Flood Potential Outlook
Issued by NWS Albany, NY

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Winter/Spring Flood Potential Outlook
National Weather Service Albany NY
600 PM EST Thu Feb 15 2018

...Increasing threat for ice jam flooding and above normal flood
potential for northern half of outlook area...

Well above normal temperatures may occur by Tuesday into Wednesday,
resulting in runoff due to snowmelt, especially in the Adirondacks
and southern Green Mountains, where significant snowpack is in
place. Ice jams will likely start moving due to the mild
temperatures and could increase the flood potential in some areas.
The determining factor for flooding due to ice jams or snowmelt will
be the amount of rainfall that occurs with this system. However,
there is still considerable uncertainty regarding how much snowmelt
and rainfall occurs.

A map of the flood potential outlook, not including ice jam
potential, can be found at:
http://www.weather.gov/nerfc/springfloodpotential

This is the fourth in a series of hydrologic outlooks issued by the
National Weather Service every two weeks...which refers to the
potential for flooding across eastern New York State, southern
Vermont, Berkshire County Massachusetts and Litchfield County
Connecticut. The major river basins in this area are the Hudson,
Mohawk and Housatonic.

This outlook is valid for the two-week period from February 15th to
March 1st.

...OBSERVED SNOW DEPTHS AND WATER EQUIVALENTS...

North of I-90, snow depths are above normal in the Adirondacks and
portions of the southern Green Mountains. Adirondack snow totals
ranged from 12 to 30 inches; this equates to between 3 and 8 inches
of liquid equivalent. Southern Vermont is carrying snow depths of 6
to 20 inches, with 2 to 5 inches of measured liquid equivalent in
the snowpack. Snow amounts are below normal for this time of year
south of I-90, where any snow that remains is hydrologically
insignificant.

...RIVER ICE CONDITIONS...

The breakup of river ice the weekend of January 13th resulted in
multiple ice jams across the service area. Ice jams that remain in
place bear watching with the warmup and attendant snowmelt forecast
for the middle of the next work week.

Ice jams that are no longer in place since the last outlook include:

Based on Civil Air Patrol aerial photos from February 13th, two ice
jams that had been in the vicinity of Kent, CT were flushed out with
river rises over the weekend.

The ice jam on Zimmerman Creek in St. Johnsville, NY is no longer in
place, however sufficient shear walls and shore ice remain to
potentially cause future issues.

A jam on the West Canada Creek upstream of the Mohawk River in
Herkimer, NY has opened up significantly since the last outlook two
weeks ago.

Ice jams that are frozen in place with no flooding currently
observed:

A five to seven mile long ice jam is in place on the upper Hudson
River in New York from Thurman, NY to the Stony Creek, NY town line.
This jam has a history of causing flooding that closes 418 at the
bridge as well as a portion of River Road.

On the Mohawk River in New York, an approximately 17 mile ice jam
remains in place from the Schenectady-Montgomery County line to just
downstream of the Route 146/Rexford Bridge.

The ice jam that was in place on the Hudson River in New York from
about Green Island to the Menands (378) bridge two weeks ago now
only extends as far upstream as the Route 2 Bridge; an open channel
exists through the jam, indicating weakening. Thus far it has not
caused any flooding.

Ice has jammed where the West River meets the Connecticut River on
the Vermont-New Hampshire border. The jam extends up the West River
for about a mile.

On the 23rd and 24th of January, an ice jam on Sunkauissia Creek
backed water up close to Route 7 and Maple Way in Rensselaer County,
NY. The water has receded but the jam remains in place.

...STREAMFLOW AND SOIL MOISTURE CONDITIONS...

Due to recent slow snowmelt and rainfall, streamflow and soil
moisture are currently above normal. According to U.S. Geological
Survey (USGS) streamgages, 28 day streamflow averages across western
New England and eastern New York are above normal. There was
sufficient snowmelt and rainfall to also remove any "abnormally dry"
designation from the area by the U.S. Drought Monitor.

...WATER SUPPLY...

New York City Department of Environmental Protection (NYCDEP) water
supply reservoirs are very close to normal for this time of year;
the system as a whole is at 87.9 percent of capacity, which 0.3
percent below normal storage capacity.

Hudson River Black River Regulating District reservoir levels in the
Upper Hudson/Sacandaga watershed are generally high for this time of
year due to the mid-January rain/snow event and subsequent rainfall
events. Indian Lake is about one foot above normal while the Great
Sacandaga Lake is about two feet above normal. In the Black River
watershed, Stillwater Reservoir is about 4 feet above historical
averages while Sixth Lake and Old Forge are within a foot normal.

...TEMPERATURE AND PRECIPITATION OUTLOOK...

The 6 to 10 day (for Feb 20 to 24) and 8 to 14 day (for Feb 23 to
March 1) outlooks call for above normal temperatures and
precipitation.

...SUMMARY...

For the two week outlook period, any ice jams that are currently in
place are at risk for causing new or renewed flooding in the event
of a large scale thaw or runoff event. These ice jams remain a
serious situation and could show some movement over the next two
weeks. Those with interests near ice jams currently in place are
urged to closely monitor future forecasts and heed instructions from
emergency management officials and local law enforcement.

Temperatures and precipitation are forecast to be above normal for
the outlook period, with some melting of the deeper than normal
snowpack resulting. As a result, flood potential from snowmelt is
above normal in the Adirondacks and southern Green Mountains.

In the near term (next week) the determining factor for flooding due
to ice jams or snowmelt will be the amount of rainfall that occurs
with the mid-week system. However, there is still considerable
uncertainty regarding how much snowmelt and rainfall occurs.

The fifth Winter/Spring Flood Outlook is scheduled for Thursday,
March 1st.

It is important to remember that heavy rain can cause flooding at
any time of year. Extended hydrologic information will be included
in the Hazardous Weather Outlook when necessary at

forecast.weather.gov/product.php?site=NWS&product=HWO&issuedby=ALY

Observed and 3 day forecast river information can be found on our
web page at www.weather.gov/albany. Three to seven day ensemble
forecast information can be found at www.weather.gov/erh/mmefs.

$$

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