A surprise snow event dropped 3 to 5 inches of snow in the Island Park region with US Highway 20 closing from milepost near Island Park to the Montana border by 6 pm on the 21st. The road was blocked due to a truck accident for several hours.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. 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 PIH wrote it up.
A surprise snow event dropped 3 to 5 inches of snow in the Island Park region with US Highway 20 closing from milepost near Island Park to the Montana border by 6 pm on the 21st. The road was blocked due to a truck accident for several hours.
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 Pocatello, ID wrote its last area forecast discussion before the first event at May 21, 1:05 AM MST, 11 hours 55 minutes earlier.
Area Forecast Discussion National Weather Service Pocatello ID 205 AM MDT Fri May 21 2021 .SHORT TERM...Today through Sunday night. Upper low this morning is over the Lake Tahoe area giving us a broad southerly flow. Radar is indicating a line of showers from the Magic Valley to the Sawtooth Range, and also some showers along the MT border. High-res models develop more showers along the Eastern Highlands this morning, while the line of showers pushes slowly to the west. Periods of snow are likely in the Central Mountains throughout the day with only light accumulations. High-res models are developing convection this afternoon over the Eastern Highlands, and drive another round of convection to the rest of the forecast area later this evening and through the night. Snow will continue in the Central Mountains tomorrow while the upper low spins over OR/NV, though a dry slot may curtail any precip chances in the Southeastern Highlands. Thunderstorms may once again generate along the WY border tomorrow afternoon, though some CAMs are holding off until later in the evening. The low will begin to slide northeastward over Idaho on Sunday, giving us our best chance of soaking rains as well as some isolated thunderstorms. Hinsberger .LONG TERM...Monday through next Friday. With the main low circulation ejecting NE through Montana early Monday, trailing short- wave energy noted in both the GFS and ECMWF will support scattered showers across the region, primarily focused along the Wyoming border. A transient short-wave ridge cycles through the area Monday night for a brief period of dry conditions before then next Pacific disturbance rotates through the region Tuesday and Wednesday resulting in another round of showers and scattered afternoon thunderstorms. For Thursday, the operational GFS and ECMWF are at odds with the strength and timing of trailing energy and the extent of potential precipitation across the region. For now, we have a chance mention of showers to cover the model uncertainty. Daytime temps will run about 5 to 10 degrees below normal through the period. Huston && .AVIATION...Early morning satellite and radar imagery showed a low pressure system positioned over NW Nevada as associated light showers lifted north through BYI into the CNTRL mountains and a dry slot nosed north across the ERN mountains. Numerical models show the low rotating into south-central Nevada today and then lifting north through Ely into SW Idaho tonight. For now, it looks as if we will see VFR sct-bkn clouds this morning transitioning towards widespread showers and scattered thunderstorms with MVFR CIGS (perhaps even lower at DIJ) this afternoon and evening. Partial clearing is expected from south to north late tonight as the dry slot works north out of Utah. Huston && .FIRE WEATHER...A low pressure system positioned over Nevada will promote widespread shower and scattered thunderstorm activity across most areas this afternoon and evening. Drier conditions follow late tonight and Saturday morning as the low begins to partially open up and extend north toward Pendleton. We may see scattered thunderstorms along the Wyoming border Saturday afternoon but for now, it looks like a dry slot on the ERN periphery of the low will keep southeast Idaho mostly dry Saturday. The SRN extent of the low begins to eject NE through the Eastern Great Basin Saturday night and Sunday resulting in widespread moderate showers and scattered afternoon thunderstorms across mainly the Central and East Idaho Dispatch areas. What's left of the low trails across the region Monday for scattered showers mainly along the Wyoming border. We don't get much of a break before then next storm system rotates through the region Tuesday and Wednesday and perhaps even Thursday if you through in the variability in the model solutions that far out. Daytime temps will run about 5 to 10 degrees below normal through the week. Huston && .PIH WATCHES/WARNINGS/ADVISORIES... None. &&
Special Weather Statement National Weather Service Pocatello ID 1214 PM MDT Fri May 21 2021 IDZ069>074-221000- Lost River Range-Challis/Pahsimeroi Valleys- Frank Church Wilderness-Sawtooth/Stanley Basin-Sun Valley Region- Big Lost Highlands/Copper Basin- Including the cities of Borah Peak, Challis, Clayton, Stanley, Ketchum, Sun Valley, Galena, and Copper Basin 1214 PM MDT Fri May 21 2021 ...Significant snow accumulations above 7000 feet... A mix of rain and snow is likely tonight for the valleys. Above 7000 feet, snow is likely tonight with accumulations of 5 to 10 inches possible through Saturday morning. The snow may be heavy at times. Accumulating snow of 2 to 5 inches is likely around Galena Summit on highway 75 through Saturday morning. 13
The national radar mosaic for the moment the first event began.
1 winter weather. Local standard time, as filed.
A surprise snow event dropped 3 to 5 inches of snow in the Island Park region with US Highway 20 closing from milepost near Island Park to the Montana border by 6 pm on the 21st. The road was blocked due to a truck accident for several hours.
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: 962606.