Flood Potential Outlook
Issued by NWS Caribou, ME

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
327 PM EST Thu Jan 5 2017

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

This is the first Winter/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 January 5 to January 19, 2017.

The winter/spring potential for both open water flooding and
flooding due to ice jams is near normal across our entire forecast
area.

...CLIMATOLOGICAL GUIDANCE...

The northeastern United States continues to be in an active storm
pattern. Many of the storm systems have been characterized by a
primary low lifting to our north and west while a secondary low
develops off the coast. This has allowed for mixed precipitation
types over much of the region. Even in those locations that
remained all snow, enough warm air intruded to make for heavy wet
snow with more moisture content.

The overall pattern is not expected to change overly much over the
next few weeks. With no blocking downstream, cold air
intrusions, like the one expected this upcoming weekend, will be
fairly short lived. Rather, a switch to zonal or southwest flow
will allow for warming temperatures along with a storm track up
through the Great Lakes. Indeed, one such system and associated warmup
is currently forecast for the middle of next week. A rain/snow
mix looks most likely across the region, though models are hinting
that coastal low development will also occur with this system,
making for a tricky temperature and precipitation type forecast.
Either way, the warming looks to be relatively brief with a return
to colder temperatures toward the end of the week.

The official 6 to 10 day forecast for January 10 through 14
matches the above thinking well, as it is calling for warmer than
normal conditions with above average precipitation. Beyond this
timeframe, heading into the latter half of January, there are
hints that there could be a shift toward a colder pattern, but
this is no where near certain.

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

December was very cold and snowy across the region. Northern Maine
in particular was hit hard with the white stuff; Caribou finished
the month with 41.2 inches of snow, which is nearly double what is
expected in a normal December. Many locations averaged 1 to 3
degrees colder than normal for the month as well. This allowed the
snowpack to grow substantially through the month over northern
Maine and the Central Highlands. More southern areas, including
Bangor and Downeast Maine, saw more rain or sleet and freezing
rain rather than snow, so the snowpack is a bit more scanty there.

Northern Maine and the Central Highlands, generally along and
north of a Danforth to Dover-Foxcroft line, are blanketed with
near to above normal snow, mainly in the range of 20 to 30 inches.
The higher terrain around the Katahdin region and the North Woods
have around 3 feet of snow. The snowpack decreases rapidly as one
heads toward the coast; the Bangor region has 5 to 10 inches of
snow cover, while the immediate coast has little to no snow on the
ground. This is near to just a bit below normal for early January.

The snow water equivalent, or the amount of water contained in the
snowpack, is also highest in the northern and central areas of our
forecast area. Three to six inches of water is common, with 6 to
8 inches in the higher terrain. This is likely a bit above normal,
especially given the wet nature of the snow that has fallen
through the month. Downeast and along the coast, SWEs are 2 to 4
inches at the most.

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

Soil moisture conditions are generally near normal across much of
northern and eastern Maine. Coastal areas are a bit wetter owing
to the active pattern and their warmer temperatures. This is
evidenced in the latest Palmer Drought Severity Index which shows
moderately moist conditions along the coast but normal conditions
elsewhere.

Groundwater levels are also mainly near normal, with a few
exceptions, as shown by the groundwater monitoring wells from the
USGS. The long- term dryness from this summer is still evident in
the Central Highlands with wells in that area reporting much
below normal water levels. Meanwhile, wells near Bar Harbor and
Eastport are much above normal. Again, this is due to the fact
that these regions have seen the majority of their precipitation
fall as rain.

...RIVER AND ICE CONDITIONS...

River flows are mainly near to above normal across Maine`s
waterways, with the highest flows (relative to normal) Downeast.
With the cold temperatures in December, river ice formed
relatively early in the northern basins where ice was seen in
early to mid December. This ice was quickly blanketed with deep
snow, so it has likely been slow to grow and should be at most
near normal thickness for early January. The central and southern
waterways, including the Piscataquis and Penobscot Rivers, formed
ice cover a bit later, mainly in the middle to latter half of
December. The ice should also be near normal along these rivers,
though the lower Penobscot has seen a bit less snow for
insulation. There are no known ice jams in the NWS Caribou
forecast area.

...IN CONCLUSION...

Based on the above information, the winter/spring flood potential
is near normal across all of northern, central, and Downeast
Maine. In these areas, the snowpack is near to above normal.
Rivers flows are near to above normal, though the above-normal
river flows are in areas with little to no snow cover. Likewise,
soil moisture is near normal in the snowier areas and above normal
where there is less snow. With no abnormally heavy runoff or
significant snowmelt events seen in any of the model guidance
over the next two weeks, the chances for river flooding are deemed
to be close to normal.

The potential for flooding due to ice jams is also near normal.
While river ice formed relatively early along the Saint John and
Aroostook Rivers, these waterways have a thick covering of snow
which should serve to slow ice growth. As such, expect ice
thickness is near normal. Southern waterways, likewise, should
have ice coverage of near normal thickness. Significant river
rises are unlikely, so the potential for ice movement is low.
Therefore, the threat for ice jam flooding is normal for early
January.

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 Winter/Spring Flood Potential Outlook will be issued by
NWS Caribou on Thursday, January 19, 2017.

$$



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