July 23, 2020 – Slightly below normal temperatures continue, trending a little above normal by Sunday. A few late day thunderstorms are possible over the Sierra Crest south of I-80. Southwest breezes continue near the Delta with periods of breezy conditions spreading into the Valley.
Discussion
The upper level low which has brought cooler temperatures and mountain thunderstorms in recent days is now centered over the northern San Joaquin Valley. This will gradually shift to the southeast before opening up into a wave later today. Additional shortwaves passing through the Pacific Northwest will maintian the general upper level trough pattern over the West through Friday. The 4-Corners ridge will begin expanding westward bringing some gradual warming for the weekend, though a weak negative tilt trough along the coast will limit this and continue some weak, cooling onshore flow.
With the low shifting southeast, the potential for mountain thunderstorms this afternoon and evening will be limited to the higher mountains (+6500 feet) of the Sierra south of I-80. This pattern continues into the weekend, with dry weather elsewhere. Hikers and campers in the area should continue to exercise caution late in the day.
Highs are forecast in the 80s in the Delta this afternoon, low 90s in the southern Sacramento and northern San Joaquin valleys, and mid to upper 90s in the northern Sacramento Valley. Delta flow increases tonight and Friday, bringing a few degrees of cooling into Delta influenced areas, while locations elsewhere see a little bit more warming. Much of the Valley should be in the 90s through the weekend, typical weather for this time of year.
Redding is forecast to reach 100 Friday, beginning a new streak of triple digit highs that ended at 13 on Wednesday. Redding is forecast to continue low triple digits through the weekend into next week. Of course, 100 is the normal high for this time of year there, so this is not really out of the ordinary.
Extended Discussion (Monday through Thursday)
Dry weather and near to slightly above average temperatures expected next week. Weak troughing on Monday is taken over by a longer wave trough which moves in from the PacNW by mid-week. Temperatures look to range anywhere from average to just above average through the work week. Triple digit temperatures will continue in the northern Sac Valley early next week, with other Valley locations in the mid to upper 90s. Lows range widely from the Northern and Central Valley due to the marine and Delta influenced areas cooling off much more each night (in the upper 60s and low 70s in the north, to the upper 50s to mid 60s in the Central Valley).