Unseasonably cool weather continues today. Warming trend returns over the weekend, then much warmer next week.
Discussion
Unseasonably strong upper level trough continues over the Western States and is bringing well below normal temperatures to NorCal. Reinforcing energy will drop south Friday with the trough shifting a bit west over the eastern Pacific. This will allow heights to gradually rise over the weekend causing a warming trend. A few light showers will be possible over the Coast Range and Western Shasta county Friday and Saturday, rainfall amounts should be less than 0.10 inches. Little to no instability is forecast, so not expecting any thunderstorms at this time.
High temperatures over the Valley will be in the upper 70’s today, warming to near 80 Friday and near 90 over the weekend. Breezy onshore winds will continue through the Delta at times through the weekend.
Extended discussion (Monday through Thursday)
Ensembles continue to show the region sandwiched between an eastern Pacific trough and 4-Corners ridging. An upper level shortwave with a surface cold front will brush through northwestern California on Monday. National Blend of Models brings a 10 to 15 percent of rain showers to western Shasta County on Monday. Rainfall amounts should be light.
Model trends are consistently showing strong growth of the 4-Corners ridge westward as the trough passes inland to the northeast. This is an unseasonably strong ridge with a 600 dam height. Area temperatures begin to gradually trend upwards early next week as the ridge expands westward, with Valley highs reaching the low 90s by Tuesday. By Wednesday, triple digits are possible across much of the Valley. EC ensembles show 850 mb temperatures anomalies of +10C on Thursday. Latest NBM projects Valley surface highs of 102-107, which along with warm overnight lows could bring potential heat impacts. Stay tuned to see how this develops.