MODERATE ATMOSPHERIC RIVER WILL TRANSIT SONOMA COUNTY TUESDAY BETWEEN 5PM AND 11PM. HIGHEST RAIN RATES EXPECTED THEN.

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Detailed high resolution models are now in agreement that Sonoma County and the North Bay will experience up to 6 hours of atmospheric river rains from Tuesday afternoon until almost midnight. Rain intensity is expected to peak around 9-11PM. This will be the period of highest rain rates and greatest danger of debris flows and flash flooding.

The National Weather Service has issued a Flash Flood Watch through Thursday afternoon, and a High Wind Warning through Wednesday morning for the North Bay.

In terms of moisture transport, the AR will be weak to moderate over the North Bay before the deepest core of moisture comes ashore to our south overnight Tuesday and early Wednesday across portions of the Bay Area and Monterey County.

Tuesday at midday the storm was approaching from the northwest. (Image 1)

High resolution forecast models have sped up the arrival of AR rains across the North Bay. Here is the HRRR model, showing the area of heaviest rain at 8PM Tuesday. (Image 2) And then at 10PM. (Image 3) And at midnight. (Image 4)

The NAM model agrees, showing the AR core moving through around 9-11PM Tuesday. (Image 5) And south of our area by 1AM Wednesday. (Image 6)

What that means for Sonoma County and the North Bay is that the heaviest rains, with the highest rain rates, will likely be centered between 5PM and 11PM Tuesday.

The Scripps AR model shows the atmospheric river peaking at moderate strength just before midnight at Bodega Bay, with peak moisture transport and rain rates. (Images 7 and 8) Moisture transport drops quickly early Wednesday morning as the AR core moves south.

By early Wednesday, high resolution models expect urban areas of Sonoma County to have received 1.5 to 2.5 inches during the AR, with up to 4+ inches in the coastal hills. This will create dangerous debris flow and flash flood conditions near burn areas. (Image 9)

By 4PM Wednesday morning models forecast the atmospheric river to have passed through the Bay Area and reached the Monterey area. (Image 10)

Although the AR will have passed south by early Wednesday, rain will continue off and on through the day. Our rain totals are expected to be impressive. (Images 11 and 12) The second image shows enhanced rain totals expected over the hills and mountains of the North Bay and Bay Area.

The brunt of the atmospheric river will be focused on the central California coast, where 10+ inches of rain is possible in the hills from Big Sur south to San Luis Obispo county.

News of the North Bay will keep you updated as weather conditions warrant.