Tornado and Winter Storm in California, February 26 to 28, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
948 AM PST Wed Feb 26 2014

.Synopsis...
A change to a wetter and colder weather pattern will continue
through at least the weekend. Accumulating mountain snow is expected
to cause travel difficulties later today into Thursday and from
another storm Friday into Saturday. Thunderstorms in the Valley
and Delta are possible later today and tonight, continuing through
early Thursday. Isolated severe storms are possible in the Delta
and Valley south of Red Bluff late tonight into Thursday.

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.Discussion...
A weak wave ahead of the main system is spreading some rain into
the area this morning. The Coastal Mountains/southern Cascades and
portions of the western Valley have seen 0.10-0.20 inches this
morning with a few hundredths on the eastern side. Heavier,
widespread rainfall is on the way as the main wave moves onshore
later this afternoon/evening. This will bring a strong diffluent
pattern providing large scale lift over the region.

Instability off-shore with this system is already generating quite
a bit of lightning over the ocean. Model soundings suggest stronger
convective showers and perhaps an isolated thunderstorm or two
could spread into the Delta and adjacent western Valley by mid to
late afternoon, so have introduced a slight chance of
thunderstorms in that area. Radar shows an area of somewhat heavier
rain currently moving through the Bay area and extending into
the Delta. More extensive moderate showers and thunderstorm
activity is possible by early evening across the Valley south of
Red Bluff as a frontal boundary moves through. This negatively
tilted system with southerly low level flow will provide strong
shear and instability as the cold core moves over the southern
portion of the forecast area tonight. The 12z NAM sounding for Sac
Exec Airport shows CAPE peaking over 400 j/kg at 6 am Thursday
morning. The fact that this is not a favorable time may be the
limiting factor for the development of severe storms. If there are
some breaks in cloud cover by later morning, though, this could
further destabilize the atmosphere and produce some stronger
thunderstorms. Weather spotters should closely monitor conditions
overnight into Thursday.

Little precipitation has reached the Sierra so far, but that will
change by this afternoon. Profilers show snow levels are currently
a little above 6500 feet but these should drop to around 6000
feet by this evening and around 5500 feet by early Thursday. A
Winter Weather Advisory continues with up to around a foot of snow
possible over higher elevations. Another storm with a little more
snow is possible Friday into Saturday, with somewhat lower snow
levels. EK

&&

.Extended Discussion (Sunday through Wednesday)

The main Low passes through northern CA by Sunday with a weak
ridge moving in behind. A lingering chance of showers may
continue Sunday over the Sierra, and to a lesser extent, in the
valley. The next system shows it's face Monday with a slight
increase in probability of precipitation, mainly over the northern
mountains. The broad eastern Pacific Low moves slightly closer to
the West Coast Tuesday/Wednesday, increase chances of
precipitation. The models have some timing issues
Tuesday/Wednesday with the relative flat/weak anticyclonic flow
and broad troughing offshore. However, the GFS/ECMWF/GEM all are
impressively in phase with a broad eastern Pacific trough. As a
result, we increased probability of precipitation to slightly
above climatology for Tue/Wed (day 7/8).    JClapp

&&

.Aviation...

Pac fntl sys movs thru nxt 24 hrs with wdsprd pcpn ovr NorCal. In
Cntrl Vly, genly VFR tda exc lcl MVFR/IFR bcmg wdsprd MVFR with areas
IFR aft 00z contg into Thu mrng. Isold TSRA poss in Cntrl Vly
mnly S of a KUKI-KCIC ln btwn 00z-18z Thu. Ovr Cstl and Shasta
mtns, wdsprd MVFR with lcl IFR/LIFR thru Thu mrng. Sn lvls abv
6000 ft lwrg to nr 5000 ft Thu mrng. For Wrn Plumas and Nrn
Siernev, lcl MVFR/IFR tda bcmg wdsprd IFR and areas LIFR tngt into
Thu. Sn lvls 6000 to 7000 ft lwrg to 5000 to 6000 ft Thu mrng.
S-SW sfc wnds 20 to 35 kts with gusts up to 50 kts ovr hyr mtn
trrn.

&&

.STO Watches/Warnings/Advisories...
winter weather advisory from 4 pm this afternoon to 4 pm pst
thursday above 6000 feet in the west slope northern sierra
nevada...western plumas county/lassen park.

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