Area Forecast Discussion
Issued by NWS Sacramento, CA

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364
FXUS66 KSTO 182249
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
349 PM PDT Mon Sep 18 2017


.SYNOPSIS...
Cooler weather this week with a chance of showers tomorrow night
into Friday.

&&

.DISCUSSION...
Satellite imagery shows cloudy skies across interior NorCal as a
frontal system continues to make its way southward across the
forecast area. Current temperatures are running 3 to 8 degrees
cooler than 24 hours ago, with Valley highs in the 80s. Breezy
winds have developed this afternoon as the system pushes through
and will continue into tonight, with strong gusts over higher
terrain. Below freezing temperatures in high mountain valleys are
possible along with patchy frost after midnight.

A better chance of showers will be possible further south into
NorCal Tuesday night into Thursday as a deep trough and associated
frontal system move in. The best chance of precipitation will
remain over the mountains and possibly over the northern
Sacramento valley. As cold air drives further south, snow levels
will drop to around 6500 feet so a few light snow showers could
be possible late Wednesday night into Friday. This might catch
off guard high elevation travelers and outdoor enthusiasts.

Temperatures will continue to trend downward through the forecast
period as synoptic cooling takes place. Daytime highs are
expected to be 10-20 below normal for this time of the year. The
coolest day of the week should be Thursday, with Valley highs in
the low to mid 70s and mid 40s to 60s for the mountains.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)
One more day of cool weather is expected on Friday as the upper
level trough moves east of the area. Temperatures across interior
NorCal will be about 5 degrees warmer than Thursday, though still
around 5-15 degrees below seasonal normals. Valley temperatures
will rise to the high 70s and the foothills and mountains will
range from the 40s at the higher elevations to the low 70s in the
foothills. Precipitation chances are limited to the higher central
Sierra elevations on Friday as the trough pushes east. Ridging
builds in Saturday through early next week allowing temperatures
to rise back to seasonal normals. Valley temperatures will be back
in the mid to high 80s by Sunday, a 15 degree temperature change
from Thursday. Most valley locations may reach the 90s again by
Monday due to the persistent northerly winds that will dominate in
the valley throughout the entire extended forecast period. HEC

&&

.AVIATION...
VFR conditions for valley terminals. Breezy conditions will
continue through 6z Tuesday with gusts up to 20 kts for the valley
and up to 30 through the delta and for Sierra ridgetops.

&&

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

$$



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