…Unsettled weather to persist across the Northwest U.S. into early next
week with much colder temperatures and heavy snowfall across the Cascades,
northern Great Basin, northern Rockies and northern High Plains…
…Strong atmospheric river will continue over the next couple of days
across northern and central California with heavy rains and areas of
flooding likely…
…Storm system crossing the Great Lakes region to bring accumulating
snowfall to parts of the Northeast…
…Record high temperatures are expected across portions of the Southwest
out through the Southern Plains through the middle of the week…
A persistent trough of low pressure and associated closed low will
continue to impact the Pacific Northwest and the northern Rockies going
through the first half of the week ahead with widespread unsettled weather
expected. Moist onshore flow into the higher terrain coupled with colder
temperatures filtering south from southwest Canada will drive heavy
accumulating snowfall across the Cascades and especially interior mountain
ranges such as the Sawtooth, Bitterroots, Tetons and Absaroka Range. In
fact, the strong atmospheric river that is bringing very heavy rainfall to
areas of northern California is being steered up the larger scale pattern
northeastward up across areas of southern and eastern Oregon, and into the
southwest facing slopes of the northern Rockies where there is plenty of
cold air in place for very heavy snowfall accumulations and including even
some lower elevation locations. For the Cascades, generally an additional
6 to 12 inches of snow is expected through early Wednesday, but
considerably heavier amounts are expected for the Shasta/Siskiyou Ranges
northeastward into the aforementioned terrain of the northern Rockies
where an additional 1 to 3+ feet can be expected. The deep layer fetch of
Pacific moisture is also overrunning Arctic air that is well entrenched
over the northern High Plains, and this coupled with upslope flow here
just east of the Continental Divide will allow for heavy snowfall to
accumulate here as well.
The strong atmospheric river bringing the heavy flooding rain concerns
over northern California should persist through the first part of the week
as a stationary front remains anchored in place. Multiple waves of low
pressure will traverse this boundary, and this coupled with the Pacific
moisture transport and upslope flow/forcing over the higher terrain of the
coastal ranges and northern Sierra Nevada foothills should yield as much
as an additional 5 to 10 inches of rain. The Weather Prediction Center has
depicted a Slight Risk (level 2 of 4) of excessive rainfall across
northern California going through early Tuesday. By later Tuesday and
Wednesday, the front will be finally settling southward, but this will
bring heavy rainfall down into central California including the Bay Area
and portions of the Central Valley. Several inches of new rain can be
expected here, and a Slight Risk of excessive rainfall has been depicted
going into early Wednesday.
Farther off to the east, a combination of Pacific moisture arriving from
the Western U.S. along with a frontal system traversing the Great Lakes
region will bring a swath of accumulating snow for today across areas of
Wisconsin and Michigan eastward into northern New York and northern New
England. Locally several inches of new snow accumulation is expected. This
system will pull away through southeast Canada tonight with a trailing
cold front then crossing the region and bringing a new surge of much
colder temperatures.
Arctic high pressure will be settling south from Canada across much of the
northern tier of the nation early this week with temperatures falling
locally well below normal. This will especially be the case over the
northern High Plains where temperatures will be as much as 15 to 30
degrees below normal, with daytime highs locally staying below zero.
However, south of the Arctic front going through the middle of the week,
very warm temperatures will be pooled across much of the southern tier of
the country. This will include temperatures reaching well into the 80s
across the interior of the Southwest and also across the southern Plains.
Record high temperatures are expected with some locations seeing high
temperatures as much as 20 to 30 degrees above normal.
Orrison
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
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