Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 042328

Area Forecast Discussion
National Weather Service Burlington VT
728 PM EDT Mon Jul 4 2022

A complex area of low pressure approaching the region will support
periods of showers by morning. Following a final round of showers
and isolated thunderstorms Tuesday night, a return to drier
conditions is expected on Wednesday. Quiet weather then takes hold
through early Friday, then low chances of precipitation follow to
end the week.


As of 553 PM EDT Monday...An ill-defined warm front/moisture
boundary is nosing northeastward into the region from Ontario.
Along and behind the front, scattered showers are streaming
east/southeastward over Lake Ontario in NY. Current forecast has
these showers covered well, and just made some minor tweaks.
Expect these showers to remain mainly to the south of our
forecast area this evening/early tonight, with a dry rest of the
day on tap before more widespread precip develops tomorrow.

Previous discussion...It`s another seasonable, dry day
across the North Country. However, we`ll keep an eye on the
cumulus field this afternoon, which was driven by steep low
level lapse rates and enhanced by warming 850 temperatures, that
has led to analyzed 100-250 J/kg CAPE. CAMs are suggesting a
sprinkle or brief rain shower is possible through the rest of
the day. Where greater instability, upwards of 1000 J/kg CAPE,
resides in Quebec, some thunderstorms have developed and are
rolling towards the southeast along with the rest of the cumulus
field. If a stray shower develops downstream closer to the
International Border through the rest of the day, best chances
of it impacting our area would be through the next couple of
hours and over northeastern New York.

Then our attention turns to the ill-defined low pressure system over
the Midwest which has produced thunderstorms along its warm front
today. In contrast, precipitation for our area will become very
disjointed, as that frontal precipitation looks to pass to our
south while a new boundary develops and lifts northeastward into
our area by morning. Light amounts of rainfall are expected
with this first batch of showers associated with some isentropic
lift. The surface warm front is not expected to actually make it
into our area, leaving us out of the warmest air and surface-
based instability for the rest of the day. Generally, there
remains substantial differences in model output for timing of
rainfall, but the best forcing for rain across the North Country
shows relatively good agreement of taking place in the 5 PM to
10 PM period associated with the mid-level trough passing
overhead with a weak surface low approaching.

There still are some thunderstorm chances, but the convective
threat is low. Where we see drier low level air advect in
during the afternoon, deeper mixing will occur with modestly
gusty conditions. Gusts up to 25 MPH are likely during the
afternoon associated with the southwesterly 850 millibar flow
temperatures could rise to near or above 80 in southern Addison
and valleys of Rutland and Windsor counties. The relatively low
humidity in the air mass should preclude any substantial CAPE.
Once the low levels saturate better tomorrow evening, expected
elevated instability to develop. This will correspond to
stronger synoptic-scale vertical motions, allowing for
development of some tall, skinny updrafts capable of producing a
thunderstorm, with instability above the moist layer.
Therefore, have maintained at least a slight chance of thunder,
with relatively high chance in southern portions of northern New
York and Vermont where this is more likely to occur.

Storm total rainfall ranges from about 0.25" in portions of
south central Vermont to near 1" in northwestern Clinton County
and some of the higher terrain. The afternoon/evening
precipitation will be most widespread and pose the best chance
of heavier rainfall. However, the ingredients for heavy rain are
a mixed bag as we won`t see much instability to get rainfall
rates particularly high within any convective elements. There is
a high (90%) chance of seeing at least 0.1" of rain across the
North Country during the evening as low level convergence ramps
up just ahead of the surface low tracking near or over the
region. At the same time, HREF probability of 3-hr rainfall in
excess of 1" is 30% or less within a 40 kilometer radius of any
location. Given recent wet weather in southern and western
portions of the Champlain Valley and northern New York, the
marginal risk of flash flooding seems reasonable, but the threat
appears to be low.

Working against a particularly strong system is an unfavorable
jet streak depicted by model guidance. It features a 250
millibar wind speed max approaching to our north and one exiting
to our south Tuesday afternoon, putting us in an area of upper
level convergence. It suggests a weaker low pressure system that
prevents better moisture convergence and organized heavier
rainfall. We will not see a particularly deep moist column once
the low approaches in the afternoon, and it will tend to dry out
top-down as mid-altitude winds become northwesterly.

The final period of possible rain will be associated with a
secondary surface cold front moving through overnight. Have
offered diminishing precipitation chances through the overnight
hours, as the main cold front looks to move east of the region
after 2 AM and widespread showers are unlikely with that
secondary front. It should serve to shift winds to a northerly
direction but lingering low level moisture should keep things
humid through daybreak.


As of 348 PM EDT Monday...Chances for precipitation are expected to
linger a little longer over the Greens of central/southern Vermont
and lower elevations of southern Vermont with models slowing the
exit of the Tuesday system. The result will be light showers with
little further additions to rainfall amounts and continued
cloudiness through early Wednesday. High pressure drops out of
Canada by Wednesday night keeping with drier conditions developing.
Some fog development may be possible but will need to be resolved
closer to Wednesday to evaluate surface flow overnight since
northwesterly breezes will linger behind the exiting cold front.
Overnight lows will dip 5-10 degrees below the previous night in the
mid/upper 40s for the Adirondacks and northeast Vermont and low to
mid 50s for main valleys.


As of 348 PM EDT Monday...High pressure is progged to remain over the
North Country through Thursday night with temperatures around
seasonal averages. Model consensus brings the next chances of
precipitation in on Friday with development of a low over the Ohio
River Valley. Most projections keep strongest forcing and the low`s
track south of Vermont. Some interactions with a trough phasing out
of Canada may occur but more time is needed to resolve how far south
this trough will dip towards the region. Marginally increased
precipitation chances to account for this possibility with slight
chances extending northward towards the Canadian border in Vermont.
Either way, it appears that the region will be between split energy
with much more limited forcing than locations in southern Canada or
towards the New England coast. Kept mention of thunder out since
parameters were not favorable in model consensus, but GFS continues
to show 250-500j/kg CAPE; we`ll keep evaluating the convective
threat over subsequent shifts. Temperatures will trend cooler at
least for the start of the weekend with highs in the mid/upper 70s.
Looking further, there is potential for a sizable, but transient,
ridge to build over the region Sunday into Monday suggesting
increasing temperatures with high temperatures possibly heading
above normals. For now, have temperatures warming to the low/mid 80s
by Monday with 925mb temps increasing 18-20C.


Through 00Z Wednesday...VFR conditions expected through 12Z. A
weak warm front will move through the area overnight, allowing
for ceilings to gradually lower from 10,000 ft AGL to 3000 to
6000 ft AGL range by 12Z. Between 12Z and 00Z, expecting
ceilings to further lower to MVFR levels as showers associated
with the warm front spread over the area. Some localized IFR
conditions are possible after 21Z, especially over areas of
higher terrain. Visibilities should remain mainly VFR through
15Z, becoming periodically MVFR between 15Z and 00Z as some
light showers develop. There is a small chance of some
thunderstorms developing Tuesday afternoon over southern
Vermont, which may briefly affect KRUT, but coverage will be
isolated with any storms that do develop.

Light and variable winds overnight will become south at 5-10
knots after 12Z. Some afternoon gusts 10-20 knots are possible.
A weak southwesterly low-level jet will develop over southern
Vermont after 21Z, which may lead to some marginal LLWS over


Tuesday Night: Mainly MVFR, with local IFR possible. Chance SHRA,
Slight chance TSRA.
Wednesday: Mainly VFR, with local MVFR possible. Slight chance
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. Slight chance SHRA.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.




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