Public Information Statement
Issued by NWS Portland, ME

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
NOUS41 KGYX 161403

Public Information Statement
National Weather Service Gray ME
1000 am EST Fri Mar 16 2018

The National Weather Service has declared the week of March
12th through 16th Flood Awareness Week in Maine and New
Hampshire, as well as in the remainder of New England.


To help determine the potential for flooding, the National
Weather Service Offices that serve northern New England
continually monitor hydrological conditions throughout the
region.  River statements are issued daily and contain
forecasts of the water levels for the major rivers in the area.
Also, during the late winter and early spring the National
Weather Service, in coordination with other federal and state
agencies, power companies, and cooperative observers, surveys
the snow pack across the area to determine the potential for
spring flooding.

There are several factors that contribute to the spring flood
potential.  These include the amount of snow on the ground, the
amount of water contained in the snow (often referred to as
water equivalent or water content), the density of the
snowpack, and current river and stream levels.  The water
equivalent of the snowpack represents the water that will be
released as the snow melts.  The density of the snow is an
indication of whether any melted snow (or subsequent rain) can
be absorbed by the snowpack, or will be released.  Another
factor is how fast the snow will melt.  As a general rule, the
rate of melting is related to the temperature, humidity, and
wind.  Warm temperatures accompanied by high humidity and wind
cause the greatest amount of melting.   In addition, the state
of the soil (frozen versus thawed and saturated versus
unsaturated) determines whether any melting snow will be
absorbed by the ground.  Most importantly, however, the
greatest contributing factor to flood potential is rainfall.
In New England, major flooding does not typically occur due
solely to melting snow.

In addition, flooding can occur due to ice jams.  Ice jams tend
to occur in the spring when water levels on rivers start to
rise and when there is still a significantly thick layer of ice
on the rivers.  The rising water in rivers causes the ice to
break up, allowing large chunks of ice to start flowing.  These
chunks of ice can jam as they flow downstream.  The jammed ice
can then act as a dam and can prevent water and ice from
flowing downstream.  Ice jams are unpredictable and water
behind ice jams can rise very quickly.  In addition, when an
ice jam breaks up, the resulting release can flood downstream
areas very rapidly.

Please refer to the following web site (in lower case) for the
latest snow conditions in Maine and portions of New Hampshire

The following web site provides up-to-date
river and flood information.

The following web site provides information on ice jams.


.Current snow depth and water equivalent...Snow depths across
New Hampshire range from about 1 to 3 feet with locally higher
amounts in the mountains.  The water equivalent generally
ranges from 2 to 5 inches across lower elevations with up to 10
inches along the Canadian border and in the mountains.  These
values are generally near normal for this time of year except
in northern New Hampshire where they are above normal.

In western Maine snow depths range from 1 to 3 feet in coastal
and interior zones with 2 to 4 feet in the foothills and
mountains with locally higher amounts.  The water equivalent of
the snowpack in western Maine ranges from 2 to 5 inches in
coastal and interior zones to 5 to 10 inches in the foothills
and mountains.  These values are generally above normal for
this time of year.

.Current snow density...The density of the snowpack generally
ranges from about 20 to 30 percent across the region.  A snow
pack with a density of at or above 40 percent is considered
"ripe" because it will hold no more water and any rainfall or
melting with result in runoff.

.Current river levels...Water levels and flows in rivers and
streams throughout western Maine and New Hampshire are
generally above normal for this time of year.

.Forecast temperatures and precipitation...
Below normal temperatures are expected for the next two weeks
with near normal precipitation.  Below normal temperatures at
this time of year delay the snowmelt and increase the chances
for flooding later in the season due to the possibility of a
rapid warm-up in temperatures.  In addition, the current
computer model forecasts show a continuation of East Coast
storms that could possibly increase the snowpack and water
equivalent across the region.

.River ice and ice jam potential... Although ice remains on a
few headwater rivers and streams, most rivers are now open and
free of ice.

.Flood potential outlook...The overall spring flood potential
across Maine and New Hampshire is above normal across New
Hampshire and western Maine.

Flooding is the top storm-related killer in the United States.
Many fatalities occur because people attempt to drive through
flooded roadways.  Remember, if you encounter a flooded road,



NNNN is the U.S. government's official web portal to all federal, state and local government web resources and services.