…Atmospheric river to bring unsettled weather to the Northwest,
including heavy rains for the coastal ranges and accumulating snow for the
higher elevations of the Cascades…
…Above average temperatures expected for much of the lower 48 into
mid-week…
The pattern will remain active across the northwestern U.S., especially
the Pacific Northwest, as a strong atmospheric river takes aim across
Washington and Oregon for Tuesday. Low level onshore flow will remain
across the Pacific Northwest as the latest in a series of upper level
troughs moves inland tonight while weakening, followed by stronger but
quick moving system for Tuesday afternoon/evening. Showers will transition
to steady rain tomorrow with areas of heavy rain becoming likely late
Tuesday morning into the evening ahead of a warm front. As a cold front
nears the coast late Tuesday afternoon/evening, heavy rain is likely for
the Coastal Ranges of northern Oregon into Washington along with the
Cascades. While light to moderate snow is anticipated for portions of the
Cascade Range through Tuesday morning, snow levels will rise to 7000-8000
ft above sea level for the Washington Cascades during the height of the
atmospheric river event late Tuesday with accumulating snow changing to
locally heavy rain. The heaviest rain is expected into the Olympics where
2-day rainfall totals of 5 to 7+ inches are expected through Wednesday
morning.
Elsewhere across the country, the weather will be relatively quiet. A pair
of cold fronts moving eastward from the Great Plains/Midwest over the next
few days will maintain wet and unsettled weather from the lower/middle
Mississippi Valley to the East Coast. Across Florida, locally heavy rain
will be possible along the east coast of the Peninsula on Tuesday with an
easterly low level flow regime in place, tapping into anomalous moisture
over the Caribbean. Rain will linger into Wednesday across Florida.
Temperatures for many in the lower 48 will run 10-20 degrees above
mid-December averages with the exception of the north-central U.S.
Temperatures from eastern Montana to the upper Mississippi Valley will
likely be 5 to 15 degrees below average and carry light snowfall
accumulations for portions of the region.
Otto
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php