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CNRFC Hydrometeorological Discussion

AGUS76 KRSA 191707
HMDRSA

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

$$