Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
1148 AM EST Fri Feb 17 2017

...WINTER/SPRING FLOOD POTENTIAL OUTLOOK FOR NORTHERN...
CENTRAL...AND DOWNEAST MAINE...

This is the fourth winter/spring flood potential outlook for 2017,
issued by the National Weather Service in Caribou, Maine. This
outlook is for northern, central, and Downeast Maine for the two-
week period from February 16 to March 2, 2017.

The winter/spring flood potential is above normal for all of
Maine. Meanwhile, the potential for flooding due to ice jams is
near to slightly above normal across the entire region, mainly in
the longer term.

...CLIMATOLOGICAL GUIDANCE...

After a very mild January, early to mid February has been marked
by cold and stormy conditions as a deep trough became established
across the East Coast. This trough looks to weaken as we head
into the second half of the month, however. After a brief storm
system this weekend, which will bring snow and perhaps even rain
to northern and western areas, we look to have a brief respite
from precipitation before the next possible system to arrive the
middle of next week. With the jet stream pushing back north,
milder air will make a push into the region while a storm system
moves through every few days. This warmer and active pattern looks
to persist through the end of February.

The official 8 to 10 day forecast from the Climate Prediction
Center for February 24 through March 2 supports the above thinking
as it is calling for warmer than normal and wetter than normal
conditions into early next month.

...OBSERVED SNOW DEPTH AND WATER EQUIVALENTS...

The snowpack grew significantly over the past two weeks,
particularly across the Central Highlands, Downeast, and the
Bangor region. These areas were hit by two significant storms
over just a few days, allowing the snowpack to grow substantially.

Snow depths are now above normal across the entire state. Just
about everywhere is covered with at least 20 inches of snow, with
30 inches or more in many locations. The higher terrain in the
Central Highlands is covered with 50 inches or more, with Chimney
Pond reporting an estimated 95 inches, or more than 7 feet.

The snow water equivalent, or the amount of water contained in the
snowpack, also increased over the past couple of weeks, especially
in the hardest hit areas. The snowpack contains 3 to 6 inches of
water along the coast. This increases substantially as one heads
inland, with most locations reporting 5 to 8 inches of water.
Again, the Central Highlands have the most water content,
generally 7 to 9 inches, with 10 inches or more across the highest
terrain. Needless to say, SWEs across the state are now above
normal.

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

Near term soil moisture states are near to above normal, with
coastal areas considered excessively wet while the remainder of
the region is wet. Groundwater monitoring wells, courtesy of the
USGS, are above normal in the Bangor region and parts of interior
Downeast, while coastal areas and far northern Maine are near
normal. The only well in our area that is still below normal is
the one in Millinocket, but given the abundant snowpack available
for spring melt, this is not a concern. The longer-term soil
moisture is now near normal across northern, central, and Downeast
Maine. This is evidenced by the latest Palmer Drought Severity
Index, issued February 11. This index typically looks at
conditions in the longer term of weeks to months.

...RIVER AND ICE CONDITIONS...

River flows remain near normal. With warmer conditions expected
heading into early next week, runoff from some snowmelt will
likely keep flows in this range. However, significant runoff is
not anticipated as snowmelt will be limited since nighttime
temperatures will drop below freezing. Plus, the snowpack itself
will absorb much of the melt, so significant river rises are not
anticipated over the next several days.

River ice is well established across our area. The northern
rivers, including the Saint John, Allagash, and Aroostook, likely
have ice that is 2 to 3 feet thick, while central rivers, such as
the Penobscot and Piscataquis, have 1 to 2 feet of ice. This is
close to normal. The latest reports, which came from earlier this
month, indicated a lot of gray ice with little black ice noted.
As such, it is suspected that the ice may weaker than normal. This
is especially true across the north, where the ice was covered
with significant snow early in the season.

...IN CONCLUSION...

Based on the above information, the winter/spring flood potential
for open water flooding is above normal across all of northern,
central, and Downeast Maine, particularly in the long term. This
is mainly due to the abundant snowpack and water available for
melt. The concern is that snow of this depth will take a long time
to melt, leaving the area vulnerable to any heavy rainfall events
as we head into spring. It is important to note that there is no
immediate threat for flooding in these areas, but the flood threat
will remain elevated as long as the abnormally deep snowpack
lingers.

The potential for flooding due to ice jams is near to slightly
above normal. The ice is well established and near normal
thickness for this time of year. Although we are anticipating
warmer conditions, the ice is not likely to move over the next few
weeks. However, as we head through March, ice movement and any
resultant ice jams and flooding are very much possible if snowmelt
and rainfall combine to increase river flows quickly. Therefore,
a near to slightly above normal ice jam flood threat seems
reasonable at this juncture.

It is important to remember that very heavy rainfall can bring
flooding at any time of the year, even in areas that don`t have a
significant snowpack.

The next winter/spring flood potential outlook will be issued by
NWS Caribou on Thursday, March 2, 2017.

$$

Hastings



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