ISSUED 07/27/2025 9:45 P.M. MDT/8:45 P.M. PDT
SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):
Shortwave that was not picked up very well by models passed through the region on Sunday bringing some surprise showers and thunderstorms across much of North Idaho and the northern portions of Lincoln County in Northwest Montana. Unfortunately at least one fire was sparked by these passing thunderstorms as a dry strike occurred outside of the heavier rain cores of these high based cells. The HI-RES NAM/WRF model which often does well in depicting thunderstorms did not pick up on the shortwave that passed through the region on Sunday however the 00Z run has picked up on another weak shortwave disturbance that passes through during the morning hours on Monday and generates a few fast moving, high based cells passing across North Idaho. After what happened on Sunday have gone ahead and included mostly silent 10% pops in the forecast but left out wording for showers and thunderstorms for Northwest Montana but included it in North Idaho. The timing of these weak features in the developing upper level pattern is problematic at best and cannot completely rule out at least isolated showers and thunderstorms over the next few days as a general weakness remains along the California coast with a weak and diffuse yet diffluent south to southwesterly upper level steering flow remaining across the region. Any thunderstorm clusters that develop associated with the upper level weakness off the California coastline could spin up a vort max or weak shortwave that would lift north into our region and when it encounters some upper level jet dynamics can kick off some fast moving high based thunderstorms as was the case on Sunday. Upper level ridging will continue to slowly build along the spine of the Continental Divide through Tuesday causing a deepening Gulf of Alaska adjustment wave or upper level low to amplify some and dig further south. As this transition occurs our upper level steering flow will back to a more southerly pattern which will help steer weak shortwave rotating around the Intermountain western ridge to move north into our area. This will have potential large implications on our weather pattern this week. Read below for details.
LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):
The airmass across our region will become increasingly more hot and unstable as the continental ridge remains anchored along or just east of the Continental Divide with its axis extending up into southern Canada while the Gulf of Alaska adjustment wave continues to also amplify offshore. The flow between these two opposing features will be almost due southerly which will also become increasingly diffluent across our region helping to generate vertical motion through the atmosphere and lift which, in turn will result in increasing chances for showers and thunderstorms. The atmosphere will NOT be “advecting" monsoon moisture” into the region as some forecasters are suggesting but rather as the airmass remains rather stagnant and daily thunderstorms increase in coverage especially across Oregon and Central Idaho the airmass will continue to modify over time and become increasingly moist and unstable. Despite increasing surface dewpoints and higher relative humidity values much of the thunderstorms that develop across our region from Wednesday through Friday will be of the elevated, forced convective type as surface based convection looks to be largely capped by the presence of the upper level ridge. With our convection largely being elevated and dynamically forced much of the activity is likely to occur during the evening and overnight into early morning hours before waning during the later morning into the afternoon hours. By later Friday and into Saturday the weak upper level low that has been spinning off the California coast will finally move northward with colder air aloft and will aid in finally allow convection to become surface based in addition to elevated. Showers and thunderstorms will become increasingly heavy rain producers as the airmass modifies with cloud bases lowering and convection starting earlier in the day. The Gulf of Alaska adjustment wave will finally begin to push east into British Columbia by Sunday which will shift our upper level steering flow to a more southwesterly and westerly flow which will shunt any additional shortwaves rotating around the Continental ridge to also shift further east. This will result in a drying trend with near seasonal to slightly below seasonal high temperatures by Sunday with convection likely becoming focused more along the Canadian border and eastern mountains of Montana. Interestingly enough we are now at our climatologically hottest time of the year for high temperatures which range from 85-93 degrees, hottest in Northwest Montana valleys of Troy, Libby, Thompson Falls. As for low temperatures those readings begin to decrease from a climatological scale on July 28th so the nights on average will now begin to cool as the daylight continues to decrease each day allowing for more effective radiational cooling. We are now loosing almost 3 minutes of daylight each day now. Autumn will be here before we know it.
ISSUED 07/13/2025 7:45 P.M. MDT/6:45 P.M. PDT
SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):
Another hot and dry day across the region on Sunday with most valley locations away from and upwind from the larger lakes seeing their temperatures soar into the 90s or 10 to 15 degrees above seasonal averages. This will only make the changes coming in about 24 to 36 hours even more brutal to bear as temperatures on Tuesday will be 10 to 20 degrees below seasonal averages for mid July and with a brisk northeast wind will make it feel very fresh indeed. A cold (for July) upper level trough is currently pushing into British Columbia as of this writing on Sunday evening and will begin to drop southeast through the province overnight into the day on Monday. As this system approaches surface pressures will fall along the Continental Divide on Monday morning allowing for a breezy day with west to southwest winds to develop. Monday will still be very warm and anywhere from 5 to 10 degrees above average for mid July. Here are the main takeaways from this unusually strong summer system:
* Showers and thunderstorms will begin to develop along the Canadian border Monday afternoon and progress southward as convergence and instability increases along with strong jet dynamics associated with the incoming strong vort max and upper level trough. These convective showers will likely begin to organize into a more consolidated area of rain overnight with the focus occurring over Northwest Montana.
