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  Friday July 19, 2019

 

NWS Area Forecast Discussion


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756
FXUS61 KBTV 190535
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
135 AM EDT Fri Jul 19 2019

.SYNOPSIS...
An active period of weather is expected across the North
Country beginning Friday through Sunday. Humidity will be
increasing tonight with hot and humid conditions expected on
Friday and Saturday. Chances for thunderstorms exist Friday
through Sunday. More seasonable weather returns by early next
week.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 135 AM EDT Friday...No real changes made with this
update, just ingested latest obs and tweaked cloud cover to
match trends in satellite. Otherwise going forecast in good
shape.

Previous Discussion...Generally quiet weather expected tonight.
There is a modified maritime layer wrapping anticyclonically
around the sfc ridge in the Gulf of Maine, which has resulted in
mostly cloudy conditions across portions of s-central and
central/ern VT this evening. As sfc-850mb flow gradually veers
into the southwest, should see these clouds dissipate toward
daybreak on Friday. Adjusted low temperatures upward across
central/ern VT tonight to account for reduced radiative cooling
with cloudiness in place. Lows generally in the lower 60s across
ern VT, and mid- upper 60s elsewhere across the North Country.

Previous Discussion...Ridge of surface high pressure will slide
eastward overnight, and a warm front will push into our area
from the west. Warm and moist airmass slides into the North
country, remaining through Friday night. Southerly flow will be
in place and a moist air mass will move into the region.
Overnight minimum temperatures will range from the upper 50s in
our eastern zones to upper 60s in the Saint Lawrence valley.
Pwats will be above 1.5", though highest pwat air reminds south
of our region. Shortwave energy and some surface based
instability will increase chances for showers and afternoon
thunderstorms on Friday. Models indicate decaying convection
will enter our western northern New York zones by Friday
morning. The chance for afternoon thunderstorms still looks
possible with plenty of CAPE (~1500-2000 J/kg) and moisture,
however shear is marginal and mid-level cap and dry air will
limit both vertical and areal extent of storms. Maximum
temperatures on Friday will reach the upper 80s to lower 90s and
produce heat indices above 95 in the Champlain and Saint
Lawrence valleys especially. A heat advisory is in place for
these areas beginning at noon. Friday night will remain pretty
mild, and any afternoon convection that develops will be dying
down. Overnight minimum temperatures will be in the upper 60s to
lower 70s.

&&

.SHORT TERM /SATURDAY NIGHT/...
As of 315 PM EDT Thursday...The big story will be the heat and
humidity levels on Saturday with heat index "feel like"
temperatures near 100 degrees in the valleys.

Large scale pattern shows strong mid/upper level ridge across
the se conus with axis of very warm temps extending from the
Ohio Valley into the NE CONUS. Moderate 925mb to 850mb flow of
20 to 30 knots will help advect very warm and humidity
conditions into our region with 925mb temps btwn 26-28c on Sat.
Adding 8-10C to these values supports highs upper 80s to mid 90s
most locations with a few spot upper 90s lower CT River Valley
and central CPV. These values combined with dwpts in the upper
60s to lower 70s will result in heat index values in the 96 to
104 degree range, solid advisory criteria for most locations.

The next concern will be chances for afternoon/evening showers
and storms. There is plenty of uncertainty with regards to
potential convection, as 12z guidances still has a large spread.
NAM continues to trend north with ridge roller MCS on Sat
aftn/evening, while GFS/ECWMF and CMC show leftover convective
vort riding near the international border. This will interact
with plenty of instability with CAPE values in the 2500 to 3500
j/kg, while best 0 to 6 km shear of 35 to 40 knots hovers near
the border. These parameters would support organized convection,
however when viewing the NAM sounding data, our atmosphere is
strongly capped due to warm nose btwn 850-750mb with deep dry
layer present and without the forcing from upstream convective
vort, the overall threat of convection would be minimal. In
addition, its interesting the potential impacts convection has
and pushing cooler air south on Sunday. GFS shows axis of
warmest 925mb to 850mb air mainly south of our cwa with
northwest flow, while NAM continues to place most of our fa in
the warm sector with another day of heat and humidity. Based on
uncertainty, especially with regards to convection, which is
typical given upstream activity will continue to mention chc
pops for northern NY into northern VT on Sat aft/evening. No
mention of enhanced wording, given the uncertainty. Either way,
Saturday Night lows warm and muggy with lows mainly in the upper
60s to mid 70s, but if front is slower lows in the CPV could
hold in the upper 70s near the UHI.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 315 PM EDT Thursday...The uncertainty on heat/humidity
and potential for convection increases on Sunday, given the
large amount of spread in guidance, especially with regards to
position of boundary and degree of heating/instability. Have
followed superblend guidance closely which supports l/m 90s
southeast cwa near VSF to l/m 80s northwest area/dacks.
Additional heat advisories maybe needed for portions of the cpv
and ct river valley on Sunday. The NAM solution would support a
threat for strong to severe storms on Sunday now, while GFS is
much further suppressed with activity. For now will continue to
mention chc pops and add additional details as event becomes
closer. Neither Sat or Sun should be complete wash outs, but
indoor plans with AC are probably a better choice, given the
heat. Much cooler and drier air advects into the North Country
for early next week. Guidance in decent agreement with overall
large scale pattern change, but still some uncertainty on
evolution timing of development of mid/upper level trof across
the Great Lakes/NE Conus. The development of trof and associated
1018mb high pres will suppress heat/humidity to our south,
along with best instability through early next week. Progged
925mb temps range btwn 16-18c on Mon/Tues, but warm to near 20c
by Weds. These values support highs near normal with readings in
the mid 70s to mid 80s most locations and lows generally in the
mid 50s to lower 60s. Timing embedded vorts and associated
ribbons of enhanced moisture in the flow aloft becomes
increasingly more difficult in days 4 thru 7, so have trimmed
back pops with just isolated/scattered wording toward mid week.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Through 06Z Saturday...VFR through the TAF period under mostly
clear skies. Some scattered/broken 2500-3500ft ceilings may be
possible across southern VT but should dissipate by morning.
Decaying storms across southern Quebec will bring chance for
showers/TS across northern VT tomorrow morning (have mentioned
VCSH at KMPV), elsewhere chances for an isolated TS during the
afternoon hours are possible but areal coverage will be limited
so have omitted VCSH/VCTS from TAF at this time. Winds through
the period will be generally light out of the south around 5 kts
increasing to 5-10 kt with gusts up to 20 kt possible in the
afternoon especially in CPV. Winds will gradually turn out of
the SE between 5-10 kt towards 22z.

Outlook...

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory from noon to 8 PM EDT Saturday for VTZ003-004-
     006>008-010-012-016>019.
     Heat Advisory from noon today to 8 PM EDT Saturday for VTZ001-
     002-005-009-011.
NY...Heat Advisory from noon to 8 PM EDT Saturday for NYZ029>031-
     034.
     Heat Advisory from noon today to 8 PM EDT Saturday for
     NYZ026>028-035-087.

&&

$$
SYNOPSIS...Neiles
NEAR TERM...Banacos/LaRocca/Neiles
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...LaRocca



 
 
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