Winter/Spring Flood Potential Outlook For Northern & Eastern Maine - 03/04/2021

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK

NATIONAL WEATHER SERVICE CARIBOU ME

509 PM EST Thu Mar 4 2021

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

DOWNEAST MAINE...

This is the fifth Winter/Spring Flood Potential Outlook for 2021,

issued by the National Weather Service in Caribou, Maine. This 

outlook is for Northern, Central, and Downeast Maine for the two- 

week period of March 4th to March 18th, 2021.

The flood potential for open water flooding remains slightly 

below normal across the entire region. The flood potential due to 

ice jams remains near normal across the Northern Maine rivers, 

while the Central and Downeast region is below normal.

...CLIMATOLOGICAL GUIDANCE... 

There were several minor winter storms that moved across the

region the previous two weeks. These storms produced approximately

2-5 inches at a time across portions of the area. 

There were a few shots of modified arctic air but no extreme cold

during the month. The coldest minimum temperature at Caribou was

minus 10 while Houlton dropped down to -11 on the 19th of 

February. Caribou rose to as warm as 41F with Bangor rising to 45F  

on the 24th of February.

The North Atlantic Oscillation (NAO) continues to trend neutral to

weakly positive. A neutral to slightly positive NAO favors more

zonal upper level flow with most of the arctic air locked up

across Canada with only brief intrusions into the northeast.

In addition, the Pacific North America (PNA) pattern is forecast

to be mainly negative heading into and through the middle of

March. With a negative PNA patter, upper level ridging is favored

across the southeast U.S. which tends to result in southwesterly

upper level flow across New England. 

The official National Weather Service 6 to 14 day outlook is calling

for above normal temperatures and near to possibly above normal 

precipitation.

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

Snow depths increased over the last two weeks across Northern

Maine into the Maine Central Highlands, while the Penobscot Valley

into the Downeast region saw a decrease in snow depths.

Snow depths ranged between 22 to 32 inches across Northern and 

Northwest Maine, while the Maine Central Highlands recorded 14 to

21 inches of snow depth. As of 8 AM this morning, the NWS office 

in Caribou had a 25 inch snow depth, while Winterville had around

32 inches of snow on the ground. Interestingly enough, Chimney

Pond in the Baxter State Park region reported 42 inches of snow on

the ground. Snow depths across the Penobscot Valley into the 

Downeast region decreased to 2 to 8 inches. 

Snow depths were near to slightly below normal across Northern 

Maine and the Maine Central Highlands, while snow depths from 

the Penobscot Valley into the Downeast region were below normal. 

The snow water equivalent, or the amount of water contained in 

the snowpack, increased over the two weeks across Northern Maine 

and the Maine Central Highlands. Northern Maine was seeing 5 to 7

inches, while the Maine Central Highlands had 4 to 6 inches. The 

NWS in Caribou recorded a snow water equivalent of 5.5 inches. 

This is an increase of 2 inches over the last two weeks. The 

highest snow water equivalent was reported in Winterville with 7.1

inches of water in the snowpack. 

Snow water equivalents across the Penobscot Valley and the

Downeast region ranged from 1 to 3 inches.

Snow water equivalents are near to slightly below normal across

the region. 

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

The latest Palmer Drought Severity index, which measures soil 

moisture in the longer term, continued to show near normal 

conditions, with Hancock County coast seeing slightly below

normal.

A look at the groundwater levels, courtesy of the USGS, showed

mainly near normal across the region. There were a few sites such

as Clayton Lake in Northwest Aroostook County and Amherst in

Hancock County, reporting below normal groundwater levels. There

still exists enough of a snowpack across the region that is 

available for recharge. 

...RIVER AND ICE CONDITIONS...

River flows were near normal across much of the region, with the

exception of the St. Croix River Basin, as flows were slightly 

below normal.

About 95% of the streams and rivers across the region are snow 

and ice covered, including the St. Croix River basin. Although, 

there are sections of open water that exist, especially along the

Penobscot, Piscataquis and St. Croix Rivers.

Ice thicknesses ranged from 12 to 18 inches across the Aroostook

and St. John River basins, including the Allagash River. The

thickest ice was across the St. John River basin, which includes

the Allagash and Fish River with up to 18 inches of hard ice. The

Fish River saw an expansion of ice over the two last weeks, with 

just a small stretch of open water in the Fort Kent region. 

The Penobscot River remained iced in around the Bangor region for

approximately 3 miles, including where the Kenduskeag Stream 

joins the Penobscot. Open water was noted north toward the Old 

Town area, with some open areas as far north as the Millinocket 

area. The East Branch of the Penobscot River at Grindstone was ice

covered with a couple of open stretches to the south. Ice 

thickness was measured by the USGS to be 10-12 inches at 

Grindstone, and along the stretch of Kenduskeag Stream meeting up 

with the Penobscot River at Bangor. The Piscataquis River from 

Blanchard to Dover-Foxcroft was ice covered with some open 

sections along the sides, while some open water was noted toward 

the Medford region. The USGS measured ice thicknesses of 8 to 14 

inches on the Piscataquis River along the stretch from Blanchard 

to Dover-Foxcroft.

There are some ice jams remaining in place. One bunched up jam 

resides on the Aroostook River from just east of Caribou to the 

Fort Fairfield bridge. This jam is approximately 7 miles in 

length. The jam remains broken up in spots along this stretch. An

ice jam remains in place on the Allagash River near the bridge 

where the Allagash River meets the St. John River. The ice jams in

Crouseville on the Aroostook River and near Lille on the St. John

River let go over the last two weeks with no issues.

Despite the ice coverage expanding over the last two weeks, ice 

coverage and thicknesses remain below normal for this time of 

year. 

...IN CONCLUSION...

The flood potential for open water flooding is slightly below normal

across the entire region. The flood potential due to ice jams 

remains near normal for the Northern Maine River basins. The flood

potential for ice jam flooding across the Piscataquis and 

Penobscot River basins is below normal for this time of year.

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 Outlook will be issued on Thursday, 

March 18th.

$$

Hewitt/Farrar