Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 280555
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
955 PM PST Fri Feb 27 2015

.Synopsis...
A weather system will move across California this weekend, leading to
cooler and wetter weather. Snow will impact travel in the mountains
above 3500 feet, and more so above 5000 feet.

&&

.Discussion...
Active evening across portions of NorCal with thunderstorms
producing copious amounts of small hail over Glenn and Butte
counties during the afternoon and the foothill areas this evening.
Numerous reports of hail accumulations of several inches have been
received. Snow levels are currently around 5000 feet and will fall
to 4000 feet by morning. Have adjusted mountain precip/snow
amounts to align better with current radar trends and short range
HRRR model. As a result have extended winter weather advisory
down to 5000 feet and increased snow amounts...with 4-8 inches now
foretasted to 5000 feet including Blue Canyon along Interstate 80.
Given the convective nature of the precip would not be surprised
to see isolated amounts to a foot or more...but these won`t be
widespread enough to reach warning levels. Showers over Butte and
Yuba counties are foretasted to shift south and expand over
Sacramento and Placer counties after midnight as shown by HRRR.
Have updated forecast to increase precip chances and amounts over
the Sierra through noon Saturday.

.Previous Discussion...
Precip continues to be highly scattered in nature this afternoon
although is expanding in coverage over the past few hours. Latest
hires guidance still depicts convective nature to showers with
more widespread precip confined to the mountains. Moisture fairly
limited, esp in the valley. Showers will continue to be hit-or-
miss in the valley through Saturday with some locations staying
dry. Again, cannot rule out a thunderstorm or two this afternoon
and again on Saturday afternoon but threat remains relatively low
given lack of moisture and marginal instability. Snow levels are
around 6000 feet early this afternoon and will drop to near
3500-4000 feet on Saturday. Total accumulations of 4-8 inches
expected above 5500 feet with some locally higher totals along
highest elevations. Elevations below 5500 ft may see some light
accumulations but amounts will be limited. Saw a few accidents on
I-80 near pass levels earlier this morning with hardly any snow
falling so still expecting some travel headaches as showers get
going later this evening into tonight and weekend travel picks up.
Advisory remains intact and will continue until 1 pm Saturday at
which time it can be reevaluated by later shifts. Precip will
begin to taper off Saturday night as northerly winds develop
although a few snow showers may linger over the central Sierra
into early Sunday morning. Dry weather then briefly returns for
Sunday with clearing skies, some locally breezy north winds, and
temperatures in the mid 60s in the valley and 40s to 50s in the
mountains.

Next system quickly moves thru on its way to SoCal for Monday into
early Tuesday. Moisture is even less than current system with PWAT
values topping out around a quarter of an inch. Early estimates
for QPF totals range from a hundredth or two in the valley to
around a quarter inch in the mountains. Best chances for any
precip look to be across the Sierra again with snow levels around
4000 feet. Could see a couple of inches but not expecting major
impacts.

CEO

&&


.Extended Discussion (Tuesday through Friday)

Models trending drier for Tuesday as subsidence increases under
Northerly flow aloft. Dry weather with warmer temperatures expected
through the remainder of the week as upper level ridging off the
West Coast builds inland. High temperatures in the Central Valley
expected in the upper 60s to lower 70s with mostly 50s to 60s for
the mountains and foothills.

&&

.Aviation...

Upr low drops S ovr Intr NorCal nxt 24 hrs with areas MVFR/IFR
poss in shwrs...mnly omtns. Isold aftn/eve -tsra/tsrags poss again Sat.
SN lvls arnd 055 tngt lwrg to nr 035 Sat mrng. Lcl W-NWly sfc wnd
gsts to arnd 25 kts poss ovr hyr trrn tngt into Sat.


&&

.STO Watches/Warnings/Advisories...
winter weather advisory until 1 pm pst saturday above 5000 feet
in the west slope northern sierra nevada...western plumas
county/lassen park.

&&

$$






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