A slow-moving low pressure system accompanied by unusually-large amounts of moisture affected Montana on the 16th through 19th of June. This system resulted in widespread steady to heavy rainfall across southwest and north-central Montana.
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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.
A slow-moving low pressure system accompanied by unusually-large amounts of moisture affected Montana on the 16th through 19th of June. This system resulted in widespread steady to heavy rainfall across southwest and north-central Montana. The highest rain totals were concentrated along the Rocky Mountain Front, where up to about 8-inches of storm-total rainfall were recorded and resulted from northeasterly to easterly low-level upslope flow enhancing precipitation. Numerous rivers flooded and Rogers Pass was closed for a time due to excessive runoff and a debris flow. Flooding impacts lingered for several days beyond the 19th, including flooding along the Sun River, as it took time for runoff to travel downstream.
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 Jun 19, 4:28 AM MST, 2 hours 53 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 528 AM MDT Tue Jun 19 2018 UPDATED AVIATION .SYNOPSIS... A slow-moving upper-level low will continue to affect the region today. Expect widespread rain this morning over Central and North Central MT to become more scattered showers and thunderstorms across the entire region this afternoon. The upper level low begins to break down on Wednesday, as warmer air slowly moves back into the region, however a few thunderstorms will still be possible. A cool front moves through the region on Thursday allowing for a better chance for storms after a warm afternoon. && .DISCUSSION... Today and tonight...A slow-moving low pressure system continues to affect our CWA today as the system taps into abundant moisture from the Pacific and northern Great Plains. Models are in general agreement that the primary 700 mb low pressure center will meander near Lewistown and Great Falls today, allowing abundant cloud cover and widespread steady to heavy rain to persist amidst large-scale ascent, including isentropic lift. In addition, northeasterly low- to mid-level upslope flow will continue to enhance rainfall rates along the Rocky Mountain Front. As has been the case the past few days, weak instability should permit the development of a few thunderstorms this afternoon and early evening. Precipitation then becomes more scattered in coverage tonight as the low pressure system begins to depart our area to the southeast. Additional rainfall through daybreak Wednesday is expected to generally reach 0.10" to 0.50". However, much of the Rocky Mountain Front should receive another 0.50" to 1.00" of rain, with localized higher amounts possible. Hydrological concerns, including flood warnings, remain valid for our region. Please see the hydrology section for additional details. Wednesday through next week Tuesday...The overall drying trend continues into Wednesday as the low pressure system moves farther southeastward and high pressure builds-in from the north and west. However, the first in a series of disturbances aloft begins breaking- down the ridge Wednesday afternoon and evening. Thus, isolated to scattered showers and thunderstorms remain in the forecast for Wednesday. Additional disturbances aloft traverse the CWA generally from west to east Thursday through Saturday, resulting in more scattered showers and thunderstorms. In addition, moderate instability and vertical wind shear may contribute to some severe thunderstorms Thursday afternoon and early evening. A drying trend should commence Sunday and especially Monday and Tuesday of next week as another high pressure ridge looks to become established over our CWA. Temperatures trend warmer during this period, including highs reaching the low to mid 80's this Thursday and next week Monday and Tuesday. - Jaszka && .HYDROLOGY... Flood watch will continue for portions of North Central and Southwest MT as moderate rainfall continues to move through the region. The watch area was expand a bit overnight. Lewis and Clark County....Flood warning for the entire county. Potential flooding north of Lincoln as 4 to 7 inches of rainfall have been reported in this region over the past few days. The Dearborn River could go above moderate flood stage later today. Tenmile Creek in the