A cut off upper low drifting slowly southward off the central California coast pulled up a surge of sub-tropical moisture which produced thunderstorms and flash flooding in the Kern County Deserts on the afternoon of September 9.
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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 HNX wrote it up.
A cut off upper low drifting slowly southward off the central California coast pulled up a surge of sub-tropical moisture which produced thunderstorms and flash flooding in the Kern County Deserts on the afternoon of September 9.
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 Hanford, CA wrote its last area forecast discussion before the first event at Sep 9, 2:10 PM PST, 5 minutes earlier.
Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 310 PM PDT Sat Sep 9 2017 .SYNOPSIS... An upper level low pressure system off the central California coast will be nearly stationary this weekend through the middle of next week. Increased southerly flow will bring tropical moisture northward across the region Sunday and Monday with increased chances of showers and thunderstorms. Low will move inland on Wednesday. && .DISCUSSION... Cut-off low off the west coast making today's forecast a bit more challenging while raising the threat of monsoonal convection. Current position of the low just southwest of Monterey is keeping the flow aloft over the district under a slight southwesterly component. This direction in the flow is placing the bulk of today's monsoonal moisture surge over the Colorado River Valley – where convection is already occurring. Satellite Precip-Water imagery is showing the plume of moisture extending from Yuma, AZ through Las Vegas, as the gradient of drier air extends toward the Kern County Desert. Upper air observations from this morning (1200 UTC) show the desert southwest locations reporting precip- water values at or near their climo max values. Therefore, while models do show significant instability over the Central California Interior, the best values currently reside over the Desert Southwest where the plume of moisture is also located. Yet, with monsoonal moisture surging northward, afternoon convection can not be ruled out as any little piece of energy rotating around the closed low can fire-up a thunderstorm over the mountains. Later tonight, models showing high confidence in shifting the low southward to a position about 300 miles west of San Diego. This change in the position of the low's center will shift the flow aloft to a more southerly to southeasterly direction. In addition, possible difluent flow over the district late tonight and Sunday may help support better precipitation efficiency during the heavy precipitation event. Therefore, will maintain the Flash Flood Watch for Sunday and Sunday Night across the Kern County Mountains and Desert. Once the flow turns more southeasterly, precip-water values of over one inch will surge toward Central California. Along with pieces of vort max energy rotating around the closed low and some orographic effects could provide for heavy rain in a flash flood prone areas. After dropping toward Southern California, the cut-off low begins lifting northward back to the Monterey area early next week. While confidence in this solution decreases, model consensus does lean toward this possibility. While not eliminating the threat of thunderstorms, the threat will become more isolated toward mid- week. Therefore, by mid-week, models still progging the closed low being caught-up in the digging trof that will push into the Pacific Northwest by Wednesday night. With confidence levels at around the medium level on a low passage by mid-week, will maintain the threat of precipitation through at least Wednesday. By Thursday, the cut-off low finally leave the region as a disturbance moves into the Pacific Northwest/Inter-mountain region and turns to flow over Central California to an onshore (westerly to northwesterly) direction. Cooling that will be felt early in the week as the low pushes through will be re-enforced once the onshore flow kicks-in. At that point, the threat of convection will finally diminish through the end of the forecast period. Weak ridge next weekend allow slow down the cooling trend, but another trof in the long term progs may prevent any big warm-up beyond day seven. && .AVIATION... Areas of smoke from wildfires will continue to produce MVFR visibility over the southern Sierra Nevada and adjacent foothills. Scattered thunderstorms in the afternoon over the Southern Sierra Nevada producing local mountain obscurations through 04Z Sun. Otherwise, VFR conditions can be expected over the Central CA Interior during the next 24 hours. && .AIR QUALITY ISSUES... Please see SFOAQAHNX for an Air Quality Alert. On Saturday September 9 2017...Unhealthy for sensitive groups in Kern County. Further information is available at Valleyair.org && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.php for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories... Flash Flood Watch from Sunday morning through late Sunday night for the Kern County Mountains and Southeastern Kern County Desert /CAZ095-099/. && public...Molina avn/fw...Riley/BSO synopsis...Molina weather.gov/hanford
The Edwards AFB radar (KEYX), 66 km away, was scanning. The volume nearest the first event began at 22:12 UTC.
2 flash flood, 1 thunderstorm wind. Local standard time, as filed.
Nine trees were reported blown down in Inyokern from a thunderstorm downburst.
California Highway Patrol reported flash flooding on South Brown Rd between Wiknich Rd. and U.S. Highway 395 south of Inyokern. South Brown Rd. was closed due to the flooding.
California Highway Patrol reported closure of Redrock-Randsburg Rd. between State Route 14 and U.S. Highway 395 due to flash flooding and debris on the road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2017Every state in 2017This day in weather historyWarnings in California, September 2017
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: 720453, 720451, 720452.