Flood Potential Outlook
Issued by NWS Burlington, VT

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Winter/Spring Flood Potential Outlook
National Weather Service Burlington VT
528 PM EST Thu Jan 18 2018

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

This is the second flood outlook for the 2018 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 threat of flooding due to snowmelt is near normal, though the
threat for flooding due to ice jams is above normal.

...Snow Depths and Water Equivalent...

As of Thursday morning, snow depths across the North Country were
slightly below normal due to the recent rainfall and brief warm
up. Snow depths across the Champlain Valley ranged from 3 to 7
inches with snow depths along the Saint Lawrence valley ranging
from 8 to 12 inches. In the higher elevation sites of the
Adirondacks and Greens, snow depths range from 8 to 16 inches
with 2+ feet locally in some of the higher peaks.

This corresponds to snow water equivalents of 0.3 to 0.75 inches
in the lower valleys and up to 1 to 2 inches in the lower slopes.
In the Saint Lawrence valley, snow water equivalents range from
1.5 to 2.5 inches. In the higher elevations, water equivalents
range from 1 to 2.5 inches with up to 3+ inches of snow water
equivalent in the high peaks.

...River and Soil Conditions...

Streamflows were generally above normal due to the recent
rainfall and snowmelt in January. With expected rain and a
forecast of above normal precipitation river flows are expected to
remain above normal.

Ice thickness varys from river to river as the thaw caused many
rivers to lose their ice coverage. However numerous rivers now
have formed breakup and freeze up jams.

The following is a list of ice jams courtesy of the USGS and NWS
reports:

In Vermont...

There is a six mile ice jam along the Missisquoi river in Swanton
Vermont...Causing local flooding along Route 78 near the
Missisquoi National Wildlife Refuge.

January 13th an ice jam was reported with flooding along the West
River in Jamaica Vermont.

January 12th An ice jam was reported in Tory along the Missisquoi
River.

January 12th An ice jam was reported in New Haven Vermont along
the New Haven River.

January 12th An ice jam was reported in Moretown along the Mad
River.

In New York...
There is an ice jam on the Great Chazy near Perry Mills.

There is an ice jam on the Saranac River near Plattsburgh with
major flooding at the Underwood Estates Mobile Home Park.

There is an ice jam at the base of the Route 9 bridge on the
Ausable river near Au Sable Forks.

There is an ice jam below Au Sable Chasm to Lake Champlain on the
Ausable river near Au Sable Chasm.

There is an ice jam on the Ausable river near Clintonville from
old ice related to the ice jam on January 12th near Au Sable
Forks.

January 12th...A break up ice jam was reported at Au Sable Forks
along the Ausable River.

Flight lines on January 15th indicated partially open channels
along the Salmon River near Fort Covington New York with some ice
jams observed.

The recent warm up has lead to ground temperatures no longer
being frozen across much of the region. Soil moistures across
Vermont are unusually moist with wetter than normal moisture
across Northern New York. The Palmer Drought Severity Index, which
looks at moisture levels in the longer term of weeks to months,
shows very moist conditions in the Saint Lawrence Valley, while
the Adirondacks and Champlain Valley are unusually moist.

Groundwater wells, courtesy of the USGS, due to the recent
rainfall have improved significantly to near to above normal with
groundwater levels between 50 to 75th percentile.

...Weather Outlook...

A gradual moderating trend is expected over the next couple of
days with another warm up and rain expected early next week. This
will have the potential to cause more ice jams to develop but
there is significantly less rainfall expected and temperatures are
not expected to be nearly as warm. There is also less snow in the
snowpack and the ice thickness are lower than during the previous
flood event.

The official 6-14 day outlook for January 23 to January 31 issued
by the Climate Prediction Center is calling for above normal
temperatures and better chances for wetter than normal conditions
through the period.

...Summary...

Based on the above information, the winter/spring flood outlook
for open water flooding due to snowmelt and runoff is near normal
over the next couple of weeks. Even with the recent loss of snow
in the snowpack, moist soil conditions and wetter than normal
weather conditions will lead to a near normal flood outlook.

The threat for flooding due to ice jams is above normal for the
next couple of weeks especially given the number of ice jams
already in place. The loss of a deeper snowpack from the January
9-12 thaw will offset heavier runoff potential for future events
but the combination of warming temperatures and runoff will cause
some additional backup of water and a gradual release of ice.
With above normal precipitation expected this should contribute to
more runoff and the potential for an above normal threat for
flooding due to ice jams.

It is important to note 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 Outlook will be issued on Thursday,
February 1, 2018.

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

$$

Deal



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