Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
341 PM EDT Thu Apr 13 2017

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

The flood potential is above normal for the time of year across
western Maine and northern New Hampshire. flood potential is
about normal for the time of year across southern New Hampshire.

The potential for ice jam flooding has passed for the season.

This is the eighth 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 turned out to be colder than normal and colder than
February with a very active weather pattern. So far April is
warmer than normal with above normal precipitation. The pattern is
expected to change somewhat over the next 2 weeks with colder
than normal temperatures but continued above normal precipitation.

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

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

...NEW HAMPSHIRE...

The ground is now bare across much of southern New Hampshire.
Snow depth increases to 6 to 12 inches in portions of the
Pemigewasset and Saco River basins. Above about 1500 feet in
these areas snow depth is still 1 to 2 feet. From the White
Mountains north to the Canadian border snow depth ranges from less
than 6 inches in the valleys to 1 to 2 feet above 1500 feet in
elevation. Moose Falls near the Canadian border reported a snow
depth of 34 inches Tuesday morning.

There is little if any snow water equivalent left in southern New
Hampshire. Snow water equivalent increases to 2 to 4 inches in
portions of the Pemigewasset and Saco River basins. Above 1500
feet snow water equivalent in the Pemigewasset and Saco River
basins ranges from 3 to 7 inches. From the White Mountains to the
Canadian border snow water equivalent ranges from 1 to 3 inches in
the valleys with up to 10 inches in the higher terrain of
northern Coos county. Moose Falls near the Canadian border is
reporting SWE of 12.6 inches Tuesday morning.

Snow depth and water equivalent are generally above normal in the
mountains and below normal in southern New Hampshire.

...WESTERN MAINE...

The ground is bare within 10 or so miles of the coast. Father into
the interior snow depth increases to 3 to 6. From the foothills to
the Canadian border snow depth ranges from 6 to 18 inches with
locally higher amounts in the higher elevations.

Snow water equivalent ranges from 1 to 3 inches in southern
interior Maine up to 3 to 8 inches of water in the snowpack from
the foothills to the Canadian border. Locally higher amounts of 10
to 12 inches exist in the higher elevations of northwest Maine.

Snow water equivalent is below normal in southern Maine and near
to above normal in the mountains.

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

Soil moisture anomaly maps indicate normal soil moisture across
western Maine and all of New Hampshire.

The long term term Palmer Drought Severity Index shows normal
conditions across Maine and New Hampshire.

Reservoirs in the Kennebec River basin have fallen to just below
normal for the time of year.

Reservoirs in the Androscoggin River basin are 47 percent full
which is 7 percent above normal.

At the end of March First Connecticut Lake in northern New
Hampshire was 215 percent of normal and 57 percent full. Lake
Francis was 180 percent of normal and 67 percent full. Lake
Winnipesaukee was 82 percent of normal and 81 percent full.

In New Hampshire groundwater levels courtesy of the USGS show a
mix of above and below normal groundwater. Those wells that are
below normal are rising as the recent rain and melting snow have
started the recharge. However with little if any snow left in
southern New Hampshire we will have to rely on precipitation
before leaf out begins to get those wells to normal.

In Maine most wells are near to above normal. Those few that are
below normal are rising fairly quickly. At this time there appears
to be enough water stored in the snowpack to see a normal
recharge this spring in Maine.

...RIVER AND ICE CONDITIONS...

River flows are above normal for the time of year in both western
Maine and New Hampshire.

Ice jam flooding is no longer a threat for western Maine or New
Hampshire.

...IN CONCLUSION...

Based on the above information the flood potential is above
normal for the time of year across western Maine and northern New
Hampshire and near normal in southern New Hampshire. The main
reasons for an above normal flood potential are due to the high
water content of the remaining snowpack especially in the
headwaters of the major rivers and the active weather pattern we
see shaping up as we go through the month of April.

The potential for ice jam flooding has passed for the season.

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.

Another Winter/Spring Flood Potential Outlook will be issued by
8 AM Friday April 28.

$$

TFH



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