Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 171731

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Fri Feb 17 2017



A cold front and ample moisture moving through Northern and Central
CA (to around Point Conception) brought precipitation in the past 24
hours. 1-2.6 inches for the Smith Basin 0.33-1.00 for Eel River
Basin and Shasta area, 0.5-1.5 for the Northern Sierra, 0.25-1.25
around Monterey Bay 0.33-0.85 in Santa Barbara County and half an
inch or less for the Upper Klamath Basin, Central Sierra and
Sacramento Valley and a third of an inch or less for Ventura County
and Southern Sierra and around a tenth of an inch or less for LA
County and San Joaquin Valley.


A moisture plume is surging into srn CA this morning.  GPS-MET
sensors at 15 UTC indicated 1.1-1.2" PW values in San Luis Obispo,
Santa Barbara, and Ventura Counties.  VWP data shows winds in the
transverse ranges are SE at 30-50 kts at 925 MB and SSE at 40-60 kts
at H85.  Heaviest precip in the past few hours has been in srn Santa
Barbara County, where totals are 1-2" since 12 UTC.  Overall,
however, precip was still ramping up over much of srn CA and QPF
seemed a bit overdone compared to obs and model guidance.  QPF was
reduced for almost all of the cntrl coast as well as for most of srn
CA.  Elsewhere, light to moderate precip is affecting nrn/cntrl CA
and portions of NV and srn OR.

Expect the heaviest precip to push east across the transverse ranges
and coastal areas of srn CA this afternoon and evening.  Heaviest
amounts 18-00 UTC should be from wrn Santa Barbara County to the San
Gabriel Mtns.  Heaviest amounts in the evening should be from the
San Gabriels to San Diego County.  Trend in the models was to shift
timing faster a little this afternoon and even more this evening.
Overall expected amounts are lower for the transverse ranges and
higher for San Diego County.  Expect light to moderate amounts to
continue elsewhere.

Expect mainly diminishing amounts Sat-Sun for most areas.  Expect
freezing levels roughly 5000-7000 ft across the Sierra during the
short-term forecast period.


A moist system will bring more precipitation late Sunday into Monday.
This system has a subtropical moisture tap with a 1.3 inch PW plume
around the Bay area with around 1.0 making it into the Central
Valley Monday morning. The models are coming into a little better
agreement for Monday. Increased precipitation amounts for northern
and Central CA around the Russian Basin and into the Northern Sierra
and south to the Big Sur Coast and Southern Sierra for Monday.
Freezing levels around 6000 ft over Shasta area and around 7000-8500
ft over the Sierra Sunday night and may rise briefly with warm air
advection Monday and then drop behind the cold front to around 5000-
6500 ft over the Sierra Monday night.

Precipitation will taper off late Monday into Tuesday morning
between the systems. An upper level trough moves through late
Tuesday into Wednesday bringing more precipitation.  Although not as
much moisture or as strong of dynamics so precipitation amounts are
expected to be lower than Monday.  Timing and details still
uncertain with The 12Z GFS slower and not as deep compared to the
06z but GFE is deeper and a little quicker than the 00Z EC. The
trough shifts to the east Wednesday night bringing drier condition
except for a few lingering showers over the Sierra and Nevada.
Freezing levels around 4500 to 6000 ft over the Sierra on Tuesday
and drop to around 2500-4000 ft Wednesday as precipitation tapers


Heavy rain across Santa Barbara and Ventura counties this morning
will lead to rapid rises this morning into the early afternoon.
Flood stages are being forecast for Sespe Creek, Ventura River, and
Calleguas River for early this afternoon. Rainfall will spread
further south as the day progresses where area rivers will rise
across the desert basins and San Diego County.

Flows will remain high on the upper Sacramento River through the
weekend with releases from Keswick. River levels across the Feather
River are expected to take a big drop over the weekend as Oroville
is expected to stop releasing water for a short time. Be sure to
check the forecast later today and through the day on Saturday for
the latest developments.

Flows will also remain high on the San Joaquin River as reservoirs
continue to release water. Vernalis is expected to rise above flood
stage this weekend and  approach danger stage again by early next
week. Reservoir releases and local flows from downstream of the
reservoirs will govern just how high the river will rise through the
weekend into next week.

Heavy rainfall across the area Sunday night into Monday will lead to
renewed rises on rivers in the Russian/Napa basins and along the
Cosumnes River. Flood stages area expected on the Narvarro River,
the Russian River and Guerneville, and on the Cosumnes River at
Michigan Bar.

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



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