AGUS76 KRSA 151557
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
800 AM PST Fri Dec 15 2017

...WEAK SYSTEM DIVES SOUTHEAST TODAY INTO SAT...
...NEXT OPPORTUNITY FOR PRECIP ARRIVES LATER TUE INTO WED...

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

The upr ridge just off the west coast has been temporarily flattened 
by a s/wv trof making its way toward the Pacific Northwest. This 
system will then dive southeast with main precip impacts across 
northern and eastern areas from near the CA/OR border...across the 
east slopes of the northern/central Sierra...and over the northern 
two-thirds of NV. Latest WV imagery shows this system with its s/wv 
trof axis mainly from northwest BC south between 130W and 140W. The 
associated sfc cold front is poised to move inland across the 
Pacific Northwest before arching back southwest off the northern CA 
coast. Available moisture is not overly impressive with a very 
narrow band of approx 1.00-inch PW according to the latest Blended 
TPW imagery.

Overall...models are in decent agreement with the progression of 
this system across the area with some minor difference on how strong 
the southern piece of the s/wv trof is while attempting to form a 
cutoff low. The EC is the strongest and actually brings some very 
light precip to portions of southern CA. Other models are not as 
bullish with this idea. For now...left this area dry.

After this s/wv trof exits to the east and the upr low spins near 
the desert southwest...the upr ridge will once again rebuild across 
the far eastern Pacific for a dry Sunday into early next week.

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

Monday will be a dry day with ridge of high pressure over the 
eastern Pacific nudging into the region.  An upper level trough 
moves in later Tuesday into Wednesday bringing precipitation to 
Southern Oregon, Northern CA and Northern and Central Nevada. The 
00Z EC is a little quicker than the GFS in bringing the trough in.
The 00Z EC is a tad deeper than the 12Z. The 06Z GFS has the trough 
a little deeper than the 00Z run which would bring precip a little 
farther south.   The morning forecast uses a blend with uncertainty 
in the timing and the southern extent of the precipitation.


.HYDROLOGICAL CONDITIONS...

Mostly dry conditions across the area will keep rivers near baseflow 
conditions for the next 5 days. 


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

DRK/HSO/MI

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