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Area forecast discussion 
National Weather Service Burlington Vermont
406 am EDT sun Jul 24 2016

Synopsis...
other than areas of fog this morning it looks like we will have a
break from the storms today with plenty of sunshine and high
temperatures generally in the 80s. The dry weather will be short
lived as the threat for more showers and thunderstorms returns
Monday afternoon and evening. And as has been the case with the
last couple of events...some of the storms could be strong to
severe.

&&

Near term /through tonight/...
as of 406 am EDT Sunday...drier northwest flow aloft will prevail
across the area for a good part of the day today before the flow
aloft backs to the west tonight. Still some lingering clouds over
the area early this morning along with some fog and these elements
will be gradually eroding and should be gone by mid-morning. The
resulting sunshine should help temperatures climb into the 80s
during the afternoon hours.

The flow aloft begins to back to the west tonight and moisture will
begin to increase. Most of the night will remain dry but as
shortwave trough approaches...potential for some isolated convection
will exist out across the Saint Lawrence valley by Monday morning.
Lows will range from the upper 50s east to the upper 60s west.

&&

Short term /Monday through Tuesday night/...
as of 406 am EDT Sunday...monday: 00z guidance suite in okay
agreement amongst one another, but as typically the case, it's
those subtle differences that really are the Keys to locking in
the details. That said, there still continue to be a number of
items in the "pro strong convection" category. Those being:
shortwave moving into the area at peak heating time, an elevated
mixed layer (eml), surface instability (model mean cape values
1500-2000 j/kg), decent 0-6km shear of 40- 45kt (esp later in the
afternoon). In the "con strong convection" Arena, question about
how much sunshine we'll be able to get as there could be some
debris clouds during the morning, no strong low level convergence,
fairly warm layer around 800 mb which may act as a cap to
updrafts. After back and forth discussion (in my head, and with
the other forecaster here), I think most things will come together
for at least scattered convection to develop - that will have the
potential to become locally strong. Spc's latest day 2 outlook
keeps the region in a "marginal risk" for severe thunderstorms due
to the uncertainty. That assessment seems reasonable at this
point.

Have added some enhanced characteristics to the forecast, namely to
add in the potential for strong gusty winds and small hail with
thunderstorms during the afternoon/early evening.

Speaking of that warm layer aloft, models indicate 925mb
temperatures could warm to as much as 25c. Mixing that down to the
surface under perfect situation (sunshine and well mixed boundary
layer) would result in temperatures reaching the mid-90s!

In fact, some aspects of monday's setup appear similar to what we
saw on Friday, where the warm layer aloft did cap convection for
much of the day and allowed temperatures to soar into the 90s. At
this point due to the uncertainty of cloud cover (thinking there
will be some) and the fact that the majority of guidance has mid 80s
for highs, I did go warmer than most guidance, but still played it a
bit conservative and painted in upper 80s to a few spot 90f in the
valleys.

Anticipate scattered thunderstorms to develop in the morning across
northern New York and then spread east throughout the afternoon. Bulk of
the storms should be east of the forecast area shortly after 21z
(5pm), however some instability will continue across western half of
the region into the early evening as those areas could have a chance
to "reload" thanks to sunshine after the initial batch of storms
earlier in the afternoon. So for pops, I ramp up to the 45-60%
level by mid afternoon, then show a decrease, but keeping some 20-
30% pops going until a bit after midnight for eastern Vermont.
Convective Mode will probably start with isolated cells, a line
forming during the afternoon. Primary threat would be strong wind
gusts.

Monday night: residual thunderstorms wind down for the first half of
the night across eastern sections. It will still be warm/muggy
overnight as there isn't any cold front out there.

Tuesday: we'll be on the backside of the trough responsible for
monday's action. Generally means subsidence aloft, and this should
be the case. Thus looking for a mostly sunny day. Guidance does
suggest a little bit of moisture hung up across the Northeast
Kingdom of Vermont and with that area being closer to the upper trough, a
shower or two is not out of the question early in the day.
Otherwise with 925mb temperatures in the 18-20c range, we will
readily top out in the lower to mid 80s in the valleys. This is
several degrees above normal.

Tuesday night: quiet and calm, but still mild. Generally lows in the
upper 50s to lower 60s.

&&

Long term /Wednesday through Saturday/...
as of 406 am EDT Sunday...decent agreement between the 00z GFS
and European model (ecmwf) for much of the period. Wednesday should be dry and very
warm. 925mb temperatures are a couple of degrees warmer than
Tuesday, so we'll see highs well into the 80s, perhaps a few lower
90s in the southern valleys. Hints of slight 500mb height falls
and a weak surface front to our north that will probably be a
focus for a few thunderstorms across Quebec. That feature should
stay away from here based on 00z guidance, but previous runs
didn't have it as close. So perhaps that is a trend?

Thursday is a little trickier. Even though the 00z suite are
similar, they are differing from the 12z counterparts. At face
value with the 00z models, it would be a generally sunny and hot
day (925mb temperatures pushing 24c which would be mid 90s in
valleys) and still show a front just to our north. Previous runs
had moisture pushing up from the southwest. Thus will maintain
idea of 20-30% chance of showers/T-storms. Won't buy into the heat
just yet, but even then, it will be another warmer than normal
Summer day (mid 80s at least). Friday a deeper southwest flow
pattern should be established, and models bring increasing
moisture into the region. Thus we should see more in the way of
clouds and scattered showers/T-storms, and temperatures closer to
normal assuming more clouds. Saturday is more "iffy". GFS
continues the moist southwest flow pattern with a shortwave off to
our west. That would mean a rather unsettled day. 00z Euro has a
weak ridge in place with light northerly flow, which would suggest
dry and mild. Forecast will show a blend, which actually works out
to climatology. Don't cancel outdoor plans yet for Saturday.

&&

Aviation /08z Sunday through Thursday/...
through 06z Monday...areas of fog and low clouds are expected
through 14z which will cause LIFR and vlifr conditions. Otherwise...
VFR conditions are expected through the rest of the period with
little in the way of cloud cover expected. Winds will generally be
under 10 knots through the period.

Outlook 06z Monday through Thursday...
VFR conditions through much of the period. Showers and thunderstorms
Monday afternoon and night could be strong to severe with gusty
winds and hail and ceilings/visibilities lowering into the MVFR
and IFR categories with any of the showers and storms.

&&

Btv watches/warnings/advisories...
Vermont...none.
New York...none.

&&

$$
Synopsis...evenson
near term...evenson
short term...Nash
long term...Nash
aviation...evenson

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