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Area Forecast Discussion (AFD)

Issued by Burlington, VT (BTV)

                            
583 
FXUS61 KBTV 180753
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
353 AM EDT Mon Jun 18 2018

.SYNOPSIS...
An active weather day is anticipated today with several rounds of 
strong to severe convection, along with very warm and humid 
conditions. Thunderstorms will develop ahead of a cold front, mainly 
this afternoon into the evening, then come to an end thereafter. Any 
thunderstorms that form will be capable of producing very heavy 
downpours with potential for isolated flash flooding, gusty winds, 
and frequent lightning. Temperatures are expected to reach the mid 
to upper 80s this afternoon, with localized valley locations around 
90. This combined with dewpoints around 70 will create heat index 
values well into the 90s. Much cooler and drier air will follow the 
frontal passage, leading to a pleasant day on Tuesday. 

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 351 AM EDT Monday...Still anticipating active weather 
today with showers and thunderstorms developing through the day,
with a couple of rounds of convection through this evening. 
Main threats continue to be heavy rainfall and gusty, possibly 
damaging winds. 

Scattered convection is ongoing just to our north this morning, the 
remnants of an MCS that affected the Upper Midwest yesterday. This 
should mainly stay north of the international border, perhaps 
brushing along the northern tier of counties in NY/VT. The bulk of 
the activity will occur this afternoon into the evening hours, 
likely in a couple of rounds. Scattered showers/thunderstorms will 
develop early this afternoon with a pre-frontal trough, particularly 
over the higher terrain. This activity will quickly move east, 
giving way to the second round with the cold front that will cross 
from northwest to southeast late this afternoon into the evening 
hours. Moisture will surge out ahead of the front; PWATs will 
approach 2.25 inches as dewpoints rise to around 70F. With warm 
cloud depths in the 12-14 kft range, expect any thunderstorms will 
be very efficient rainmakers. Mid-level flow will be sufficient 
enough to keep storms moving, but MBE vectors indicate the potential 
for back-building or training of cells. While widespread flooding is 
not anticipated, isolated flash flooding will be possible if/where 
any training does occur. Note that much of the North Country remains 
in the Slight Risk area in the latest Day 1 Excessive Rain Outlook 
from WPC. The other concern from this convection will be the 
potential for strong or severe thunderstorms as equilibrium levels 
exceed 40 kft. Low-level lapse rates will steepen ahead of the 
front, and the surging moisture will allow for CAPEs of 1200-2000 
J/kg. Meanwhile, a 700-850mb jet of around 45 kt will allow 0-6km 
shear of 35-45 kt. Mid-level lapse rates won't be very impressive 
given the deep warm layer. Hence the main severe potential will be 
for strong to damaging winds due to wet microbursts, while large 
hail is not anticipated. SPC's Day 1 Outlook keeps our region in 
Slight Risk, with 15% damaging wind potential. As per the above, 
have kept gusty winds and heavy rainfall in the forecast through 10 
pm this evening. 

The other concern for today is the potential for elevated heat 
indices due to warm temperatures and high humidity. Complicating 
factor is the copious amounts of convective debris clouds currently 
seen on satellite upstream of our area. This increased cloud cover 
will keep temperatures down a bit, especially across the north. 
However, should much clearing occur, temperatures will quickly 
approach 90 in southern Champlain/Connecticut Valleys. Add this to 
the high dewpoints and heat indices of 95+ will be possible. Have 
therefore kept the Heat Advisory in place in these areas. Elsewhere, 
highs in the mid 80s will keep the heat index around 90F, below 
criteria. 

For tonight and Tuesday...the front moves through the area by 
midnight, ushering in cooler and drier air. Showers/thunderstorms 
will come to an end and skies will gradually clear by mid-morning 
Tuesday. Lots of sunshine expected by the afternoon, along with a 
bit of a northwest breeze. Tuesday's highs will be in the lower to 
mid 70s, after lows tonight in the mid 50s to around 60. 

