Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Wed Jan 17 2018

...INCOMING SYSTEM ARRIVES TONIGHT LASTING THROUGH FRIDAY...
...ANOTHER SYSTEM OVER NORTH SUNDAY INTO MONDAY...

.METEOROLOGICAL CONDITIONS (SHORT TERM: WED AM - SAT AM)...

WV/IR imagery shows a positively tilted upr ridge situated across
the region this morning...extending from near 25N/127W toward the
north-northeast. Offshore...a vertically stacked well-defined system
is spinning toward the northeast Pacific with its center near
45N/138W. The associated warm front brushed the north coast last
night on its way toward the Pacific Northwest...where it currently
crossing the OR/WA border. The cold front...which is starting to
show some enhancement...extends from along 130W west of the OR coast
before arching back southwest south of 40N. Blended TPW imagery
shows a narrow plume of moisture entrained just ahead of the cold
front with values hovering right around the 1.00-inch mark.

Models continue to be in reasonable agreement with the overall
progression of the system and the timing of the precip across the
region. If anything...the latest models are just a tad slower than
the previous forecast...and this was the primary change for today.
Precip will reach the north coast this evening as the moisture plume
sags south from the Pacific Northwest to south of the CA/OR border
with nearly 1.00-inch. Initially...the overall flow is parallel to
the boundary...leading to confidence the slower solutions are the
way to go. This will keep precip heaviest along the north coast into
tomorrow morning...before eventually shifting down to the I-80
corridor by the afternoon hours as the overall s/wv trof moves
toward the coastal waters...pushing the cold front inland across
northwest CA during the evening hours. This will move the heaviest
precip onto the west slopes of the northern and central Sierra with
decent upslope conditions interacting with the moisture plume and
the approaching cold front.

For Friday...precip will push across central CA inland over the
state of NV...as the positively tilted s/wv trof moves inland across
the region. There may be a slight uptick in precip along the north
coast as the core of the s/wv trof passes by late Thursday into
early Friday.

Freezing levels this morning are fairly high with the lowest in a
stripe from northwest to southeast across the CA/OR border area down
over northern and eastern NV...near 9000-feet. Elsewhere...freezing
levels are at or above 10000-feet. The cold front is fairly potent
and there is a rather cool airmass behind the boundary. By late
Friday...freezing levels will be down near 2500-feet near the CA/OR
border to 3500-feet along the I-80 corridor down through central
CA...and down between 4000- and 5000-feet for southern CA.


.METEOROLOGICAL CONDITIONS (LONG TERM: SAT AM - TUE AM)...

Lingering showers possible over Eastern Nevada and over the north
slope of the Srn CA mountains on Saturday as upper level trough
moves SE into Nevada and on into the four corners regions. Light
precip is also possible along the far NW CA coast on Saturday.
Decreased amounts along the NW CA coast for Saturday into Sunday
morning with slower timing of the next system.  Moderate to Heavy
precip may move onto the Northern Ca coast on Sunday afternoon and
spread south and east Sunday night into early Monday. 12Z GFS is
weaker with the front and lighter with the PW plume which lead to
lower QPF amounts than 06Z run. 06Z and 12Z GFS bring some weak
waves through Monday for some showers possible over Northern and
Central CA, especially over the Sierra and Nevada. Although the EC
is drier and diminishes precip Monday night.  The forecast leans
more towards the GFS with lingering showers Monday afternoon into
night. Freezing levels around 3500-5500 ft on Sunday rising to
around 4000-65000 ft on Monday.

.HYDROLOGICAL CONDITIONS...

No locations are forecast to exceed monitor stage over the next 5
days. Within this time period, rivers in the north coastal region
and Klamath watershed will see increases resulting in the later part
of this time window due to the forecasted precipitation. More
information is provided on the CNRFC website at
http://www.cnrfc.noaa.gov

DRK/HSO/BMM

$$



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