Flood Potential Outlook
Issued by NWS Portland, ME

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Winter/Spring Flood Potential Outlook
National Weather Service Gray ME
1218 PM EDT Thu Apr 16 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 has passed for the season.

This is the eighth 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...
Winter and the first half of spring has been decidedly warmer
than normal. The pattern now appears to be changing with
temperatures expected to average below normal through the
remainder of April and into May.

The weather pattern will also remain active as upper level
troughing will result in potential coastal storm development.
However it is impossible to know at this point whether any coastal
lows will make it as far north as New England or remain to the
south of the area. Any coastal low has the potential to produce
heavy precipitation, either rain or snow.

The official National Weather Service 6 to 10 day and 8 to 14 day
forecast is calling for temperatures to average below normal and
precipitation to average above normal.


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

...NEW HAMPSHIRE...

Southern New Hampshire and most of the Connecticut River valley
are now devoid of snow. Snow is now confined to the higher
terrain of Coos county.

Snow depth from the White Mountains north to the Canadian border
ranges from just patchy snow in the valleys to 1 to 2 feet above
about 1500 feet in elevation.

Snow water equivalent from the White Mountains to the Canadian
border range from less than 1 inch in the valleys up to 4 to 8
inches above 1500 feet. Moose Falls in northern New Hampshire near
the Canadian border reported 2 feet of snow with 7.6 inches of
water equivalent at an elevation of 2000 feet.

Snow depth and water equivalent are about normal for this time of
year in New Hampshire except in northern New Hampshire where it
is somewhat above normal.

...MAINE...

Snow has decreased significantly in Maine and now the only snow
cover is north of a line from Newry, Rumford, Farmington and
Bingham. Snow depth is less than 10 inches in the valleys with 1
to 2 feet in the higher terrain.

Snow water equivalent ranges from 1 to 3 inches in the valleys up
to 4 to 7 inches in the higher terrain and closer to the Canadian
border.

Snow depth and water equivalent are about normal for this time of
year.

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

Soil Moisture anomaly maps from April 15 show above normal soil
moisture across western Maine and New Hampshire.

The Palmer drought severity index from April 11 indicates above
normal moisture conditions in New Hampshire and central and
coastal Maine. Near normal moisture conditions exist in the
northwest Maine.

Reservoir Storage is above average on the Kennebec, with
reservoirs averaging 67.9 percent full which is 40 percent above
normal. On the Androscoggin, storage was 65 percent full which is
21.8 percent above normal. Lake Winnipesaukee is about 0.5 ft
above normal for this time of year.

Due to the recent heavy rain and melting snow, groundwater levels
are not surprisingly above normal. In western Maine the USGS
reports that 2 monitoring wells, one in Weld and the other in
Augusta, are at record high levels for this time in April.

...RIVER AND ICE CONDITIONS...
River flows are mostly above normal for this time of year.

All rivers in western Maine and New Hampshire are now ice free.
The threat of ice jam flooding has passed for this season.

...IN CONCLUSION...
Based on the above information the flood potential is normal for
New Hampshire and western Maine.

Temperatures over the next couple of weeks in the mountains
should be conducive to slowly melting the remaining snowpack.
High temperatures are expected to be mostly in the 40s to around
50 with low temperatures falling below freezing each night.

The threat of flooding due to ice jams has passed for the season.

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 will be the last Winter/Spring Flood Potential Outlook for
this season.

$$

TFH


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