Forecaster's Discussion - Updated Daily

000
FXUS66 KSTO 182303
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
303 PM PST Sun Feb 18 2018


.SYNOPSIS...
A COLD WEATHER SYSTEM BRINGS BREEZY WINDS AND SNOW OVER THE
MOUNTAINS AND FOOTHILLS INTO MONDAY, IMPACTING TRAVEL. THIS WILL
BE FOLLOWED BY NEAR RECORD COLD TEMPERATURES WITH A POSSIBLE
WIDESPREAD FREEZE.

&&

.DISCUSSION...
SCATTERED SHOWERS ARE SPREADING ACROSS THE MOUNTAINS, WITH THE
HEAVIEST SHOWERS CURRENTLY OVER THE NORTHERN SIERRA NORTH OF
HIGHWAY 50. WEBCAMS ON I80 SHOW MODERATE TO HEAVY SNOW SHOWERS.
SNOW SHOWERS OVER THE SIERRA ARE EXPECTED TO BRING SLIPPERY ROADS
AND TRAVEL DELAYS. A WINTER WEATHER ADVISORY CONTINUES TO BE IN
EFFECT UNTIL 4 PM MONDAY. USE CAUTION IF TRAVELING IN THE
MOUNTAINS AND UPPER FOOTHILLS. A DUSTING OF SNOW WILL BE POSSIBLE
ACROSS THE FOOTHILLS OVERNIGHT INTO MONDAY. SNOW ACCUMULATIONS ARE
NOT EXPECTED TO BE IMPRESSIVE, BUT THIS HOLIDAY WEEKEND
TRADITIONALLY SEES A HIGH VOLUME OF TRAFFIC OVER THE MOUNTAINS AND
SNOW COULD CAUSE EXACERBATED IMPACTS.

WHAT WILL LIKELY BE THE COLDEST AIR OF THE WINTER SEASON WILL
BEGIN TO IMPACT PORTIONS OF THE REGION TONIGHT. FOR LOWER
ELEVATIONS, THE COLDEST TEMPERATURES TONIGHT WILL LIKELY BE ACROSS
THE NORTHERN VALLEY, WHERE SKIES CLEAR AND WINDS SLACKEN. SKIES
SHOULD CLEAR FURTHER MONDAY NIGHT INTO TUESDAY MORNING, AND
CURRENTLY APPEARS TO BE THE COLDEST NIGHT OF THIS EVENT.
WIDESPREAD FREEZE CONDITIONS MAY CONTINUE TUESDAY NIGHT. WIDESPREAD
FROST IS EXPECTED. AGRICULTURAL IMPACTS COULD BE SIGNIFICANT, DUE
TO AN EARLY BLOOM FROM UNUSUALLY MILD WEATHER IN RECENT WEEKS.
PEOPLE SHOULD BEGIN PLANNING NOW ON WAYS TO PROTECT SENSITIVE
PLANTS, OUTDOOR PETS, AND OUTDOOR PIPES.

ANOTHER SYSTEM WILL BRING LIGHT SNOW SHOWERS TO THE MOUNTAINS ON
WEDNESDAY. SNOW LEVELS WILL BE AROUND 1000 FEET, POSSIBLY LOWER,
BUT JUST A DUSTING OF SNOW IS EXPECTED.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)


A series of cold shortwave troughs will pass through NorCal for
the extended period. Models are more aligned today with timing and
placement. The first system arrives Wednesday night into Thursday
and will bring precip chances for both the Valley and higher
elevations. The best chances for Valley showers will be Thursday
afternoon when some weak instability builds in and the trough axis
swings through. With not a ton of moisture to work with, precip
totals should remain rather low. Low snow levels will be a
concern though as they will be 1000 to 2500 feet. Hazardous
Mountain travel will be possible Thursday lasting into Friday
morning.

A weak ridge builds in Friday into early Saturday with another
short wave trough passing just to our east on Saturday. This will
bring the chances for light showers mainly to the northern
Mountains. Another system arrives Sunday into Monday. The EC is
just a bit further to the west with it and is able to pull in
higher moisture levels but the GFS is drier. Cool temperatures
will remain in place for the period running 5-10 below normal to
start but will gradually warm a few degrees each day.

-CJM

&&

.AVIATION...


Generally VFR conditions are expected at the TAF sites the next 24
hours. SCT to BKN clouds between 5000 and 10000 feet can be
expected this afternoon rising to around 10000 feet overnight.
Scattered snow showers continue in the higher elevations through
15z Monday and MVFR/IFR conditions can be expected in any
showers. Breezy northerly winds 15-30 knots diminish to 5-11 knots
overnight.

-CJM


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 4 PM PST Monday for West Slope
Northern Sierra Nevada.

Freeze Warning from 2 AM Monday to 8 AM PST Wednesday for
Carquinez Strait and Delta-Central Sacramento Valley-Clear
Lake/Southern Lake County-Motherlode-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Shasta Lake Area / Northern Shasta County-
Southern Sacramento Valley.

&&

$$

NWS Sacramento, CA (STO) Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather