Severe Thunderstorm Warning 1, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
315 PM PST Sat Feb 2 2019

.SYNOPSIS...
Series of Pacific storms will impact Northern California through
Tuesday. Periods of moderate to heavy precipitation with gusty
wind and a few thunderstorms are expected. Drier weather returns
by midweek.

&&

.DISCUSSION...
Frontal precip band has moved over the Sierra and Srn Cascades and
should wind down during the evening there. As expected, the partial
clearing behind the frontal band in the Valley filled in with low
clouds, and scattered light showers developed in the the Valley as a
vort max rotated Nwd around the offshore closed upper low. Later
this evening, after 8-10 pm or so, showers should become more
widespread over interior Norcal as the upper low moves onshore and
becomes an open wave. There will be some mid level WAA with this
open wave so snow levels won't drop too low (generally 4-5 kft), but
certainly lower than what we saw last nite and early this morning
at the onset of our shift. Colfax snow level profiler shows the
snow level just above 5 kft after a dip to around 4.5 kft with the
convective band that moved through this morning.

This afternoon's main convective band extends from the Mother
Lode into the San Joaquin valley where there was some clearing
today. For Norcal standards, quite a few lightning flashes/pulses/
strikes with this line. Meanwhile, the cloud cover put a damper
on surface-based convection over most of the area, but there are some
breaks in the area, especially W side of the Valley, so will
continue our thunder chances into this evening for now.

Norcal will be in between systems early Sun morning before the next
system, currently vcnty of 45N/140W approaches the coast on Sun
afternoon/evening and moves inland Sun nite. This will be a colder
storm with lowering snow levels to 2500-4000 feet overnight and
increasing showers during the afternoon and evening. Thunderstorm
potential looks lower on Sun than today, given the timing of the
approaching trof favoring the evening and overnite period.

The third storm from B.C. will be even colder, digging Swd along the
West Coast Mon, and moving inland over central CA on Tue. This will
result in additional precipitation for CWA with heavy mountain snow.
Snow levels will lower into the foothills Monday and possibly some
rain/snow mix in portions of the Northern Sac Valley Tue as snow
levels lower to near/below 1 kft. Five to 10 feet of new snow is
expected in the Sierra Nevada through Tue with local amounts up to
13 feet possible over the highest terrain. (Measuring the snow will
be easier using a yard stick rather than a foot ruler.) The cold,
deep low pressure system will result in strong large-scale ascent
and strong mid-level CAA which will steepen lapse rates. In
addition, with the cold mid level temps (-12 to -18 deg C) in the
dendritic (snow) growth zone, and favorable RH, forecast/research
studies have shown that snowfall rates of 1-4" per hour are
possible, especially over the high Sierra where orographics also
are a factor. Also, can't rule out the possibility of Valley
thunder as well, mainly on Mon. Needless to say, temps will be
trending downward, and it will feel like winter around Norcal
after a stretch of mild wx.    JHM

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Dry conditions expected across Interior NorCal on Wednesday as
system pushes into the Great Basin and exits the region. Below
normal morning lows expected Wednesday and Thursday, with
temperatures in the mid 20s to low 30s in the Central Valley.
Morning lows could be in the single digits to teens over the
highest peaks and mountain valleys and basins. Forecast guidance
indicates a cold system dropping down along the West Coast late
next week, which could bring Valley rain, and low elevation snow.
Stay tuned for details.

&&

.AVIATION...

Widespread MVFR with local IFR next 24 hours. Southeasterly
surface wind gusts 25-35 kts from KSMF southward in the Central
Valley thru about 18Z, becoming southerly 10-20 kts. Lighter
southerly winds north of KSMF. Southeasterly winds increasing
again after 06Z Sunday from KSCK southward.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Monday afternoon for Central
Sacramento Valley-Clear Lake/Southern Lake County-Mountains
Southwestern Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Shasta
Lake Area / Northern Shasta County-Western Plumas County/Lassen
Park.

Winter Storm Warning until 4 PM PST Tuesday for Burney Basin /
Eastern Shasta County-Motherlode-Mountains Southwestern Shasta
County to Northern Lake County-Northeast Foothills/Sacramento
Valley-Shasta Lake Area / Northern Shasta County-West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

Special Weather Statement
National Weather Service Sacramento CA
230 PM PST SAT FEB 2 2019

CAZ019-067-069-022330-
Northern San Joaquin Valley-Motherlode-West Slope Northern Sierra
Nevada-
230 PM PST SAT FEB 2 2019

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHWESTERN TUOLUMNE
COUNTY...

At 229 PM PST, radar indicated strong thunderstorms were located
along a line extending from Chinese Camp to near La Grange. Movement
was northeast at 20 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Sonora, Tuttletown, Keystone, Springfield, Chinese Camp, Phoenix
Lake-Cedar, Groveland-Big Oak Flat, Mono Vista, Columbia, Jamestown,
Groveland-Big Oak, Phoenix Lake-Cedar Ridge, East Sonora, Tuolumne
City, Soulsbyville and Twain Harte.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 3773 12031 3772 12034 3770 12033 3767 12036
      3768 12039 3766 12038 3765 12039 3782 12063
      3808 12038 3793 12009
TIME...MOT...LOC 2229Z 188DEG 18KT 3788 12044 3767 12040

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Special Weather Statement
National Weather Service Sacramento CA
314 PM PST SAT FEB 2 2019

CAZ016-030000-
Central Sacramento Valley-
314 PM PST SAT FEB 2 2019

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN COLUSA COUNTY...

At 313 PM PST, a strong thunderstorm was located over Colusa
National Wildlife, or 11 miles southeast of Maxwell, moving
northeast at 20 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
Colusa, Colusa National Wildlife and Williams.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 3903 12194 3904 12209 3926 12214 3936 12214
      3936 12194 3924 12195
TIME...MOT...LOC 2313Z 186DEG 18KT 3914 12206

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