Runoff from mountain snowmelt and periods of rain renewed flooding along Tenmile Creek in the Helena area by early May. This flooding finally receded by May 19th.
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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 TFX wrote it up.
Runoff from mountain snowmelt and periods of rain renewed flooding along Tenmile Creek in the Helena area by early May. This flooding finally receded by May 19th.
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 Great Falls, MT wrote its last area forecast discussion before the first event at May 6, 11:00 AM MST, 2 hours earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1200 PM MDT Sun May 6 2018 .UPDATE... Only minor updates to the forecast this morning. Today should start out warm with light winds across the region. Afternoon heating coupled with some instability looks to bring a good chance for isolated to scattered thunderstorms, mainly over Southwest Montana. As a frontal boundary moves north through the evening there will be a chance of an isolated thunderstorm or two during the early evening. && .SYNOPSIS... High pressure aloft will bring warm temperatures to the region today. An approaching weather system will bring scattered to numerous showers and thunderstorms to central and southwest Montana late this afternoon, tonight and Monday. Temperatures will be about 10 degrees cooler on Monday but mostly dry and warmer conditions return Tuesday. Unsettled conditions and slightly cooler temperatures can be expected late in the week. && .DISCUSSION... Sunday and Monday...A moist and somewhat unsettled southwesterly flow aloft prevails over western and central Montana today as an upper trough along the West Coast moves inland. Temperatures will warm well above seasonal averages with a few rain showers expanding in coverage and combining with scattered thunderstorms by late this afternoon. The upper trough moves over the region tonight and Monday for widespread showers and scattered thunderstorms. A few of the storms this afternoon and this evening could become marginally strong, producing wind gusts (possibly as high as 55 mph) and small hail. Locally heavy rain is also possible overnight and on Monday. Afternoon high temperatures on Monday will likely be about 10 degrees cooler than those of Sunday due to cloud cover and precipitation as the troughs moves overhead. mpj Tuesday through Sunday...Progressive flow aloft builds a shortwave ridge over the Intermountain West for mostly dry and warmer conditions from Tuesday afternoon through Wednesday morning. For Wednesday afternoon, models bring another round of showers and thunderstorms to the forecast area as an upper trough moves through the state. Models diverge somewhat for Thursday and Friday before solutions converge again next weekend and carve out a closed low over the Pacific Southwest. Have continued an unsettled forecast for Thursday through Saturday with high temperatures expected to top out only in the 60s. By Sunday, mostly dry and warmer conditions are expected as stormy conditions move well south of Montana with the closed low. mpj && .AVIATION... Updated 1800Z. Scattered mid and high level clouds with VFR conditions. Scattered showers and isolated thunderstorms develop over Southwest Montana and the Continental Divide after 22Z, then become more widespread and move northeast after 00Z Monday, possibly continuing into early Monday morning. Areas of IFR/MVFR conditions are possible in precipitation with terrain obscuration at times. Skies begin to clear after 12Z but scattered showers will remain across the region and thunderstorms may develop once again after 20Z Monday. && .HYDROLOGY... Scattered showers/thunderstorms will move through the region tonight through Sunday. The heaviest showers could produce up to a half inch of precipitation. Since the areal coverage of the heaviest precipitation should be small, significant impacts to flooding are not expected at this time. Any new flooding from the heavier rainfall over the weekend should be short lived, as these will be fast moving showers. With temperatures in the 70s most days over the upcoming week, expect small streams and creeks to remain high. The latest forecast holds off on any flooding on the major rivers at this time. However, the latest GFS model has significantly warmer temperatures over the region next weekend than previously forecasted and this could impact higher elevation runoff, possibly resulting in some additional flooding. Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 78 52 67 49 / 10 60 70 50 CTB 76 51 69 47 / 0 70 70 40 HLN 77 49 67 45 / 20 80 50 30 BZN 74 44 68 41 / 30 50 50 30 WEY 64 35 59 32 / 20 30 30 10 DLN 74 41 67 39 / 40 70 40 10 HVR 80 54 74 51 / 0 20 60 60 LWT 76 49 69 46 / 10 20 60 50 && .TFX WATCHES/WARNINGS/ADVISORIES... A Flood Advisory remains in effect until further notice for Lewis and Clark and Meagher counties. && http://www.weather.gov/greatfalls
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Helena Independent Record reported flooding at Rossiter Elementary School and the Helena Campground and RV Park around 2 PM MDT on Sunday, May 6th. Runoff from melting mountain snowpack and recent rainfall caused flooding along Tenmile Creek and nearby irrigation channels.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2018Every state in 2018This day in weather historyWarnings in Montana, May 2018
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: 763409.