Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
231 PM EST Thu Feb 20 2020

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

This is the fourth Winter/Spring Flood Potential Outlook for
2020, issued by the National Weather Service in Caribou, Maine.
This outlook is for Northern, Central, and Downeast Maine for the
two-week period of February 20th to March 5th, 2020.

The flood potential for open water flooding and flooding due to
ice jams remains near normal for this time of year.

...CLIMATOLOGICAL GUIDANCE...

The last two weeks turned out to be rather active with a series of
storms affecting the region with snow and mixed precipitation.
The most significant event came on the 6th and 7th, where snow and
mixed precipitation fell. Northern and Northwest Maine received
anywhere from 16 to 23 inches of snow, while the Maine Central
Highlands picked up 6 to 10 inches of new snow with some locations
reporting 1 to 2 inches of sleet. Further south from Bangor to
the coast, 1 to 3 inches of snow fell with a changeover to sleet
and freezing rain and then rain, as warmer air was pulled into the
Downeast region of Maine. A few other systems brought additional
snowfall from Northern Maine to the coast.

Temperatures over the last two weeks averaged above normal. During
the last two weeks, there were a few mornings where temperatures
dropped to a range of 20 to 30 below zero, mainly across the
central and northern areas. This aided in expanding the ice cover
on the rivers and streams with the increased snowpack.

The weather pattern over the next 5 to 10 days will start out
quiet with a moderation in the temperatures through the first
five days. The pattern looks like it will become more active by
the end of the month with the potential for a significant storm to
affect the region. This system could bring more snow or a mixed
bag of precipitation to the region. The storm track will
determine the amount and type of precipitation. At this time,
confidence with this system is low given the differing solutions
of the long range model guidance.

The official National Weather Service 6 to 14 day outlook
is calling for near to slightly below normal temperatures and
above normal precipitation.

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

As of 7 AM this morning, snow depths ranged from 22 to 32 inches
across Northern and Northwest Maine, with Allagash Maine reporting
31 inches of snow on the ground. The NWS office in Caribou
reported 26 inches of snow depth. Chimney Pond in the Baxter
State Park region, reported a snow depth of 49 inches this
morning. Snow depths across the Maine Central Highlands increased
over the last two weeks to a ranged of 18 to 24 inches. Snow
depths from the Bangor area to the Interior Downeast region ranged
from 7 to 11 inches. Along the coast, snow depths ranged from 2
to 8 inches. Snow depths across Northern Maine were near to
slightly above normal, while across the Maine Central Highlands,
snow depths increased to near normal. From Bangor to the coast,
snow depths continued to be below normal.

The snow water equivalent, or the amount of water contained in
the snowpack increased across the region over the last two weeks.
Northern and Northwest Maine recorded 6 to 9 inches of water
in the snowpack. Across the Maine Central Highlands, snow water
equivalents were in the range of 4 to 7 inches. Across the Bangor
region to the coast, 2 to 3 inches of water was measured in the
snowpack.

The snow water equivalent is near to slightly above normal
across the Northern and Northwest Maine, while across the Maine
Central Highlands, water equivalents are near normal. Water
equivalents from Bangor to the coast, were below normal.

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

Soil moisture is near to slightly above normal for the entire
region. The latest Palmer Drought Severity Index, which measures
soil moisture in the longer term, continues to show normal
conditions.

A look at the groundwater levels, courtesy of the USGS, shows levels
are near to slightly above normal across northern and central
areas, while from Bangor to the Downeast region, levels continue
above normal.

...RIVER AND ICE CONDITIONS...

River flows continue to be near to slightly above normal as we
head toward the last week of February. The exception to this
continues to be across Washington County along the St. Croix River
basin, where flows are above normal.

As of 7 AM this morning, ice covers about 100% of the rivers and
streams across Northern and Northwest Maine. Open stretches
remain on the St. John and Aroostook Rivers. The Piscataquis River
and Penobscot Rivers had ice reforming on them, including in the
Bangor region, with 90% coverage. There was a stretch of the
Penobscot River that was open from Bangor to Old Town. North of
Old Town, the Penobscot River remained completely iced in. In
downtown Bangor, where the Kenduskeag meets the Penobscot River,
there was solid ice in place with a section of the Kenduskeag
Stream open, west of the city. Across the Downeast region which
included the St. Croix River, ice had reformed with a good section
of the river still open.

Ice thicknesses ranged from 18 to 22 inches along the Aroostook
River with 18 to 25 inches of ice thickness on the St. John and
Allagash River. According to the latest ice measurements done by
the USGS, ice thickness on the St. John River at Nine Mile Bridge
was measured to be around 25 inches. Big Black River had an ice
thickness of 27 inches. Ice thickness along the Piscataquis River
and Penobscot River increased over the last week, with 9 to 12
inches. The exception to this was along the East Branch of the
Penobscot River at Grindstone, where the ice thickness remained at
15 inches. The Kingsbury Stream at Abbot in Piscataquis County
hung on with an ice thickness measured at 15 inches. The ice
thickness along portions of the St. Croix River was estimated to
be 5 to 9 inches in spots.

An ice jam remains in place on the Aroostook River in Fort
Fairfield. This ice jam was one mile long and remained in place.
There were some bunches of ice in place on the Aroostook River in
the vicinity of Washburn. Ice was also reported to be bunched up
on the St. John River from the town of St. John to St. Francis.

Ice coverage and thicknesses are near normal across the St. John
and Aroostook River basins, while ice thicknesses further south
along the Penobscot, Piscataquis and the St. Croix river basins,
are below normal.

...IN CONCLUSION...

Based on the above information, the flood potential for open water
flooding remains near normal across the region at this time. The
threat for ice jam flooding continues near normal, especially
across the northern rivers.

It is important to remember that a heavy rainfall event along
with mild temperatures can lead to an increased potential for
flooding with snowmelt and runoff. Ice breaking up and jamming can
elevate the threat for flooding in a short period of time.

The next Winter/Spring Flood Outlook will be issued on Thursday,
March 5th.

$$

Hewitt



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