Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 151557
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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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