Heavy Snow in California, December 15 to 16, 2016

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
517 AM PST Thu Dec 15 2016

.SYNOPSIS...
A strong storm system will move across Central CA today through
Friday. Heavy rain and higher elevation snow along with gusty
winds will accompany the storm as it passes. Temperatures will
lower to below normal by the end of the week and into the weekend.

&&

.DISCUSSION...
The anticipated rain and snow event for our area is nearing our
doorstep as mid and high level moisture streams overhead in
advance of approaching Pacific low pressure. Radar returns
tracking northeast across central California are mainly moist mid
level clouds with some virga, though light precipitation could be
intersecting the higher terrain. More significant radar echoes are
still well north of us, over northern California.

Short term high-res models increase the moisture plume overhead
and show some precipitation beginning across our area by later
this morning, most notably over the Sierra zones. The precipitation
area to our north, meanwhile slides southward into our region by
early this afternoon. Precipitation is progged to continue into
tonight before the colder and drier air sweeps in and ends precip
from the north through the early morning hours. QPF with this
event continues to look impressive as NAEFS pwat guidance shows
the plume increasing to 1-1.25 inches as it slides slowly
southward across the area. This is as much as 3-5 standard
deviations above CFSR climatology. In this west to southwest flow
in advance of the approaching cold system, snow levels will remain
generally above 8000 ft, leaving much of the precip falling as
rain. But above 8000 ft, snow accumulations of 2-4 feet are
expected through Friday morning with as much as 6 ft at the
highest elevations. A Winter Storm Warning for this heavy
snowfall and strong winds accompanying the storm is in effect for
the Sierra above 8000 ft through Friday morning.

With several inches of rain expected below 8000 ft, Flash Flood
Watches are in effect for the foothills and mountain terrain below
8000 ft later this morning through Friday afternoon. Recent burn
scars will be of particular concern, though mud and rock slides
will be possible in any vulnerable steep terrain. The anticipated
rainfall has also caused the forecast for the Merced River at
Pohono in Yosemite to go above flood stage this evening and a
Flood Warning is in effect there.

1/2 inch to over an inch of rain is forecast for the San Joaquin
Valley and this could lead to nuisance flooding there through
Friday afternoon as well. Lesser amounts are expected in the
desert zones but they could also see some localized street
flooding during the event.

As the cold air moves in Friday, snow levels will quickly drop to
below 3000 ft. By this time, models show precipitation rapidly
ending so little snow accumulation is expected during this phase
of the event. Some lingering upslope precipitation in the Kern
County mountains could however produce a dusting of snow affecting
the passes there, but there is little confidence in significant
impacts with this lingering light precip.

Southerly Winds will increase as the storm approaches and then
become gusty from the north with the passing frontal system
Friday. There may be some brief local gusts around 30 mph in the
Valley and near 50 mph in some of the wind prone Kern County
mountain and desert areas, but currently widespread strong winds
are not anticipated.

Colder air with the system will drop temperatures below climo for
early next week with some early morning lows dipping below
freezing in the San Joaquin Valley Sunday and Monday.

&&

.AVIATION...
The San Joaquin Valley...VFR conditions through 18z today. the
chances of rain will increase after 18z today with a good chance of
MVFR conditions by 21z today. a slight chance of IFR conditions in
heavy precipitation may develop between 21z today and 03z tonight.

The Southern Sierra Foothills...VFR conditions through 18z today.
the chances of rain will increase after 18z today with a good chance
of MVFR conditions by 21z today along with a chance of IFR
conditions in heavier precipitation between 21z today and 03z
tonight.

The Central and Southern Sierra Nevada...MVFR conditions this
morning will give way to widespread IFR conditions in rain and snow
along with mountain obscuring ceilings after 18z today.

The Tehachapi Mountains...VFR conditions will prevail through 22z
today. MVFR conditions becoming more widespread after 22z today with
local mountain obscuring IFR conditions.

The Kern County Desert...VFR conditions will prevail for the next 24
hours. strong surface winds may develop toward friday morning.

&&

.AIR QUALITY ISSUES...
None.

&&

.CERTAINTY...

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

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...
Flash Flood Watch from 10 AM PST this morning through Friday
afternoon CAZ093>097.

Winter Storm Warning from 10 AM this morning to 10 AM PST Friday
ABOVE 8000 FEET FOR THE CAZ096-097.

Flood Watch from 10 AM PST this morning through Friday afternoon
CAZ089>092.

&&

public...JEB
avn/fw...Molina
synopsis...JEB

weather.gov/hanford