393 
FXUS65 KMSO 282120
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
320 PM MDT Mon Jun 28 2021

...DANGEROUS HEAT FOR NORTHERN ROCKIES THIS WEEK...

.DISCUSSION...

Both daytime and overnight temperatures will continue their steady 
increase through midweek, beneath mostly clear skies. Remember to
stay hydrated, take frequent breaks from daytime sun, seek out 
air conditioned spaces, do not leave anyone 
(pets/children/elderly) in an automobile, and limit physical 
exertion. Record high and record warm overnight temperatures are a
distinct possibility. Considering that the main portion of the 
high pressure responsible for the current heatwave across the 
western US is located east of the Northern Rockies, easterly winds
will continue to be present through midweek as well.

Temperatures will be blunted a bit by slight increases in shower and 
thunderstorm activity across the Northern Rockies Thursday through 
the weekend. Outside of the thunderstorm periods (mainly afternoon
and evening), the well above normal temperatures will continue
(particularly true of overnight temperatures). Most of the storm 
activity will develop over the southern Clearwater Mountains, 
southern Bitteroot, Lemhi County, and southwest Montana. There is 
much changeability in the thunderstorm forecast, so please check 
the forecast regularly. The main impact from any thunderstorms 
that develop is erratic, gusty winds and cloud-to- ground 
lightning. There is currently little opportunity for beneficial 
rainfall throughout the next week.

Long-range models and their ensembles suggest that the Northern
Rockies will see a pattern transition to southwest flow aloft late
this weekend through early next week, followed by another surge of
heat from high pressure east of the Rockies later next week.
Southwest flow may be conducive for some beneficial moisture,
however lightning and erratic winds will be a more significant
characteristic of the thunderstorms present. There is a chance
that a passing, weak storm system could move through the upper
level southwest flow and provide the background conditions that
favor a bout of strong to severe thunderstorms. 

&&

.AVIATION...Northeast winds aloft and clear skies will continue to 
be present across Northern Rockies air space during the next 24 
hours. There may be a few surface wind gusts to 20 knots through 
29/0300Z.

&&

.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 until 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.

&&

$$