Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 151749
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
950 AM PST Mon Jan 15 2018

...WET PATTERN BEGINS TODAY WITH PERIODS OF PRECIP EXPECTED THROUGH
THE WEEK...

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

A change to a wetter pattern, especially across northern areas, is
expected to begin today as a NE Pacific trough breaks down the
western U.S. ridge as shifts it further to the east.  Expect precip
to be light and confined to the north coast through this afternoon
as weak warm advection followed by a weak cold front affect the
region.  Additional warm advection is expected later this afternoon
or evening, followed by a cold front reaching the north coast late
this evening.  Precip tonight is expected to spread across all of
northern CA and southern OR, with generally moderate amounts
expected over the north coast and light-to-moderate amounts
elsewhere.  Expect the system to push east with precip ending
quickly across the region on Tue.  Expect freezing levels generally
9000-10000 ft falling to 5000 to 9000 ft.

Expect ridging in between systems to provide dry conditions Tue
night into Wed morning.  Agreement among the models is pretty good
at this point regarding the next system expected to affect the area
Wed into Sat.  Expect higher totals with this system compared to the
first with decent isentropic lift ahead of a cold front and more
impressive upper-level dynamics as well.  Highest totals are
expected on the north coast, southern OR Cascades, in the Shasta
drainage, and across the northern half of the Sierra.  Precipitation
is overall expected to impact almost all of the forecast area.
Heaviest precip should be near or just ahead of the cold front Wed
evening into Wed night on the north coast and Thu into Thu evening
in the Sierra, and plenty of post-frontal showers are expected under
the accompanying trough.  Behind the cold front and as the upper
trough moves overhead, expect freezing levels to fall from an
initial 8000-10000 ft to 4000-5000 ft just behind the front, and
eventually to 3000-4000 ft later on Fri in post-frontal showers.
Models indicate yet another system moving into the north coast near
the end of the forecast window Sat night.


.HYDROLOGICAL CONDITIONS...

After calm conditions over the holiday weekend, rivers will be on
the rise this week as a series of storms moves across the region.
Expect the biggest rises to occur on rivers across northern CA,
especially those on the north coast. No forecast locations are
expected to approach monitor stage for the next 5 days.


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

KL/MI

$$



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