July 12, 2018 – Well above normal temperatures next several days with hottest temperatures over the weekend. Monsoonal moisture will bring chances for showers and thunderstorms to the higher elevations today into next week.
Weak upper through that moved through the Pacific Northwest Wednesday has moved eastward into the northern Great Basin this morning. This should allow monsoon moisture over the southwest U.S to move at least a little farther up the Sierra today so Isolated thunderstorms remain in the forecast south of about Tahoe. Some high cloud cover will likely occur elsewhere. Daytime highs today will remain quite warm under upper level ridging. Overall airmass remains about the same but with high clouds and a slightly deeper marine layer there may be a drop of a degree or two.
As upper ridge pushes back to the northwest on Friday, monsoon moisture should make it up the Sierra a bit farther north. The west side of the forecast area may see a bit of action as well on Friday as a weak offshore low pivots a shortwave disturbance up the north state coastline which may generate a few showers or thunderstorms along the coast range.
Otherwise, cloud cover and a slight airmass cooling should bring a slight cool off for the end of the week but highs will still remain a few degrees above normal. Overall airmass warms over the weekend as high pressure strengthens over the west coast.
Highs by Sunday will reach or top 100 across most of the central valley with well above normal temperatures all areas. Heat risk indicators show heat advisory should be considered Saturday over the northern Sacramento valley and foothills with a still bigger consideration area on Sunday as daytime highs push to about 10 degrees above normal. Southeast to south flow aloft will continue to bring monsoon moisture up the coast so Sierra crest thunderstorms will remain in the forecast.
Extended discussion (Monday through Thursday)
Strong high pressure will maintain hot weather across the region next week. The northern Sierra Nevada will continue to see a slight chance for late-day showers and thunderstorms. Highs across warmest portions of the forecast area will be around 5-10 degrees above average.