Significant runoff from periods of rain and melting of a deep mountain snowpack allowed flooding to begin in the Lincoln area on April 29th and persist into May. Floodwaters finally receded on May 27th.
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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.
Significant runoff from periods of rain and melting of a deep mountain snowpack allowed flooding to begin in the Lincoln area on April 29th and persist into May. Floodwaters finally receded on May 27th.
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 25, 11:19 PM MST, 6 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1219 AM MDT Sat May 26 2018 ...UPDATED AVIATION DISCUSSION... .UPDATE... Minor update to POP tonight, but still expecting only a chance of rain east of the Continental Divide overall. Some scattered showers and a few thunderstorms do continue to move northeast across Central Montana so cannot totally rule out an isolated storm holding together. No change for Saturday, still expecting a good chance for strong to severe storms in the afternoon. && .SYNOPSIS... Shower and thunderstorm activity will increase late this afternoon and evening...with the best chances coming across the west and southwest...possibly moving into central and northern portions overnight. Expect continued warm temperatures on Saturday with scattered to numerous showers and a chance for strong to severe thunderstorms. Unsettled conditions and warm temperatures will continue through the holiday weekend. && .AVIATION... Updated 0600Z. Showers will move out of western, central, and northern portions through the early overnight hours....with mainly VFR conditions expected. Mostly cloudy and unsettled conditions are expected to redevelop Saturday afternoon. Scattered strong to severe thunderstorms look to develop over Southwest Montana after 18Z, spreading north and east after 20Z. Some storms could produce erratic winds, heavy rainfall with MVFR conditions,and hail. Thunderstorm activity then moves out of the region late Saturday evening, returning VFR conditions. Anglin && .HYDROLOGY... Adjustments this evening... The Sun River at Simms has risen above flood stage. The latest forecast will keep the river at/or above flood stage for the next several days, with a good rise expected later in the weekend into early next week. Thus a flood warning is now in effect until Thursday evening of next week for this section of the river. Canyon Ferry is going to increase releases into the Missouri River. The current forecast/plan is to keep the river below flood stage at Ulm, Great Falls, and Fort Benton. However the river could rise to near bankful in low areas. No flood watch will be issued at this time, but any adjustments in the next few days could change that. For the Missouri River near Landusky, including the James Kipp Campground, the river is likely to go above flood stage sometime next week with the increased releases. Flood highlights are likely for this section of the Missouri River in the coming days. The small stream flood advisory for Meagher County has been extended until Sunday evening. Local DES reports minor problems continue. With scattered thunderstorms through Saturday, minor problems are expected to continue through much of the weekend. Current Highlights: Small stream flood advisory for Meagher County until 615 PM Sunday. Flood Warning until 715 PM Thursday for the Sun River in Cascade County west of the city of Vaughn. Flood Warning in effect until 300 PM MDT Sunday for the Big Hole River near Melrose in Beaverhead and Madison Counties. Flood Warning in effect until 145 AM MDT Monday for the Jefferson River near Three Forks. Flood Warning in effect until 1000 PM MDT Saturday for the Missouri River near Toston in Broadwater County. Flood Warning in effect until 1015 PM MDT Saturday for the Gallatin River near Logan. && .PREV DISCUSSION... /ISSUED 610 PM MDT Fri May 25 2018/ Tonight through Memorial Day...Ridge of high pressure continues moving eastward through the region tonight with a weak warm front lifting from south to north late this afternoon and evening. Weak instability and shear along this front will trigger isolated to scattered showers and thunderstorms through early evening, mainly across the west and southwest. Showers and thunderstorms will lift