Below normal temperatures today, warmer weekend ahead

September 18, 2020 – Weather system moves across NorCal today bringing a few showers to the foothills and mountains along with cooler temperatures and locally breezy to windy conditions. Warmer and drier weather returns for the weekend into next week.

Discussion

Clear to partly cloudy skies cover NorCal early this morning as the mid/upper front pushes gradually to the southeast across the region. Areas of south to southwest wind gusts in the 20s and 30s mph have been occurring across the foothills and mountains, while southerly gusts in the teens to lower 20s mph have been common across the northern Sacramento Valley. The southerly breezes have brought a return of good AQI has throughout the Sacramento and northern San Joaquin Valleys.

Moisture from the remnants of Karina continues to move up from the southwest into central California, and radar has been indicating a few light showers at times across the far southeast corner of the forecast area.

Upper trough moves across the area this afternoon. Some light showers will be possible into this evening across the northern Coast Range and northern mountains, and a few showers will likely continue into the afternoon across the foothills and northern Sierra south of Lake Tahoe as the front moves through and interacts with the Karina moisture. Thunderstorm threat likely to remain well to the north of the region.

Strong gusty southwest winds will be likely today across the higher ridges of the northern Sierra as the front gradually works its way south. Locally breezy southerly winds likely to continue elsewhere. High temperatures today expected to be around 10-15 degrees cooler compared to Thursday’s.

Warmer and drier conditions return over the weekend as ridging returns. Generally light north winds likely Saturday into early Sunday, but surface gradients will be much weaker than previous recent events.

Extended Discussion (Tuesday through Friday)

Warm and dry pattern early next week under zonal flow. Ridge then amplifies into Wednesday, resulting in a slight warming trend. Near normal temperatures are expected through Thursday, with Valley highs generally in the mid 80s and low 90s. Models have moved away from their deeper trough solution late next week. Thus, confidence is low in terms of breezier conditions and how much cooling is anticipated. At this point, most of the moisture would appear to be confined to far northern CA but timing is uncertain.