690 FXUS66 KSTO 192115 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 215 PM PDT Thu Jun 19 2025 For additional details on weather and expected impacts over the next 7 days, please visit weather.gov/sto/briefing. .DISCUSSION... .SYNOPSIS... Seasonable high temperatures with enhanced onshore flow today and tomorrow. Elevated fire weather conditions in the northern and central Sacramento Valley today and tomorrow from breezy west- southwest winds and low daytime humidities around 10-25%. This weekend, a mainly dry weather system builds north of the area and bring slight (5%) chances of light showers in northern Shasta County and southern Cascades Friday PM - Saturday AM. As system moves through, winds will begin to shift from the north on Saturday and Sunday morning, introducing periods of critical fire weather in the Valley, Coastal Range, and northern San Joaquin Valley. && .KEY MESSAGES... * Today: -Combination of warm weather with dry conditions may bring a brief period of locally elevated fire weather conditions, mainly across the northern and central Sacramento Valley. -Please continue to practice heat and fire safety such as , avoiding activities during the heat of the day, properly extinguishing any campfires, and not driving over dry grass. *Friday-This Weekend: -Gradual cooling trend expected with stronger onshore flow Friday. Strongest winds expected through the Delta and over the Sierra. South to west forecasted shifting to north to west winds over the weekend. -Elevated fire weather conditions expected across the Sacramento Valley tomorrow due a combination of low humidity and locally breezy winds, particularly across the northern Sacramento and northern San Joaquin Valleys. -Critical fire weather conditions expected across the Sacramento Valley, Coastal Range, and northern San Joaquin Valley Saturday AM - Sunday AM. Latest forecast runs have increased wind gusts in the aforementioned areas, along with lower daytime humidity values around 15-25%, and north wind gusts 30-40 mph. A Fire Weather Watch has been issued for most of the Sacramento Valley and northern San Joaquin Valley Saturday AM - Sunday AM. -Min RH values in the teens to low 20s Friday - Sunday across the northern Sacramento Valley, Valley Foothills, and Northern San Joaquin areas -Probability of wind gusts > 30 mph: *60-95% Friday across the Northern/Central Sacramento Valley *60-90% Saturday across the Sacramento Valley and Delta. -Isolated showers over northern Shasta County and Southern Cascades Friday into Saturday morning but little to no impacts expected. * Next Week: -Dry conditions with a warming trend as we move into the middle of next week. Broad zonal flow will allow onshore winds to continue in the Delta and adjacent areas. Stagnate flow elsewhere will allow temperatures to begin to climb into the upper 90s and triple digits by Wednesday in the northern Sacramento Valley. Minor HeatRisk is expected at this time, thanks to Delta Breeze helping improve overnight relief with low temps in the mid 50s to mid 60s in the Valley/Delta. .Changes from previous forecast... -Fire Weather Watch issued for most of the Sacramento Valley, Coastal Range, and northern San Joaquin Valley beginning Saturday morning through Sunday morning. North winds of 10-20 mph, with gusts 30-40 mph and daytime humidity values in the 15-25% range will allow critical fire weather conditions to develop. && .AVIATION... VFR conditions continue at TAF sites over the next 24 hours. Gusty west to southwest wind gusts around 15-30 kts across interior NorCal until around 12z Thursday and again after 18z Friday. Strongest winds are expected through the Delta and vicinity and over the mountains. && .STO WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch from Saturday morning through Sunday morning for Carquinez Strait and Delta-Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-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-Southeast Edge Shasta- Trinity NF and Western Portions of Tehama-Glenn Unit-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. && $$