Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 191707
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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Fri Jan 19 2018

...SOME SHOWERS AND LOWER SNOW LEVELS INTO SATURDAY...
...ANOTHER SYSTEM MOVES OVER THE NORTH FOR MORE PRECIP ON SUNDAY...
...LIGHT PRECIP MAINLY NORTH ON MON WITH WIDESPREAD PRECIP TUE/WED...

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

Precipitation amounts for past 24 hours ending at 4 am are 1-2
inches for the Smith and Eel River Basins and from Feather Basin
down to American River Basin and the east side of Shasta Basin.
Other locations were generally a tenth to 0.6 inches. Northern
Sierra received about 6-12 inches of snow with snow levels lowering
to around 5000 ft this morning.

Weakening cold front has moved south and east and is draped from
around Point Conception and into Northeast Nevada this morning. The
upper level trough will move onshore and through the region today
into Saturday afternoon.  Some showers behind the front with
freezing levels lowering to around 3000 ft in the north to around
4000 ft near the I-80 corridor and around 6000 ft for the Southern
Sierra today. Only made little rises to forecast for today over the
Southern Sierra and the north facing slopes of the Tehachapi
Mountains, and So Cal transverse mtns and over NE Nevada.  The
trough shifts to the east with weak ridging moving in between
systems on Saturday. Only a couple tweeks for Saturday with
lingering showers over the So Cal Mountains and eastern NV and far
NW CA coast.

A system moves into the Pacific Northwest with the front trailing
through Northern CA on Sunday bringing more precipitation. PW plume
about an inch of nrn CA coast around Cape Mendocino Sunday afternoon
and sags south to South Bay area by Monday morning. Increased
amounts for Sunday, especially from Cape Mendocino down to the north
Bay area and over the Northern Sierra and Shasta area Sunday
afternoon and evening.  Freezing levels expected to be around 3000ft
near Shasta and around 5000 ft near I-80 corridor.


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


Beginning of the period will see a narrowing moisture plume sinking
south across central and southern CA with WAA/isentropic lift type
precip dissipating across the region. Best amounts look to fall over
the eastern half of the Shasta Lake drainage down across the
northern and central Sierra. Also...a band of precip will fall over
extreme northern NV.

The next upr trof moving toward the northeast Pacific will draw a
moisture plume toward the region that will begin to impact the
region on Tuesday. There are some timing differences amongst the
models with the initial WAA/isentropic lift type precip and then the
progression of the cold front across the region. Depth of the
overall system is in question this far out as well. For now...the
better agreement with the evolution of precip across the region
looks to be between the 19/00Z EC and GEM...and these two were
followed for the Tuesday through Wednesday time periods.

Light to locally moderate precip associated with WAA/isentropic lift
will develop across northern CA on Tuesday morning into the
afternoon primarily from the I-80 corridor northward. The cold front
will then begin to drop southward across the region and move inland
on Tuesday evening and overnight...increasing precip intensity along
and just ahead of the boundary. The associated s/wv trof will reach
the coastal waters Wednesday morning and swing inland on Wednesday
afternoon/evening. This will push the better precip amounts across
central CA. Given the current thinking on the depth of the
system...at this time...only expected light precip to make its way
south of Point Conception.


.HYDROLOGICAL CONDITIONS...

Over the next 5 days flows in rivers in the northern half of
california will will vary as a result of incoming storm systyems.
Current forecast shows the largest flows resulting near the end of
the 5-day forecast window. During this time, no locations within
the CNRFC area are forecast to reach monitor levels.

Additional information is provided at the CNRFC website at
http://www.cnrfc.noaa.gov

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

HSO/DRK/BMM

$$



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