A weak disturbance and instability brought afternoon thunderstorms over the mountains, with an isolated strong storm in the southern Cascades.
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.
A weak disturbance and instability brought afternoon thunderstorms over the mountains, with an isolated strong storm in the southern Cascades.
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 Aug 9, 2:10 PM PST, 1 hour earlier.
Area Forecast Discussion National Weather Service Sacramento CA 310 PM PDT Wed Aug 9 2017 .SYNOPSIS... Showers and thunderstorms are possible tonight and Thursday, mainly over the mountains. Temperatures expected near to slightly above normal into the weekend, then slightly below normal early next week. && .DISCUSSION... Thunderstorms popping up this afternoon over the Coastal Range in response to UVM provided by upper low currently near the NW CA coast. Low also providing some cooling, deeper marine layer, and enhanced Delta flow. Afternoon temps running cooler in most areas, minus the Northern Sacramento Valley, with greatest cooling in the vicinity of the Delta. Water vapor imagery showing stronger vort max rotating around base of upper low. Latest 18z NAM showing a weaker feature and take a more southern track as it moves inland tonight. Mesoscale models continuing to show little if any storms overnight in our CWA with this feature, given limited available moisture. Flow through the Delta expected to increase this evening and remain fairly strong overnight. Given current depth of marine layer, expect stratus in the Delta later tonight and may see some short lived stratus in the Southern Sac Valley tomorrow morning. Models similar in slowly tracking upper low inland across Interior NorCal Thursday. Little change expected in max temps tomorrow with highs near normal. Showers and thunderstorms will again be possible, mainly over the northern mountains in the afternoon. Low lifts NE into SE Oregon Friday with weak height rises over Interior NorCal. Temperatures likely to warm a couple degrees and drier SW flow should suppress deep moist convection. Little change expected into the weekend with weak upper troughing continuing off the West Coast. PCH && .EXTENDED DISCUSSION (Sunday THROUGH Wednesday) Models are still having an upper level low track south along the B.C. coast on Sunday but the latest runs are no longer dropping that low south into our area on Monday. This will still bring troughing to NorCal for the start of the extended period and a weak cold front dose move into the region late Sunday into Monday. We do see an increase in moisture ahead of the front and the trough axis but things still look dry, not expecting any precip but scattered clouds are expected. The trough axis moves through on Monday and should remain dry with some clouds. Monday will also be the coolest day we have seen in quite awhile, upper 80's to right around 90 in the souther Valley and mid 90's in the north Valley. The trough pushes east on Tuesday and temperatures warm a few degrees each day. -CJM && .AVIATION... VFR conditions at the TAF sites the next 24 hours. Isolated to scattered thunderstorms possible over the mountains between 21z Wednesday and 06z Thursday. Winds generally 5-10 knots but gusts to 17 knots will be possible at KSAC and KSCK this evening. Higher gusts will also be possible in the vicinity of any showers or t-storms and the Delta with gusts to 30 knots. A few clouds between 10000 and 15000 feet will push into the Sacramento area Thursday morning. -CJM && .STO WATCHES/WARNINGS/ADVISORIES... None. &&
Special Weather Statement National Weather Service Sacramento CA 223 PM PDT WED AUG 9 2017 CAZ063-092215- Mountains Southwestern Shasta County to Northern Lake County CA- 223 PM PDT WED AUG 9 2017 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN LAKE COUNTY UNTIL 315 PM PDT... At 223 PM PDT, Doppler radar was tracking a strong thunderstorm 10 miles northwest of Fouts Springs, or 15 miles south of Alder Springs, moving north at 10 mph. Dime size hail and winds in excess of 40 mph will be possible with this storm. This storm will remain over mainly rural areas of northern Lake County. PRECAUTIONARY/PREPAREDNESS ACTIONS... This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. && LAT...LON 3938 12286 3951 12289 3954 12277 3942 12275 TIME...MOT...LOC 2123Z 185DEG 7KT 3944 12282
Special Weather Statement National Weather Service Sacramento CA 327 PM PDT WED AUG 9 2017 CAZ013-014-068-092315- Burney Basin / Eastern Shasta County CA- Western Plumas County/Lassen Park CA- Shasta Lake Area / Northern Shasta County CA- 327 PM PDT WED AUG 9 2017 ...SIGNIFICANT WEATHER ADVISORY FOR EASTERN SHASTA COUNTY UNTIL 415 PM PDT... At 327 PM PDT, Doppler radar was tracking a strong thunderstorm 9 miles southwest of Johnson Park, or 22 miles south of Dana, moving northwest at 10 mph. Dime size hail and winds in excess of 40 mph will be possible with this storm. This storm will remain over mainly rural areas of eastern Shasta County. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. && LAT...LON 4073 12164 4082 12189 4092 12180 4080 12158 TIME...MOT...LOC 2227Z 125DEG 10KT 4080 12171
The Beale AFB radar (KBBX), 128 km away, was scanning. The volume nearest the first event began at 23:11 UTC.
1 hail. Local standard time, as filed.
Hail covered the ground. Some of the hail stones were as large as an inch in diameter.
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, August 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: 720630.