The month of May started with a bang as a low pressure system moved through the Intermountain West, producing thunderstorms with severe winds, dust storms and small hail.
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 BOI wrote it up.
The month of May started with a bang as a low pressure system moved through the Intermountain West, producing thunderstorms with severe winds, dust storms and small hail.
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 Boise, ID wrote its last area forecast discussion before the first event at May 1, 1:26 PM MST, 44 minutes earlier.
Area Forecast Discussion National Weather Service Boise ID 226 PM MDT Sat May 1 2021 .SHORT TERM...Tonight through Monday night...At 2 PM MDT showers and scattered thunderstorms were developing in eastern Oregon and moving rapidly into southwest Idaho. Expect showers and thunderstorms in the Lower Treasure Valley, Upper Weiser Valley, and Owyhee Mountains between 3 PM and 6 PM MDT. Thunderstorms may contain small hail and gusty winds. After 6 PM showers and storms will continue both north and south of the Snake Basin but decrease within the Snake Basin. Thunderstorms should end by sunset. The showers should end before midnight except lingering rain and snow showers in eastern Valley County. West to northwest winds will continue gusty through tonight and Sunday, strongest Sunday afternoon, with gusts to 35 mph in the Snake Basin. Models see a chance of showers, but not thunderstorms, in south-central Idaho Sunday morning, then into the Camas Prairie Sunday afternoon. The rest of western Idaho and southeast Oregon will become mostly sunny Sunday and 4 to 8 degrees cooler than today. Clearing and cooler Sunday night with diminishing winds. Monday looks mostly sunny and about 5 degrees warmer as an upper ridge briefly passes through. A short wave trough to our north will bring a chance of rain and snow showers to our northern-most mountains Monday night. Southern areas will become mostly cloudy but stay dry. .LONG TERM...Tuesday through Saturday...An exiting trough on Tuesday will continue to produce showers in central Idaho and extreme eastern Oregon. A ridge will rebuild behind the trough on Wednesday into Thursday for a brief break in the precipitation. Temperatures could reach 15 to 20 degrees above normal on Thursday as a result of this ridge. A strong upper level low pressure system off the Pacific Northwest coast will begin to move onshore Thursday bringing a return of southwest flow aloft. This flow will permit limited moisture over the higher terrain with a few showers Thursday afternoon with more showers possible Friday and Saturday. Much of the forcing and moisture look to remain north of the forecast area at the moment, which has remained the trend in the ensemble guidance thus far. Cooler temperatures are expected, dropping to a few degrees cooler than normal by Saturday. && .AVIATION...Isolated MVFR showers and thunderstorms this afternoon and evening with a cold-frontal passage. Mountain obscurations. Surface winds: Northwest 8 to 15 kts except across the Treasure and Magic Valleys with winds of 15 to 25 kts. Gusts of 35 to 40 kts possible this afternoon. Stronger and erratic winds possible in thunderstorms. Winds aloft at 10k feet MSL: West to northwest 15 to 25 kts. Sunday Outlook...Showers and local mountain obscuration will linger through Sunday afternoon, mainly over the central Idaho mountains. Drier conditions are expected Sunday evening. Gusty west to northwest winds will continue, with the strongest winds expected south and east of Boise through the Magic Valley. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise SHORT TERM...LC LONG TERM....JDS AVIATION.....JDS
Special Weather Statement
National Weather Service Boise ID
251 PM MDT Sat May 1 2021
IDZ012-014-012130-
Upper Treasure Valley ID-Lower Treasure Valley ID-
251 PM MDT Sat May 1 2021
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN ADA...CANYON AND
NORTHWESTERN OWYHEE COUNTIES UNTIL 330 PM MDT...
At 251 PM MDT, Doppler radar was tracking a strong thunderstorm over
Caldwell, moving east at 30 mph.
Pea size hail and wind gusts up to 50 mph will be possible with this
storm.
This strong thunderstorm will be near...
Nampa around 300 PM MDT.
Star and Kuna around 310 PM MDT.
Meridian, Eagle and Firebird Speedway around 320 PM MDT.
Boise, Garden City and Hidden Springs around 330 PM MDT.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
When safe to do so, please relay storm reports to the National
Weather Service in Boise via local law enforcement, or National
Weather Service Boise Facebook and Twitter accounts.
&&
LAT...LON 4339 11682 4376 11690 4382 11628 4377 11623
4348 11615
TIME...MOT...LOC 2051Z 256DEG 27KT 4361 11667
LCPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
303 PM MDT SAT MAY 1 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0301 PM HAIL 1 S NAMPA 43.57N 116.56W
05/01/2021 M0.50 INCH CANYON ID TRAINED SPOTTER
GUST UP TO 50 MPH
&&
JSMITHThe Boise radar (KCBX), 9 km away, was scanning. The volume nearest the first event began at 21:09 UTC.
2 thunderstorm wind. Local standard time, as filed.
The ASOS at Boise measured a 62 MPH wind gust and numerous reports of damage were reported by the public and National Weather Service employees.
The AWOS at Mountain Home AFB measured a 58 MPH wind gust with several reports of damage received by the public. A dust storm from the gust front of a nearby thunderstorm reduced visibility to near zero, resulting in a 7 car accident with 3 fatalities. Idaho State Police officials reported the accident was on Highway 51, southeast of Mountain Home. ISP officials have determined the dust storm reduced visibility significantly and was the cause of the accident.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Thunderstorm Wind, Elmore | 2021-05-01 | 1 | Male | Vehicle/Towed Trailer | Direct |
| Thunderstorm Wind, Elmore | 2021-05-01 | 38 | Female | Vehicle/Towed Trailer | Direct |
| Thunderstorm Wind, Elmore | 2021-05-01 | 34 | Female | Vehicle/Towed Trailer | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2021Every state in 2021This day in weather historyWarnings in Idaho, May 2021
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: 952423, 952438.