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October 29, 2019 – Critical fire weather concerns today and Wednesday. Dry weather expected through at least the next week with temperatures warming to a little above average by the end of the week.

Discussion

Other than a few high clouds moving down from the north, skies are clear across the region early this morning. With lighter winds, current temperatures are considerably colder through the Central Valley compared to 24 hours ago and are mainly in the upper 30s to mid 40s. With higher dew points, some patchy frost may occur in the outlying areas around sunrise.

The brief lull in the north wind pattern will end shortly as winds pick up again this morning. The center of the next low dropping down from the north is over Idaho, and it is forecast to track into the southern Rockies by early Wednesday.

The track of this one will be further to the east. However, it will still bring a period of strong, dry north to easterly winds to the region accompanied by critical fire weather conditions. The expected KSAC-KMFR pressure gradient will be around 10 mb which is 5 to 6 mb weaker than on Sunday.

A Red Flag Warning has been issued for a majority of interior Northern California through Wednesday. Additional fire starts are possible with conditions supporting the rapid spread of any new or existing fires. Relative humidities will be extremely low, generally in the mid-single digits to low teens during the day with very poor overnight recoveries.

In addition to the fire weather concerns, strong winds have prompted the issuance of a Wind Advisory for much of the Sacramento Valley into the Carquinez Strait and Delta region through late this evening. Power outages, downed trees which were weakened from the weekend, as well as difficult driving conditions are all possible. Breezy conditions will continue into the overnight hours and Wednesday morning with occasionally gusty easterly winds lingering into Wednesday night over the Sierra foothills. Overall, please exercise fire prevention techniques and have an evacuation plan in place if a fire starts near you.

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Heading into the second half of the week, the offshore ridge will edge closer to the Pacific coast which brings an end to the active fire weather pattern. However, humidities remain on the low side, albeit with much lighter winds. High temperatures to remain slightly below to around late October climatology while chilly overnights are likely. Optimal radiational cooling conditions will be in place with mid/upper 30s on Thursday morning which may support some patchy frost.

Extended Discussion (Saturday through Tuesday)

Upper level high pressure ridge over the eastern Pacific and west coast will dominate the weather pattern through the extended period. Daytime highs will start out a bit above normal on Saturday warming slightly going in to early next week. Nearly clear skies will allow for a little below normal overnight low temperatures. Winds should remain fairly light under the ridge staying mostly northerly during the weekend then more southerly early next week as a weak low develops off the SoCal coast. Even with the light winds, daytime humidity and overnight RH recovery will remain low under the subsidence of the ridge. The offshore low may start to have to minor impacts by the middle of next week but still too early for any details at this time.