Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CARIBOU ME
532 PM EDT Thu Apr 12 2018

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

This is the eighth 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
April 12th to April 26th, 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 above normal, mainly
north of the Bangor region. The potential for flooding due to ice
jams is near normal for the northern rivers.

...CLIMATOLOGICAL GUIDANCE...

The past two weeks featured below normal temperatures for the most
part across the area, with a few days reaching near seasonal norms.
Snowfall so far this season is above normal, with the National
Weather Service office in Caribou recording 136 inches so far this
season, which is 30 inches above normal. Bangor recorded 111 inches
this season which is around 47 inches above normal. Precipitation
continues to run above normal across much of the region since
January 1st.

The first week of April featured a storm system which brought a
significant snowfall for Northern Maine on the 3rd and 4th. Snowfall
amounts from this storm ranged from 5.3 inches at the National
Weather Service office in Caribou to 14.5 inches in Madawaska. This
event added additional snowfall to the existing snowpack. The second
week of April featured below normal temperatures with a weak storm
system that brought a few inches of snow to portions of Northern and
Western Maine.

Below normal temperatures are anticipated into the last week of
April with an active weather pattern expected. The official National
Weather Service 6 to 14 day outlook is calling for below normal
temperatures with above normal precipitation.

There is potential for a significant storm system to affect the
region on April 16th and 17th. This system could bring some snow at
the onset of the event and then a changeover to all rain is possible
with potential for heavy rainfall. Depending on the track of this
system and the amount of rainfall, there could be the possibility of
open water flooding as well as ice jam flooding across Northern
Maine. It must be stressed that there is still uncertainty in
regards to the track of this system and how much precipitation will
occur.

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

Snow depths and snow water equivalents increased during the first
week of April across Northern Maine while values dropped across the
rest of the region. The second week of April saw a drop in snow
depths and snow water equivalents across the region.

Snow depths ranged from 2 to 3 feet across Northern and Northwest
Maine. Winterville came in with a depth of 37 inches as of April
9th, while the National Weather Service in Caribou had depth of 18
inches. Snow depths across the Central Highlands ranged from 10 to
17 inches with Dover-Foxcroft in Southern Piscataquis County
reporting a snow depth of 17 inches. Snow depths across the Downeast
region ranged from 1 to 4 inches with most of the snow located in
the woods. Snow depths were slightly above normal across Northern
Maine and the Central Highlands while the Downeast region was near
normal.

The snow water equivalents, or the amount of water contained in the
snowpack, ranged from 7 to 10 inches across Northern and Northwest
Maine. The forecast office in Caribou recorded 8.1 inches of water
in the snowpack with 18 inches on the ground as of this morning.
Across the Central Highlands, snow water equivalents ranged from 3
to 7 inches. The snow water equivalents were above normal across the
north with near normal values across the remainder of the region.

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

Soil moisture across the region was near to slightly above normal.

The latest Palmer Drought Severity Index, which measures soil
moisture in the longer term, continued to show near normal
conditions for all but Downeast Maine where unusually moist
conditions exist.

A look at the groundwater levels, courtesy of the USGS, continued
to show levels remaining near normal across the region.

...RIVER AND ICE CONDITIONS...

River flows were near normal throughout much of the region with the
exception of Washington County, where river flows continued above
normal.

River ice in northern Maine varies with ice thicknesses ranging from
20 to 30 inches, with the thickest ice being across the St. John and
Allagash Rivers. Rivers are about 90% snow and ice covered across
the Northern Maine, while the Piscataquis, Penobscot and
Mattawamkeag Rivers are open with some residual ice. The Allagash
River was mostly snow and ice covered with some open spots on the
sides. The St. John River had a large open section between the towns
of St. Francis and St. John. The Fish River was open with some ice
remaining in the sides. The Aroostook River had open sections from
Presque Isle to Caribou and from Ashland to just north of town of
Masardis.

There are no ice jams reported at this time.

...IN CONCLUSION...

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

The threat for ice jam flooding is near normal for the northern
river basins. Ice thicknesses continue to be significant. The
Allagash, St. John, Aroostook and the northern branch of Penobscot
River near Grindstone continue to be locations to watch for
potential ice jam flooding.

There is the possibility that a significant storm system could
affect the region on April 16th and 17th. It is important to
remember that a heavy rainfall event along with mild temperatures
can lead to an increased threat 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 Spring Flood Potential Outlook will be issued by the
National Weather Service in Caribou on April 26th.


$$

Hewitt



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