598 
FXUS61 KBTV 161710
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
110 PM EDT Thu Jul 16 2020

.SYNOPSIS...
Surface high pressure moving eastward into the Gulf of Maine 
will maintain mostly dry and warm conditions across the North 
Country today. Breezy south wind conditions will also develop as
a frontal system makes its way eastward across the Great Lakes 
region. This frontal system will bring widespread rainfall 
tonight into Friday morning, with a few embedded thunderstorms 
anticipated. Rainfall amounts of a half to three-quarters of an 
inch are possible, likely highest along the international 
border. The weekend will be drier and trend much warmer with 
higher humidity and heat indices. Valley heat indices in the mid
90s are expected Sunday.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 1014 AM EDT Thursday...Cloud cover is being stubborn
across much of Vermont this morning. High resolution guidance
from this morning depicted our mixing heights increasing this
morning to help scour out some of the cloud cover but instead we
have strengthened our low level inversion based on latest RAP
mesoanalysis. Nevertheless, satellite does show pockets of less
clouds over the Adirondacks which should shift eastward through
the afternoon hours. The 12Z NAM3 is being aggressive with
depicting convection across the St. Lawrence Valley this
afternoon but the model soundings depict any instability
associated with this convection to be elevated. This should help
to produce efficient rainfall but won't produce any hail or
strong wind gusts as out lapse rates are beginning to trend
toward moist adiabatic as we see moisture stream into the
region. Overall, the forecast is in good shape and just tweaked
the sky and temp forecast to reflect current trends and
increased PoPs a little earlier for the St. Lawrence Valley.

Previous Discussion...Ridge of high pressure along coastal
New England remains our controlling weather feature today,
despite variable cloudiness expected thru the day. GOES-16 
10.3-3.9um product indicates widespread low stratus across 
s-central and ern VT, which will be slow to mix out this 
morning. However, with increasing southerly gradient flow, PBL 
eventually mixes out bringing a period of partly sunny 
conditions to the North Country late morning/afternoon. Already
seeing abundant mid-level clouds moving ewd from the shortwave
trough over the southern Great Lakes region. 

Channeled flow in the Champlain Valley results in south winds 
12-20 mph around BTV, with gusts up to 25-30 mph. Have issued a
Lake Wind Advisory for Lake Champlain with sustained winds of 
15-25kt over the water. High temperatures this afternoon 
generally reach the upper 70s to lower 80s, and locally into the
mid 80s across the St. Lawrence valley.  

Progressive mid-level shortwave trough brings increasing mid- 
level cloudiness later this afternoon across the St. Lawrence 
Valley and nrn Adirondacks, followed by potential for widespread
showers and a few embedded thunderstorms during the 
evening/overnight hours. Have indicated 70-90% PoPs shifting
from west to east across the forecast area, highest during the
pre-dawn hours Friday. Some continued indication in NAM/GFS model
soundings for a swly low-level jet of 40-45kt overnight at 
4-5kft, and this allows PW values to increase to 1.7-1.9". As 
such, could be some brief heavy rainfall with any embedded 
convective elements overnight. That said, MUCAPE values remain
around 500 J/kg, so severe threat remains low. All in all, mid-
level trough is progressive enough that we should avoid any 
flooding concerns, but generally looking at 0.5-0.75" basin-
averaged rainfall. Currently, appears highest rainfall will be 
across nrn areas, and this will bring much needed rainfall to 
the St. Lawrence Valley, where precipitation deficits remain 
large during the past 2-3 months. Lows tonight generally upper
50s to mid 60s, highest in the Champlain Valley as PBL remains
well-mixed (Champlain Valley winds hold 10-20 mph much of
tonight). 

