Thermalito, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

330
FXUS66 KSTO 202024
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
124 PM PDT Sun Jul 20 2025

.DISCUSSION...

.SYNOPSIS...
Seasonable temperatures today, then cooldown begins tomorrow
across interior NorCal. Temperatures are forecast to be 10 to 15
degrees cooler from daily normals through at least Thursday. Off-
shore trough expected to linger through the week, introducing
isolated high elevation showers/t-storms Tuesday through Friday.
Breezy to gusty onshore winds to continue through the week as
well.

&&

.KEY MESSAGES...

*  Today:

 - Seasonable high temperatures across the region today
 - Green Fire up to 51% containment this afternoon; smoke plume
   less visible on GOES-18. Southerly winds in Redding will help
   to continue clear the sky out.
 - Breezy to gusty southerly winds expected this evening, especially
   in the vicinity of the Delta.

*  Monday:

 - Upper level low in the PacNW begins to retrograde; lowering our
   heights and introducing enhanced onshore flow to the area and
   isolated shower chances mainly in the higher elevations of the
   Sierra and Southern Cascades.
 - A few higher resolution models depict a narrow line of showers
   moving through the northern Sacramento Valley tomorrow morning.
   Frontal boundary may not have enough moisture to bring
   widespread showers, but a a 10-20% chance of a morning sprinkle
   or light shower will be possible.
- Confidence very low on frontal boundary producing rain
 - Temperatures begin to fall as trough continues to dominate our
   synoptic pattern. Highs are forecast to be roughly 10 degrees
   below July normals for most of the region.
 - Enhanced onshore flow will bring periods of breezy to gusty
   winds in the vicinity of the Delta. Around 40-60% chance of
   wind gusts reaching 35 mph in the Delta tomorrow evening as the
   Delta Breeze strengthens.

* Tuesday - Friday:

 - By Tuesday, off-shore low continues to bring breezy to gusty
   onshore winds in the afternoon and evening. High temperatures
   will continue to be below July normals by 10-15 degrees, with
   Tuesday looking to be the coolest.
 - Isolated high elevation mountains showers and t-storms will be
   possible. Main concern with any convection developing will be a
   potential lack of moisture. In any case, we added a mention of
   a possible shower or t-storm through Thursday into the
   forecast, with overall confidence on precipitation development
   remaining low.
- Better chances Thursday in the Sierra and Southern Cascades
 - Breezy onshore winds continue under this pattern through at
   least Friday. Upper level low projected by the ECMWF to remain
   offshore; which will continue to enhance cooling around
   NorCal.

* Long Term:
 - Cluster Analysis depicts upper level troughing may continue
   into next weekend. Heights may flatten slightly, reducing some
   of the cooling effects for the area.

-Wood

.Changes from previous forecast...
 - Added slight chances of a morning shower/sprinkle/virga for the
   northern Sacramento Valley for tomorrow.
 - Added slight chances of afternoon showers/t-storms in the
   higher elevations Tuesday - Thursday, although confidence on
   development is very low.

&&

.AVIATION...

Primarily VFR conditions expected next 24 hours across interior
NorCal, although some 5-10% chance of isolated -SHRA/-TSRA in RDD
vicinity 14z-18z Monday may introduce brief MVFR/IFR conditions.
West-southwest winds become breezy through the day, with late day
gusts 20-25 kts through the Delta and much of the Valley. Winds to
remain breezy overnight, with more widespread 20-25 kt gusts
returning after 12z.


&&

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

$$