Flash Flood and Flooding in California, January 12, 2017

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
455 AM PST Thu Jan 12 2017

.SYNOPSIS...A cold storm system will bring rain and mountain
snow to the central California interior into tonight along with a
slight chance of afternoon and early evening thunderstorms in the
San Joaquin Valley. Showers and higher elevation snow showers will
linger over the foothills, mountains and desert through Friday.
Dry weather will prevail Saturday through Martin Luther King Jr
day with areas of night and morning fog in the San Joaquin Valley.

 &&

.DISCUSSION...The caboose storm in a train of storms lately will
bring another round of wet weather to the central California
interior during the next 24 hours. This is a much colder storm
than its predecessors and it will bring wintry weather to
elevations as low as 3500 feet by this evening. The storm is
currently centered just offshore Northern California. A
southwesterly flow aloft out ahead of this storm is bringing
numerous showers over the northern half of our cwa early this
morning. These showers are ahead of a cold front that is going
to march eastward through the central California interior later
this morning into this afternoon. In the post frontal environment,
the atmosphere will become convectively unstable across at least
the western third of the San Joaquin Valley this afternoon with
widely scattered showers and isolated thunderstorms, some with
small hail. Meanwhile, steadier precipitation will likely continue
over the mountains into this evening. The air will become cold
enough for accumulating snow over the Kern County mountain passes
by early this evening. Farther north, a few locations in the
Sierra foothills above 3500 feet could end up with a light dusting
of snow after dusk. Meanwhile, this storm will bring heavy snow
to the higher elevations. Up to a foot of new snow could fall
in the Sierra above 8,000 feet by late tonight. Although QPF with
this storm will generally be lighter than the past few storms,
additional rainfall in the foothills and the valley will keep the
threat of localized flooding pretty high through this evening.
Many streams and creeks are running high with fast flows, so it
would not take much additional rain to bring them out of their
banks. We will be issuing a small stream flood advisory for the
Sierra foothills and an urban and small stream flood advisory
for the entire San Joaquin Valley shortly, effective through
8 pm and 4 pm, respectively.

In the broader picture, the models agree in bringing this cold
storm system southward down the California coast during the next
48 hours. Once this storm gets just south of Point Conception
Friday afternoon, the only lingering showers in our cwa will be
confined to the mountains and desert.  There may be some residual
clouds Friday night in the Tulare County foothills, the south end
of the San Joaquin valley and the north facing slopes of the
Tehachapi mountains while the remainder of the central California
interior clears out. Where skies are clear in the San Joaquin
Valley, fog is sure to form and become rather dense in some areas by
daybreak Saturday. Fog will likely become more extensive each night
in the San Joaquin Valley later this weekend through early next
week.

Otherwise, an upper level ridge of high pressure will gradually
build into central California this weekend and remain in control
through Tuesday. This will give the cwa its longest respite from wet
weather so far this year. (Of note, 8 of the past 11 days have seen
precipitation.)  As mentioned earlier, night and morning fog will be
commonplace in the San Joaquin Valley during this time and
undoubtedly cause travel woes for many motorists.

The longer range models are coming into better agreement now
that another atmospheric river will set up over northern California
during the middle of next week. This AR is forecast to shift
southward into central California by next Thursday. We've raised
POPs accordingly during this period now that our confidence has
increased and the models are more clear on the evolution of the
overall pattern in the 5 to 7 day period.

Temperature-wise, we can expect chillier nights than we've been
accustomed to lately with seasonably cool afternoons through the
weekend. Temperatures will trend milder by the middle of next week,
especially at night, thanks to a southerly flow aloft and an
increase in cloudiness.

&&

.AVIATION...
IFR conditions will prevail over the higher elevations of the
Sierra during the next 24 hours with precipitation and mountain
obscurations. MVFR ceilings with local IFR in precipitation can
be expected in the Sierra foothills and along the west facing slopes
of the Tehachapi mountains through 06z Friday. Local MVFR conditions
in scattered showers in the San Joaquin Valley.  VFR conditions can
be expected elsewhere across the central California interior during
the next 24 hours.

&&

.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 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 PM PST this evening CAZ096-097.

Winter Weather Advisory until 10 AM PST Friday CAZ095.

&&

public...Durfee
avn/fw...Andersen
synopsis...Durfee

weather.gov/hanford