April 27, 2020 – Dry weather with above normal temperatures continue through the middle of next week, with Valley highs in the mid to upper 80s through early next week. Near record highs are expected Tuesday, with Valley locations in the 90s.
Today will see weather similar to that of Sunday. A shortwave trough passing to the north will flatten the ridge with some onshore flow. This will limit heating today to some extent. The Delta Breeze has helped cool temperatures overnight, which are generally a few degrees lower than yesterday, while locations in the Valley further to the north, such as Redding, are a few degrees warmer. Cloud cover with the shortwave will be a little higher north of I-80, though, and this will keep temperatures down for the northern Sacramento Valley into the low to mid 80s.
Upper level ridging rebuilds on Tuesday and will bring high temperatures well above normal for this time of year, with Valley highs peaking in the low to mid 90s. These highs are 15 to 20 degrees above the daily normal, which in the Valley are generally in the mid 70s. Some locations could see record highs, such as Red Bluff at 94 degrees, set in 2013. Sacramento Executive has a forecast high of 91, close to the record of 92, also set in 2013. Those sensitive to the heat as well as outdoor workers could be impacted by this heat and should take precautions. There is increasing confidence that light onshore flow will kick by late Tuesday afternoon which could keep the high temperatures slightly below 90 in the Delta and some Delta influenced areas.
The heat is expected to be short lived as model ensembles show a trough beginning to approach the California coast Wednesday. This will push the ridge axis east and bring in cloud cover over the area. Low temperatures Wednesday morning will be in the upper 50s to low 60s for the Valley. High temperatures will drop back down to the mid to upper 80s for Wednesday afternoon.
A shortwave trough moves in Thursday. Most precipitation should remain to the north, maybe just clipping northern Shasta County. Increased cloud cover and cooler temperatures will be the main affects for most of the area, with Valley and Delta highs in the low 80s.
Extended Discussion (Friday through Monday)
Weak upper trough moves through Friday with little impact, then deeper trough moves through over the weekend. Models suggest cooling with increased onshore flow and a threat of showers, mainly north of I-80, with best chances over the foothills and mountains. Upper ridging builds inland Monday for drier weather.