-- Discussion containing changed information from previous version are highlighted. --
480
FXUS61 KBTV 180912
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
512 AM EDT Tue Jun 18 2024

.SYNOPSIS...
Dangerous levels of heat begin this afternoon and will persist
into Thursday. Highs will reach well into the 90s each day, and
overnight temperatures will remain muggy and uncomfortable.
Please be sure to take appropriate precautions to avoid heat
stress through the remainder of this week. Isolated to scattered
thunderstorm are expect this afternoon and Wednesday with
potential for strong, gusty winds. Best chances for rain
arrive late Thursday into Friday with a cold frontal passage.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 503 AM EDT Tuesday...A mesoscale convective vortex, the
leftover remnants of a large area of thunderstorms from
yesterday, has ignited over the north end of Lake Ontario and is
now moving into portions of northern New York. This feature will
kick off rain and thunderstorms that will have implications for
today`s heat, potential for localized heavy rainfall, and add
additional forcing for thunderstorms to form. This area of
mesoscale vorticity could produced more than an inch of rain in
portions of the Mohawk Valley and the Adirondacks. It should be
noted that models are not handling this feature well, but expect
this to be a focal point for thunderstorm initiation through the
afternoon. Given PWATs and other significant convective
parameters are anomalously high, strong storms are possible in
addition to the lake breeze initiated storms. Models do project
this moving into portions of west central Vermont, so the threat
area for strong storms may expand eastward from what was
previously thought. Heat-wise, locations that experience rain
from this feature will likely see mitigation of the hottest
conditions.

Previous Discussion...Oppressive heat conditions remain on
track to begin today and continue through Thursday. The one
caveat will be for locations that end up getting a thunderstorm
or remain under convective overhang for a decent portion of the
afternoon. Best chances of thunderstorms today will be along the
western shore of Lake Champlain as lake breeze initiates and
pushes westward into prevailing southwesterly flow. Given the
heat, lack of strong cape, and high levels of CAPE/DCAPE, gusty
winds will be a threat. Steering flow aloft will be weak today
favoring more of a pulse variety initiation, then transition to
outflow boundary interactions. This isn`t the strongest trigger
mechanism, but there should be a few thunderstorms given the
high levels of instability and ample CAPE; SPC concurs and has
included northern New York and portions of the Champlain Valley
in a Marginal(5% chance) risk of a severe thunderstorm. Vermont
locations will be spared the early thunderstorm chances, but
prevailing flow and any outflows tracking east could trigger
more storms along the slopes of the greens with maintenance
parameters favoring a continued eastward propagation. Southern
Vermont chances will be lower, generally less than a 20% chance.
A weak trough could be the triggering mechanism for Wednesday
as some models project a weak trough embedded in flow around the
periphery of the ridge. Again, gust winds will be the primary
threat.

Otherwise, heat will build today with AM temperatures starting
higher than previously expected. 90s will be readily achievable
and may continue to warm until convection gets going in earnest.
Champlain Valley locations may benefit the most from convective
overhang clouds for the mid/late afternoon hours. Still, plan on
dangerous heat conditions and have a plan to beat the heat.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
As of 332 AM EDT Tuesday...Thursday should be the last of the
significant heat days. Lows in the morning will be incredibly mild
with temperatures remaining in the upper 60s and 70s for most.
During the day, temperatures will again reach the upper 80s and 90s
and the humidity will remain high. Dew points will be in the upper
60s and low 70s. There will also be some afternoon convection, but
the extent is still uncertain. With the warm moist airmass, there
will be plentiful CAPE and it looks to be uncapped, so there will
likely at least be a couple terrain and lake breeze induced storms.
How much more forms depends on if there will be any other sources of
lift. The deterministic Euro and some of the ensembles bring a weak
shortwave through that is just enough to to form more organized
convection, and some bring an MCS through the region from north to
south. The other ensembles keep the storms scattered. The NAM has
stronger forcing and also brings the 1000-500 mb wind shear above 30
KTs, which would indicate the possibility of a higher severe threat.
For now, went chance PoPs for most areas as showers look likely, but
there is the potential for more widespread convection.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 332 AM EDT Tuesday...A cold front moves through on Friday and
ends the significant heat, though temperatures will remain above
average and some humidity will remain, so it won`t exactly feel
refreshing. The timing of the front is key on Friday. There should
be adequate forcing and wind shear for severe storms, but the
instability will depend on if it comes through earlier or later in
the day. A majority of the Euro and GFS ensembles bring it to the
south in the morning which would significantly reduce the
instability and prevent much of a severe threat. Only around 40
percent even have 500 J/KG of CAPE for southern Vermont and only
about 20 percent have higher than 1000 J/KG. In northern Vermont,
these probabilities are much lower. Overall, the severe threat seems
relatively low and limited to southern Vermont but it bears
watching. Behind the front, drier weather should prevail through
Saturday, before more widespread rainfall is possible Sunday into
Monday as a low pressure moves in from the west. Despite looking
cooler than this week, temperatures look to remain above normal and
the ridge will sit ominously to the south, but far enough away to
not directly impact the weather.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
Through 06Z Wednesday...VFR conditions are expected overnight
except for some moderate fog potential at SLK which is showing
near saturated conditions and decreases below 10SM already at
the VIS sensor. Result was to include some MVFR conditions 7-11Z
with a lower potential of worse than MVFR mainly if mist can
consolidate into a 100ft cloud layer. Otherwise, included some
convective clouds for the 17-22Z period with VCSH at PBG. Best
chances of thunderstorms will be along the west shore of Lake
Champlain as lake breeze results in surface convergence. Should
TS form, gusts will likely be strong given the expected heat.
Tonight, rather benign conditions return.

Outlook...

Wednesday: VFR. Slight chance SHRA, Slight chance TSRA.
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. Chance SHRA, Chance TSRA.
Thursday Night: VFR. Chance SHRA, Slight chance TSRA.
Friday: VFR. Chance SHRA, Slight chance TSRA.
Friday Night: VFR. Slight chance SHRA.
Saturday: VFR. Chance SHRA, Slight chance TSRA.

&&

.CLIMATE...
Hot temperatures will result in values near records by the
middle of next week. Below are some of the records under threat
of being broken.

Record High Temperatures:

June 18:
KBTV: 97/1994 Forecast 95
KMPV: 93/1994 Forecast 92
KPBG: 94/1994 Forecast 91
KMSS: 97/1994 Forecast 93
KSLK: 94/1907 Forecast 90

June 19:
KBTV: 100/1995 Forecast 95
KMPV: 95/1995 Forecast 93
KPBG: 93/2001 Forecast 92
KMSS: 94/1955 Forecast 92
KSLK: 93/1994 Forecast 89

June 20:
KBTV: 95/2012 Forecast 93
KMPV: 90/2020 Forecast 92
KPBG: 94/1964 Forecast 90
KMSS: 92/2012 Forecast 89
KSLK: 92/1995 Forecast 87


Record High Minimum Temperatures:
June 18:
KBTV: 73/1994 Forecast 74

June 19:
KPBG: 70/1949 Forecast 74

June 20:
KPBG: 70/1953 Forecast 74
KSLK: 68/2012 Forecast 65

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory from noon today to 8 PM EDT Thursday for
     VTZ001>011-016>021.
NY...Heat Advisory from noon today to 8 PM EDT Thursday for
     NYZ026>031-034-035-087.

&&

$$
SYNOPSIS...Boyd
NEAR TERM...Boyd
SHORT TERM...Myskowski
LONG TERM...Myskowski
AVIATION...Boyd
CLIMATE...Team BTV