Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
312 PM EDT Thu Mar 21 2019

...WINTER/SPRING FLOOD POTENTIAL OUTLOOK...

The flood potential is above normal across western Maine and New
Hampshire.

The threat of flooding due to ice jams is above normal across
Maine and central and northern New Hampshire.

This is the sixth in a series of regularly scheduled flood
potential outlooks that are issued during the winter and spring
seasons. These outlooks will be issued every two weeks until the
end of the snow melt season, and will assess the potential for
flooding based on a number of factors.

...CLIMATOLOGICAL GUIDANCE...

March has been colder than normal with temperatures averaging 3 to
4 degrees below normal. This has allowed the snowpack in southern
areas to melt slowly. Precipitation has also been below normal for
the month which in combination with below normal temperatures
allows for an orderly snow melt. However there remains a deep and
moisture laden snow pack in the foothills and mountains.

The storm track has remained to the west of or through New England
for several weeks. This storm track is expected to continue into
April. In the short term low pressure will move through southern
Maine Friday with rain in southern areas and mixed precipitation
and snow in the mountains. Rainfall of 0.50 to 1.25 inches is
expected with several inches of snow possible in the mountains.
Some minor flooding is possible due to ice movement, but
widespread flooding is not anticipated. Cold air is expected to
move back into northern New England and will be with us through
the middle of the next week.

Model guidance is indicating a warmup for Maine and New Hampshire
beginning next weekend into the first week of April.

The official National Weather Service 6 to 10 day forecast calls
for normal temperatures and below normal precipitation. The 8 to
14 day forecast calls for above normal temperatures and normal
precipitation.

...OBSERVED SNOW DEPTH AND WATER EQUIVALENT...

...NEW HAMPSHIRE...

The recent warmup has caused much of the snow across southeast New
Hampshire to melt away. Across the rest of southern New Hampshire
snow depth is less than 12 inches. with snow water equivalent of 1
to 3 inches.

From the lakes region north to the Canadian border snow depth
increases rapidly. Most locations are reporting 1 to 3 feet of
snow in the valleys and 2 to 4 feet in the higher elevations with
water equivalent of 6 to 12 inches. Moose Falls in northern New
Hampshire reported a snow depth of 42 inches with a water
equivalent of 14 inches Tuesday morning. Snow depth is less than
1 foot west of the White Mountains in the Connecticut River Valley
with a water equivalent of 2 to 5 inches.

Snow water equivalent is above normal in central and northern New
Hampshire and near to somewhat below normal in southern New
Hampshire.

...WESTERN MAINE...

Snow depth near the coast is now down to 6 inches or less. Just
inland snow depth ranges from 6 to 18 inches. Snow depth from the
foothills to the Canadian border ranges from 1 to 3 feet, with
local amounts of 3 to 4 feet.

Snow water equivalent ranges from 1 to 2 inches along the coast.
Just inland water equivalent rises to 3 to 6 inches. from the
foothills to the Canadian border snow water equivalent rises to 6
to 12 inches with locally higher amounts.

Snow water equivalent is mostly above normal in Maine.

...SOIL MOISTURE AND WATER SUPPLY CONDITIONS...

Soil moisture anomaly maps from March 20 continue to indicate
above normal moisture conditions in western Maine and New
Hampshire.

The long term Palmer Drought Severity Index from March 16
indicates very moist conditions in southern New Hampshire, and
normal conditions in northern New Hampshire. Very moist conditions
exist in coastal Maine with unusually moist conditions in central
Maine and normal conditions in the mountains.

River basin managers continue to lower reservoir levels in
preparation for the spring runoff. Reservoirs in the Androscoggin
River basin are now 37.7 percent full as of March 18, which is
5.8 percent above normal.

In the Kennebec River basin both Flagstaff Lake and Moosehead Lake
are below normal for the time of year. Brassua Lake is just above
normal levels for the time of year.

Lake Winnipesaukee in New Hampshire is at a normal pool level for
the time of year.

Groundwater levels courtesy of the USGS are mostly near to above
normal with few exceptions.

Water supply shortages are not expected this spring as there is
plenty of water in the snowpack to bring groundwater levels to
normal or above.

...RIVER AND ICE CONDITIONS...

River flows are generally above normal for the time of year.

Ice jam remains in place along the Piscataquog River from
Goffstown to New Boston and Pemigewassett River in Plymouth and on
the Upper Ammonoosuc River in Milan. The ice is weakening and on the
Piscataquog and Pemigewasset rivers above and below the jams is
mostly open water now.

Recent ice information from the USGS indicate that rivers and
streams in central and mountain locations of Maine and New
Hampshire have 1 to 2 feet ice. This ice is weakening due to some
recent warm spells and the increasing sun angle. On the Kennebec
River at Gardiner and Richmond the ice is a bit less than a foot
thick and is weakening also. The US Coast Guard is expected to
start ice breaking on the Kennebec River today. This will help
to mitigate the chance of flooding due to ice jams.

...IN CONCLUSION...

Based on the above information the The flood potential is above
normal across western Maine and New Hampshire. The snow pack is
ripening and as we approach the end of March a rapid warmup with
rainfall is increasingly likely. There is a deep and water laden
snow pack in the mountains and foothills and we will have to
continue to monitor the situation until the snow pack has melted
out.

The threat of flooding due to ice jams is above normal.

It is important to note that major flooding does not occur from
snowmelt alone. Rainfall, how much and in how short a period of
time is the most important factor in determining the severity of
flooding.

The next Winter/Spring Flood Potential Outlook will be issued by
8 AM Friday April 5.

$$


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