Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
641 PM EST Thu Feb 20 2020


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

The flood potential is near normal for western Maine and New
Hampshire.

The threat of flooding due to ice jams is near normal except for
along the immediate coast and far southern New Hampshire.

This is the fourth 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...
The past two weeks have had generally above normal temperatures
across the region with short lived very cold Arctic air giving way
to a few days of below normal temperatures. This past weekend low
temperatures dropped to -41F in Jackman and -35F at First
Connecticut Lake that rebounded quickly with high temperatures in
the low 30s on the same day. Average temperatures for the first 3
weeks of February are around 1.5 to 4.5 degrees above normal. The
warmest areas is near the coast and south of the mountains. The
weather patter over the last two weeks has been a little more
active than before with near normal precipitation values across
the area.

The official 6 to 10 day outlook indicates for both temperatures
and precipitation to be above normal. The official 8 to 14 day
forecast calls for below normal temperatures and above normal
precipitation. The next system expected in the next Tuesday
timeframe looks to be snow and rain with about 0.5 inches of
melted precipitation. Next week temperatures will be above normal
with a potential cool down at the beginning of March. The above
normal precipitation during this same time could lead to adding
more snow pack for early March.

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

...NEW HAMPSHIRE...
Snow depth varies greatly from north to south with near to above
normal in northern areas to below normal in southern areas. South
of Concord there is around 2 to 10 inches of snow depth and this
includes the most recent snowfall on February 18. From Concord
through the Lakes Region and west to the Connecticut River Valley
snow depth is around 8 to 16 inches. From central New Hampshire
north to the Canadian border snow depth is 12 to 24 inches and 18
to 38 inches above 1500 feet. Snow depth of around 4 to 6 feet
exists on the higher elevation slopes of White Mountains.

Snow water equivalent varies from north to south with near normal
in northern areas and below normal in southern areas. South of
Concord around 1.0 inch or less of water content. From the Lakes
Region through the Connecticut River Valley and north to the
Canadian border snow water equivalent ranges from 2 to 6 inches
with 6 to 12 inches in the higher terrain from the White
Mountains north. From central New Hampshire south SWE is generally
less than 50 percent of normal. Snow water equivalent is near
normal closer to the Canadian border.

...WESTERN MAINE...
Snow depth is near normal across western Maine. Snow depth ranges
from 6 to 12 inches along the coast up to 1 to 2 feet in the
foothills. North of the foothills to the Canadian border snow
depth ranges from 18 to 28 inches. In the higher terrain snow
depth ranges from 24 to 36 inches.

Snow water equivalent along the coast is 3 inches or less and 2 to
5 inches to the foothills. North of the foothills are 4 to 8
inches with a few higher amounts up to 10 inches near the Canadian
border at elevations over 1500 feet. Snow water equivalent is on
the higher end of normal along the Canadian border and near to
slightly below normal through the rest of western Maine.

...SOIL MOISTURE AND WATER SUPPLY CONDITIONS...
Soil moisture anomaly maps continue to show above normal soil
moisture across the region.

The Palmer Drought Severity index from February 15 indicates
very moist conditions along coastal Maine with unusually moist
conditions for the coastal plain through the foothills. The entire
state of New Hampshire is unusually moist conditions. Across the
mountains in western Maine the conditions are near normal.

Reservoir storage is above average. The Kennebec is 12% above
normal with the Androscoggin 33% above normal for this time of
year. Lake Winnipesaukee is near normal for this time of year.

...RIVER AND ICE CONDITIONS...
River flows remain above normal for this time of year in Maine
and New Hampshire.

River ice is near to below normal for the time of year. River ice
has continued to thicken across northern areas of New Hampshire
and interior Maine. Significant ice remains on the Swift,
Carrabassett and Sandy Rivers. Ice thickness is estimated between
8 to 16 inches in northern areas and 4 to 8 inches in southerns
areas with ice. In southern New Hampshire most of the rivers and
streams are open with a few exceptions.

...IN CONCLUSION...

Based on the above information the flood potential is normal
across western Maine and New Hampshire.

The threat of flooding due to ice jams is near normal except for
along the immediate coast and far southern New Hampshire where it
is below normal.

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.

The next Winter/Spring Flood Potential Outlook will be issued by
8 AM Friday March 6.

$$

NB


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