Key messages
- Change to more typical fall weather coming Friday.
Discussion
Temperatures warm yet again towards late summer levels, however satellite clearly shows clouds moving up from the south.
Showers develop this evening from south to north. A few thunderstorms will also be possible in Idaho and Lemhi Counties. For most locations at least a tenth of an inch of rain is likely, in northwest MT precipitation will be showery along the front and there is a 40 to 60% chance of receiving up to a tenth. After a fairly dry start to October, from Lost Trail Pass through southwest MT there is a 70 to 90% chance of receiving up to 1/2 of an inch of total precipitation by Friday evening. Above 6000 feet, as precipitation is ending a change over to snow is possible with a slushy trace to 3 inches in accumulations at locations like Georgetown Lake and Homestake and MacDonald Passes. Due to the timing of snow around rush hour Friday evening a winter weather advisory has been issued for the potential of slick driving conditions.
The models continue to have significant uncertainty after day 3 (Sunday). What is clear is temperatures will catch up to the calendar and October temperatures arrive. High temperatures are expected to be in the 50s for western MT and 60s for north-central ID, while low temperatures routinely fall into the teens and 20s in MT. Weather systems are less clear but there are more solutions depicting a system by mid-week. More details to come.
Aviation
A low pressure system will move northward into the Great Basin this afternoon, sending atmospheric moisture and instability northward. This will set the stage for numerous showers and isolated thunderstorms across north-central Idaho and southwest Montana by mid-afternoon through the evening hours. Precipitation becomes more widespread after 23/0600z, with periods of lowered visibility and ceilings expected through 23/1800z. Freezing levels will lower to around 5000 feet Friday evening, and while no impacts are expected, precipitation may end as wet snow at KBTM.
Mso Watches/Warnings/Advisories
MT...Winter Weather Advisory from 3 PM Friday to midnight MDT Friday night for Butte/Blackfoot Region.
ID...None.