June 13, 2018 – Dry with well above normal temperatures today with a slight cooling through the end of the week. Nearer to normal temperatures and a chance of mountain showers or thunderstorms over the weekend and the first part of next week.
High pressure over the southwest U.S. will bring another very warmand dry day today. Most locations will see similar or a little warmer Temperatures than Tuesday. Exception will be areas north of about Chico which will see a little cooling thanks to an upper low moving into the Pacific northwest this afternoon.
Still more cooling is in store for Thursday as weak upper troughing develops along the west coast. Even with the cooling, daytime highs Thursday will remain several degrees above normal. An upper level low developing over the Pacific Northwest will bring still cooler air and onshore flow for more cooling on Friday although highs will still come in just above normal.
Upper low over the Pacific Northwest drops southward going into the weekend although models differ on the details. This low should create enough instability for some showers or afternoon thunderstorms but whether this shower activity makes it southward far enough to impact the northern CWA mountains Saturday remains in question. Either way, daytime highs for the first half of the weekend should drop to below normal.
Extended discussion (Sunday through Wednesday)
Longer range models continue to trend toward a cooler and more unsettled weather pattern next week. It is becoming more likely that a closed upper low dropping south from the PacNW will remain quasi-stationary over the region early next week. Where precisely this sets up is uncertain at this stage, but there appears to be enough dynamics for a chance of showers and thunderstorms over higher terrain through the extended period.
Given the GFS and ECMWF trend toward a more unsettled pattern, we lowered our forecast high temperatures several degrees through the extended period. Our current forecasts in this time frame are closet average.