…Strong atmospheric river to take aim at north-central California with
heavy rain and possible flooding over the next couple of days…
…Active pattern for the northwestern U.S. with heavy snow from the
Cascades to the northern Rockies…
…Above average temperatures for much of the nation this weekend…
The upper level pattern will transition to a zonal flow regime this
weekend with the jet stream aligning from west to east. This pattern will
produce focus most of the active weather over the western U.S., largely in
the form of an atmospheric river which is expected to bring increasing
intensity of precipitation to central California starting on Saturday.
While light rain/mountain snow was ongoing Friday afternoon from central
California to the Pacific Northwest and northern Rockies, low level winds
will strengthen on Saturday from the San Francisco Bay region to locations
just northward, with a plume of anomalous moisture extending inland into
the Great Basin. The plume of moisture will vary in latitude over the next
couple of days but remain focused over portions of central to northern
California, sandwiched between low pressure along the coast of British
Columbia and high pressure to the west of southern California. Snow levels
will be relatively high within the core of the atmospheric river which
will keep heavy snow confined to elevations above 7000 feet in the Sierra
Nevada. The remainder of the precipitation will fall as rain with the
Coastal Ranges, just north of San Francisco Bay into the Sierra Nevada,
likely picking up the highest rainfall totals over the weekend. Through
Sunday, 2 to 4 inches of rain is expected for the Coastal Ranges with 3 to
7 inches for the Sierra Nevada (locally higher). Rain is likely to
continue through Monday as well. While rainfall is needed for many of
these areas, it may be too much at once, resulting in flooding concerns
and potential for debris flows within areas of sensitive terrain and area
burn scars. Heavy snow with 1 to 2 feet is expected for the higher
elevations of the northern Cascades into central Idaho, far northern Utah
and northwestern Wyoming. Below average temperatures will filter into the
Pacific Northwest this weekend, perhaps allowing for snow into the cities
of Seattle and Portland, though any accumulations are expected to be minor
(if any).
Elsewhere across the lower 48, temperatures will be above average from the
southern Great Basin into the Great Plains, Midwest, Gulf Coast and
Southeast. The core of the warmth will extend from the southern High
Plains into the Midwest where high temperatures are expected to climb to
15 to 25 degrees above average for Sunday. After the departure of a cold
front in the East tonight, drier weather is expected for most locations
east of the Rockies the weekend. The exception will be from the Great
Lakes to the Northeast where a quick moving disturbance will bring light
snow to the region along with colder than average temperatures, especially
across northern New England where high temperatures are forecast to be
10-20 degrees below average on Saturday, with some modest warming on
Sunday.
Otto
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
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