Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
826 AM EDT Fri Apr 27 2018


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

The flood potential is somewhat above normal across interior
western Maine and northern New Hampshire. Across the remainder of
western Maine and New Hampshire the flood potential is normal.

There is no longer a threat for ice jam flooding this season.

This is the ninth 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...

April temperatures are averaging 3 to 5 degrees below normal with
above normal precipitation. The colder than normal weather has
allowed the mountain snowpack to remain longer than normal.

We will likely see much of the remainder of the snowpack melt
away next week due to a shift in the weather the pattern. Upper
level ridging will develop over the northeast bringing with it
warmer weather for the at least the first week of May.
Temperatures may reach into the 70s by mid to late next week.

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

Low pressure is expected to produce one third to one half inch of
precipitation over the next couple of days.

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

...NEW HAMPSHIRE...

The ground is now bare across the southern half New Hampshire. The
only snow remaining, is in the higher elevations of the upper
Pemigewasset and upper Saco River basins, and points north to the
Canadian border.

Above about 1500 feet in the Upper Saco and Upper Pemigewasset
River basins snow depth up to 20 inches still exist with water
equivalent ranging from 4 to 8 inches. From the White mountains
north to the Canadian border snow depth is negligible in the
valleys but increases quickly above 2000 feet to 1 to 2.5 feet
with water equivalent ranging from 4 to 8 inches with locally
higher amounts. Moose Falls near the Canadian border is reporting
29 inches of snow with 10 inches of water equivalent.

Snow depth and water equivalent are near to above normal in the
mountains and normal elsewhere.

...WESTERN MAINE...

South of the foothills in western Maine the snow is now gone.
North of the foothills to the Canadian border valley locations
and open areas are reporting 6 inches or less of snow remaining
on the ground. Snow water equivalent here is 3 inches or less. Snow
depth does increase above 2000 feet with 1 to 2 feet of snow
still remaining on the ground with 4 to 8 inches of water
equivalent with locally higher amounts.

Snow depth and water equivalent is about normal for the time of
year.

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

Soil moisture anomaly maps from April 25 indicate mostly above
normal moisture conditions in western Maine and northern New
Hampshire with normal soil moisture in southern New Hampshire and
mid-coast Maine.

The long term Palmer Drought Severity Index from April 21
indicates unusually moist conditions in coastal Maine and southern
New Hampshire. The PDSI for central and northern Maine and
northern New Hampshire is in the normal range.

Reservoirs in the Androscoggin River basin are 51.5 percent full
which is 3.7 percent below normal.

All reservoirs in the Kennebec River basin are now below normal
for the time of year.

Groundwater levels courtesy of the USGS show that monitoring
wells in western Maine are near to above normal. In New Hampshire
groundwater is mostly at normal levels for the time of year.

...RIVER AND ICE CONDITIONS...

River flows are above normal due to the recent rain and snowmelt.

There is no longer any ice cover on rivers in western Maine and
New Hampshire. The threat of ice jam flooding has ended for the
season.

...IN CONCLUSION...

Based on the above information the flood potential is somewhat
above normal across interior western Maine and northern New
Hampshire. Across the remainder of western Maine and New Hampshire
the flood potential is normal. It is expected that next week with
very warm temperatures spreading into northern New England, the
remaining snowpack will melt off.

There is a threat of minor flooding over the next couple of days
as melting snow and 1 to 3 inches of rain cause a few rivers in
western Maine and New Hampshire rise to near or just above flood
stage.

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.

This will be the last Winter/Spring Flood Potential Outlook of
the season unless conditions change drastically.

$$
TFH



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