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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
735 AM PDT Sat Oct 16 2021

...TURNING COOLER WITH PRECIP CHANCES INCREASING NORTHERN AREAS...

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

Latest setup shows an upr ridge over the interior...aligned from the 
4-Corners region up across the Great Basin well north into Alberta. 
Upstream over the northeast Pacific...an upr trof is aligned along 
140W with a modest moisture plume entrained just ahead of the cold 
front with the latest Blended TPW imagery showing PW values 
generally from 1.25- to 1.50-inches. 

Today will be a dry day...ahead of the approaching cold front. 
However...through the morning hours tomorrow look for the upr trof 
to sharpen as it reaches the coast and begins to spread precip along 
the north coast. With this system...16/00Z models are in reasonable 
agreement with the progression of the precip across the region on 
Sunday...primarily impacting areas near and north of I-80 and the 
best amounts over the higher terrain along the coast from the Eel 
River basin northward...and then inland along the west slope and 
crest of the Cascades and Sierra down to about the 
Stanislaus/Tuolumne river basins. As the s/wv trof moves 
inland...look for the system to form an upr low across northern NV 
on Monday and slow its progression to the east a bit. Best precip 
will be mainly over northern NV from about I-80 
northward...impacting the Humboldt River basin.

A transitory s/wv ridge will slide across the area late Monday into 
Tuesday...bringing dry conditions to much of the area with the next 
system rotating from offshore toward the northeast with the best 
forcing clipping the region as it makes its way over the Pacific 
Northwest. This will confine the best precip to coastal areas from 
about the Russian River basin northward. As the cold front drops 
south toward the I-80 corridor it will weaken with the better 
forcing to the north...and slow as the steering flow becomes more 
parallel to the boundary. There will be plenty of PW still available 
with a moisture plume advecting toward the west coast from the 
southwest toward the I-80 corridor. With little forcing...expect 
precip to be generally light on Wednesday.

Models start to show some discrepancies for the latter half of the 
week as the EC shows a more shallow upr trof offshore...making its 
way toward the coast quicker than what the GFS is indicating. The 
GFS digs the system southward a bit more...which results in an 
overall slower arrival of precip. For now...used WPC as the main 
influence with some slight inclusion of the EC and GFS.

Overall...the upcoming week will be cooler with opportunities for 
precip across northern areas. Definitely welcome considering how 
meager precip has been during recent Octobers.