Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
346 PM EDT Thu Mar 30 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 in
southern New Hampshire and southern Maine and is near normal for
northern New Hampshire and the mountains of Maine.

This is the seventh 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...

After a colder than normal December and a very warm January that
saw average temperatures 7 to 8 degrees above normal, February
ended quite warm with temperature departures ranging from 3 to 6
degrees above normal. All but 5 days of February were above
normal in Portland. The wild temperature swings that occurred in
previous months have continued in March. The first 2 days of the
month were 15 to 20 degrees above normal, then only 2 days later
15 to 20 degrees below normal. two of the coldest days this winter
occurred on March 4 and 11. March will end in the top ten coldest
in Portland. We have seen an active weather pattern with several
intense storms moving through New England since the beginning of
February. This trend will continue with a late winter snowstorm
expected this weekend.

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

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

...NEW HAMPSHIRE...

Snow depth in southern New Hampshire is generally less than 10
inches. The only exception to this is in the higher terrain where
snow depth ranges from 10 to 20 inches. From the White Mountains
north to the Canadian border snow depth ranges from 6 to 12
inches in the valleys to 24 to 48 inches above 1500 feet. At
Moose Falls near the Canadian border snow depth currently stands
at just under 39 inches.

Snow water equivalent /SWE/ in southern New Hampshire is on the
order of 1 to 3 inches. In the higher terrain of southern New
Hampshire mostly above 1000 feet water equivalent is 3 to 5
inches. From the upper Pemigewasset and upper Saco River basins
north to the Canadian border SWE ranges from 3 to 6 inches in the
valleys up to 5 to 10 inches in the higher terrain. In the higher
terrain of northern Coos county near the Canadian border SWE of
10 to 15 is common. Moose Falls near the Canadian border is
reporting SWE of 13.1 inches.

Snow depth and water equivalent are near to above normal in the
mountains and below normal for the time of year in southern New
Hampshire.

...WESTERN MAINE...

Snow depth ranges from 2 to 8 inches near the coast, up to 8 to
18 inches through southern interior locations. From the foothills
to the Canadian border snow depth ranges from 1 to 3 feet.

Snow water equivalent /SWE/ is running from 1 to 4 inches near
the coast to 4 to 8 inches through the foothills up to 7 to 10
inches from the mountains to the Canadian border. Local amounts of
10 to 15 inches are possible above 1500 feet.

Snow depth is about normal for the time of year. Snow water
equivalent is above normal in the mountains and about normal
elsewhere.

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

Soil moisture anomaly maps indicate that soil moisture is normal
for western Maine and most of New Hampshire. Soil moisture is
below normal in southwest New Hampshire.

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

Reservoirs in the Kennebec River basin are above normal for the
time of year.

Reservoirs in the Androscoggin River basin are 48 percent full
which is 17 percent above normal.

At the end of February First Connecticut Lake in northern New
Hampshire was 191 percent of normal and 54 percent full. Lake
Francis was 169 percent of normal and 67 percent full. Lake
Winnipesaukee was 87 percent of normal and 76 percent full.

Groundwater levels courtesy of the USGS show a mix of above and
below normal groundwater. However at this time there is enough
water stored in the snowpack to see a normal recharge this
spring.

...RIVER AND ICE CONDITIONS...

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

Ice jam flooding is no longer a threat in southern and central New
Hampshire or southern Maine. Ice jam flooding is also becoming
less of a concern in northern New Hampshire and the mountains of
northwest Maine. In these areas the ice is slowly eroding and
weakening as the higher sun angle is taking a toll on it.

...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 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 in
central and southern New Hampshire as well as southern Maine. The
potential for ice jam flooding is near normal for northern New
Hampshire and the mountains of Maine.

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 14.

$$

TFH



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