Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
723 am EDT Tue Jul 26 2016
high pressure slowly builds into the region today and Wednesday.
Dry weather is expected along with a warming trend as temperatures
by Wednesday will be well into the 80s with a few lower 90s
expected. The pattern will change later Wednesday night through
Friday as a broad trough of low pressure moves into the region and
enhances the potential for precipitation. High temperatures will
be at or slightly above normal on Thursday and Friday.
Near term /through tonight/...
as of 630 am EDT Tuesday...quiet weather is expected in the near
term period. Have made just some minor tweaks based on current
temperatures and some clouds already developing over parts of
northern New York.
Today: dry weather is expected as high pressure begins to slowly
build into the region. Water vapor imagery shows plenty of dry
air over the region in the mid and upper levels...but there will
be lower level moisture in place. This combined with steepening
lapse rates should help generate some shallow cumulus clouds over
the higher terrain...but no precipitation is expected.
Temperatures at 925 mb support the idea of highs in the upper 70s
to mid 80s with a few spots reaching the upper 80s.
Tonight: high pressure continues to build into the region for a
continuation of dry weather. Any shallow cumulus over the higher
terrain will dissipate around sunset and clear skies/light winds
will take over. This could lead to some fog in the favored
locations. Low temperatures will range from the mid 50s to mid
Short term /Wednesday through Thursday night/...
as of 331 am EDT Tuesday...00z guidance suite did not indicate
the need to make any substantial modifications to the forecasts
we've been offering for the last couple of days. So with that, a
few thoughts on each day
Wednesday: all guidance indicates 925mb temperatures will be about
23c (give or take a degree) as the westerly flow aloft will advect
in a little piece of the heat that is solidly in place to our west
and south. Given plenty of sunshine and expected deep mixing to
about 6000ft (800mb), we'll end up with a deep dry adiabatic lapse
rate and even super-adiabatic near the surface. What does this mean?
Well, a hot day. 23c at 925mb supports temperatures topping out into
the lower 90s in the valleys. Well into the 80s elsewhere. Followed
the previous forecaster and painted in temperatures that were closer
to the warmest guidance. There will be a weak cold front north of
the border during the day that will likely spark some T-storms
across Quebec. By very late in the afternoon/early evening, that
front will have sagged south enough that we may have and isolated
shower/T-storm working their way through US customs and border
protection. Thinking any isolated convection would probably be
getting into far northern New York and Vermont just before sunset. Minimal
instability, so not looking for anything strong. Given the warm
airmass, we will continue to have minor amounts of instability much
of the night. Add in a little bit of low-level forcing with that
weak front, and isolated shower or T-storm Wednesday night for
northern sections seems reasonable. Temperatures will only drop to
the mid-upper 60s for most areas.
Thursday: weak front continues to slowly move south, and will act as
a focus for scattered showers and a few T-storms. Models show
precipitable water values rising above 1.5" as the moisture pools
along the front, so could be an isolated heavy downpour. More in the
way of clouds and a bit cooler temperatures aloft will result in
temperatures about 5 to 7 degrees cooler than Wednesday. Still above
normal however. Ranging from lower 80s across the north to perhaps
around 90 down in the Connecticut River valley around Springfield
Vermont. Kept pops in the 35-45% range at this point. Later forecasts may
show an increase. At this point not expecting any strong storms as
guidance doesn't show over the top instability or dynamics. Probably
more just "garden variety" type stuff. Thursday night the bulk of
the showers will push south of the region -- perhaps still hanging
on around Rutland. Overnight lows will range from the upper 50s to
lower 60s. Might be still a bit muggy down south.
Long term /Friday through Monday/...
as of 331 am EDT Tuesday...00z GFS and European model (ecmwf) continue to be
similar to their own previous runs, and have diverging solutions
between one another. So confidence is not all that high,
especially for the weekend and early next week. At least there
does not appear to be any high impact/significant weather on the
Friday: weak/diffuse front will be somewhere to the south, but close
enough that southern sections will see more clouds and a chance for
a shower or isolated T-storm. Could end up being a sunny/dry day
closer to the Canadian border. GFS and European model (ecmwf) are in decent
agreement, though GFS has a low pressure moving south of New England
during the day. Not really a player in our weather. Temperatures
should be close to normal (upper 70s to lower 80s).
Saturday/sunday: model differences more significant. GFS takes it's
surface low off the coast, and we have a light northerly flow
develop which cools US down and dries US out. At face value, GFS
says below normal temperatures with highs only in the 70s on
Saturday, and back to near normal Sunday with plenty of sun. European model (ecmwf)
keeps the diffuse front stationary to our south thru the weekend,
and has a couple of weak lows move along that front. It paints a
generally mostly cloudy weekend with scattered showers both days.
Given this continued uncertainty, the best course of action remains
sticking to a blend. Thus 20-35% pops for both days (lowest north,
Monday: both models indicate a shower is not out of the question,
but how they get to their solution is different. GFS in the process
of bringing back warmer air and more moisture, while European model (ecmwf) shows a
shortwave zipping out of the region during the afternoon with
slightly cooler temperatures coming in. We'll know exactly how
things will turn out on Tuesday of next week. For the time being,
the forecast will feature a blend of the previous 12z data plus the
latest 00z output from the GFS and European model (ecmwf).
Aviation /11z Tuesday through Saturday/...
through 12z Wednesday...relatively quiet weather is expected with
VFR conditions expected through much of the period. The only
exception to this will be the potential for IFR conditions at kslk
and kmpv between 08z and 12z Wednesday morning where fog and low
clouds are expected to form. Winds will become west-northwest at
speeds of 10 knots or less before become light and variable after
Outlook 12z Wednesday through Saturday...
12z Wed - 00z Fri: mainly VFR under high pressure. Isolated showers
possible Wed/Thu afternoons.
00z Fri - Sat: increasing chances for widespread MVFR showers and