Flood Potential Outlook
Issued by NWS Burlington, VT

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Winter/Spring Flood Potential Outlook
National Weather Service Burlington VT
216 PM EST Thu Jan 5 2017

...Winter/Spring Flood Potential Outlook /1/...

This is the first flood outlook for the 2017 winter/spring
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.

...Overview...

The flood potential due to snowmelt is near normal for northern
New York and eastern Vermont, and below normal for western Vermont
and the Lake Champlain Valley. The ice jam threat is near normal.

...Snow Depths and Water Equivalent...

Snow depths in the Adirondacks of northern New York and along and
east of Vermont`s Green Mountains were 1 to 2 feet in the higher
elevations and 8 to 16 inches in the valleys. The deeper snow was
more widespread in the Northeast Kingdom. The Lake Champlain and
St. Lawrence Valleys had four inches or less with plenty of bare
ground showing in the Lake Champlain Valley.

Snow water equivalents, or the amount of water held by the
snowpack, was 2 to 4 inches in the valleys of the Adirondacks and
eastern Vermont, and 5 to 6 inches in the higher terrain. Isolated
mountain summits had 6 inches to a foot of liquid in the snow
pack. The Lake Champlain and St. Lawrence valleys had zero to two
inches of water equivalent in the snow pack.

Snow depth and water equivalent were near normal in the
Adirondacks and Northeast Kingdom, and below normal elsewhere.

...River and Soil Conditions...

Rivers have begun to ice over, although mild temperatures have
prevented very thick ice from forming. Periodic warmups have
broken up river ice, with minor jams and blockages from ice on
northern rivers such as the Missisquoi on December 27.

Soils are generally frozen, with ground frost sensors showing
frost depths up to six inches deep.

Long term precipitation deficits continue, although recent
snowmelt and liquid precipitation events have increased stream
flows and soil moisture, which were near to above normal. Ground
water has been more slow to react. While ground water levels have
rebounded, USGS monitoring wells show below normal ground water
levels especially in the Lake Champlain Valley and in east-central
Vermont.

Lake Champlain continues to trend below normal by about a half
foot. Based on the present snow pack conditions there is a low
probability of Lake Champlain flooding this spring, however it is
too early to make an accurate assessment for the lake.

...Weather Outlook...

The weekend will be seasonably cool, followed by a warmup to
above normal. The weather patterns through mid January favor storm
systems from the west moving across the Great Lakes and St.
Lawrence Valley. This will allow for brief warmups followed by
brief intrusions of colder air, but no organized heavy
precipitation or prolonged outbreak of colder temperatures.
Temperature and precipitation outlooks from the NWS Climate
Prediction Center show higher probabilities of above normal
temperature and precipitation through mid month. The outlooks for
the next three month indicated better chances for above normal
temperatures and near normal chances for precipitation.

...Summary...

The winter/spring flood potential is off to a normal start for
the 2017 season. Much of the area is under a normal flood threat
based on snowmelt and ice jams, with a below normal flood threat
for the Lake Champlain Valley. It is still early in the season
however, and additional snowfall can change the flood risk.

It is important to note that heavy rainfall on top of snowmelt is
the driving factor in spring flooding, and flooding can occur
with little or no snow on the ground.

The next Winter/Spring Flood Outlook will be issued on Thursday
January 19.

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

$$

Hanson


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