Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
537 PM EDT Thu Mar 21 2019

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

This is the sixth Winter/Spring Flood Potential Outlook for 2019,
issued by the National Weather Service in Caribou, Maine. This
outlook is for Northern, Central, and Downeast Maine for the
two-week period of March 21st to April 5th, 2019.

The flood potential for open water and ice jam flooding remains
well above normal for Northern Maine and the Maine Central
Highlands due to a series of ice jams locked in place. The flood
potential for open water and ice jam flooding is near to slightly
above normal for the Interior Downeast to the coast. Ice has been
thinning and weakening with open water on the Penobscot River.

...CLIMATOLOGICAL GUIDANCE...

A rather quiet weather pattern over the last two weeks. One
significant event affected the region during the first week of
March with 4 to 12 inches of snow across the region, with the
highest amounts along the Downeast region. This snow event added
to the existing snowpack. The region saw a moderating trend toward
the end of the second week with temperatures hitting well above
normal. This allowed for an erosion of the snowpack across the
region along with some ice movement on rivers and streams across
the southern portion of the region. One thing to note however was
the very cold nights during the second week, with some areas such
as Estcourt Station and Big Black River, seeing at least 10 below
zero. This was well below normal for overnight low temperatures.

The official National Weather Service 8 to 14 day outlook is
calling for above normal temperatures with precipitation expected
to be near normal.

The weather pattern over the next 7 to 14 days looks to be
somewhat active. A storm system moving up along the Maine coast
Friday into this upcoming weekend will bring snow and rain to the
region. There could be some significant snowfall across Northern
and Northwest Maine with up to 6 inches of snow after a period of
rain. Rainfall of 1 to 1.25 inches is expected across the Bangor
and Downeast region. This rainfall will reduce the snowpack but
will also allow runoff and ice breakup to occur across some of
the streams and rivers, such as the Piscataquis and Penobscot
Rivers. Temperatures are expected to drop back by early next week
which will slow the runoff process. There is potential for a
significant warmup by the last few days of March which would
enhance a reduction in the snowpack, increased runoff, and
possibLe ice break up.

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

Snow depths did see a reduction over the last two weeks. Snow
depths across Northern Maine and the Central Highlands ranged
from 30 to 40 inches with some sites reporting snow depths in the
lower 40s. Allagash came in with a snow depth of 41 inches, while
the NWS office in Caribou recorded 36 inches of snow depth. The
interior Downeast region came in with 6 to 14 inches of snow depth
with some sites seeing above 16 inches of snow depth. An observer
in the town of Robbinston, which is in central Washington County,
recorded 17 inches of snow depth, as of early this morning. The
coastal recorded 2 to 7 inches of snow on the ground.

Snow depths were above normal, especially from the Maine Central
Highlands to the Maine-Canadian border.

The snow water equivalent, or the amount of water contained in
the snowpack continued to remain the highest across northern and
central areas with 9 to 12 inches with a few sites hitting near 13
inches. Knowles Corner in Southeast Aroostook County recorded 13
inches of snow water equivalent. The NWS office in Caribou saw
the snow water equivalent increase to 11.5 inches. Across the
Bangor and interior Downeast region, 2 to 7 inches of water was
measured in the snowpack. The coastal regions recorded 1 to 3
inches of water equivalent in the snowpack.

The snow water equivalent remains well above normal for Northern
Maine and the Maine Central Highlands, while from Bangor to the
Downeast coast, snow water equivalents were near to slightly above
normal.

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

Soil moisture remained above normal across the entire region. The
latest Palmer Drought Severity Index, which measures soil moisture
in the longer term, was showing above normal conditions.

Looking at the groundwater levels, courtesy of the USGS, we
continue to see the levels slightly above normal. Some sites
across the Downeast region such as Acadia reported above normal
levels.

...RIVER AND ICE CONDITIONS...

River flows continued to run near to slightly above normal for
this time of year throughout the region.

Ice coverage on the rivers across the region was 90-95% as of
this morning, with some open sections on the rivers where the
flow is strong. These open sections included the Penobscot River
near Millinocket and south of Bangor. The Fish River southwest of
Fort Kent had some open channels as did the Aroostook River near
Presque Isle and Ashland.

Ice thickness on the Penobscot River varied from 6 to 12 inches
in the Bangor region with up 16 inches north of the city. On the
northern branch of the Penobscot River at Grindstone, the ice
thickness was estimated to be greater than 18 inches. Ice
thickness on the Kenduskeag Stream in Bangor was estimated to be
8 to 16 inches especially in the downtown section of Bangor. The
Piscataquis River had ice thicknesses of 8 to 12 inches, with the
thickest ice near Dover-Foxcroft.

Ice thicknesses across the Northern Maine rivers remained the
same with some slush on top of the ice. Ice thickness on the
Allagash River in Northwest Maine remained near 18 inches. Ice
thicknesses on the St. John River from Fort Kent to Dickey were 8
to 14 inches, while east of Fort Kent down to Madawaska and Grand
Isle, ice thicknesses remained estimated at 12 inches. The ice
thickness on the Aroostook River was holding around 24 inches, or
2 feet thick.

Ice jams remain locked in on the Northern Maine Rivers. The ice
jam on the Aroostook River south of Washburn to Crouseville.
A few smaller ice jam remained in place on the Aroostook River
near the Caribou-Fort Fairfield town line. Across the St. John
River Basin, ice jams remained locked in place, with a large ice
jam from St. Francis to St. John. Other notable ice jams remain
southeast of Fort Kent downstream to the town of Grand Isle. An
ice jam is in place on the Pleasant River in Milo, and another jam
in place on the Piscataquis River near Dover-Foxcroft. Both of
these jams were approximately one half mile long.

Ice coverage and ice thickness is considered to be near normal
for this time of year.

...IN CONCLUSION...

Based on the above information, the flood potential for open
water and ice jam flooding remains well above normal for Northern
Maine and the Maine Central Highlands. The flood potential for
open water and ice jam flooding is near to slightly above normal
for the Interior Downeast to the coast.

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 is scheduled for Thursday,
April 5th.

$$

Hewitt


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