Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 271610
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
810 AM PST Fri Feb 27 2015

.Synopsis...
A weather system will move into the area today, leading to cooler
and wetter weather into the weekend. The potential exists for snow
impacting some travel in the mountains above 3500 feet, and more
so above 6000 feet.

&&

.Discussion...
Precip expected to move into the area this afternoon as system
drops south into CA with snow beginning in the mountains after the
19-21z timeframe. Latest hires guidance still depicts convective
nature to showers with more widespread precip confined to the
mountains. Moisture fairly limited, esp in the valley. A few
thunderstorms cannot be ruled out in the valley and adjacent
foothills this afternoon/evening with marginal instability
developing and steepening lapse rates. Outside of these
showers/thunderstorms, some locations across the valley may remain
dry. Have cut back sky cover a bit this morning through early
afternoon as most of the valley remains mostly sunny. Rest of the
forecast remains on track and no major changes needed. CEO

.Previous Discussion...
An upper level trough is currently situated off the Washington
coast, with northwesterly flow persisting aloft across California.
A series of vorts has begun to move across portions of the area,
and mosaic radar imagery shows a few showers over the Great Basin
and far NW California. Across our forecast area however, primarily
clear skies and generally light winds continue.

The aforementioned trough will continue to shift southward through
the course of the day. Look for precipitation to begin filling in,
especially along the mountains starting around midday into the
afternoon and evening. The latest NMM/ARW runs continue to show an
unstable atmosphere this afternoon, and we`ve opted to expand the
"slight chance of thunderstorms" area across the Sacramento Valley
and adjacent Sierra foothills. Still believe accumulating small
hail to be the greatest convective threat, but can`t rule out a
brief funnel cloud either. Given the convective nature of today`s
precipitation, showers could be hit- or-miss especially across the
lower elevations.

The greatest overall impact with this system will likely be wintry
travel across the Sierra. Still expecting roughly 4-8" of snow
accumulation above 5500 ft this afternoon through Saturday, with
up to a foot at the highest elevations. Snow levels should begin
around 5500 ft, lowering to about 4000 ft by Saturday. Given the
high traffic volume across the Sierra on Fri/Sat, some spinouts,
slower travel, and chain controls should be expected.

The upper low shifts overhead Saturday, and moves south Saturday
night. Some northerly winds should begin to develop along the
northern CWA by Saturday afternoon. Often times this focuses
convection along the Coastal Range and the Sierra, with less for
the Valley. Regardless, showery precipitation should continue
through Saturday, and gradually diminish from north to south
Saturday evening and into Sunday.

Sunday currently looks dry across interior Northern California,
although some locally breezy north winds are likely. The next
system will be quick on its heels, with an elongated N-S vort
moving through the area Monday. This should be a drier system than
today`s, although some showers are possible especially over the
Sierra.

Dang

&&


.Extended Discussion (Tuesday through Friday)

Shower activity will continue into Tuesday but diminish by
Tuesday night. Snow levels will rise on Tuesday becoming
4000-5000 ft. Northerly winds will be breezy in the valley with
gusty downslope (easterly) winds along the Sierra on Tuesday as
the system tracks across our region. Ridging will dominate the
west coast again on Wednesday putting our CWA back into a drier
and warmer pattern with light winds through Friday. JBB


&&

.Aviation...

Cold front will move Swd over interior Norcal today bringing
locally breezy and unsettled wx today and into the weekend.
VFR conditions this morning...giving way to scattered showers and
isolated thunderstorms (-TSRAGS) and local MVFR/IFR conditions
mainly E side of Sac Vly and into Siernev Foothills this
afternoon. Showers or isold TRW moving SE 25 kts. Over higher
Siernev numerous showers developing this afternoon and evening
and lingering overnight with widespread MVFR/IFR conditions.
Showers likely redeveloping in the Valley on Sat along with
isolated thunderstorms (-TSRAGS). Freezing level 5000-6000 ft
today...lowering to around 3500 ft Saturday. Local S to SW wind
gusts up to 25 kts possible in the Valley and mtns.


&&

.STO Watches/Warnings/Advisories...
winter weather advisory from 1 pm this afternoon to 1 pm pst
saturday above 5500 feet in the west slope northern sierra
nevada...western plumas county/lassen park.

&&

$$







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