Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 201644

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Mon Nov 20 2017



An upr ridge is situated just to the west of Baja this morning with
a s/wv trof beginning to nudge inland across southern BC and the
Pacific Northwest. The associated cold front stretches from western
Washington arching back toward the southwest and eventually west of
the Oregon coast. Blended TPW imagery shows a healthy moisture plume
stretching north-northeast from a source near 20N between 140W and
150W toward the CA coast. IWV sensors along the north coast indicate
values near 1.25-inches advecting inland across northern CA. The
majority of precip across areas north of I-80 this morning is
dominated by WAA and isentropic lift. Heaviest amounts are expected
to fall this morning and afternoon along the north coast from Cape
Mendocino northward with lesser amounts over the upper
Klamath...Shasta Lake drainage...and northern Sierra. Freezing
levels this morning are near 9500-feet along the CA/OR border to
11000-feet for the I-80 corridor.

For Tuesday and Wednesday...the upr ridge will continue to build
across the region with the center near northern Baja. At the same
time...a deep upr trof will set up shop over the eastern Pacific
between 140W and 150W. The moisture plume will narrow but remain
fairly potent with PW values somewhere between 1.25- and 1.75-inch
and take aim toward the Pacific Northwest. The edge of this moisture
will be close enough to the north coast to bring the possibility of
precip mainly to the immediate coast. Freezing levels will nudge
upward with the high pressure strengthening. Near the CA/OR border
look for 11500-feet and 13000-feet near I-80. For central and
southern CA the freezing level is up between 14000- and 16000-feet!

On Thursday...a s/wv trof will rotate toward the southern BC and
Pacific Northwest coast as the overall upr trof becomes more
positively tilted. This will bring a shot of precip to areas near
the CA/OR border with much lighter amounts making their way down to
the Russian River basin inland toward the northern Sierra. Freezing
levels will dip back down to near 9000-feet along the CA/OR border
and a lesser drop for I-80 closer to 12000-feet.

Friday will see a break from the precip with the next round of
precip for northern areas primarily from I-80 northward will arrive
on Saturday into Sunday.


The majority of the 24-hr observed precipitation has occurred early
this morning along the North Coast tapering off near Ukiah with
amounts of 2 - 3 inches in the Smith basin, 0.5 - 1.5 inches in the
Eel, and < 0.5 inches in the upper Russian basin. Temperatures are
fairly warm across the state and freezing levels remain high. Rivers
along the North Coast are starting to rise due to this mornings
precipitation with continued moderate rises expected for today. The
remainder of the rivers effected by last weeks` storm continue to
recede. No monitor stages are forecast at this time.

More information on the CNRFC website at http://www.cnrfc.noaa.gov



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