Issued Sunday August 10, 2025 3:50 P.M. PDT

* HEAT ADVISORY FROM 12:00 P.M. MONDAY THROUGH 8:00 P.M. PDT TUESDAY *

Tonight…Fair skies. Lows in the upper 40s to upper 50s except lower 70s in thermal belts on slopes and hillsides with near 60 around 6000 feet. Light wind.

Monday…Mostly sunny and hot with a few afternoon clouds. Areas of smoke and haze along the Montana border. Highs in the upper 80s to mid 90s except locally in the mid 80s along the immediate shorelines of Pend Oreille and Priest Lakes with mid 70s around 6000 feet. Afternoon west to southwest wind 10 to 15 mph.

Monday night…Fair skies except for areas of smoke and haze along the Montana border. Lows in the upper 40s to upper 50s except lower to mid 70s in thermal belts on slopes and hillsides with lower 60s around 6000 feet. Light wind.

Tuesday…Mostly sunny and hot except for areas of smoke and haze along the Montana border. Highs in the lower to mid 90s except locally mid to upper 80s along the immediate shorelines of Pend Oreille and Priest Lakes with mid 70s around 6000 feet. Afternoon west to southwest winds 10 to 20 mph.

EXTENDED OUTLOOK (WEDNESDAY THROUGH SUNDAY):

Wednesday and Thursday…Dry, locally breezy to windy with a cooling trend. Lows in the 50s to near 60 Wednesday cooling to the 50s Thursday except mid 60s in thermal belts on slopes and hillsides Wednesday morning. Highs in the mid 80s to lower 90s Wednesday cooling to the upper 70s to lower 80s Thursday. Around 6000 feet lows in the upper 50s Wednesday cooling to the lower 50s Thursday. Highs near 70 Wednesday cooling to near 60 Thursday.

Friday through Sunday…Variable clouds with a slight chance of showers. Lows in the upper 40s to mid 50s with upper 40s around 6000 feet. Highs in the 70s with near 60 around 6000 feet.

In-Depth Weather Discussion for Northwest Montana/North Idaho/Northern Rockies

ISSUED 08/10/2025 5:10 P.M. MDT/4:10 P.M. PDT

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

Amplifying upper level ridge with axis along the West Coast stretching southeast toward the Colorado River will maintain its location while slowly expanding eastward with time. The hottest temperatures aloft remain to our west closer to the Cascades but by Tuesday the ridge axis will be overhead with the corresponding surface thermal trough also migrating east beneath the ridge. Tuesday will likely be the hottest day of this latest heatwave across our region with high and low temperatures by Tuesday nearly 10 degrees above average and 5 to 8 degrees above average for high and low temperatures respectively. We have already passed our climatologically hottest time of the year and with the rapidly shortening daylight hours now both our average high and low temperatures have also started to slowly decline. The main weather focus for the next few days besides the hot temperatures will be fire danger as the region is beginning to dry out after the beneficial rains that have fallen across Boundary County in North Idaho and most areas of Northwest Montana along and east of Lake Koocanusa as well as across Central and Southern Sanders Counties. For the rest of the region it has been incredibly dry with most areas in Bonner County in North Idaho not seeing even average rainfall since April, a rather remarkable 3 months going on 4 of well below average rainfall and therefore very high to borderline extreme fire danger. Unfortunately there are not really any signs as of this forecast writing for significant rainfall at this time.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

The upper level ridge will finally begin to get shoved further east by a rather strong and cool upper level low pushing in from the Gulf of Alaska and then dropping southeast along the British Columbia coastline. This will result in lowering atmospheric heights and thickness values leading to a cooling trend by the end of the week and next weekend along with a small chance for rainfall, especially across North Idaho. As the ridge axis finally shifts east of the region on Wednesday and takes the surface thermal trough with it coupled with rising surface pressures along the Washington coastline a tighter surface pressure gradient will develop across the region leading to a rather breezy to perhaps windy day on Wednesday. This will be the main day for fire weather personnel to pay attention to as the combination of warm to hot temperatures, low relative humidity values and gusty winds could lead to rapid growth of any new or existing fires. By Thursday heights and thickness values begin to drop more significantly with cooler air and temperatures dropping down to near seasonal averages at least during the day while the overnight lows will remain a bit more on the mild side with an increase in cloud cover. By Friday there are some signs of better jet dynamics and lift associated with the incoming upper level trough to help produce a few showers especially across North Idaho. With the flow pattern becoming increasingly cyclonic and southwesterly this will also tend to favor Bonner County with better upslope flow into the Northern Pandhandle and bring this region better chances for rainfall whereas they have largely missed out on the summer thunderstorms this season. The upper level trough looks to stick around for a while with cooler and slightly unsettled conditions remaining in the forecast throughout the weekend.