000
FXUS66 KSTO 211016
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
316 AM PDT Fri Sep 21 2018


.SYNOPSIS...
Continued warm with improving humidity levels with return of onshore
flow today. Cooling trend continues through the weekend with
locally breezy winds over the Sierra. Warming above normal next
week with breezy north winds and drying on Monday. No
precipitation expected over interior Norcal through the extended
period.

&&

.DISCUSSION...
Winds a little lighter over the northern Sacramento valley and
over the coast range now that northerly surface gradient has
relaxed. Surface winds should shift to mainly onshore today as the
upper ridge over the west coast slips inland this afternoon. By
this evening the upper ridge axis should be over the Great Basin
but daytime highs today should still come in about the same as
yesterday. RH values should creep up a bit today thanks to the
more onshore flow. A low pressure system moving out the the Gulf
of Alaska is predicted to move into the Pacific Northwest on
Saturday. Main impact of this system will be a drop in daytime
temperatures over the weekend and breezy winds over the higher
Sierra elevations. Any precipitation should remain well north of
the forecast area with just a few clouds expected over the
northern most zones. Just a bit more cooling is expected on Sunday
as the upper trough axis shifts into the northern Great Basin.
Breezy southwest winds will continue over the Sierra. Breezy north
winds will return in the wake of trough on Monday bringing drying
again especially over the northern zones and down the coast
range. These breezy north winds and a several degree warm up will
likely increase fire danger. Highs on Monday will likely climb to
a few to several degrees above normal as high pressure aloft
begins building in over the west coast.

&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

The highly amplified ridge over the eastern Pacific will likely
build into California on Tuesday, with strong subsidence remaining
over Northern CA through midweek. NAEFS ensemble analysis suggests
this system will bring warmer than normal temperatures, but isn`t
particularly anomalous for this time of year. Current blended
guidance suggests temperatures will be in the 90s across the
Valley Tuesday through Thursday, with 70s to 80s over the
mountains.

The closed upper low associated with this Rex Block will very
slowly approach the West Coast. Current guidance suggests that
this low will move inland late next week...but model performance
of these closed lows is notoriously poor in the medium-range.

Dang

&&

.AVIATION...

Mainly VFR conditions the next 24 hours, except local MVFR
conditions due to smoke near the Delta Fire in Shasta County.
Winds will remain below 10 kt across Valley TAF sites. Local gusts
up to 20 kt near the Delta this afternoon and tonight.

Dang

&&

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

$$