Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
825 AM EDT Fri Apr 14 2017

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

This is the eighth spring flood potential outlook for 2017, issued
by the National Weather Service in Caribou, Maine. This outlook is
for northern, central, and Downeast Maine for the two-week period
from April 13 to April 27, 2017.

The spring flood potential for open water flooding is above normal
for all of northern, central, and Downeast Maine. The threat for
ice jams exists only across far northern Maine and only in the
near term. Elsewhere, the threat for ice jams has passed.

...CLIMATOLOGICAL GUIDANCE...

After a cold March, the last two weeks have finally seen the
appearance of Spring. Temperatures have averaged three to five
degrees warmer than normal. This warmth has been accompanied by
rainfall; monthly rainfall totals were near to slightly above
normal.

The mild conditions will continue through the near term as
temperatures through this weekend will be above normal. Rain
chances increase later in the weekend and early next week as a
cold front crosses the region. This will usher in cooler
temperatures through much of the remainder of the week. After a
brief dry spell, more rain threatens for the end of next week.
Extended model guidance hints that additional storm systems will
be possible the following week, as well.

The official 6 to to 14 day outlook for April 19 to April 27
matches the above thinking well, calling for wetter than normal
and cooler than normal conditions across the entire region.

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

The snowpack shrank considerably due to the warm temperatures and
recent rainfall. Outside of the woods and higher terrain, northern
Maine has less than 10 inches on the ground now. More protected
and elevated locations still have 10-18 inches or so. The Central
Highlands have a bit more, perhaps as much as 2 feet across the
higher locations in Piscataquis County. This decreases quickly as
one heads south and east; most locations along and south of I95
have 6 inches or less. Little to no snow cover exists from Bangor
south to the coast.

The snow water equivalent, or the amount of water contained in the
snowpack, also took a big hit over the past couple of weeks. We
started the month with some very impressive SWE amounts; some
locations had 10-12 inches of water locked in the pack. Now, the
highest totals, which still lie across portions of the Central
Highlands, are down to 5 to 8 inches. This decreases to 2 to 5
inches heading north and east into Aroostook and northern
Penobscot Counties. From Houlton south, SWEs are 1 to 3 inches.
Those locations in Downeast Maine, including the Bangor area, that
have little to no snow cover are below normal for SWE.

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

The recent spate of snowmelt and rainfall has kept the near
surface soil very moist. However, since this is the normal
snowmelt season, the soil is not unusually moist for mid April,
except for the far northeastern part of the state. The latest
Palmer Drought Severity Index, which measures soil moisture in the
longer term, is also near normal. Meanwhile, groundwater
monitoring wells, courtesy of the USGS, are mainly near to above
normal. The exception is near Bangor, where wells are indicating
high groundwater levels.

...RIVER AND ICE CONDITIONS...

Outside of one or two localized gages in the Saint Croix basin,
river flows are now above to much above normal across the entire
region. Flows increased dramatically over the past week as runoff
surged from snowmelt and rainfall. This allowed river ice to
break up and has caused some waterways out of their banks. The
Mattawamkeag River is currently above flood stage and is causing
flooding along the Bancroft Road in southern Aroostook County.
Many rivers are forecast to crest over the next 6-12 hours and
then slowly fall through the weekend. However, given the continued
snowmelt and chances for rainfall, river flows will remain high
over the next several days in spite of any receding.

As mentioned above, river ice broke up over the past week. Some
ice jams resulted; along the Aroostook, ice jammed up in Fort
Fairfield, causing flooding along Russel Road, but this has since
released. A large jam formed in Crouseville, which resulted in
flooding on Route 164. Although it has partially released, the
remaining section looks to be well locked in place. With water
flowing around the remnants of the jam, it may take a large surge
of flow to finally get it to budge. Ice jams formed on the Saint
John River as well, initially near St Francis. This jam gradually
moved downstream and eventually released. Ice also jammed up down
in the Grand Isle/Van Buren area, but this too has released.

Further south, the Pleasant River also had an ice jam which
developed in the Brownville area. This has also flushed out.
No other ice jams were reported along the Piscataquis, Penobscot,
or their tributaries.

The ice jam threat has passed for the most part, excepting those
ice jams that already exist, of course. Although some ice may
still exist in the highest reaches of the rivers, the bulk of the
ice cover has now flushed out.

...IN CONCLUSION...

Based on the above information, the spring flood potential for
open water flooding is above normal across all of northern,
central, and Downeast Maine. Rivers flows are currently above
normal in many locations. Although flows may recede a bit over the
next day or two, additional rainfall and snowmelt will likely
cause them to rise again or, at least, slow their descent. Soils
are moist, so any rain or snowmelt will runoff directly into
waterways rather than percolate through the soil.

The threat for additional ice jams has pretty much passed for the
season. There are still a few localized spots dealing with ice
jams at the time of this writing across far northern Maine. These
areas will need to be monitored, especially since there could well
still be a bit of ice still to break up upstream. However, the
bulk of the ice has flushed out. Therefore, the threat is really
in the near term. The Aroostook River has the highest threat, as
the ice jam that is currently in place in Crouseville could cause
additional issues once it moves downstream. The Saint John and
Allagash Rivers seem to have mostly flushed out, though there may
still be a bit of ice still in the upper reaches.

Waterways across central and Downeast areas have also pretty much
flushed out. River gages across the Piscataquis and Penobscot
basins show no signs of being ice affected, and no ice jams have
been reported. Therefore, the ice jam threat is deemed over in
these locations.

It is important to remember that very heavy rainfall can bring
flooding at any time of the year, even in areas that don`t have a
significant snowpack.

The next spring flood potential outlook will be issued by NWS
Caribou on April 27, 2017.

$$

Hastings



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