Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 201600

900 AM PDT Mon Oct 20 2014

Frontal system will provide cooler temperatures and precipitation
chances from this morning through tonight. Thunderstorms expected
this afternoon/evening, especially the Sacramento Valley. Another
storm system will cause shower chances mainly for northern areas
from Wednesday into the weekend.


.Updated Discussion...
Light rain has entered western Shasta and Tehama counties this
morning. Redding has had some light rain in the area, but not
quite to the airport yet. This front is a fairly slow mover.
Tracking the back edge of the frontal band, it is moving at about
15 mph. So based on the front edge of the radar returns, rain
should begin by 1000 for Chico and probably not until around noon
for the Sacramento area. The front is weakening as it moves
inland, so not much rain is expected.

Spotters in northern Sac Valley and adjacent foohills...keep your
eyes peeled, please.

As the front tracks eastward, the northern Sacramento will move
into the more unstable post-frontal air. The cold core portion of
the Low is showing some enhanced convection near and just inside
of 130W off NW CA. Skies should clear out across the northern Sac
Valley by early afternoon. BUFKIT NAM shows CAPE of 200-300 by
late afternoon and over 800 in the evening, while the HRRR shows
between 200-600 J/kg. The BUFKIT soundings even look to be
underestimating the max heating surface temperature of 17C. Our
forecast has 21C and the NAM CAPE would be significantly higher
with an adjusted sounding.


.Extended Discussion (Friday through Monday)
The next main weather impact will be a large low that develops in
the Gulf of Alaska by Wednesday and impacts our region into the
weekend. Rain chances should nudge into the Coastal Range late
Wednesday night with light rain that will spread farther inland at
times for the rest of the week. For Thursday, rain chances will
stay generally north of Interstate 80. Main change from previous
forecasts is that the models are in better agreement as to our wet
weather outlook for the end of the week. From Friday into
Saturday, that low in the Gulf of Alaska will dig southward and
move into the west coast which should spread chances of rain
across all of our CWA into the San Joaquin valley so have
increased PoPs to reflect this. This trough will push eastward on
Sunday and Monday. There will still be lingering chances of rain,
but they will be diminished in areal coverage and be limited to
areas north of I-80 and mainly across higher terrain. Daytime
highs in the extended period will be fairly consistent at near
seasonal to about 5 degrees below normal. JBB



Generally VFR conditions today with lowering clouds and stronger
southerly winds as a cold front moves through the area today.
Precipitation and lower clouds over the coastal mountains will
spread inland extending over the northern Sacramento Valley by
around 15 z, bringing local MVFR conditions there. MVFR
conditions with local IFR are possible over the Mountains. ISOLD
TSRA possible this afternoon and evening. EK


.STO Watches/Warnings/Advisories...

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