Critical Fire Weather today through Saturday

August 10, 2018 – Near to slightly above normal temperatures through the forecast period. Onshore flow increases today into the weekend with locally breezy wind at times. Smoke from wildfires will continue to impact air quality.

Discussion

Upper low near 43N 134W will progress towards the PacNW coast today as 596 DM upper high remains centered over NV. Flow through the Delta is stronger attm than 24 hours ago, but expected to trend down again this morning. Smoke will continue to impact air quality over Interior NorCal. However, latest HRRR smoke model suggests improving conditions this afternoon as upper low approaches, onshore flow strengthens, and mixing heights increase. High temperatures forecast to be similar to Thursday.

Some cooling expected though in the Coastal Range, Carquinez Strait, and southern portions of the Sacramento Valley as Delta breeze strengthens again this afternoon. Locally gusty westerly wind this afternoon into evening can be expected in the mountains impacting wildfires. Upper low tracks across the PacNW over the weekend. Interior NorCal remains sandwiched between troughing to the N-NW and upper ridging to the SE.

Onshore flow remains enhanced with gusty afternoon to evening wind through the Delta and in the mountains. High temperatures expected to be near to a few degrees above normal. Models suggest mid-level flow becomes more southerly next week. This would result in increasing monsoonal moisture spreading northward into our mountains, leading to a threat of afternoon deep moist convection.

Extended discussion (Tuesday through Friday)

Upper ridging pattern will gradually rebuild across interior NorCal. Afternoon convection could be possible Tuesday and Wednesday over the northern Sierra, and possibly over the northern mountains given enough instability and moisture. However, model guidance differs in terms of thunderstorm coverage, with the GFS being the most aggressive. Elsewhere, no precipitation is expected. Near or slightly warmer than average highs expected through the period. Warmer temperatures could return by the end of next week as high pressure rebuilds, but models differ on the exact details.

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