Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 161656

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
855 AM PST Mon Jan 16 2017



Dry conditions were the rule yesterday as high pressure built in
across the area.


Latest WV/IR imagery shows a positively tilted upr ridge extending
from near Hawaii northeast across northern CA to the northern
Rockies. This has resulted in dry north to northeast flow with PW
values running below seasonal normals near 0.33-inch or less. The
only exception is near the US/Mexico border where values are closer
to normal just over 0.50-inch. A deep moisture plume stretching from
well back over the lower latitudes of the western Pacific is
advecting east-northeast and is approaching the Vancouver Island
area this morning. This will be the initial focus of the heavier
precip through Monday with dry conditions across CA and NV with the
upr ridge hanging on strong.

Today will be the last dry day across the region this week as a
series of storms affects CA and NV through the upcoming weekend. A
s/wv trof moving toward the coast near the US/Canada border will
begin to sag the moisture plume southward early on Tuesday with
light precip commencing near the CA/OR border during the afternoon
hours. A deepening s/wv trof moving from the central Pacific toward
the coastal waters on Wednesday will spread precip across the
majority of the region for Day 2. The 16/00Z EC and GFS...along with
the 16/06Z GFS are in good agreement with the timing and trajectory
of this system...which is just a tad faster than previous thinking.
Adjustments were made accordingly as compared to the forecast issued
yesterday afternoon. Heaviest precip will begin to spread along the
north coast during the afternoon hours on Wednesday before spreading
across the rest of northern CA and down along the coast between the
Santa Cruz mountains and the Big Sur coast between 19/00Z and
19/06Z. The s/wv trof axis will move inland early Thursday morning
and this will spread precip down across the southern Sierra toward
the Point Conception area as the moisture plume erodes somewhat and
continues to sink south...intersecting the coast between the LA
basin and San Diego. Precip in general will be on the decrease on
Thursday with scattered showers focused over the higher terrain.
Freezing levels will range from 7000-feet in the north to 10000-feet
in the south early on in the event...to 4000-feet in the north to
6500-feet in the south by the time the cold front clears the region.

The next system is right on the heels of the first...spreading
precip to the north coast during the evening hours on Thursday. This
is also slightly faster than yesterday/s thinking by about 6 hours.
A deep upr low will move toward the northeast Pacific with an
impressive sfc low down to near 970-mb. The EC is actually even a
little deeper. This should kick up a tightening MSLP gradient with
increasing southerly winds at the sfc veering to southwest or west
at 700-mb. Also...the nose of a fairly impressive slightly anti-
cyclonic upr jet reaches near the central CA coast. So...although
the deepest moisture in the plume associated with this system does
not reach the coast...the favorable dynamics and orographic
enhancement should take full advantage of the PW just below 1.00-
inch reaching the coast. Precip with this system will once again
spread across the majority of the area as the s/wv trof digs toward
southern CA later on Fri. Freezing levels will begin and end lower
with this system as compared to the first. Up north they will start
around 4000-feet with 6000-feet down south...and wrapping up close
to 2500-feet north and 5500-feet south.

Precip will once again turn more scattered and lighter...focused
over the higher terrain early on Saturday as the s/wv trof moves
inland and the moisture plume sinks south of the area. However...the
beginning of the next s/wv trof rotating toward the northeast
Pacific will spin up another sfc low (this one a bit farther south
just off the north coast) before riding up toward the Pacific
Northwest coast. Precip will just begin spreading across the north
coast with this system at the end of Day 6.


Dry conditions are allowing rivers to slowly recede from the high
flows last week.

On the Upper Sacramento River, overflow into the the Butte Basin at
Moulton Weir ended overnight.  Renewed overflow is expected to begin
late Thursday night. Overflow into the Sutter Bypass at the Colusa
Weir and Tisdale Weir is expected for the next 5 days. Overflow in
the Yolo Bypas at Fremont Weir is also expected for the next five
days.  The Sacramento Weir also continues to flow.

The Lower Sacramento is expected to recede slowly over the next few
days.  Flood stage exceedance in the Yolo Bypass at Lisbon is
expected to last until Tuesday morning.

Cosumnes River flows continue to recede. The peak flow on the San
Joaquin River appears to be near Patterson this morning.  Slow rises
are to be expected over the next several days on the Lower San
Joaquin River. Vernalis stages could rise another 2 feet over the
next week depending on reservoir releases and future storm runoff.

Expect additional rises throughout the region with the storm systems
arriving Wednesday through Friday.

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



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