Flood Potential Outlook
Issued by NWS Burlington, VT

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Winter/Spring Flood Potential Outlook
National Weather Service Burlington VT
111 PM EST Thu Feb 18 2021

...Winter/Spring Flood Potential Outlook...

This is the fourth flood outlook for the 2021 winter/spring flood
season. Flood outlooks are issued bi-weekly by the National
Weather Service in Burlington, Vermont to summarize the flood
potential due to snowmelt and break up of river ice across central
and northern Vermont and northern New York. This outlook is valid
for the two week period of February 18 to March 3, 2021.

...Overview...

The flood potential is generally near normal across the area,
except for the Northeast Kingdom of Vermont where the threat is
somewhat below normal. The potential for flooding due to ice jams
is now considered normal across the North country.

...Snow Depths and Water Equivalent...

Over the past two weeks the snowpack has continued to deepen and
is now near normal in most places. Across Northern New York, snow
depths in the valleys average 1 to 2 feet with amounts up to 3
feet in the higher terrain of the Adirondacks. Snow depths are
also slightly above normal in the Saint Lawrence valley. Across
valley locations in Vermont, snow depths are very uniform, ranging
from 10 to 20 inches, including 15 inches at the Burlington
International Airport. Snow depths are a bit lower across far
southwestern Vermont along the border with New York state where
depths of just 5 to 10 inches have been observed. Across the
higher elevations of the Green Mountain spine and the Northeast
Kingdom in Vermont, snow depths increase to between 20 and 30
inches with only localized higher amounts. The latest snow depth
at Mount Mansfield is 47 inches. Snow depths are near normal
across Southern and Western Vermont, but below normal across the
northern Green Mountain and Northeast Kingdom regions for mid-
winter.

The snow water equivalent (SWE), or the amount of water contained
in the snowpack, is also near normal for this time of year.
Across Northern New York, SWE values are averaging between 2 and 5
inches in the valleys, increasing to 4 to 8 inches above 2500
feet in the Adirondack Mountains. Across the valleys of Western
Vermont, SWE values are between 1 and 3 inches. In the valleys of
Eastern Vermont, SWE values range from about 2 to 5 inches with
around 6 inches in the Northeast Kingdom. Above 1500 feet along
the spine of the Greens, SWE values are between 4 to 8 inches. SWE
values are near normal across much of Western and Southern
Vermont but are below normal across the Northern Green mountains
and Northeast Kingdom for mid-February.

...River and River Ice Conditions...

River flows across the region are near to below normal, except
much below normal in the Saint Lawrence valley. River ice
thicknesses are estimated to be between 6 to 12 inches. The ice in
Northern New York and Vermont is of sufficient thickness and
integrity to cause potential flooding if any rapid runoff and
significant river rises were to occur and move the ice, even
though thicknesses are a bit less than normal for mid-February.
Aside from a few streamgages in the northeastern part of the
state, most rivers in Vermont have normal streamflow. In Northern
New York, streamflows in the Saint Lawrence valley and the western
slopes of the Northern Adirondacks are below to much below
normal. This reflects the longer term drought and water storage
issues arising last spring/summer in these areas. Given recent
additions to the snowpack and SWE, some modest recharge into near-
surface soil layers is expected once thawing conditions arrive
this spring.

...Soil Moisture and Groundwater Conditions...

The latest near-surface soil moisture anomaly maps show much
drier than normal soil moisture states across the region. The
dryness is not really a serious issue right now as there is a lot
of snow in most areas available for recharge. The latest Palmer
Drought Severity Index map showed all of the region having normal
moisture states with the exception of the Saint Lawrence valley
where severe drought conditions were indicated. Examining
groundwater monitoring wells across the region courtesy of the
United States Geological Survey (USGS) shows much of the region
with below to much below normal groundwater levels. The lowest
groundwater levels continue to be found from Northern Vermont west
into Northern New York. The Saint Lawrence valley has been seeing
much below normal groundwater levels for several months. The low
groundwater levels are a bit concerning although we still have
quite a bit of snow available to recharge the system.

...Weather Outlook...

The current outlook from the Climate Prediction Center (CPC)
calls for above normal precipitation and above normal temperatures
over the next two weeks. The weather pattern looks like it will
be warming up as we head through late February into early March,
also remaining active.

...Summary...

The Winter/Spring Flood Potential for open water flooding is near
normal across most of the North Country over the next two weeks.
In the Northeast Kingdom of Vermont, the flood potential is
somewhat below normal. Snow cover and the associated snow water
equivalents have made significant gains bringing us closer to
normal readings. In general, warmer and more active weather is
forecast. River ice coverage is still a bit below normal, with
greatest coverage across northern watersheds. Given this
information, a near normal threat of ice jam flooding exists
across the area over the next two weeks.

It is important to remember that heavy rainfall can result in
flooding at any time of the year, even in areas that have little
or no snow on the ground.

The next Winter/Spring Flood Potential Outlook will be issued by
the National Weather Service in Burlington, Vermont on Thursday,
March 4, 2021.

Access current weather conditions and forecasts on our web site
at www.weather.gov/btv.

$$

Neiles



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