Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
1101 AM EST Thu Jan 4 2018

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

The short term flood potential is below normal for the time of
year. The longer term flood potential is near normal.

This is the first 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...

Maine and New Hampshire have been in an arctic airmass for over a
week. Average temperatures throughout this period have ranged from
20 to 30 degrees below normal. Temperatures for the month of
December were on average 4 to 6 degrees below normal. Snowfall
for the month of December has been above normal at most climate
sites.

The weather pattern has been active and this is expected to
continue through January. However it is expected that the pattern
will change enough to allow the coldest air to retreat back to the
north. This will result in moderating temperatures next week and
beyond. Before this however we will have to deal with another
brutally cold arctic airmass this weekend.

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

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

...NEW HAMPSHIRE...

Snow depth ranges from 6 to 12 inches in southern locations up to
12 to 24 inches from central New hampshire to the Canadian border.

Snow water equivalent ranges from 1 to 2 inches in southern New
Hampshire up to 2 to 4 inches from central New Hampshire to the
Canadian border with locally higher amounts. A snow survey at
Moose Falls near the Canadian border reported a snow water
equivalent of 5.46 inches.

Snow water equivalent is mostly below normal for the time of year,
except for far northern New Hampshire where it is above normal.

...WESTERN MAINE...

Snow depth ranges from 6 to 12 inches near the coast to 12 to 24
inches from from interior Maine to the Canadian border.

Snow water equivalent ranges from 1 to 2 inches near the coast to
up to 2 to 4 inches from interior Maine to the Canadian border.

Snow water equivalent is mostly below normal for the time of year.

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

Soil moisture anomaly maps indicate normal soil moisture across
most of western Maine and New Hampshire. the only exception to
this is an area of below normal along the southwest coast of Maine
and southwest New Hampshire.

The long term term Palmer Drought Severity Index shows normal
conditions across Maine and New Hampshire except for an are of
unusually moist conditions in southern New Hampshire.

Reservoirs in the Androscoggin River basin are 73.7 percent full
which is 12.9 percent above normal.

Flagstaff Lake and Brassua Lake in the Kennebec River basin are
above normal. Moosehead Lake is right at normal for the time of
year.

In New Hampshire groundwater levels courtesy of the USGS show
wells are mostly near normal with a few exceptions.

In western Maine groundwater levels courtesy of the USGS show
wells are mostly in the normal range with a few exceptions. The
monitoring well at Augusta and North Windham are near record low
levels for the time of year.


...RIVER AND ICE CONDITIONS...

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

Due to the very cold weather over the last 10 days ice has formed
rapidly on all rivers. Rivers and streams are no full of ice. the
web camera on the Kennebec River at Augusta provided bu the USGS shows
a river full of ice. Ice coverage and thickness is above normal
for the time of year. Computers models indicate that ice thickness
is on the order of 8 to 12 inches in the mountains with 4 to 8
inches elsewhere.

...IN CONCLUSION...

Based on the above information the short term flood potential is
below normal for the time of year across western Maine New
Hampshire. The longer term flood potential is about normal.

The threat for ice jam flooding in the near term is normal but
could very well rise to above normal as the season progresses due
to the amount of ice that is currently in the rivers and streams.

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
January 18.

$$



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