Area Forecast Discussion
Issued by NWS Sacramento, CA

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647
FXUS66 KSTO 162113
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
213 PM PDT Sun May 16 2021

.SYNOPSIS...
Shower and thunderstorm chances will continue into the evening
across the NorCal mountains, then drier weather is expected.
Slightly warmer temperatures are expected early this week before
another cool down begins mid-week with unsettled weather returning
for the end of the week.

&&

.DISCUSSION...
The low is currently centered over southeastern California with
wrap around moisture continuing. Winds aloft are from the
northeast but will become northerly by late afternoon. Currently
it looks like activity could reach the foothills but not the
valley as a result of the wind shift. Temperatures are trending a
lot warmer over the northern valley with similar temperatures
compared to yesterday over the southern areas. As the low moves
east tonight activity will diminish. The Delta breeze looks to
become stronger and we should have a slightly higher marine layer
than last night with winds gusting to up to 40 mph in the Delta
and around 25 mph around the Sacramento region. Low clouds will
have a chance of advecting into the Sacramento region by Monday
morning.

Monday will be dry other than a chance for some afternoon pop up
showers and thunderstorms near the crest from around Alpine county
southward. Temperatures will be slightly warmer for most areas
with slight cooling over the north end of the valley and
surrounding mountains. Moderate Delta breeze expected to continue
through the day and night.

Weak ridging on Tuesday will keep the area dry with some minor
cooling in the north to several degrees warmer in the valley
further south. A weaker Delta breeze during the daytime on Tuesday
will help to warm inland temperatures near the Delta. Moderate
Delta breeze will continue other than weakening a little during
the day on Tuesday.

Wednesday a low pressure area will approach the region during the
day. This will bring some synoptic cooling to the region. Delta
breeze looks to remain moderate. Earliest chances of some showers
will be over Shasta county during the evening with chances mainly
over the western slopes spreading further south late at night.

&&
.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

Ensemble guidance is in good agreement an area of low pressure is
forecast to impact the region during the extended forest period.
This low is expected to move south down the Pacific Northwest
coast bringing much cooler and somewhat unsettled weather to
California mid to late week. EOF cluster analysis indicates some
differences in the depth of the trough, however these differences
are minor in terms of expected impacts to interior Northern
California. Under this synoptic set-up, high temperatures are
forecast to be 5 to 10 degrees below average across the Valley and
up to 20 degrees below average for this time of year over the
higher elevations on Thursday. Also with these cool temperatures,
snow levels are expected to be below pass levels. We could see
several inches of snow over the southern Cascades and high Sierra
with this system. Also with the cold upper low over the region,
there will also at least be a chance of thunderstorms. Thereafter,
a gradual warming trend is forecast into the weekend into next
week as high pressure slowly builds in behind the departing low.

&&

.AVIATION...

Through early evening, isolated TRWs and scattered showers are
forecast to develop over Sierra from Wrn Plumas to Yosemite NP
with chance of localized MVFR/IFR conditions over the higher
elevations. Moderate Delta breeze through the night with gusts to
around 35 kts in the Delta and up to 25 kts further inland. A
chance of a stratus intrusion into the Valley Monday morning into
the Sacramento area with cigs between 1000 to 1500 ft deep.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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