Helena valley is above flood stage and should crest around 4.8 feet later this morning. However, additional rises are possible later today with additional rainfall. Teton County...Flood warning for the entire county. Heavy rainfall over the county could lead to flooding at anytime. Widespread rainfall amounts of 3 to 6 inches across the county. The Sun River is expected to flood along the county line. Cascade County...Flood warning for the Sun River and Dearborn River. Rainfall of 3+ inches today and over 6 inches in the past 3 days has lead to significant rises on the Sun River. The river is expected to go above flood stage later this morning and could go over 9 feet by Wednesday. This would be the highest crest this year. Moderate flooding is possible along the Dearborn River in Cascade County. Meagher County...Flood warning for the Martinsdale area. Minor flooding continues to affect areas around Martinsdale, mainly from the Musselshell River. - Brusda && .AVIATION... Updated 1128Z. A low pressure center aloft will meander near KLWT and KGTF through about 00Z/Wed. Thereafter, this low should be absorbed by a separate low moving eastward over northeastern WY. This new primary low should then reach western SD by 12Z/Wed. This complex system will result in widespread steady rain through 00Z/Wed, especially along and west of a KCTB-KGTF-KBZN line. In addition, a few thunderstorms are possible this afternoon. After 00Z/Wed, precipitation should become more scattered over our area as the low pressure system pulls away and a high pressure ridge builds-in. Widespread VFR/MVFR CIGS and mountain obscuration are expected. In addition, brief CIGS down to VLIFR and VSBY down to MVFR are possible with steadier rain. Partial clearing of skies and light surface winds may allow patchy fog to develop along the Hi-Line, including KCTB and KHVR, toward 12Z/Wed. - Jaszka && .PRELIMINARY POINT TEMPS/POPS... GTF 56 49 74 53 / 90 70 20 10 CTB 61 46 73 50 / 90 50 10 10 HLN 58 49 74 52 / 90 60 20 10 BZN 59 46 71 49 / 60 50 30 20 WEY 55 37 64 40 / 40 50 20 20 DLN 59 42 70 47 / 60 50 10 10 HVR 66 51 77 54 / 70 30 20 10 LWT 60 47 68 49 / 80 70 60 20 && .TFX WATCHES/WARNINGS/ADVISORIES... Multiple flood highlights remain in effect until further notice. && http://www.weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
619 AM MDT TUE JUN 19 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0617 AM HEAVY RAIN 3 WNW MONTANA CITY 46.55N 112.00W
06/19/2018 M1.45 INCH JEFFERSON MT TRAINED SPOTTER
STORM-TOTAL RAINFALL SINCE 9 PM MDT SUNDAY,
17 JUNE 2018.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
629 AM MDT TUE JUN 19 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0626 AM HEAVY RAIN 2 SE MONTANA CITY 46.52N 111.90W
06/19/2018 M1.04 INCH JEFFERSON MT TRAINED SPOTTER
1.04 INCHES MEASURED FROM 6 AM 6/18 TO 6 AM
6/19. 0.05 INCHES FROM 6 AM 6/17 TO 6 AM
6/18. 2.3 INCHES TOTAL SINCE RAIN BEGAN
6/16.
&&
CCThe national radar mosaic for the moment the first event began.
8 flood. Local standard time, as filed.
Report of 8 to 12-inches of floodwater along Main Street in Augusta due to Elk Creek overflowing its banks.
Spotter reported flooding along Dearborn and Missouri Rivers. Water levels were highest he had ever seen. Flooding caused minor fence damage on his property.
Multiple media outlets reported flooding along Tenmile Creek near McHugh Lane in Helena. Roadways were flooded and water was waist-deep in some areas.
Spotter reported flooding at multiple fishing access sites along Dearborn River and downstream portion of Missouri River near Craig.
Spotter reported Blackfoot River overflowing its banks 8-miles ENE of Lincoln. Highest river level seen all year and water was nearing houses.
Spotter reported flood water was still flowing across Rogers Pass and the pass remained closed. Excessive runoff from significant rainfall on June 16th through 19th and debris from a recent wildfire burn scar clogged culverts along the pass, leading to erosion and unstable road conditions.
Broadwater County Emergency Manager reported flooding along Highway 285. Floodwater was from Crow Creek overflowing its banks.
NWS Great Falls hydrologist reported and photographed flooding in the town of Sun River due to the Sun River flowing out of its banks.
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, June 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: 760601, 760604, 760602, 760603, 760605, 752020, 760606, 763401.