Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
346 PM EST Thu Jan 18 2018


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

The flood potential is normal for the time of year except for the
portions of central New Hampshire and western Maine where it is
above normal. The potential for ice jam flooding is above normal.

This is the second 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...

From late December through the first week of January Maine and
New Hampshire was in the grip of an arctic airmass. Average
temperatures throughout this period 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. So far
January has seen average departures of 3 to 5 degrees below normal.

The weather pattern has been very active lately and this is
expected to continue through the remainder of January. However
temperatures are expected to be mostly above normal leading to
more mixed precipitation or rain. The next chance of significant
precipitation will occur Tuesday next week. This system may
produce 1 to 1.5 inches of rain and mixed precipitation. Beyond
Tuesday the next significant precipitation event will be around
January 29 and with rain and mixed precipitation expect again.

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

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

...NEW HAMPSHIRE...

Snow depth ranges from 4 to 12 inches across southern New
Hampshire with lesser amounts near the coast and higher amounts in
the Monadnock region. From the Pemigewasset and Saco River basins
north to the Canadian border snow depth ranges from as little as 7
at First Connecticut Lake up to 21 inches at Moose Falls.

Snow water equivalent in southern New Hampshire ranges from less
than 0.5 inch near the seacoast up to 2 inches in the Monadnocks.
From the lakes region north to the White Mountains water
equivalent ranges from 2 to 4 inches. In far northern portions of New
Hampshire snow water equivalent ranges from 3 inches at First
Connecticut Lake up to 6.9 at Moose Falls.

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

...WESTERN MAINE...

Snow depth ranges from 6 to 12 inches near the coast to 10 to 18
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 below normal for the time of year.

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

Soil moisture anomaly maps from January 17 indicate above normal
moisture conditions in western Maine and northern New Hampshire.
Normal conditions exist in southern New Hampshire.

The long term term Palmer Drought Severity Index from January 13
indicate unusually moist conditions prevail across western Maine
and all of New Hampshire.

Reservoirs in the Androscoggin River basin are 70.9 percent full
which is 14.8 percent above normal.

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

Groundwater levels courtesy of the USGS show that monitoring wells
in western Maine and New Hampshire are mostly above normal.

...RIVER AND ICE CONDITIONS...

Due to the recent heavy rain and warm weather rivers are above
normal for the time of year in both western Maine and New
Hampshire. In addition the high flows caused many ice jams to
form. There is an ice jam on the Kennebec River from Farmingdale
to Hallowell. In New Hampshire there is an ice jam on the South
Branch of the Piscataquog River in New Boston. This jam is around
3500 feet in length and is located near the 4H Fairgrounds. There
is an ice jam in North Stratford, NH on the Connecticut River.
There is an ice jam on the Saco River at Fryeburg, Maine.

...IN CONCLUSION...

Based on the above information the flood potential is normal for
the time of year except in portions of central New Hampshire and
western Maine where it is above normal.

The threat for ice jam flooding is above normal. The ice jams that
are currently in place will have to be monitored closely over the
next couple of weeks as we expect additional rainfall and above
normal temperatures.

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
February 1.

$$

TFH



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