National Weather Service California Nevada River Forecast Center Department of Commerce National Oceanic and Atmospheric Administration National Weather Service
Printer Version
CNRFC Hydrometeorological Discussion

AGUS76 KRSA 191715
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Sun Nov 19 2017

...MAIN FOCUS OF PRECIP FOR THE WEEK ACROSS THE NORTH COAST...

.METEOROLOGICAL CONDITIONS (SUN AM - SAT AM)...

Overall pattern this morning shows an elongated positively tilted 
s/wv trof moving toward BC and the Pacific Northwest this 
morning...while an upr ridge centered just west of Baja extends 
north-northeast into west-central Canada. As a result...the 
southwest flow across the eastern Pacific is advecting low-latitude 
moisture from a source near 20N between 140W and 150W toward the 
Pacific Northwest. 

For today...the upr ridge will continue to strengthen as the s/wv 
trof moves onshore well to the north of the area. WAA/isentropic 
lift type precip will develop across northern CA up into the upper 
Klamath River basin late tonight into tomorrow with precip generally 
remaining near and north of I-80 for tomorrow. Freezing levels will 
start near 9000-feet at the CA/OR border and 11000-feet in the 
vicinity of I-80. By the time precip diminishes...look for freezing 
levels to jump to 10500-feet near the CA/OR border and along I-80 
over 12000-feet.

Then for Tuesday through Wednesday...look for the upr ridge to hold 
on strong across much of the region with this feature centered over 
northern Baja. A fairly deep but narrow wavelength upr trof will set 
up offshore between 140W and 150. With the moisture plume generally 
focused toward the Pacific Northwest...the eastern fringe will still 
bring light to at times moderate precip to the north coast from 
about Cape Mendocino northward. Freezing levels will generally be 
from 11500-feet near the CA/OR border to 13000-feet for the I-80 
corridor and above 14000-feet for central and southern CA.

A s/wv trof moving toward the Pacific Northwest on Thursday will 
flatten the upr ridge a bit and spring precip inland across the 
CA/OR border area...Shasta Lake drainage and potentially the 
northern Sierra. Freezing levels fall to near 8000-feet at the CA/OR 
border and 11500-feet along I-80. 

There are decent differences with the models bringing another s/wv 
trof up from the southwest toward the CA on Friday or Saturday. The 
19/00Z GEM is the fastest and wettest...while the 19/00Z EC is 
slowest and weakest. 19/00Z GFS is somewhere in-between the 
two...but the 19/06Z GFS sped up the system and increased its 
strength a bit. Low confidence Day 6 forecast at this time.


.HYDROLOGICAL CONDITIONS...

A break in the weather means the rivers across the state continue to 
recede. Freezing levels are 10,000+ ft with remnants of the colder 
air still moving out of the Humboldt basin. Upper soil zones are 
saturated along the North Coast, decreasing through the Russian/Napa 
drainages and partially saturated moving south along the Central 
Coast. The same is true for the Sierras - mostly saturated surface 
soil conditions in the North and decreasing in the South with 
partial saturation in the Kings and Kern basins.


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

DRK/NB

$$