FROST POSSIBLE ACROSS NORTH BAY VALLEYS TUESDAY MORNING. LOCAL GARDENS AND AGRICULTURE WILL BE IMPACTED.

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A very cold airmass will drop nightime lows to near freezing early Tuesday, threatening damage to outdoor plantings and agricultural interests across the North Bay valleys and much of Northern California.

Here is the forecast location of the very unusual and very cold low pressure center early Tuesday morning as it slides south over the North Bay. (Image 1)

Cold, convective showers will pop up at times across the region as cold air aloft moves in. That was already happening at midday Monday. (Image 1A)

At approximately 5000 feet, the core of the cold air can be seen in this graphic. Right over the North Bay. (Image 2) Needless to say this is unusually severe cold for this time of year in our region. At approximately 5000 feet, temperatures will be in the low 20s. (Image 3)

How does this translate to nightime lows in our region? Widespread temperatures in the 30s will occur Tuesday morning across the North Bay valleys. It is not out of the question for some locations to approach 30 degrees. Here are various model estimates of lows expected Tuesday morning. As you can see, areas around Healdsburg and Santa Rosa are forecast to be in the mid 30s. Right now the GFS model is coldest. (Images 4-6)

If you are in one of the coldest microclimates in the area be sure to cover sensitive outdoor plantings as the potential for isolated areas of frost definitely exists early Tuesday.

One thing that may help are the occasional clouds and breezy conditions expected as the low center passes overhead. That may stir up the air a bit keeping the coldest air from setting for too long in the valleys.

Needless to say, temperatures will be 10-20 degrees below average for this time of year. (Image 7) Even during the day Tuesday, temperatures will stay way below normal. Mainly 55-62 degrees. HIgher elevations in the region may be up to 25 degrees below normal. (Image 8) A freeze warning has been issued from Mendocino and Lake counties north.

Although severe, the cold blast will be short lived. Temperatures will recover just a bit Wednesday morning but stay well below normal, probably in the high 30s. Then a gradual warming trend will begin as a high pressure ridge pushes in, with daytime temperatures likely exceeding 80 degrees by the weekend. (Image 9)

And, one more piece of good news. Due to cool and showery weather, the energy release component of fuels across the region (blue line) remains below average. (Image 10)