Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 221748
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Mon Jan 22 2018

...SHOWERS OVER NORTH TODAY...
...PRECIP OVER NORTH LATE TUESDAY INTO THURSDAY...
...PRECIP RETURNS FOR FAR NORTHERN AREAS FRI INTO SAT...

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

Precipitation amounts for the past 24 hours generally 1-3 inches for
the Smith and Eel and Russian Basins and along the North Coastal
range and 0.5-1 inch for Shasta area elsewhere in Northern CA
generally less than half an inch. Snow levels around 5000 ft in the
Northern Sierra this morning. Some precipitation along the weakening
front around south Bay Area to Monterey Bay and into the Central
Sierra and over Northern Nevada this morning. Also a few showers
behind it. Increased amounts around bay area to around Monterey Bay
and stretching into the Northern and Central Sierra this morning
with showers. Showers are expected to diminish by this evening as a
weak ridge of high pressure builds in ahead of the next system.

The 06Z GFS and 00Z EC slow down the timing a little for the next
system and keep moisture a little farther north on Tuesday. PW plume
about an inch off Cape Mendocino at 12Z Wed.  Decreased amounts for
far NW CA and Srn Oregon with warm air advection precip on Tuesday
and slowed down the southern progression of cold front on Wednesday.
The cold front may be around the I-80 corridor late Wednesday
afternoon into evening. Freezing levels around 4500 ft neat ORCA
border and around 7500 ft near I-80 Wednesday lowering to around
2500 ft and 5000ft respectively by Thursday morning behind the
front.

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

Both the 22/00Z EC and GFS show good agreement with the s/wv trof
axis right along the coast to start the period. Precip associated
with the cold front will be across the southern Sierra up toward
northeast NV. Also...at the core of the system...another area of
slightly higher precip will fall along coastal sections from near
the Golden Gate northward to the Smith River basin. The s/wv trof
will move inland during the afternoon hours with a secondary
disturbance moving toward the north coast. This will bring an uptick
in precip to much of northern CA as this feature moves across the
area. Afterwards...precip will be on the decrease at this system
moves toward the east Friday morning.

An upr ridge will build just off the west coast for Friday into
Saturday. However...at this time...this feature doesn/t appear to be
too strong. The next moisture plume will ride up and over the upr
ridge...taking aim at the area near the CA/OR border on Saturday.
WAA/isentropic lift type precip will increase primarily near the
CA/OR border with the best amounts along the coast from Cape
Mendocino northward. Eventually by the end of the forecast period on
early Sunday...the upr ridge will shift inland and strengthen a
bit...pushing the moisture plume northward across the OR coast. This
will bring an end of the precip across the area.

.HYDROLOGICAL CONDITIONS...

The precipitation that fell overnight and into this morning resulted
in small rises along the coastal rivers north of San Francisco and
in the Northern Sierra. The next system arriving Tues/Wed will
result in slightly larger rises in the Northern/Central CA rivers,
but well below monitor levels.


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

HSO/DRK/BW

$$



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