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 351 AM EDT Monday...Generally quiet weather is expected 
during this period with mean surface high pressure in control of
regional weather conditions. After a mainly clear night and 
seasonable temperatures overnight Tuesday (45 to 55 F) skies 
trend partly cloudy over time by Wednesday afternoon as a weak 
surface trough approaches from the north. This feature will 
approach the intl. border/nrn tier of counties later in the day 
with perhaps a stray sprinkle or shower as advertised in some of
this morning's output. Dry lower levels and only a narrow mid-
level moisture axis along the wind shift should keep coverage 
rather minimal and as such have only carried lower end pops 
generally below 30 percent in these areas accordingly. Highs to 
rebound quite nicely, topping out in the upper 70s to lower 80s 
in most spots.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 351 AM EDT Monday...Any lingering spotty sprinkles/light 
showers across the northern counties will end Wednesday evening 
as the surface trough clears southward and skies trend mainly 
clear. Lows again near seasonable norms in the mid 40s to mid 
50s.

Thereafter, fair and seasonably mild to warm weather is 
expected to round out the work week as surface high pressure 
bridges atop the region. Thursday will be the cooler of the two 
days as highs top out in the upper 60s to mid 70s under light 
northerly winds. Then a nice rebound by Friday as the high 
slides east, southerly return flow commences and air of 
midwestern origin advects into our area - mid 70s to lower 80s. 
The next chance of appreciable precipitation arrives by later 
Saturday into Sunday of next weekend as a dampening upper 
shortwave lifts northeast from the Great Lakes and Ohio Valley 
states. This feature looks to have decent moisture and with 
lower- end boundary layer instability showers along with a few 
thunderstorms will be introduced into the forecast. Temperatures
on both weekend days to run on the warm side but not 
excessively so - mainly upper 70s to lower 80s for highs and 
corresponding lows in the 50s to lower 60s.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...High clouds will continue to spread across
the area through the overnight hours as an increasingly moist, 
unstable air mass moves in. A cluster of storms are crossing
southern Ontario/Quebec, and these will skirt just to our 
north through the early morning hours, perhaps brushing KMSS and
KPBG. After 12Z, increasing instability will allow showers to
develop, particularly over mountainous terrain. Between 15Z and
18Z, expect coverage of showers to increase some, particularly 
in northern portions of the forecast area. The better chances 
of more widespread organized convection will be after 18Z 
tomorrow, but some areas could see some showers and
thunderstorms with heavy rain before 18Z. Visibilities will be 
reduced in heavy showers, but expecting ceilings to remain above
5000 ft. 

Southerly/southwesterly winds under 10 kts will ramp up to 10 -
15 kts after 12Z, with some gusty winds possible in any storms
that develop.  Could also encounter some areas of turbulence 
tomorrow due to the thunderstorms, particularly in and around 
terrain. 

Outlook...

Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. Slight chance SHRA.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.

&&

.HYDROLOGY...
Scattered to numerous showers and thunderstorms are 
expected to develop around midday today and continue into this 
evening. The combination of precipitable water values up to 2.25 
inches and storm motions supporting some training of convection, 
supports the threat for isolated flash flooding. Given the available 
moisture in the atmosphere, any storms will be capable of very heavy 
rainfall rates of 1 to 1.5 inches in an hour, which over terrain or 
urban areas could cause isolated flash flooding. Given the very 
recent dry weather widespread large stem river flooding is not 
anticipated, but sharp rises on smaller streams in complex terrain 
where multiple rounds of storms occur is possible.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory from 11 AM this morning to 6 PM EDT this evening 
     for VTZ005-009-011-012.
NY...Heat Advisory from 11 AM this morning to 6 PM EDT this evening 
     for NYZ035.

&&

$$
SYNOPSIS...Hastings
NEAR TERM...Hastings
SHORT TERM...JMG
LONG TERM...JMG
AVIATION...Hastings
HYDROLOGY...Hastings