. At this point it
looks like each day the 850mb temperatures will cool a bit, so
upper 70s on Thursday turn into middle 70s (close to normal) for
Friday. However this far out, things are still not totally locked in.
Aviation /19z Friday through Wednesday/...
through 18z Saturday...the earlier MVFR ceilings primarily in the
Champlain Valley have lifted. Have scattered-broken ceiling made up of
shallow daytime cumulus, but VFR with cloud bases generally
3500-4000ft. Anticipate VFR for the rest of the day with
light/variable surface winds. Should be VFR overnight as well.
Guidance indicates slk and mpv will both fog in with LIFR
conditions. Think the combination of relatively dry air near the
surface, increasing middle-level clouds (especially for northern ny)
and strengthening winds a few hundred feet above the surface will
preclude much in the way of fog. Can't totally rule it out in the
valleys of eastern Vermont, so that means mpv could be impacted.
At this point think it's just an MVFR situation from roughly
06-12z. On Saturday, VFR area wide with increasingly gusty
south/southwest winds, especially in the Champlain Valley. Could
see gusts over 20kt there, less elsewhere.
Outlook 12z Saturday through Wednesday...
18z Sat Onward...mainly VFR, though MVFR/brief IFR in scattered
showers and thunderstorms that will be most numerous Sunday and
perhaps again late Tuesday.
as of 300 PM EDT Friday...south winds will increase sharply on
Lake Champlain toward daybreak Saturday as the pressure gradient
increases between high pressure departing east of New
England...and a developing low pressure system across the central
On Saturday south winds will increase from 10-20 knots in the morning to
15-25 knots during the afternoon. Waves over the broad portion of
Lake Champlain will build to 2 to 3 feet.
Saturday night winds will increase slightly higher as Champlain
Valley funnelling and nocturnal low level jet set up so winds may
nudge a bit higher 20 to just shy of 30 knots overnight. A few
waves over 4 feet may occur on the north half of the Open Lake.
There will be an increasing chance of showers after midnight.
Sunday south winds will taper off to 10 to 20 knots and waves will
subside to 1 to 3 feet. Looking for widespread showers and a chance