Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 211659

959 AM PDT Mon Jul 21 2014

An upper level disturbance combines with an eastern Pacific
trough over northern California today with morning showers and
the greatest probability for thunderstorms over the northern
mountains. Lingering thunderstorms over mountains Tuesday, then
expect a warming trend Wednesday through the weekend.


.Short Term Discussion (Today through Wednesday)...
A southwest-northeast line of clouds persists across our CWA this
morning. On radar, this band is currently situated from Southern
Lake County through Arbuckle - Yuba City and up to Downieville in
the Sierra. Although there could be sprinkles in the valley
associated with this band, observations seem to indicate that any
measurable light precipitation is likely occurring over the higher
terrain. The band is moving slowly northward and will be impacting
the Northern Sacramento Valley & surrounding terrain later today.
The cloud cover will knock daytime highs down for Redding & Red
Bluff into the low 90s compared to yesterday when the region was
in the mid to upper 90s. As we get into the warmer part of the
day, instability could spark some isolated showers/thunderstorms
in our Northern CWA.

Previous Discussion...An upper wave with the monsoonal moisture
continues to spread northward over the region today while an
eastern Pacific trough pushes southeast into Oregon. The
deformation zone stretching from SE Oregon to NW California acts
as the battle ground between the two systems. A swath of light
showers has existed virtually all night from the Delta to Plumas
county and Lake Tahoe with only a slight drift northward.

The swath of light showers will likely continue to drift
northward this morning and become more unstable with sunshine in
the mix. By this afternoon, isolated to scattered showers and/or
thunderstorms should form over the northern portion of the
forecast area from Sierra/Plumas to Tehama/Shasta counties.
Redding and Red Bluff areas have the potential to see some
isolated shower/thunderstorm activity. The increased cloud cover
for at least part of the day will likely keep temperatures cool.

The low will deepen along the coast on Tuesday and may continue to
bring afternoon thunderstorms to the northern mountain areas as a
weak disturbance moves through the region from the southwest.
Good onshore flow will continue the next several days and
temperatures will be below normal for this time of year.

The trough will begin to move into the Pacific Northwest on
Wednesday. Skies should be clearing and thunderstorm activity
should be focused more north of the area and into Oregon.
Temperatures should warm a little but still be below seasonal
normals.     JClapp

.Extended Discussion (Friday through Monday)

Upper trough forecast to move through the PacNW early Thursday
with southern portions of the trough extending into NorCal. Main
impact appears to be minor synoptic cooling with an increased
onshore flow. The SW US high is then forecast to gradually build
northwestward back into NorCal for a warming trend. Triple digit
heat appears to return to portions of the Central Valley by Friday
with additional warming into the weekend. Will need to watch for
the potential of monsoonal moisture to make its way into forecast
area late in the period. But for now, we will keep the forecast
dry.    JClapp - part deux



General VFR conditions with a narrow band of mid level clouds and
light rain showers currently located from KSTS to southern Lake
County to KBAB and up to Downieville in the Sierra. This will
continue to drift northward into the northern Sacramento Valley
by around 22z with iso TSRA developing there and the adjacent
mountains, sct TSRA eastern Shasta Cty. Iso TSRA also possible
along and east of the Sierra crest 18-24z. Lcl SW gusts to around
20 kts possible over ridges... 30 kt through the Delta. EK


.STO Watches/Warnings/Advisories...

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