Will see a gradual decrease in coverage of shower activity from
west to east during the day Friday. That said, daytime heating
may bring a renewed threat of thunderstorms, mainly central/ern
VT during the early-mid afternoon hours. Should see highs on
Friday from the mid-upper 70s across central/ern VT, near 80F in
the Champlain Valley, and 80-85F in the St. Lawrence Valley
where the best potential exists for prolonged sunshine on
Friday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
As of 258 AM EDT Thursday...A relatively warm Friday night due to
lingering low-level moisture. Clouds decreasing overnight with the
North Country waking up to 60s Saturday morning. For the afternoon,
it will be quiet, but bordering on hot for Saturday. Deep-layer
ridging and dry mid-level air will shift across the North Country
during the day. An inversion layer positioned 8000ft above sea
level. So not even elevated heating off terrain should produce
convection. We should still see some fair weather cumulus dot the
sky.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 258 AM EDT Thursday...Westerly flow aloft becomes more
southwesterly, allowing continued warming with muggier air in place.
With that, we should see better instability allowing for storms
along the high terrain, along with lee-side troughing that could
support convection from lake breeze interactions towards New York.
Temperatures should warm into the upper 80s to mid 90s as 925 hPa
temps climb up to 26 C. There could be a fly in the ointment. There
is a shortwave trough riding over the ridge Sunday, and some
guidance is suggesting convection that develops along the feature
Saturday evening might seep down into the North Country as opposed
to remaining north. Will continue to lean towards NBM output for the
time being.

Piecemeal frontal passage takes place Sunday night into Monday. The
nocturnal timing will not help us get the most out of the frontal
passage, but most should see at least some precipitation.
Afterwards, a longwave trough will nudge southwards over the Great
Lakes region. West to northwest mid-level flow should prevent moist
southerly flow from bringing oppressive heat back northwards and
with thicknesses should be lower overall. 925 hPa temps remain in
the upper teens Celsius. So it should still be seasonably warm 
(+2 to 4 F above normal), but nothing oppressive in sight for 
now. Anticipate a series of weak waves to ride confluent flow 
between the Bermuda High and the troughing centered over the 
Great Lakes, but there is some disagreement between global 
models on the finer details.

&&

.AVIATION /17Z THURSDAY THROUGH TUESDAY/...
Through 18Z Friday...A mix of MVFR and VFR ceilings prevail
across the North Country this afternoon ahead of an approaching
warm front. Conditions will likely deteriorate as we head into
the evening and overnight hours as we begin to see moisture
surge into the region with ceilings dropping to 1500 to 2500 ft
by 12Z on Friday. Isolated pockets of IFR conditions will be
possible, especially at KSLK during the morning hours initially
behind the warm front until a cold front swings through. We are
expecting convection to move into KMSS between 22Z and 00Z and
spreading eastward into Vermont just prior to 12Z. We could see
some embedded rumbles of thunder but we are generally looking at
some decent rain makers tonight and again on Friday.
Visibilities look to stay above 6SM but some stronger showers or
thunderstorms could briefly drop visibilities to 3-5SM. Wind
shear will also be a concern tonight into the early morning
hours as a strong low level jet moves overhead. We will likely
lose our gusty winds between 6Z and 14Z when we will see 40-50
knots of wind at 2000 ft. This will likely lead to some decent
turbulence during the morning hours across much of northern New
York and Vermont. Conditions will slowly improve throughout the
day on Friday as precipitation ends from west to east and
ceilings begin to slowly improve and the stronger winds aloft
exit to the east. 

Outlook...

Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. Chance SHRA.
Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA.
Monday: Mainly VFR, with areas MVFR possible. Chance SHRA.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. Chance SHRA.

&&

.MARINE...
South winds will increase to 15-25 knots this morning as
pressure gradient increases between a departing high pressure
system across the Gulf of Maine, and a frontal system across the
Great Lakes. Waves will build to 2 to 4 feet by this afternoon,
likely highest across the northern portion of the broad lake. May
see a continuation 15-25 knot winds through much of tonight as
low pressure shifts eastward into northern New York.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Clay
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Clay
MARINE...Banacos