Flood and Hail in California, January 23, 2016

Area Forecast Discussion
National Weather Service Sacramento CA
336 AM PST SAT JAN 23 2016

.Synopsis...
A winter storm will continue to bring heavy mountain snow and
Valley showers and thunderstorms Saturday. Drier weather is
expected for most of next week.

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.Discussion...
A wintry weather system continues to make its way through Northern
California, with the main frontal band passing through the region
early this morning. Most of the precipitation came in the form of
a NCFR (Narrow Cold Frontal Rainband), which brought heavy rain
rates but only for a few moments. As of this writing, that band
has moved into the Sierra, where heavy snow has started to fall.
Looking upstream, convective showers in association with the upper
low have begun to move inland along the Northern Coast. Gusty
winds also continue, especially along the Northern Sacramento
Valley, where peak wind gusts of around 50 mph were reported.

The main forecast challenge for today will be the possibility for
convection this afternoon. All short-range models forecast a
respectable amount of instability this afternoon. The HRRR and
NMM in particular show a swath of 500-1000 J/kg CAPE across the
Sacramento Valley. Wind shear profiles look favorable for
potential rotation in storms. The biggest question is whether
we'll see enough clearing to realize those high CAPEs. At this
point, the Shasta County convective line looks like a fair bet for
development later today. If we are to see stronger storms
(including an isolated tornado), they would most likely form
somewhere between the Interstate 80 corridor north to Tehama
County.

Drier weather will begin to settle in Saturday night and early
Sunday. The latest models forecast a weak shortwave trough passing
through Northern California later Sunday into Monday which
previous model runs did not indicate. Adjusted the forecast
accordingly. High pressure ridge then builds into California late
Monday into Tuesday and Wednesday. Clearing skies and lighter
winds will likely promote Valley fog formation under the ridge.

Dang

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Mainly dry conditions expected Wednesday and Thursday under upper
level ridging over the western U.S. Daytime highs several degrees
above normal. Patchy valley fog is likely with stable conditions under
the ridge. Upper ridge begins to break down late Thursday for a
chance of light precipitation northern mountains. GFS is most
aggressive at breaking down the ridge bringing precipitation
threat to entire forecast area by Friday while GEM and ECMWF keep
most of forecast area dry under flattening ridge. All models in
better agreement by end of next week shifting upper ridging east
of the forecast area and allowing Pacific storm track back to the
west coast. Forecast confidence fairly high that a wet pattern
returns by next weekend.

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.AVIATION...

VFR with occasional MVFR ceilings and visibility in showers TAF
sites through about 06z Sunday. IFR ceilings and visibility in
showers over mountains next 24 hours with some improvement after
06z Sunday. Winds southerly 15 to 25 knots through 18z with
strongest winds northern Sacramento valley and surrounding
mountains gusting to 35 knots. After 18z...winds southerly to 15
knots.
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.STO Watches/Warnings/Advisories...
Winter Storm Warning until 4 PM PST this afternoon for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

Wind Advisory until 10 AM PST this morning for Central
Sacramento Valley-Clear Lake/Southern Lake County-Mountains
Southwestern Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley.

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