Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 171701
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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Fri Nov 17 2017

...LATEST SYSTEM DISSIPATING TODAY...
...NEXT OPPORTUNITY FOR PRECIP MOVES IN LATE SUNDAY INTO MONDAY...
...ADDITIONAL PRECIP EXPECTED IN NORTHERN AREAS MON-WED...

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

Slow moving cold front is currently aligned from across central NV
just south of the I-80 corridor before arching southward toward
southern CA. Moisture plume entrained into this system ahead of the
frontal boundary is aimed at the southern CA coast with PW values
along coastal location between Point Conception and the CA/Mexico
border between 1.00- and 1.25-inches. This places the area between
175- to 225-percent of normal for this time of year. Since
17/12Z...precip gages indicate the best amounts across the southern
Sierra from the upper portions of the San Joaquin River basin
southward with totals generally from 0.25- to 0.75-inch with
localized totals nearing 1.00-inch. Behind the cold front...freezing
levels have dropped to near 3000-feet along the CA/OR border...and
5000- to 6000-feet along the I-80 corridor. Ahead of the cold
front...freezing levels are still ranging from near 8000-feet to
12000-feet.

Through the rest of today...look for the for the s/wv trof moving
across the Pacific Northwest along with northern CA and NV to exit
the area to the east. The frontal boundary will dissipate and precip
will come to an end during the afternoon period...mainly eastern NV.
High pressure will build in across the area with dry conditions
expected from Saturday through much of Sunday.

There are still some differences...now mainly in terms of
timing...with the s/wv trof expected to reach the Pacific Northwest
and northern CA sometime on Monday. The 17/00Z GEM is the fastest
taking this feature inland...while at the other end of the spectrum
the 17/00Z EC is the slowest. The 17/06Z and 17/00Z GFS is somewhere
in the middle...but leans a bit closer to the EC. For now...took a
compromise solution in timing between the EC and GFS...which will
bring light precip to far northwest CA Sunday evening...spreading
across the upper Klamath River basin and northern CA down to I-80
overnight into early Monday. Freezing levels late Sunday will
generally be from 7000- to 8000-feet near the CA/OR border and
closer to 10000-feet near I-80.


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

Expect a front and shortwave aloft to bring widespread precip to the
northern half of CA and NV as well as southern OR Mon.  Models are
struggling to lock in on this system.  GEM is slowest, ECMWF
fastest, and GFS in the middle.  For the Mon morning through evening
time frame, followed the timing of the 06 UTC GFS while blending in
a 6-hour offset version of the ECMWF.  It appears best precip could
be Mon morning in the Sierra and across to the north coast. However,
the 12 UTC GFS arriving in AWIPS now seems to be showing a slowing
trend.  Expect freezing levels generally 7000-10000 ft.

Expect a warm front to spread additional precip across the area late
Mon into Tue with a cold front moving in late Tue into Wed. Overall
precip amounts look to be mainly light except could be heavier near
the cold front with models showing a decent but narrow moisture
plume associated with the front.  Freezing levels are expected to
rise above 10000 ft with the warm front and then begin to fall by
late Wed night in far northern CA and southern OR to 8000-10000 ft.


.HYDROLOGICAL CONDITIONS...

Widespread precipitation occurred over the past 24 hrs focused on
the Northern part of the state. 24 hour rainfall totals were
heaviest in the Central Sierra with amounts ranging from 2 to 4
inches in favored locations. Bay Area and Central Coast totals of 1
to 3 inches were also observed. The Southern extent of significant
precipitation was in the mountains of the San Joaquin and Kings
basins, with lesser amounts to the South. Rivers across the state
are receeding from this early season event. No monitor stages were
reached. Temperatures should continue to warm over the next 24 hrs
melting some of the lower elevation snow.


All forecast points are expected to remain below monitor levels.


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

DRK/KL/NB

$$



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