A 50 kt jet streak traversing the northeast side of a ridge of high pressure combined with moisture and instability to produce isolated thunderstorms over North-central Montana. The storms over Liberty County quickly strengthened to severe levels as precipitable water values approached the one inch mark, MLCAPE topped 1000 j/kg, and bulk wind shear fell in the 25 to 35 kt range.
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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 50 kt jet streak traversing the northeast side of a ridge of high pressure combined with moisture and instability to produce isolated thunderstorms over North-central Montana. The storms over Liberty County quickly strengthened to severe levels as precipitable water values approached the one inch mark, MLCAPE topped 1000 j/kg, and bulk wind shear fell in the 25 to 35 kt range. This resulted in ping pong ball to lime sized hail, gusty winds, and heavy rain in the Lothair area. Broken windows and crop/tree damage were reported.
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 Jul 31, 4:27 PM MST, 1 hour 28 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 525 PM MDT Fri Jul 31 2020 Updated Aviation Discussion .SYNOPSIS... Hot and mostly dry weather continues through the weekend as a ridge remains overhead. Afternoon showers and thunderstorms will remain possible every afternoon through Monday, with any showers and storms quickly dying after sunset. && .DISCUSSION... A few isolated storms are beginning to pop up across the area this afternoon, mainly along an old outflow boundary formed from a decaying MCS over Eastern MT. Most of these should not be severe, though SPC has highlighted the area near the aforementioned boundary for a marginal risk of severe storms. Storms near this boundary will need to be watched closely for gusty winds and hail to the size of quarters. Elsewhere, storms should generally be weaker, though brief gusty winds cannot be ruled out. Tomorrow will not look that much different from today, nor will any day through Monday for that matter. Upper level ridging remains fully in control of our weather into early next week, which will keep things hot and mostly dry, save for a few isolated afternoon/evening showers and thunderstorms. Will have to keep an eye on any storms for dry lightning and outflow winds, but these impacts should be isolated. Temperatures will remain above average through Monday, with the peak of the heat coming Sunday or Monday. This will continue to create a low to moderate heat risk for those who are sensitive to the heat. For those wondering when this heat wave will end, it still appears that Tuesday will be the day to mark on the calendar. The upper level ridge will break down as an upper level trough pushes in, which will knock temperatures to around climatological average for early August (low to mid 80s). Temperatures will be highly dependent on exact timing of the arrival of this trough, though the NBM has seemed to converge a bit with some of the more recent runs. In any case, the main story on Tuesday may end up being the winds, with wind gusts across Northern Montana expected to exceed 20-25 knots. This will be a time period that needs to be watched for heightened fire danger. Looking further into next week, upper level ridging should begin to build back in, but will not be as strong as what it will be over the weekend, but temperatures should recover a bit as we head into later next week. Ludwig && .AVIATION... Updated 525 PM MDT Fri Jul 31 2020 (01/00Z TAF Period) Upper level ridge of high pressure remains centered over the Northern Rockies for generally light flow aloft with VFR conditions prevailing. Isolated thunderstorms that developed this afternoon near the mountains could bring some brief MVFR conditions to nearby sites as well as some localized gusty and erratic winds through this evening. Partial cloud-cover from thunderstorm remnants could continue across the region past this evening before skies clear again late tonight. Surface winds from the east to southeast will persist across the north-central MT plains tonight with winds otherwise light and variable outside of thunderstorm activity this evening. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing runway closure. && .FIRE WEATHER... Fire danger ratings across the region range from moderate up to high in some areas as fuels continue to dry. Lightning associated with isolated daily afternoon thunderstorms could initiate new fire starts, in addition to lightning related hold-overs that produce delayed ignition. A frontal system arrives on Tuesday, which is expected to lower temperatures back to near seasonal normals, but also cause gusty winds that could yield higher rates of spread on any new or existing wildfires. Fire weather headlines may be warranted early next week, so continue to monitor the forecast for updates. && .PRELIMINARY POINT TEMPS/POPS... GTF 61 92 62 93 / 10 10 20 10 CTB 59 89 58 90 / 10 10 20 10 HLN 60 94 60 94 / 10 10 30 10 BZN 57 93 57 94 / 10 10 10 10 WYS 45 87 47 88 / 10 20 10 10 DLN 55 90 55 90 / 20 10 10 0 HVR 61 91 61 92 / 0 0 10 0 LWT 58 86 56 88 / 10 10 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && http://www.weather.gov/greatfalls
Special Weather Statement
National Weather Service Great Falls MT
228 PM MDT Fri Jul 31 2020
MTZ047-312115-
Blaine MT-
228 PM MDT Fri Jul 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL BLAINE COUNTY UNTIL
315 PM MDT...
At 228 PM MDT, Doppler radar was tracking a strong thunderstorm 13
miles southwest of Hays, or 17 miles west of Zortman, moving south at
5 mph.
