Sunday, April 17, 2022

Winter/Spring Potential Flood Outlook For Northern And Eastern Maine - 04/14/2022

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE CARIBOU ME
1053 AM EDT Thu Apr 14 2022

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

This is the ninth Winter/Spring Flood Potential Outlook for 2022,
issued by the National Weather Service in Caribou, Maine. This
outlook is for Northern, Central, and Downeast Maine for the one-
week period of April 14th to April 21st, 2022.

...Active Ice Jams on the Allagash & St. John Rivers...

The potential for Ice Jam flooding over the next week is above normal
across the St. John River basin. The Ice Jam flood potential has
ended on all other rivers in Eastern & Northern Maine.

...CLIMATOLOGICAL GUIDANCE...

April so far is running above normal for temperatures with varying
precipitation conditions. Frenchville is currently averaging a
temperature of 36.5 degrees which is 3.1 degrees above normal. So
far Frenchville has seen 0.62 inches of precipitation which is
0.27 inches below normal. In Caribou the average temperature so
far for April is 36.7 degrees which is 2.5 degrees above normal.
1.69 inches of precipitation has fallen which is 0.43 inches above
normal with much of this falling as rainfall. This month NWS
Caribou has only seen 1.1 inches of snowfall which is 4.2 inches
below normal. Millinocket`s average temperature so far is 41
degrees which is 4.7 degrees above normal. They have seen 1.42
inches of precipitation which is only 0.05 inches below normal.
Bangor`s average temperature so far for this month is 43.9 degrees
which is 4.8 degrees above normal. Bangor has seen 2.05 inches of
precipitation which is 0.52 inches above normal for the month to
date.

The North Atlantic Oscillation (NAO) has held in slightly
negative to near neutral phase into early April allowing for some
blocking in the vicinity of Greenland and colder air being forced
south from Canada into the northeastern United States. Medium
range climate guidance now suggests the NAO index switching to
slightly positive phase during the second half of April as upper
level blocking near Greenland shifts southeast into the open
Atlantic. This would limit the timing and scope of colder air
reaching the Northeast.

The Arctic Oscillation (AO) has been in its negative phase
favoring troughing across the northern CONUS. Medium range climate
guidance suggests that the Arctic Oscillation will vacillate into
positive and then perhaps neutral or negative phase again by late
month. This would indicate transient troughing in the northern
CONUS with some colder air that temporarily reaches the Northeast.

Meanwhile the Pacific North America (PNA) pattern...which has
been in a negative phase is forecast to turn more neutral. This
would tend to favor a less amplified and more zonal pattern
developing.

A La Nina pattern remains present at this time. A La Nina
generally favors a variable Pacific jet stream with ridging most
prevalent across the western and southeastern U.S. and troughing
found near the Great Lakes region. The latest sea surface
temperature departure as of 11 April 2022 was -0.9F in the Nino
3.4 region. The La Nina is currently forecast to continue through
June-August 2022 either continuing or trending closer to ENSO
neutral beyond August.

A variable jet stream pattern is expected the remainder of April
with modified air quickly advancing from west to east from the
Pacific west. Cold air intrusions are anticipated to occur but
generally be short lived. Frequent precipitation events are
anticipated mainly due to an active Pacific jet stream. Keep in
mind that cutoff low systems more frequently develop during the
spring months. These low systems are typically challenging to
pinpoint with some significant error possible in the timing and
location details of QPF amounts and temperature.

The official National Oceanic and Atmospheric Administration`s 6
to 14 day outlook from 19 to 25 April 2022 calls for chances for
near normal to below normal temperatures and above normal
precipitation to start. Medium range climate forecasts then begin
to favor near normal to below normal precipitation heading into
the last week of April along with moderating temperatures.

