The month of September concluded with thunderstorms that brought heavy rain, rockslides, high elevation mountain snow, and a funnel cloud report.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS STO wrote it up.
The month of September concluded with thunderstorms that brought heavy rain, rockslides, high elevation mountain snow, and a funnel cloud report.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Sacramento, CA wrote its last area forecast discussion before the first event at Sep 29, 1:21 AM PST, 4 hours 39 minutes earlier.
Area Forecast Discussion National Weather Service Sacramento CA 221 AM PDT Fri Sep 29 2023 .Synopsis... Breezy onshore flow briefly returns today before a system drops southward from the Pacific Northwest and begins to impact interior NorCal. Precipitation and isolated thunderstorm chances increase late today through Saturday for much of the region, with some precipitation potential lingering into Sunday across portions of the Sierra. Accumulating snowfall will also be possible for portions of southeastern Tuolumne County, generally above 8000 ft. Quieter and milder weather is then expected next week. && .Discussion... As of early this morning, aside from a few pockets of isolated high clouds, mostly clear skies prevail. This is resulting in another cool overnight period, with temperatures throughout the Valley in the 50s to low 60s, and 40s to 50s over the mountains and foothills. An upper trough currently centered over the Pacific Northwest is progged to deepen and progress south-southwestward late today into the weekend. Prior to this, however, onshore flow looks to increase over the region. Breezy to, at times, gusty south-southwesterly winds are anticipated as a result, with strongest winds across the Delta and into adjacent portions of the Sacramento Valley. This flow pattern and increasing cloud cover from northwest to southeast throughout the day will work to keep temperatures a few degrees cooler than yesterday. As the aforementioned trough does begin to dig down over interior NorCal late today into Saturday, precipitation chances will begin to increase as well. Highest probabilities for seeing appreciable accumulating precipitation remain across the mountains and adjacent foothills, with lower, but still nonzero chances throughout the Valley. Latest NBM probabilities favor a 30-60% chance of exceeding 0.5" of precipitation over the mountains and a 20-40% chance of exceeding 0.25" of precipitation across the Foothills and into adjacent portions of the Valley. Furthermore, while the bulk of accumulating snowfall looks to remain south of the STO forecast area, a chance for accumulating snowfall is still possible over portions of southeastern Tuolumne County, generally above 8000 ft, with this system as well. Otherwise, isolated thunderstorm activity is also expected with this system, as some modest instability will be present. Highest thunderstorm probabilities initially will be across the northern forecast area, including the southern Cascades, northern Sierra, and portions of the northern Valley. Although, this activity may drop southward with the system as well. Any thunderstorms that do develop will have the potential for gusty erratic winds, brief heavy rainfall, occasional lightning, and small hail. Moving into Sunday, ensemble guidance begins to show the upper trough pushing eastward across the Great Basin and toward the Four Corners region. Resultant precipitation chances will linger over the southern Sierra on Sunday, while the remainder of interior NorCal looks to remain dry. Given the orientation of the progressing trough, some gusty northerly winds are expected on Sunday as well, particularly across the northern Sacramento Valley. Cool temperatures and quieter weather then prevail moving into early next week. && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... Latest cluster analysis is in good agreement that upper level ridging will fall into place following the weekend system. This will lead to a period of quiet, dry, and warming weather across the week ahead. Temperatures generally look to rebound to near normal values by Tuesday, and above normal through the middle and latter portions of the week. Current NBM guidance indicates a 30-50% chance of high temperatures throughout the Valley exceeding 90F from mid to late week. && .AVIATION... VFR conditions expected through 00Z Saturday. Scattered showers and isolated thunderstorms with local MVFR conditions develop near KRDD after 00Z and spread southeast overnight. Widespread IFR conditions likely in the northern Sierra by 06Z Saturday. Areas of south to west surface wind gusts 20-30 kts develop after 18Z. && .STO WATCHES/WARNINGS/ADVISORIES... None. &&
The Beale AFB radar (KBBX), 38 km away, was scanning. The volume nearest the first event began at 19:57 UTC.
2 heavy snow, 2 heavy rain, 1 flood, 1 funnel cloud. Local standard time, as filed.
The National Operational Hydrologic Remote Sensing Center reported 1 to 6 inches of snow, mainly above 8000 feet in the West Slope Northern Sierra Nevada.
The National Operational Hydrologic Remote Sensing Center reported 1-6 inches mainly in the Lassen National Park area.
California Highway Patrol reported flooding in the roadway on September 29th, 2023.
Caltrans reported a large rockslide on Highway 70, leading to closure of the road.
California Highway Patrol reported mud and debris across both lanes on September 29th, 2023.
Multiple people on social media shared photos of a cold air funnel near Sacramento International Airport on September 30th, 2023.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, September 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1141947, 1141948, 1141940, 1141943, 1141942, 1141944.