Half inch hail and winds in excess of 40 mph will be possible with
this storm.
This storm will remain over mainly rural areas of south central
Blaine County.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4792 10889 4779 10889 4778 10893 4793 10900
4794 10885 4792 10883
TIME...MOT...LOC 2028Z 343DEG 5KT 4788 10889
CMCSpecial Weather Statement National Weather Service Great Falls MT 245 PM MDT Fri Jul 31 2020 MTZ011-013-047-312130- Chouteau MT-Hill MT-Blaine MT- 245 PM MDT Fri Jul 31 2020 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BLAINE... SOUTHEASTERN HILL AND EASTERN CHOUTEAU COUNTIES UNTIL 330 PM MDT... At 245 PM MDT, Doppler radar was tracking a strong thunderstorm 13 miles southeast of Parker School, or 28 miles east of Big Sandy, moving south at 5 mph. Nickel size hail and winds in excess of 40 mph will be possible with this storm. This storm will remain over mainly rural areas of southwestern Blaine, southeastern Hill and eastern Chouteau Counties. LAT...LON 4803 10953 4815 10965 4820 10949 4809 10933 TIME...MOT...LOC 2045Z 000DEG 6KT 4813 10951 CMC
Special Weather Statement
National Weather Service Great Falls MT
312 PM MDT Fri Jul 31 2020
MTZ047-312200-
Blaine MT-
312 PM MDT Fri Jul 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN BLAINE COUNTY UNTIL
400 PM MDT...
At 312 PM MDT, Doppler radar was tracking a strong thunderstorm 19
miles southeast of Parker School, or 32 miles east of Big Sandy,
moving southeast at 20 mph.
Nickel size hail and winds in excess of 40 mph will be possible with
this storm.
This storm will remain over mainly rural areas of southwestern Blaine
County.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4797 10914 4785 10931 4807 10953 4811 10953
4815 10943
TIME...MOT...LOC 2112Z 317DEG 17KT 4806 10943
CMCSpecial Weather Statement
National Weather Service Great Falls MT
615 PM MDT Fri Jul 31 2020
MTZ045-010045-
Liberty-
615 PM MDT Fri Jul 31 2020
...A STRONG THUNDERSTORM WILL AFFECT CENTRAL LIBERTY COUNTY...
At 614 PM MDT, a strong thunderstorm was located 7 miles northwest of
Chester, moving southeast at 30 mph.
Winds in excess of 40 mph and nickel size hail are possible with this
storm.
Locations impacted include...
Chester, Lothair and Joplin.
This includes Highway 2 between mile markers 309 and 332.
Torrential rainfall is also occurring with this storm, and may cause
localized flooding. 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.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
To report severe weather, contact your nearest law enforcement
agency. They can relay your report to the National Weather Service
office in Great Falls.
LAT...LON 4857 11075 4848 11076 4832 11125 4871 11126
4878 11107
TIME...MOT...LOC 0014Z 332DEG 24KT 4859 11109
TPSpecial Weather Statement National Weather Service Great Falls MT 643 PM MDT Fri Jul 31 2020 MTZ011-010130- Hill- 643 PM MDT Fri Jul 31 2020 ...A STRONG THUNDERSTORM WILL AFFECT CENTRAL HILL COUNTY... At 643 PM MDT, a strong thunderstorm was located 8 miles east of Gildford, or 20 miles west of Havre, moving southeast at 20 mph. Winds in excess of 30 mph and pea size hail are possible with this storm. Locations impacted include... Beaver Creek and Kremlin. This includes the following highways... Highway 2 between mile markers 355 and 376. Highway 87 between mile markers 103 and 109. If outdoors, consider seeking shelter inside a building. Torrential rainfall is also occurring with this storm, and may cause localized flooding. 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. To report severe weather, contact your nearest law enforcement agency. They can relay your report to the National Weather Service office in Great Falls. LAT...LON 4865 11033 4873 11015 4851 10971 4835 11016 TIME...MOT...LOC 0043Z 333DEG 18KT 4859 11011 TP
The Great Falls radar (KTFX), 122 km away, was scanning. The volume nearest the first event began at 00:57 UTC.
2 hail. Local standard time, as filed.
A trained spotter reported ping pong ball (1.5 inch diameter) to lime (2 inch diameter) size hail and gusty winds in excess of 50 mph. Heavy rain also caused some flooding.
A trained spotter reported golf ball size (1.75 inch diameter) hail and gusty winds. Crop/tree damage and broken windows were observed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2020Every state in 2020This day in weather historyWarnings in Montana, July 2020
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 2026-10-01. Each event’s entry at NCEI: 904785, 904786.