July 14, 2018 – Heat Advisory from noon Sunday to 8 pm Tuesday. Hot temperatures this weekend and into early next week. Slight chance of thunderstorms continues over the higher elevations this weekend.
Monsoon moisture and instability continue to work slowly northward in upper level southerly flow. Some valley locations received some light rainfall earlier this evening and a lightning flash or two was even reported east of Chico. Radar is now showing some light echos north of about the Chico area and models indicate that this shower activity should move north of the CWA by sunrise.
Still can not rule out a threat of showers over the northern mountains all together today. Southeast flow aloft could still bring isolated showers over the northern Sierra crest similar to yesterday. Daytime temperatures will be on the rise today thanks to less cloud cover and a warming airmass. Daytime highs are likely to top the century mark again in the northern Sacramento valley.
A weak upper low off the northern California coast today is forecast to move into the Pacific Northwest on Sunday. This will produce enough instability for a thunderstorm threat over the northern mountains in the afternoon. Light upper level flow and model instability indicate a threat of afternoon thunderstorms just about anywhere along the Sierra Crest Sunday.
Despite weak upper troughing over the north state, airmass warms slightly so should see a bit more warming for the second half of the weekend. North Sacramento valley locations will climb to well over 100 but a continued moderate delta breeze should keep the delta influenced areas in the 90s.
Upper ridge builds over the west coast on Monday bringing a couple of impacts to the area forecast. First, subsidence under the ridge should bring enough stability to eliminate any mountain shower threat and second, warming airmass will bump up temperatures Monday to 10 to 15 degrees above normal.
The delta influenced areas will push up to near 100 but the remainder of the central valley locations will top out between 105 and 110 degrees. Dry, stable and hot conditions will continue on Tuesday as the upper ridge amplifies over the west coast.
Therefore, Tuesday could be as hot or hotter than Monday. Have therefore extended the Heat Advisory an extra day into Tuesday.
Extended discussion (Wednesday through Saturday)
Hot temperatures will likely continue through at least the middle of next week with strong high pressure in control. A slight chance of afternoon thunderstorms will still be possible across portions of the Sierra. Longer range guidance is hinting at a bit of cooling toward the end of next week as the upper ridge shifts eastward, allowing for stronger onshore flow.