Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 181149

449 AM PDT Thu Sep 18 2014

Temperatures cooling to below normal today with a chance of
showers and thunderstorms. Warmer and drier weather returns for
the weekend.

Upper level trough will be moving inland today. Radar imagery overnight
has shown shower activity in Shasta County near I-5 and westward
to the NorCal coastline. At 4 am, most of the showers were west and
north of our CWA due to a dry slot moving into our region. On
water vapor imagery, moisture offshore is digging slightly
southward and should impact our region later today. Once the
trough moves inland, models are indicating increased instability
over NorCal which will result in a slight chance to chance of
showers and thunderstorms across much of our CWA. In the morning
and early afternoon hours, instability looks best over the Coastal
and Sierra mountains north of I-80 including the adjacent
foothills into the valley. The WRF model echoes this by showing
shower activity across Lake County northward along the coastal
range...across Tehama & Shasta counties...and from Chico &
Oroville eastward into the Sierra. By late afternoon into early
evening, instability continues along the Sierra and spreads
southward of I-80, however, the WRF shows showers diminishing in
areal coverage. So have stuck with the forecast of having isolated
showers/t-storms south of I-80 and scattered showers/t-storms
north of I-80 today with showers limited to higher terrain for

Daytime highs today will be cooler than normal. Our CWA will
generally range 5 to 15 degrees below average. This will translate to
valley highs in the upper 70s to low 80s with higher terrain
warming into the 60s and 70s. However, on Friday into the weekend,
temperatures will warm again to normal and above normal.

The King Fire is still likely to cause smoky conditions as it
doesn`t look like there is a high probability for heavy rain to
dampen this wildfire. With southwest to westerly winds this
morning, smoke will spread towards the Tahoe region again. On
Friday, winds should be northerly in the morning which will spread
smoke southward. (See Previous Discussion below)

Previous Discussion...The interesting thing for Thursday night and Friday
morning will be with the spread of the smoke from the King
Wildfire. Places in the southern motherlode that have had pretty
good air quality will have smoke spread over their area. The far
eastern sections of the Northern San Joaquin valley may also get
some smoke. The Sacramento region can also expect and increase in
smoke during that time period as well.

Saturday the low will shift over Southern California. Some
afternoon showers and isolated thunderstorms near the crest will
continue for areas south of Tahoe. The flow pattern will shift
again to onshore, upvalley and upslope. Temperatures will remain
near seasonal normals.


.Extended Discussion (Monday through Thursday)

For Monday into Tuesday, weak ridging develops over our CWA which
will maintain dry weather with daytime highs near to above normal.
The extended models (ECMWF, GFS, and GEM) are in good agreement
that another trough will dig southward and swing into NorCal
Wednesday and Thursday. Daytime highs should dip below normal
starting on Wednesday. Have increased pops and lowered
temperatures to account for this cooler, wetter pattern.



Mainly VFR conditions next 24 hours with showers possible over
Shasta County and Coastal Range and spreading SE over the
northern/Central Sac valley, northeast foothills, and Sierra by
this morning. Local SWerly sfc gusts up to 30 to 45 kts over
higher mountain peaks today, decreasing by this evening.


.STO Watches/Warnings/Advisories...

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