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

Snow depths across the St. John River basin varies between 15 to
30 inches of snow with some isolated deeper snow across the
headwaters in the North Woods. This remains normal snow depth with
snow water equivalent (SWE) readings 5 to 9 inches with isolated
SWE to 10 inches. The SWE in much of the St. John River Basin is
around normal. Snow densities show much of this snowpack is above
the 0.33 reading for indicating a ripe snowpack. A
ripe snowpack is a snowpack that can no longer absorb
rainfall and would result in loss of snow due to melting in a rain
event.

In the Aroostook River basin snowpack ranges between Trace to 10
inches with the Caribou NWS Office sitting lower at a Trace snow
depth. There are isolated higher amounts in the forest to 15
inches across the basin. Snow water equivalents running near
normal between Trace and 5 inches. Everywhere else is bare ground
including the Moosehead Region much of the snow is gone except in
the woods cannot rule out some 5-10 inch snow depths. The
exception to this is the higher terrain of Baxter State Park where
20-38 inches of snowpack still remains with likely 7 to 12 inches
of snow water equivalent. The snowpack has melted completely in
southern & central areas where now the concern is fire weather.

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

Soil moisture remains near normal to slightly above normal. The
frost continues to thaw across the north with areas now down to
2-8 inch frost depth with surface thawing 1-2 inches occurring.
Elsewhere absorption is occurring since the frost has thawed
completely. A look at groundwater levels, courtesy of the USGS,
showed normal levels across the state with above normal readings
in Eastern Washington County. Calais was indicating groundwater
level between the 90th percentile and the highest median reading
into mid April for its 38 year period of record. The North Woods
continues to see D0-D2 drought conditions. D1 & D2 exists in a
very tiny location of Northern Somerset county near the Quebec
border. D0 conditions remain in place across western Aroostook,
western Piscataquis and the rest of Somerset counties.

...RIVER AND ICE CONDITIONS...

River flows are running above normal across the North into the
Central Highlands and Interior Downeast. Rivers are returning to
normal flows in the coastal Downeast areas.

Currently, St. John River is free and clear at the headwaters
based on observations from the Maine Forest Service on April 13th.
There is sheet ice breaking up on the Big Black River that has
jammed up near the Blanchette Road in T14 R15. The river will
continue to see ice rot and break up and will eventually flush
into the St. John River. The St. John River is mostly ice free in
the headwaters as noted by pictures from the Maine Forest Service
on the Maibec Road crossing. There remains an Ice Jam on the St.
John between Allagash and St. Francis which is approximately 9
miles long. This jam is holding up approx 7 feet worth of water
upstream that is slowly falling given the decreasing runoff. There
is also an Ice Jam on the Allagash River between the Town Dump
and the confluence with the St. John. This jam is stuck and cannot
dislodge into the St. John River due to that ongoing jam. There
is also a small jam on the Little Black River which is causing
some backwater flooding in Allagash off the Walker Brook Road.
Beyond St. Francis to Madawaska there is generally an open river
with some areas of ice left but given the increased flow much of
the ice is clear. There is an Ice Jam near Lille/Grand Isle
town line that is causing minor flooding upstream from the
extreme eastern portion of Madawaska to Lille. Beyond Lille to
Hamlin there is mixed conditions to Van Buren then nearly full ice
cover downstream to Hamlin. This ice is decaying but the river
still remains nearly 100% covered.

All other rivers are ice free and running mostly above normal
flows for mid April with Downeast rivers running near average.

...IN CONCLUSION...

The flood potential over the next week is above normal across
Northern Maine mainly in the St. John, Allagash & Aroostook River
Basins. This is due to ongoing Ice Jams, melting snowpack with
predicted warm temperatures and rainfall that will likely cause
ice movement and increased flow. The flood potential due to Ice
Jams in the Aroostook basin & all other areas south is over for
the season. The potential for open water flooding in Central and
Southern Areas remains at normal or below normal given the current
river flows. The potential for open water flooding on the
Aroostook River is above normal given the above average flow and
remaining melt with rainfall in the forecast.

The next Winter/Spring Flood Outlook will be issued on Thursday,
April 21st unless conditions warrant an update.

$$
Sinko

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