Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
155 PM EST Thu Feb 15 2018


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

The flood potential is normal in western Maine and New Hampshire.

The potential for ice jam flooding is above normal.

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 very cold arctic air that surged over New England from late
December through the first week of January has effectively
retreated into Canada. The upper air pattern over the next 2 weeks will
be one that keeps the cold air locked up in Canada, with only
occasional and short outbreaks of cold air making it into New
England. The expected storm track will for the most part take
storms to the west of New England. So far this month Augusta,
Portland and Concord have been 1.1, 2.4 and 2.6 degrees above
normal respectively.

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

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

...NEW HAMPSHIRE...

Across southeast New Hampshire, many locations are reporting
little if any snow remaining on the ground. Farther west and north
snow depth ranges from 3 inches up to 10 to 15 inches above 1000
feet in elevation. From central New Hampshire north to the
Canadian border snow depths range from 1 to 2 feet.

Snow water equivalent ranges from little if any in southeast New
Hampshire up to 4 inches above 1000 feet. From central New
Hampshire north to the Canadian border snow water equivalent
ranges from 3 to 6 inches. Water equivalent of 6 to 10 inches
exist in the highest elevations of northern New Hampshire.

Snow depth and water equivalent is near normal in the north and
below normal south.

...WESTERN MAINE...

Snow depth ranges from 1 foot or less in southern and coastal
locations up to 1 to 2 feet with locally higher amounts from the
foothills to the Canadian border.

Snow water equivalent ranges from 2 to 4 inches south of the
foothills to 3 to 6 inches from the foothills to the Canadian
border. Locally higher amounts of 6 to 10 inches are possible in
the higher elevations of northwest maine.

Snow depth and water equivalent are near normal in the north to
below normal in the south.

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

Soil moisture anomaly maps from February 14 indicate above normal
moisture conditions in western Maine and most of New Hampshire.

The long term Palmer Drought Severity Index from February 10
indicates unusually moist conditions across Maine and New
Hampshire.

Reservoirs in the Androscoggin River basin are 61 percent full
which is 15.8 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...

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

Ice jams remain in place along many rivers. There is an ice jam
on the Kennebec River from Farmingdale to Hallowell. An ice jam
remains in place on the Saco River in Fryeburg. In New Hampshire
there is an ice jam on the South Branch of the Piscataquog River
in New Boston. There is an ice jam in North Stratford, NH on the
Connecticut River and an ice jam remains on the Pemigewasset River
just south of Plymouth. With the above normal temperatures
expected especially next Tuesday and Wednesday, these jams will
have to be monitored closely for movement.

...IN CONCLUSION...

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

The threat for ice jam flooding is above normal. We will have to
monitor the ice jams closely over the next week to 10 days as
warmer weather especially next week will produce runoff from
melting snow.

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
March 1.

$$

TFH



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