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October 25, 2019 – Elevated fire weather concerns through early next week. Dry weather with above average temperatures through Saturday. Another strong wind event Saturday night into Monday resulting in extreme fire weather danger.

Discussion

Surface pressure gradients have relaxed compared to 24 hours ago as the upper ridge has re-centered over NorCal (KMFR-KSAC under 4 mbs and KRNO-KSAC around 8.5 mbs), and winds are considerably lighter. The easterly gradient is still strong enough that local northeast wind gusts of 25-45 mph continue near the mouth of the Feather River Canyon.

Skies are clear other than some high cloudiness circulating in the high center. With lighter winds, current temperatures are running much cooler (10-25 degrees) across the Central Valley compared to 24 hours ago and are mainly in the 50s.

Warm and dry weather, with lighter winds, will cover the region today as the upper ridge remains overhead. Slight cooling begins Saturday as the next upstream system approaches leading to minor synoptic cooling. Breezy northerly winds are expected to redevelop through the Sacramento Valley during the day on Saturday.

Main concern is the potential for extreme fire weather danger Saturday night into early Monday. Deterministic and ensemble models are in better agreement of a deepening trough late in the weekend. The pattern would result in another north/northeast wind event beginning Saturday night and continuing into early Monday.

Strong, possibly damaging, winds are likely Saturday night into Sunday as surface pressure gradients tighten, upper level support aligns with the terrain of the Central Valley, and subsidence increases in the wake of the trough. The MFR-SAC gradient is forecast to peak around 16 mbs while the RNO-SAC gradient is forecast to peak at 12-14 mbs.

Peak wind gusts across the lower elevations will be in the 45-55 mph range while the foothills and mountains will see gusts of 55-65 mph or higher. The strongest wind gusts will be observed along the western side of the Sacramento Valley, the Delta, and higher elevations. Therefore, a High Wind Watch has been issued for Saturday evening into Sunday evening. Downed trees, power outages, and difficult driving conditions are possible.

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The combination of strong winds and extremely dry conditions will bring extreme fire weather conditions to much of interior northern California. Therefore, a Fire Weather Watch has been issued for the northern/central Sacramento Valley beginning late Saturday morning, and expanding into most areas Saturday night. The extreme fire weather will continue into early Monday morning. Please practice fire safety and be ready to evacuate if a fire starts near you.

Temperatures will cool significantly early next week.

Extended Discussion (Tuesday through Friday)

Main issue for extended forecast is potential for another trough from Canada to drop southward into the Great Basin on Tuesday, bringing the potential for northerly winds and lower humidity. This continues to be favored by the ECMWF ensembles, with the GEFS showing the same trough further to the east. Northerly winds are expected either way, with the magnitude being uncertain. This event currently is not expected to be a strong one at this point, but could potentially cause fire weather concerns.

Temperature forecasts keep Valley highs in the low to mid 70s much of next week, near normal levels for this time of year. Overnight temperatures are expected be in the low 40s, while foothill locations stay in the upper 40s to near 50 in thermal belts.

Dry weather is expected through the extended period.