An unusually strong ridge of high pressure settled over the Pacific Northwest bringing hot daytime temperatures and warm overnight lows. The consecutive days of heat made it difficult to cool locations without air conditioning.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. 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 MSO wrote it up.
An unusually strong ridge of high pressure settled over the Pacific Northwest bringing hot daytime temperatures and warm overnight lows. The consecutive days of heat made it difficult to cool locations without air conditioning. Daily record highs were set for several observation sites.
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 Missoula, MT wrote its last area forecast discussion before the first event at Jun 28, 2:09 AM MST, 8 hours 51 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
309 AM MDT Mon Jun 28 2021
...DANGEROUSLY HOT ACROSS THE NORTHERN ROCKIES FOR THE COMING
WEEK...
.DISCUSSION...Not much has changed with the heat wave forecast. We
should start breaking records tomorrow, Tuesday, which isn't to
say that it won't be hot today. It will be hot today, but 2007 and
2015 were both very hot years that set the records high for today.
After this heat wave, the records for most of the rest of the week
will be on par with 2007 and 2015.
The biggest challenge in the forecast will continue to be
thunderstorms. For this region, this hot air mass will also be
very moist. Several models are showing some sort of thunderstorms
in the forecast, but there is considerable differences in the
timing and location of those storms. This is a big challenge for
some of our statistical forecast tools. It causes the probability
to get spread out over time and space, which necessarily makes it
much lower. This makes it seem like the statistical tools are
saying there won't be storms at all, but really they're just
unable to narrow down a time and location. For this reason we've
raised the probability of precipitation starting mid week just to
get some mention of thunderstorms into the forecast.
Currently we aren't expecting strong storms, but the unusual
location of the ridge does make for some interesting forecast
challenges. First, storm motion will be from northeast to
southwest, just backwards of what it usually is! Also the flow is
relatively weak, so the storm will be slow moving. All of the
extra moisture in the atmosphere and slow moving storms gives us
cause for concern about flash flooding. However, the relatively
dry conditions recently mean that the soil and river systems can
soak up quite a bit of moisture. It's not the most likely set up
for flash floods, but we'll still be watching storms closely later
this week for specifically that threat.
&&
.AVIATION...High pressure over the region will cause VFR
conditions today with some afternoon fair weather cumulus clouds.
Near record high temperatures may cause density altitudes to be
higher than usual, so use caution if flying into any back country
air strips.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Heat Advisory from noon Tuesday to 8 PM MDT Thursday
Bitterroot/Sapphire Mountains...Missoula/Bitterroot
Valleys...Potomac/Seeley Lake Region.
Excessive Heat Warning from noon today to 8 PM MDT Thursday
Kootenai/Cabinet Region...Lower Clark Fork Region.
Heat Advisory from noon Tuesday to 8 PM MDT Thursday
Flathead/Mission Valleys...West Glacier Region.
ID...Heat Advisory from noon Tuesday to 8 PM MDT Thursday Eastern
Lemhi County...Western Lemhi County.
Excessive Heat Warning until 7 PM PDT Thursday Northern
Clearwater Mountains...Southern Clearwater Mountains.
Excessive Heat Warning until 7 PM PDT Thursday Lower Hells
Canyon/Salmon River Region...Orofino/Grangeville Region.
&&The national radar mosaic for the moment the first event began.
2 heat. Local standard time, as filed.
High temperatures ranged from 100 to 110 degrees Fahrenheit in the lower elevations with overnights in the mid 50s to low 60s.
Overnight lows ranged from the mid 50s to low 60s, while daytime highs were from the upper 90s to 106 degrees in the lower elevations.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2021Every state in 2021This day in weather historyWarnings in Montana, June 2021
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: 959426, 959427.