Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 231614

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PDT Fri Mar 23 2018



WV/IR imagery shows the s/wv trof and associated cold front have
both cleared the region to the east...now moving through the
intermountain west. Blended TPW shows the deep moisture plume
associated with yesterday/s heavy precip intersecting the coast
across northern Baja...while 23/12Z RAOBs indicate PW values all
less than 0.75-inch with the highest values over extreme southern
CA. A few showers are lingering in this area under westerly onshore

Attention will next turn back to the north where an upr low is
spinning just west of Vancouver Island with individual disturbances
rotating around this primary circulation. Precip ahead of the first
s/wv trof is already beginning to affect the northern CA coast with
PW values only expected to peak near or just above 0.50-inch along
the immediate coast. This initial s/wv trof will bring precip mainly
to areas near and north of the I-80 corridor as it reaches the north
coast this evening. Overall amounts will generally range from 0.25-
to 0.75-inch across the higher terrain with localized totals from
1.00- to 2.00-inch from the Eel River basin northward to the CA/OR
border. Lighter amounts are expected over valley locations. Freezing
levels in general across northern CA will range from northwest to
southeast between 3000- and 5000-feet.

The next s/wv trof will be quick on the heels of the first and
arrive on Saturday. This one is expected to dig a bit farther south
across northern and central CA...as well as the northern half of NV.
Moisture will be even less as compared to the Friday s/wv trof...but
dynamics are expected to be more favorable. Amounts will once again
range from 0.25- to 0.75-inch over the higher terrain. Lower
elevation totals will be near or less than 0.25-inch. Freezing
levels will generally range from 2000- to 4000-feet across northern
CA...and 4000- to 5500-feet for central CA.

With general troffiness across the region on Sunday...light
lingering precip is possible across the northern two-thirds of the
region. Overall amounts will be close to 0.10-inch or less. Drier
northerly flow will begin to develop as this overall upr trof begins
to push east of the area.


A trough moves through on Sunday bringing showers to mainly over the
mountains and along the coast of Northern and Central CA and over
Nevada as a shortwave moves through. The trough stretches with
another shortwave moving through So Cal and Baja late Sunday for
possible light precip mainly over the mountains but EC has this
weaker and kept forecast dry there for now. The GFS has a
disturbance moving down the back side of the trough over the Sierra
and Nevada on Monday for possible showers mainly over the Sierra and
Nevada but the EC is dry.  The forecast used a blend of the models
for Monday. Freezing levels around 2000-5000ft. Ridge of high
pressure moves into the region from the Easter Pacific on Tuesday as
a closed low forms over Arizona.  High pressure builds over the area
on Wednesday and Thursday.  This will bring dry conditions for
Tuesday through Thursday next week.


Widespread precipitation occurred across the region in the last 24
hrs with the central Sierras receiving the highest amounts (3-5
inches). The transverse range received 2-4 inches. The North Coast,
Klamath, and Shasta drainages saw lessor amounts (1-3 inches).
Temperatures are cooling across the forecast area but were fairly
warm during the precipitation event.

Rivers are receding in most places with the exception of the slower
rising rivers - MF Feather at Portola, which should peak around 10.0
feet on Saturday morning, the Cosumnes at Benson`s Ferry should peak
Saturday morning around 14 feet.

Snow accumulation across the Sierra in the past 24 hrs ranged from 3
to 10+ inches at the higher elevations. Snow density at the
beginning of the storm saw increases due to the precipitation being
heavy/rain. 24 hr SWE values in the Sierra increased 2-4 inches.

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



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