Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
305 PM EDT Fri Apr 27 2018

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

This is the ninth Spring Flood Potential Outlook for 2018, issued
by the National Weather Service in Caribou, Maine. This Outlook
is for Northern, Central and Downeast Maine. These outlooks are
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 above normal for
Northern Maine, mainly north of the Millinocket region. There is no
threat for ice jam flooding.

...CLIMATOLOGICAL GUIDANCE...

The past two weeks featured below normal temperatures for the most
part across the area, with this last week seeing temperatures
going above normal. Snowfall this season is above normal, with
the National Weather Service office in Caribou recording 137.2
inches. Bangor recorded 111.3 inches this season. Precipitation
continues to run above normal across much of the region since
January 1st.

A few significant storm systems affected the region over the past
two weeks. This first system brought a mix of snow, sleet,
freezing rain to Northern Maine before it changed to rain. The St.
John Valley and Allagash region received up to 2 inches of
snow from this event. Precipitation ranged from 0.50 inches to
1.00 inch across Northern Maine while 1 to 1.5 inches was recorded
across the Downeast region. A second system moved through the
region this past week and brought heavy rainfall to the region.
The heaviest rainfall came on Tuesday night(April 25th) into
Wednesday(April 26th). This event brought rainfall of 1 to 1.5
inches across Northern and Northwest Maine with up to 3 inches of
rainfall across the Downeast region. This rainfall led to a
significant reduction in the snowpack across Northern Maine with
runoff into the major rivers and streams. This in turn led to sharp
rises on rivers and streams with some minor flooding.

Above normal temperatures are anticipated into the second week of
May. The official National Weather Service 6 to 14 day outlook is
calling for above temperatures and near normal precipitation.

There is potential for a series of storm systems to affect the
region into the second week of May. These systems could bring
significant rainfall leading to another surge on the area streams
and rivers with the possibility of flooding. Confidence is low at
this time in regards to the track and evolution of these systems.

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

Snow depths and snow water equivalents decreased significantly
over the past two weeks of April across the region with the
the only significant snowpack remaining across Northern and
Northwest Maine.

Snow depths ranged from 12 to 18 inches across Northern and
Northwest Maine with the North Woods reporting close to 2 feet of
snow on the ground. The Winterville area came in with a depth of
24 inches as of April 24h. Snow depths across the Central
Highlands ranged from 2 to 5 inches, with most of the snow
reported to be in the woods. The Downeast region was snow free.

The snow water equivalents, or the amount of water contained in the
snowpack, ranged from 3 to 8 inches across Northern and Northwest
Maine. The snow water equivalents were above normal.

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

Soil moisture across the region was near normal.

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

A look at the groundwater levels, courtesy of the USGS, continued
to show levels remaining near normal across the region with sites
across the Central Highlands and Downeast above normal.

...RIVER AND ICE CONDITIONS...

River flows were near to slightly above normal. The latest
rainfall event brought river flows up significantly.

River ice in northern Maine was reduced significantly over the
last two weeks with the only ice remaining along the St. John and
Big Black Rivers. This ice has since broken up and move
downstream on these two rivers.

There was an ice jam that set up on the Aroostook River near
Washburn on the 21st. This jam let go fairly quickly and moved
downstream with no flooding reported. The Penobscot and
Piscataquis River were ice free and flowing smoothly.

...IN CONCLUSION...

Based on the above information, the flood potential for open water
flooding remains above normal, mainly north of the Millinocket region.

There is no threat for ice jam flooding.

There is the possibility that a series of storm systems may bring
significant rainfall to the region into the second week of May.
This could lead to another round of rises on rivers and streams
with the possibility of flooding. Confidence is low at this time
due to the uncertainty of the evolution and track of these
systems.

It is important to remember that a heavy rainfall event along
with mild temperatures can lead to an increased threat for
flooding with runoff.

The will be the last Winter/Spring Flood Potential Outlook for
the season unless conditions warrant otherwise.


$$

Hewitt



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