Updated 9/23/21

Dry and warm weather this week. There are locally breezy north to east winds today. A cooling trend begins this weekend with the potential for a pattern change next week, including light precipitation.

DISCUSSION

NorCal is between an upper high over the eastern Pacific and a low-pressure trough over the Great Basin Region. A tightening pressure gradient between these features will bring breezy north winds to the Northern and Western Sacramento Valley today with local gusts to 25 mph. This will bring a brief period of elevated fire weather concerns over the Northern and Western Sacramento Valley, especially from around 10 am to 2 pm. Winds will begin to relax during the afternoon hours, as the high moves over the area. Very warm afternoon temperatures will be felt with afternoon highs generally from 95 to 100 degrees at Valley locations, helped by the north winds.

These readings are about 10 degrees above normal for this time of year. NBM operational guidance has been running 5 to 7 degrees too cool the past few days, so will use the 90 percentile guidance today and 75 percentile Friday. Moderate heat risk impacts are possible across portions of the Southern Sacramento Valley and the Delta today and Friday and this could impact those who are sensitive to the heat. Ensemble guidance indicates that the ridge will flatten Saturday, as troughs begin to impact the Pacific Northwest. This will likely initiate a delta breeze with a cooling trend over the weekend. Temperatures are currently forecasted to fall into the upper 80`s to low 90`s Saturday and then 80`s Sunday.

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EXTENDED DISCUSSION (Monday THROUGH Thursday)
Cluster analysis continues to indicate considerable uncertainty in timing and strength of the trough next week. Current projections indicate this to be an overall low impact event with generally low POP and QPF for interior NorCal. The main impacts will be a turn to considerably cooler temperatures (around 10-15 degrees below average) Tuesday and Wednesday along with locally breezy conditions. Modest warming is possible toward the end of next week.

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THURSDAY: Sunny with a high of 66 and a low of 61.

FRIDAY: Sunny with a high of 97 and a low of 57.

SATURDAY: Mostly sunny with a high of 90 and a low of 54.

SUNDAY: Partly cloudy with a high of 85 and a low of 52.

MONDAY: Mostly sunny with a high of 83 and a low of 57.

TUESDAY: Slight chance of rain with a high of 75 and a low of 52.

WEDNESDAY: Partly cloudy with a high of 76 and a low of 52.

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