Unseasonably warm temperatures occurred in the first two weeks of April, with highs near 80 degrees occurring at times. These warm temps, along with occasional rain, resulted in melting of a deep snowpack on top of frozen ground which led to significant runoff into area waterways.
Every event with a place to put it. 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 TFX wrote it up.
Unseasonably warm temperatures occurred in the first two weeks of April, with highs near 80 degrees occurring at times. These warm temps, along with occasional rain, resulted in melting of a deep snowpack on top of frozen ground which led to significant runoff into area waterways. Moderate to major flooding occurred along portions of the Milk River and its tributaries. Impactful snowmelt flooding also occurred across Southcentral Montana, in particular across the Gallatin Valley.
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 Apr 6, 10:05 PM MST, 1 hour 55 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1105 PM MDT Thu Apr 6 2023 ...Aviation Section Updated... .SYNOPSIS... The warming trend currently underway will continue through early next week, but will be tempered slightly Saturday. Aside from a small chance for showers and snow showers mainly along the Continental Divide tomorrow evening and tomorrow night, the next few days are looking dry. && .UPDATE... The evening update has been published. Primary update was to reduce cloud cover heading into the overnight hours for the northern and eastern portions of North-central MT. There was some evidence of minor drifting of snow in the Madison Valley northward to the Norris Hill area, but this activity has since diminished so didn't add any mention of blowing snow to the forecast. The second area of concern is the possibility of patchy fog development over the Milk River Valley. Light easterly winds combined with added moisture from today's snow melt could lead to some localized pockets of fog. This doesn't appear to be very impactful at this time, but I did maintain the inherited fog grids from the previous shift. -RCG && .AVIATION... 1105 PM MDT Thu Apr 6 2023 (07/06Z TAF Period) VFR conditions prevail across all terminals under predominately high- level clouds or clear skies. Localized patchy fog likely to develop in the Milk River Valley vicinity given the light easterly flow, mainly impacting KHVR between 9z and 15z. Brief periods of reduced visibility and lowered cloud ceilings are expected during this time. Otherwise, generally light surface winds across most terminals initially, with gusty southwesterly winds over the plains tomorrow afternoon while Southwest Montana, particularly in the KEKS vicinity, will trend gusty with southerly winds in the 15 to 30 knot range throughout the TAF period. - Pierce Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 247 PM MDT Thu Apr 6 2023/ The rest of today through Saturday... Upper level ridging is building into the region this afternoon, resulting in mostly clear skies and a second consecutive day of warmer temperatures. High pressure far to our east and a weak upper wave across North Dakota will allow for a backdoor cold front to slide in from the east/northeast this evening, though it will stall across portions of North-central Montana tonight. Another night of cold temperatures is expected across the eastern Hi-Line, and I cannot rule out some patchy fog by tomorrow morning there. Any fog that does form would be quick to diminish after sunrise, however. Additionally, surface high pressure across southern Idaho and Wyoming combined with weak surface troughing along the Rocky Mountain Front will allow for gusty southerly winds across north- south oriented valleys through tonight. Though no high winds are expected, sustained wind around 30-35 mph are forecast around Norris Hill the remainder of today and early overnight. The pressure gradient will relax and allow for wind speeds to decrease approaching sunrise tomorrow. A weakening upper wave approaching from the Pacific Northwest will allow for a small chance for showers or snow showers, primarily along the Continental Divide Friday evening and Friday night. This system will drag in marginally cooler air behind a weak Pacific Front for the day Saturday, but temperatures are still expected to rise into the 50's and lower 60's F. -AM Saturday night through Monday...cluster analysis throughout the period all strongly support broad H500 ridging over the Western CONUS, with the only uncertainty arising in how amplified the H500 ridge will be over the US Northern Rockies and Canadian Rockies. Latest NAEFS analysis suggests that anomalously (1-2 standard deviations above normal) warm air will advect east and over the Northern Rockies beneath the H500 ridge from Sunday through Monday night, with the most anomalous temperatures arriving over Central Montana during the day on Monday. This will lead to a period of well above normal high and low temperatures throughout the period for most locations. Low temperatures are forecasted to remain above freezing Saturday night over most of the plains of Central and North Central Montana, with Sunday and Monday nights seeing above freezing temperatures as high as 6500-7500ft. High temperatures on Sunday are expected to warm into the mid-50s to low 60s in the valleys of Southwest and Central Montana, with the low 60s to low 70s expected over the plains of Central and North Central Montana. Further warming is then expected into the day on Monday, with high temperatures warming into the 60s to near 70 degrees in the valleys and near 80 degrees over the plains. These anomalously warm temperatures will lead to a period of rapid snow melt in the low to mid-elevations, which could lead to flooding of low-lying areas as sub-surface temperatures remain well below freezing. In addition to the warm temperatures, predominately dry and breezy conditions are also expected, with the only exception being along the Continental Divide on Monday where rain/snow showers will be possible Tuesday through next Thursday...a transition back to a cooler and wetter conditions is generally expected as longwave troughing develops over the Western CONUS; however, a degree of uncertainty still exist in the timing and placement of the longwave trough, which will ultimately impact how much/where precipitation falls and how low/soon temperatures cool over the period. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 31 63 37 59 / 0 0 10 0 CTB 28 60 34 54 / 0 10 0 0 HLN 29 59 35 57 / 0 0 20 0 BZN 17 54 27 53 / 0 0 0 0 WYS 4 46 19 44 / 0 0 10 10 DLN 22 47 29 50 / 0 0 10 0 HVR 21 49 30 53 / 0 0 0 10 LWT 29 58 34 56 / 0 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && http://www.weather.gov/greatfalls
The national radar mosaic for the moment the first event began.
