Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Fri Dec 9 2016

...WARM HEAVY PRECIP EVENT NRN CA TONIGHT THROUGH SAT...
...WET PATTERN CONTINUES INTO NEXT WEEK...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 9 AT 400 AM PST)...

Moist onshore flow from the southwest brought precip to the northern
two-thirds of CA and the northern half of NV. Greatest amounts were
scattered about the coastal mountains down to the Santa Lucia
Mountains and over much of the Sierra. Totals were in the range of
0.50- to 1.50-inches with some locally higher totals (2.50-inches)
along the Monterey County coast and Feather River basin.

For the Central Valley...totals varied from 0.25-inch near Redding
and Red Bluff to 0.50-inch near Sacramento and finally between a few
hundredths of an inch at the south end of the San Joaquin Valley to
0.33-inch at the northern end.

Across northern NV...precip totals were greatest over Elko County
with 0.25- to 0.50-inch amounts (local to 0.75-inch near the crest
of the Ruby Mountains. Elsewhere...totals were generally near or
less than 0.25-inch.


.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI AM - MON AM)...

Light showers persist over portions of the forecast area this
morning, especially nrn NV, NW CA, and the nrn Sierra with weak warm
advection over the region.  Expect areas of light precip to continue
through the afternoon.

A warm storm expected to reach the north coast this evening and the
nrn Sierra by later tonight is looking quite impressive at this
point.  Overall precip totals have been brought up significantly in
the nrn half of the Sierra for the period from 06 UTC tonight
through 00 UTC Sun (Sat afternoon).  An impressive fetch of moisture
stretching to the Hawaiian islands and beyond is expected to reach
the north coast by late afternoon and increase this evening.
Ultimately, expect PW values along the coast to reach near 1.5"
tonight near Pt Arena, and the plume is forecast to gradually work
its way southward to near Pt Conception over a 24-hour period.  The
most impressive totals are expected to be over the Sierra with
westerly H7 flow of 40-60 kts.  Locally heavy amounts are also
expected on the north coast tonight.  Expect showers to quickly
taper off by late Sat night with lingering light showers across the
north through Sun night.

Expect freezing levels 7000-10000 ft for the most part through Sat
morning, falling to 4000-9000 ft over nrn/cntrl CA/NV behind the
cold frontal passage Sat morning in the nrn Sierra and Sat evening
or overnight further south.


.METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)...

Lowered heights extending west-southwest off the PACNW coast and
then arching toward the Hawaiian Islands to start off the
period...while an upr ridge is situated to the east of Hawaii. In
between a persistent moist southwest to west flow continues to be
aimed at the CA coast. The next surge of moisture will be
offshore...poised to affect the region primarily Tuesday into early
Wednesday. However...it can be said that at this point the location
the moisture plume intersects the coast varies greatly amongst the
models as the 09/00Z EC pumps up a decent ridge ahead of a deepening
upr low over the northeast Pacific. This places the moisture plume
shifting from northern CA up toward the OR coast. The 09/00Z GFS is
much flatter with the upr ridge and directs the moisture toward the
I-80 corridor...which would be wetter for the SF Bay Area inland
toward the central Sierra. And the 09/00Z GEM is even shallower with
the anti-cyclonic flow...bringing the lowered heights over the PACNW
down toward northern CA. This pushes the moisture well south of the
area with only scattered light precip for CA toward NV. For
now...followed the in between solution of the 09/00Z GFS...which is
decently close to the previous forecast and the overnight WPC Days 4
and 5 forecast. Freezing levels look to average 5000- to 7000-feet
during the peak precip on Tuesday.


.HYDROLOGICAL CONDITIONS...

Due to the increase in the precipitation forecast, pretty much every
Northern/Central CA river forecast location has increased from
yesterday`s forecast.  Monitor stage exceedence is still expected at
MHBC1 on the Cosumnes, and MCNC1 as well.  TRCC1 on the Truckee is
now expected to exceed flood stage this weekend, and monitor level
exceedences further down at Reno and Vista.  The Merced River at
POHC1 is expected to reach near flood stage.


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

DRK/KL/DRK/BW

$$



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