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A frost advisory in place for part of the area tonight

Frost on windshield
Posted at 4:31 PM, Nov 23, 2021

Tonight the interior valleys of SLO county will be cold. Clear skies and dry air will allow some low temps near freezing. A frost advisory is in place from 2a to 9a. Temps near freezing for a few hours can damage sensitive plants. Simple precautions like taking mobile plants inside, covering them, or showering them with water can avoid light frost damage. A hard freeze is not expected.

The reason for the clear skies is high pressure. The jet stream is developing a large ridge over the area which will create plenty of high pressure to close the week and maintain it thru the weekend. As a result, the air will dry out. Dry air can cool and warm quickly with clear skies. Additionally, there will be offshore flow Thursday thru the weekend in the night and morning hours which will also produce warmer than average daytime highs. We'll see temps generally in the 60s and 70s Wednesday but 70s and 80s Thursday thru Saturday if not longer.

The holiday forecast couldn't look more benign for the region. Perhaps the biggest concern would be the fire weather watch from Ventura county thru Orange county for the strong offshore winds there and dry and warm conditions.

With the storm path well to the north, there is not much hope for rain before early December.

What is interesting is that the American GFS did introduce some potential in early December (in the 12z run, nothing in the 18z run). However, I have been monitoring the tail ends of these runs for weeks and there appears to be a bias to introducing something at the ends of the runs which generally just gets kicked further down the road. I'll watch this potential for now but not ready to bite hard until more models see it and also maintain it run to run. Stay tuned.