9 flood. Local standard time, as filed.
Roads north of Lothair become flooded from snowmelt. Liberty Co law enforcement closed several sections of several roads across the county.
Significant snowmelt resulted in flooding along Clear Creek. The creek rose approximately four feet over a 24 hour period from April 8th to April 9th, before dramatically subsiding. A nearby reservoir about 3 acres in size filled and flooded within five hours. The river gauge for Clear Creek near Chinook crested at 8.12 feet, with 8.00 feet being the designated beginning of Major Flood Stage. Multiple nearby roads were flooded as a result.
Significant snowmelt resulted in flooding along Battle Creek, near Chinook. The creek crested on April 12th at 11.94 feet. Several roads across northern and central Blaine County were impacted as a result. Water was reported over Highway 2, west of Chinook, for a time. Runoff from Cypress Hills in southern Canada may have contributed to the flooding.
Lewis and Clark County Sheriff's Office reported the high bridge over the Dearborn River was washed out. Public works closed the road at Flat Creek. Several secondary roads across the area were flooded at times. Flooding across northwest Helena also occurred, especially west of Birdseye Road.
Significant flooding occurred along the Milk River across Blaine County. The Rocky Boy SNOTEL station which is the main Milk River basin station peaked later than normal and had over 3.5 times the snow water equivalent that it normally would on April 6 (10.7 of snow water equivalent versus a normal of 3.0 ). When this thick snowpack melted, virtually the entire Milk River system flooded in a matter of days, as a result. The Milk River near Harlem crested at 23.80 feet on April 12, which as of this entry was the seventh highest river level recorded at this site. Roughly 4,000 aces of irrigation land was flooded. Chinook water plant was surrounded by water. Several roads and homes were impacted.
Meagher County Sheriff's office stated rockslides were occurring in the Deep Creek Canyon area, affecting Highway 12, due to snowmelt and flooding.
Churchill area saw pretty good runoff occur. Several locations around Amsterdam (Camp and Godfrey Creeks) had water up against houses. The Highline Canal near Gallatin Gateway overtopped in several locations due to runoff. One house and Axtell Anceny Road were affected. Residents on Dry Creek Road and Swamp Creek Road had flood water around houses. This caused the evacuation of the Bootstrap Ranch. County Roads had several roads closed with water on them.
Chouteau County Sheriff's Office reported flood-related closures in Big Sandy at North Lonesome Lake Road between Ihmsen Well Road and Gardiner Road and from Black Coulee Road to Rudyard Road.
Mountain snowpack in the Milk River basin melted out very quickly and contributed significant flooding. Virtually the entire Milk River system flooded in a matter of days as a result, starting near the headwaters in Hill County. Big Sandy Creek near Havre crested at 12.07 feet on April 13, which (as of entry) was the fourth highest crest on record. Route 50 was greatly flooded as well as some businesses . Farther north, Lodge Creek below McRae Creek approached Major Flood stage before cresting at 10.59 feet on April 18th. Much of rural northern Hill County experienced flooding as a result. The Milk River gauge near Havre remained below flood stage, although river levels did come out of their banks farther east, ultimately impacting eastern portions of Havre.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2023Every state in 2023This day in weather historyWarnings in Montana, April 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: 1096956, 1082134, 1096908, 1096958, 1096940, 1096959, 1096960, 1096961, 1096952.