Debris Flow and Flood in California, March 1 to 3, 2018

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
250 AM PST Thu Mar 1 2018

.SYNOPSIS...A large area of low pressure will affect the
region through Saturday with several weather disturbances
moving across the forecast area. Periods of rain and snow
can be expected through Saturday before the low moves east
on Sunday.

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.DISCUSSION...Radar and satellite imagery show the first of
several bands of precipitation now moving into the Sierra and
across areas north of Kern County. There is a back edge to this
band of rain and snow now moving into western Merced and western
Fresno counties and it appears that lower elevations will see an
end to the rain until the next spoke of energy and precipitation
moves into the area from the Bay Area. Meanwhile over the Sierra
the moist southwest to westerly flow will continue to keep the
rain and snow going nearly continuously as the air is forced up
the slopes and condenses. A third band of rain is noted on
satellite and regional radars moving into the northern California
coast and the trajectory is to the southeast. This may well end up
in the Central California Interior later today. Snow levels at
this time look to be around 3500 feet based on surface
observations and the New Exchequer Dam S-band snow level radar.

For this storm system with the very cold parent low remaining off
the Oregon and Washington coast through Friday and models rotating
several troughs of energy southeast into California, the lower
elevations will see periods of precipitation with distinct lulls
between waves while the Sierra and foothills will have nearly
constant upslope precipitation between the waves of energy. Given
this, precipitation amounts will vary quite a bit from the lower
elevations such as the San Joaquin Valley to the Sierra. Both GFS
and NAM12 model storm total liquid precipitation targets the
Sierra with 4-6" of water from Sequoia Park north to Yosemite and
much lighter amounts over Kern County where the unfavorable
southwest to west flow keeps values as low as 0.25-0.50" through
Sunday. Of course above the freezing line, snow amounts up to
several feet are likely over the higher elevations of the Sierra,
especially north of Sequoia Park. The winter storm warning
continues through Saturday.

As for wind, it looks to be locally windy over the west side of
the San Joaquin Valley today with low pressure to the north and
a decent pressure gradient. I'm going to hold off on issuing a
wind advisory just now but will keep a close eye on speeds over
Merced and western Fresno Counties. Over the Kern County Desert
areas, today will be locally windy however based on high
resolution models, the strongest winds will occur on Friday and
wind advisories may be needed then.

By Sunday the system moves to the east and precipitation will come
to an end. Ridging and dry weather returns per the GFS from Monday
through Wednesday before another low pressure system is progged to
push into California Wednesday night and Thursday.

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.AVIATION...
Widespread mountain obscuring conditions over the Sierra Nevada.
Areas of MVFR and local IFR conditions in rain across the San
Joaquin Valley. Strong gusts over 50 KTS across the the Sierra crest
after 18z and 20-30 KTS in the North San Joaquin Valley including
KMCE, KMER until 03z Fri.

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.AIR QUALITY ISSUES...
None.

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.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...
Winter Storm Warning until 10 AM PST Saturday CAZ096-097.

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public...Dudley
avn/fw...MV
synopsis...Dudley

weather.gov/hanford