A strong upper level low pressure system along with a weak shortwave trough moved into Eastern Oregon during the early afternoon. This system brought strong and long lasting rotating thunderstorms that caused severe wind damage.
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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 BOI wrote it up.
A strong upper level low pressure system along with a weak shortwave trough moved into Eastern Oregon during the early afternoon. This system brought strong and long lasting rotating thunderstorms that caused severe wind damage.
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, 12:42 PM PST, 2 hours 59 minutes earlier.
Area Forecast Discussion National Weather Service Boise ID 242 PM MDT Mon May 1 2023 .SHORT TERM...Tonight through Wednesday night...Convective event still on track for later this afternoon through this evening. A strong upper level low pressure system off the Oregon coast along with a weak shortwave, at 20z over northern California, will be the focus for strong to severe thunderstorms this afternoon and evening. Thunderstorms have already initiated off the Sierra Mountains as expected. High-res models remain consistent with convective initiation over the Boise Mountains and higher terrain of Southeast Oregon around 21z. Strong surface heating, MUCAPE values reach 1000-1500 J/kg over eastern OR and in southwest Idaho from Boise- McCall toward the OR border and effective bulk shear of 40-60kt in eastern OR will support rotating updrafts. Based on the latest CAM guidance ensembles of 2-5km updraft helicity, the strongest updrafts are shown across Harney and Malheur Counties tonight as a cluster of thunderstorms from northwest NV move south to north. Although, greater instability exists across southwest Idaho, moisture remains limited and thus a few discrete storms are possible across the Boise and West Central Mountains along with the Upper Weiser basin later this afternoon. Regardless, the environment is sufficient for rotating updrafts and strong to severe thunderstorms. These storms will be capable of large hail (3% chance), and inverted V profiles will support gusty winds up to 50kt (5% chance) as well. The best chance of thunderstorms will be from around 5pm MDT to 11pm MDT. Dry air follows the shortwave passage late tonight/early Tuesday although a few showers and thunderstorms will persist across Harney County and the Boise Mountains. The dry slot remains in place through Tuesday limiting convective potential to Valley County and southern Harney County. Similar conditions are expected on Wednesday though mid level moisture is shown to increase for a chance of thunderstorms (20% chance) across the higher terrain. Southeasterly winds will keep temperatures at least 15 degrees above normal through Wednesday. .LONG TERM...Thursday through Monday...A closed low over southern California Thursday morning will begin to lift north during the day Thursday and move through our forecast area on Friday. Temperatures Thursday will be around 10 degrees above normal ahead of the low. The low will bring increased moisture into our area, with precipitable water values forecast to rise above the 80th percentile for this time of year. Weak instability ahead of the low will support a slight chance of thunderstorms on Thursday. Another slight chance of thunderstorms will redevelop Friday afternoon as the core of the upper low moves overhead. Chances of precipitation will rise dramatically late Thursday afternoon and persist through Friday as the low transits the area. Nearly all locations have at least a 90% chance of rain at some point over the 24 hours ending Friday evening. The low will lift to our north Friday night and Saturday with showers decreasing by Saturday morning. Some locations will likely see heavy precipitation totals, both from localized thunderstorm development as well as wrap around precipitation on the back side of the upper trough and surface convergence. The NBM depicts a 20-40% chance of at least 1" of rain over the mountains of southwest Idaho and southeast Oregon, and a 5-10% chance of at least 2" of rain in these same locations, through Saturday night. Locally heavy precipitation will increase hydrological concerns on areas rivers already elevated from snowmelt. Snow levels will fall to 6500- 7500 ft MSL by Friday night, so rain will change to snow on the highest peaks. Temperatures will be near to slightly below normal Friday and Saturday, and could be more below normal in areas of heavier precipitation. Another trough will move into the Pacific Northwest from the eastern Pacific Sunday into Monday, bringing additional showers into the area. This system does not appear as wet as the previous system, but will still bring rain and high elevation snow to the area. Temperatures will average near normal. && .AVIATION...Mainly VFR. Scattered showers and thunderstorms this evening, with the highest coverage across south-central/southeast Oregon, including KBNO. This area will also see the highest chance of severe thunderstorms with wind gusts 35-50 kt and large hail possible. Isolated showers and thunderstorms may linger in central Idaho overnight. Any thunderstorms will be capable of gusty outflow winds 25-40 kt. Surface winds: NW-NE 10-20 kt in east Oregon into far SW Idaho, and S-SE 10-20 kt in south-central Idaho, due to a stationary frontal boundary draped across the area. Gusts up to 20- 30 kt outside of storms. Winds aloft at 10k feet MSL: S-SE 25-40 kt. Areas of low-level wind shear in southwest Idaho after Tue/03z. && .HYDROLOGY...A Small Stream flood advisory has been issued for Baker County through the West Central and Boise mountains along with the Weiser Basin and Camas Prairie. Snowmelt from unseasonably warm temperatures will keep flows high and nearby fields and lowlands flooded. Sheet flooding from snowmelt could impact locations in higher elevation valleys that still hold a snowpack, including the Camas Prairie. In addition, widespread precipitation is forecast for later in the week which could cause further flooding across the area. Current river forecasts keep most mainstem rivers below flood stage, but these forecasts may change and folks should make sure to stay informed as new forecasts are issued. A River Flood Warning remains in effect for the Silvies River near Burns through next weekend. A river flood watch has been issued for the Middle Fork of the Payette River near Crouch as the river could reach flood stage late tonight. Flows on the South Fork of the Boise River near Pine, and the Bruneau River near Hot Springs are showing significant rises and may experience minor flooding later in the week. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise SHORT TERM...JDS LONG TERM....ST AVIATION.....ST HYDROLOGY....JDS
Special Weather Statement
National Weather Service Boise ID
428 PM PDT Mon May 1 2023
ORZ061-020015-
Harney County OR-
428 PM PDT Mon May 1 2023
...A strong thunderstorm will impact portions of east central Harney
County through 515 PM PDT...
At 427 PM PDT, Doppler radar was tracking a strong thunderstorm near
Riddle Mountain, or 44 miles southeast of Burns, moving north at 20
mph.
HAZARD...Wind gusts up to 50 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
This strong thunderstorm will be near...
Riddle Mountain around 430 PM PDT.
Barton Lake and Malheur Cave around 450 PM PDT.
New Princeton, Circle Bar, Malheur Refuge Headquarters and Malheur
Lake around 510 PM PDT.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
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 4301 11828 4295 11867 4332 11888 4340 11838
TIME...MOT...LOC 2327Z 167DEG 19KT 4306 11856
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH
SAThe Boise radar (KCBX), 172 km away, was scanning. The volume nearest the first event began at 23:42 UTC.
4 thunderstorm wind. Local standard time, as filed.
The mesonet station OD219 2.5 miles southeast of Drewsey measured a wind gust near 65 mph.
A couple of trees were knocked down on Pine Creek Road.
A trained spotter near Drewsey, OR reported a blown down willow tree and small hail.
The mesonet station ATFO3 at Antelope measured a 53 knot wind gust.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2023Every state in 2023This day in weather historyWarnings in Oregon, May 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: 1098472, 1098476, 1098473, 1098475.