Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
057 FXUS66 KSTO 192018 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 118 PM PDT Sat Oct 19 2024 .SYNOPSIS... Critical fire weather conditions from gusty north to east winds and very low humidity continue into this evening, with elevated fire weather conditions persisting along the Sierra and adjacent foothills into Sunday morning. Generally calmer and more seasonable weather is then expected through midweek, before unsettled weather looks to potentially return by the end of the week. .DISCUSSION... As of early this afternoon, cloud cover remains sparse across interior NorCal. Mostly sunny skies are leading to warming temperatures across the region as well. Additionally, gusty north to east winds have remained persistent through the morning, alongside very low attendant humidity values. While winds will continue to gradually weaken through the afternoon, relative humidity values are expected to continue falling into the single digits to teens for much of interior NorCal. As a result, the Red Flag Warning remains in effect through 5 PM this evening. While lighter winds are expected through the evening, offshore flow will persist, with breezy to gusty downslope winds again anticipated through the overnight hours. This flow pattern will in turn limit overnight humidity recovery, especially along the Sierra and adjacent foothills locations, leading to elevated fire weather conditions for these areas into Sunday morning. By midday Sunday, a shift toward more appreciable onshore flow looks likely, with gradually recovering humidity through the end of the weekend and into the week ahead. While the upper level pattern looks to remain somewhat diffuse through midweek, broad, flattened ridging will be the primary feature, with a weak shortwave skirting the region to the north on Monday. This may result in an isolated shower or two in Shasta County Monday morning, but minimal impacts are anticipated at this time. Rather, seasonable temperatures and light diurnal and/or terrain driven winds are expected through Wednesday. && .EXTENDED DISCUSSION (Wednesday THROUGH Saturday)... While cluster analysis has come into somewhat better agreement for the expected late week troughing pattern, quite a bit of uncertainty remains regarding the timing and path of this system. In essence, the Euro ensemble suite depicts a building ridge pushing the approaching trough northward with limited impacts to interior NorCal, while the GEFS ensemble suite depicts a further southward trajectory, with the trough moving onshore into the weekend. As a result, while increasing precipitation chances will be possible, they are far from certain at this time. Despite this inherent uncertainty in precipitation, probabilities of precipitation greater than 0.1" are only around 25% to 45% from I-80 northward at this time. Additionally, if the GEFS scenario comes to fruition, increasing onshore winds would also be anticipated. && .AVIATION... VFR conditions over interior Northern California over the next 24 hours. Winds in the Valley mainly below 12 kts with breezy east winds 10 to 15 kts over the foothills and mountains in the evening. && .STO WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 5 PM PDT this afternoon for Carquinez Strait and Delta-Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Portion of Shasta/Trinity NF-Northern Motherlode From 1000 to 3000 Ft. Includes portions of Nevada-Yuba-Placer-Amador and ElDorado Units-Northern Sacramento Valley to Southern Tehama County Line Below 1000 Ft-Northern San Joaquin Valley in San Joaquin and Stanislaus Counties Below 1000 ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes portions of Shasta- Trinity and Butte Units-Northern Sierra Including Lassen NP and Plumas and Lassen NF/S West of the Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)-Northern Sierra Including the Tahoe and ElDorado NF/S West of the Sierra Crest-Southern Motherlode From 1000 to 3000 Ft. Includes portions of Calaveras- Tuolumne Unit-Southern Sacramento Valley in Yolo-Sacramento Far Western Placer, southern Sutter and Solano County Below 1000 Ft- Stanislaus NF West of the Sierra Crest. && $$