Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
145 PM EST Thu Feb 15 2018

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

This is the fourth Winter/Spring Flood Potential Outlook for
2018, 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 15th to March 1st, 2018. 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.

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

...CLIMATOLOGICAL GUIDANCE...

The past few weeks have featured several systems affecting
northern and eastern Maine as the area was located close to the
main storm track. Most areas across northern and eastern Maine ran
above normal for temperature and precipitation.

The first significant event took place on the 4th and 5th which
brought 4 to 7 inches of snow across Northern Maine and the Central
Highlands while 2 to 3 inches fell across the Downeast region. The
coastal areas saw warmer temperatures during this event which
changed snow to rain with Hancock County receiving 1 to 2 inches of
rainfall. This rain helped to reduce the snowpack significantly
across the Downeast region. The next significant event took place on
February 7th and 8th where 7 to 12 inches of snow fell across
Northern Maine and the Central Highlands. Downeast Maine received 3
to 6 inches. Another event followed on the 10th which delivered 4 to
7 inches of snow for the Central Highlands and Downeast Maine. The
latest events helped to build the snowpack back up especially for
the Downeast.

The overall pattern is expected to remain fairly progressive with
an upper level ridge favored across the southeastern U.S.
resulting in the main storm track shifting to the west and
ultimately bringing mild air to the region.

The official National Weather Service 8 to 14 day outlook is
calling for above normal temperatures and precipitation.

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

Snow depths ranged from 28 to 36 inches across Northern and
Northwest Aroostook County with some areas reporting close to 40
inches. Further south into the Central Highlands, snow depths
ranged from 18 to 24 inches. The interior Downeast region
including the Bangor area was showing 8-16 inches while the coast
was averaging 4 to 8 inches in snow depth. Snow depths were near to
slightly above normal across Northern Maine while the rest of region
was near to below normal for mid-February.

The snow water equivalents, or the amount of water contained in the
snowpack, increased to 5 to 8 inches across Northern and Northwest
Maine with several sites showing 8.5 inches of snow water
equivalent. The forecast office in Caribou recorded 8 inches of
water in the snowpack with 33 inches on the ground, as of this
morning. Areas in the Central Highlands and interior Downeast
contained 3 to 5 inches of snow water equivalent. Closer to the
coast, 1 to 3 inches of snow water equivalent were common. Snow
water equivalents are near normal across Northern Maine and near to
below normal across the remainder of the area.

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

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

A look at the groundwater levels, courtesy of the USGS, showed
levels at near to above normal across the region. Groundwater
levels are highest across Downeast due to heavy rainfall and
snowmelt that occurred since mid-January.

...RIVER AND ICE CONDITIONS...

River flows were running above normal throughout the region.

Rivers across northern Maine were 90 to 95% snow and ice covered
with some open water noted on the Aroostook River near Ashland and
along the Fish River south of Fort Kent, which is typical due to the
strong flow. The Penobscot, Piscataquis and Mattawamkeag Rivers also
had open channels with good flow.

Breakup jams remain in place on the Kenduskeag Stream in Bangor. Ice
jams were also in place on the Pleasant River and Kingsbury Stream.
An ice jam also remains in place downstream of the Eddington gage on
the Penobscot River. Ice thicknesses ranged from 18 to 24 inches
across the northern rivers with thicknesses close to 30 inches on
the Seboeis River in Northern Penobscot County. Ice thicknesses
ranged from 10 to 20 inches on the Piscataquis and Penobscot Rivers
as well on the St. Croix River basin.

Most of the ice jams will most likely remain in place into the first
week of March. This will allow for ice thicknesses to increase and
for the potential for more ice formation. This bears watching
however, as some warmer temperatures are possible next week along
with some precipitation. This could lead to snowmelt and runoff
allowing for ice breakup and movement.

...IN CONCLUSION...

Based on the above information, the flood potential for open
water flooding is near normal across the region. The threat for
ice jam flooding remains above normal.

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 Potential Outlook will be issued by
the NWS in Caribou on March 1st.

$$

Farrar/Hewitt



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