* Snow levels, yes you read that correctly, will drop to between 7,000 to 7,500 feet overnight into Tuesday morning across Northwest Montana with the Whitefish Range and to a lesser extent the Cabinet Mountains seeing accumulating snowfall at the highest elevations. Anticipate between 2 to 4 inches to fall across the highest peaks above 7,500 feet.
* Rainfall totals look to be between 0.25 to 0.75 inches with local amounts up to 1.00 inch across Northwest Montana especially across Lincoln County with the lower amounts likely across Sanders County. Across North Idaho rainfall totals look to be between 0.10 inches to 0.30 inches with local amounts over 0.50 inches where thunderstorms occur and along the Montana border.
* Strong northeast winds late Monday into early Tuesday morning. Northeast winds will dramatically increase in the typical areas such as through the Purcell Trench in North Idaho between Elmira and the Kootenai County line, across Northwest Montana through the Clark Fork River Valley especially between Noxon and Heron, Bull Lake, Highway 2 between Libby and Troy, Lake Koocanusa and the Tobacco Valley. Winds in these areas will likely become sustained for a time between 25 to 40 mph with gusts to 50 mph possible. Winds could gust over 60 mph across higher elevations. Elsewhere in the typically non windy areas expect northeast winds of 15 to 25 mph with local gusts to 30 mph at times.
* Temperatures will drop from the mid 80s to mid 90s Monday to the upper 50s to near 70 in the valleys on Tuesday with brisk northeast winds. Across higher terrain above 6000 feet temperatures near 70 on Monday will drop to the mid to upper 40s on Tuesday with brisk northeast winds and wind chills in the lower to mid 30s.
* Frost potential? Colder Northwest Montana valleys and even an isolated spot or two in North Idaho away from the shoreline of Priest Lake and in portions of Selle Valley could see frost on Wednesday morning and to a lesser extent on Thursday morning. Northwest Montana valleys that are likely to see frost are Yaak, Trego, Olney, south of Libby near the airport, McGinnis Meadows, Happys Inn and possibly near Trout Creek. By Thursday morning only the Yaak and McGinnis Meadows areas are likely to have the threat of frost.
LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):
Uncertainty in the long term portion of the forecast as models are a bit split as to what the eventual pattern will set up as with outcomes ranging from upper level ridging to broad and weak troughing with ridging remaining offshore. For now with so much attention being paid to the short term broad brushed the long term forecast as a more middle of the road type with temperatures returning to above average readings but not as warm as the warmer ridge scenarios would suggest. Gut feeling is that the ridge axis may remain well to the west along the West Coast or even offshore allowing for broad and cooler northwest upper level flow to remain in place allowing periodic shortwaves to pass through. Should this solution prove correct conditions would become more unsettled and chances for periodic showers and thunderstorms will need to be reintroduced to the forecast. For now have kept things dry and will see how things play out after the significant weather event passes by Tuesday night.
ISSUED 07/06/2025 8:45 P.M. MDT/7:45 P.M. PDT
SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):
Fairly pleasant weekend across the region with temperatures running a few degrees above seasonal averages for early July, a nice break from the hot and dry conditions we have had for much of the Spring and Summer season thus far and also rather unusual but certainly not unheard of. Upper level ridging will amplify across the region ahead of a Gulf of Alaska trough that will be brushing by the region later in the day on Wednesday bringing mainly fire weather concerns but also some precipitation chances as well. Before then our atmosphere will continue to dry and warm with a stable airmass remaining in place. By Tuesday which will likely be the hottest day this week, high temperatures will be running a solid 10 to 15 degrees above seasonal averages once again but no records are likely at this time. The thermal trough will be right overhead to start the day on Tuesday which will help temperatures rise rapidly before the thermal trough axis shifts east and south which will allow for west to southwest breezes to pick up and increase fire danger.
LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):
As the Gulf of Alaska upper level trough begins to swing inland it will result in rapidly falling atmospheric height and thickness falls as this will be a rather strong and cool trough by July standards pushing into the region. With the rather robust thermal gradient between in the incoming airmass and the retreating hot airmass surface pressure falls on the lee side of the Continental Divide along with rapidly rising surface pressures along the coast will create a tight surface pressure gradient across our region. Anticipate a very breezy to windy day on Wednesday across the region and although temperatures will likely drop about 10 degrees from Tuesday’s hot readings they will still be above average and conditions will be rather dry thus increasing the fire danger. Fortunately the rains that fell late last week will help mitigate the danger slightly. By late in the day a vort max associated with the cool upper level low will move along the International border and will trigger isolated to scattered showers and thunderstorms. The main question as of now is how far south will the vort max travel. For now thinking that the precipitation threat will mainly be along and within 30 miles or so of the Canadian border but if this feature looks to track further south chances will need to be expanded as well. Thursday will see temperatures near or perhaps even a couple of degrees below mid July seasonal averages and looks to overall be a very pleasant day. By Friday the next transient upper level ridge will push through the region bringing another warm up with temperatures rising to 6-10 degrees above average once again with yet another upper level trough likely to follow up by the following Monday but that is beyond this forecast cycle. Stay tuned!