northeastward across central and northern portions of the forecast area overnight. Active weather is expected Saturday afternoon and evening. Warming ahead of a cold front will bring modest instability to the region. Large low pressure system then pushes a cold front across the region...also providing some modest shear. The result looks to be scattered showers and thunderstorms, with a few strong to severe storms possible. Large hail and strong winds will be the main threats from these storms. Those with outdoor plans should keep an eye on the skies...and plan on completing outdoor activities early. This large upper low then lingers across the region on Sunday and again on Memorial Day. The result will be near normal temperatures and chances for showers and thunderstorms. Sunday the best activity might be across the southern half of the CWA (Great Falls to Lewistown and south)...while Monday looks to be more widespread as there is slightly better instability everywhere. The outdoor enthusiasts will have to monitor the latest forecasts during this active weather. Anglin/mpj Monday night through Friday...Long term period looks to remain unsettled as multiple disturbances move through. Tuesday does see weak ridging try to build over the region...however...lingering instability and moisture could bring some scattered thunderstorms. Sometime mid week a sharper cold front could move through bringing the next best chance for widespread showers and thunderstorms. This frontal boundary then looks to stall later in the week...and moist southwest flow brings continues chances for showers and thunderstorms to the region. Near normal temperatures look to start the long term. These mention cold fronts could then cool temperatures to near to even slightly below normal readings by the end of the week. One other item worth monitoring for the long term will be some 700 mb temperatures below freezing. This may provide some chances for perhaps high elevation snow...although most other areas will see all rain. Anglin && .PRELIMINARY POINT TEMPS/POPS... GTF 52 77 53 76 / 70 40 30 30 CTB 48 78 50 80 / 30 20 10 20 HLN 52 73 52 74 / 50 60 50 40 BZN 48 69 48 71 / 40 80 60 40 WEY 39 61 37 63 / 50 70 50 50 DLN 47 65 45 68 / 40 80 70 40 HVR 53 82 54 81 / 50 20 20 20 LWT 51 72 50 69 / 60 50 40 40 && .TFX WATCHES/WARNINGS/ADVISORIES... Numerous flood highlights are in effect until further notice. && http://www.weather.gov/greatfalls
Special Weather Statement
National Weather Service Great Falls MT
822 PM MDT FRI MAY 25 2018
MTZ014-048-260300-
Southern Rocky Mountain Front MT-
Central and Southern Lewis and Clark MT-
822 PM MDT FRI MAY 25 2018
...SIGNIFICANT WEATHER ADVISORY
FOR CENTRAL LEWIS AND CLARK COUNTY UNTIL 900 PM MDT...
At 820 PM, Doppler radar was tracking a strong thunderstorm 9 miles
north of Lincoln, moving northeast at 30 mph.
Half inch hail and wind gusts up to 50 mph will be possible with this
storm.
Locations impacted include...
Nilan Reservoir and Bean Lake.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm. Do not drive
your vehicle through flooded roadways.
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.
&&
LAT...LON 4752 11257 4740 11218 4696 11249 4706 11280
4717 11279 4718 11284
TIME...MOT...LOC 0221Z 201DEG 26KT 4709 11262
BrusdaSpecial Weather Statement
National Weather Service Great Falls MT
1008 PM MDT FRI MAY 25 2018
MTZ012-260445-
Cascade MT-
1008 PM MDT FRI MAY 25 2018
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN CHOUTEAU AND NORTH
CENTRAL CASCADE COUNTIES UNTIL 1045 PM MDT...
At 1008 PM MDT, Doppler radar was tracking a thunderstorm near Great
Falls, moving northeast at 15 mph.
Winds around 40 mph will be possible with this storm.
Locations impacted include...
Great Falls, Black Eagle, Malmstrom Afb, First Peoples Buffalo Jump
State Park and Ulm.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4736 11143 4739 11158 4747 11155 4770 11129
4751 11102
TIME...MOT...LOC 0408Z 225DEG 14KT 4747 11138
JANGLINThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Lincoln Volunteer Fire Chief reported flooding in subdivision along Stonewall Creek just north-northwest of Lincoln. A debris flow from the Park Creek Fire's burn scar entered the creek and diverted the streamflow, leading to flooding.
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: 763414.