Issued Sunday June 22, 2025 4:20 P.M. MDT
Tonight…Showers and thunderstorms ending from north to south towards morning. Thunderstorms may contain very heavy rain, small hail, frequent lightning and gusty winds. Patchy fog developing overnight. Lows in the 40s with near 40 around 5000 feet. Light wind except gusty winds possible near thunderstorms.
Monday…Areas of fog and low clouds in the valleys through mid morning otherwise variable cloudiness with scattered showers and thunderstorms in the early morning across central and southern Sanders County and region wide in the afternoon. Warmer with highs in the mid 60s to mid 70s with mid 50s around 5000 feet. Afternoon west to southwest winds 5 to 15 mph except gusty winds possible near thunderstorms.
Monday night…Partly cloudy in the evening with isolated to widely scattered showers and thunderstorms then fair skies overnight with patchy valley fog and low clouds developing. Lows in the mid 30s to mid 40s except lower 50s in thermal belts on slopes and hillsides with upper 40s around 5000 feet. Light wind.
Tuesday…Mostly sunny in the morning. Partly cloudy and warmer in the afternoon. Isolated late afternoon showers and thunderstorms along the Canadian border. Highs in the mid 70s to mid 80s with upper 60s around 5000 feet. Afternoon southwest winds 5 to 15 mph.
EXTENDED OUTLOOK (WEDNESDAY THROUGH SUNDAY):
Wednesday through Saturday…A slight chance of showers and thunderstorms, especially along the Canadian border. Lows in the upper 30s to upper 40s with lower to mid 50s around 5000 feet. Highs in the mid 70s to mid 80s with lower to mid 60s around 5000 feet.
Sunday…Mostly sunny and warmer. Lows in the 40s except mid to upper 50s in thermal belts on slopes and hillsides with mid 50s around 5000 feet. Highs in the lower 80s to lower 90s with lower 70s around 5000 feet.
In-Depth Weather Discussion for Northwest Montana/North Idaho/Northern Rockies
ISSUED 06/22/2025 3:40 P.M. MDT/2:40 P.M. PDT
SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):
Scattered showers and thunderstorms are developing as of this writing on Sunday afternoon across much fo the region with the focus for now located across Northeast Washington and North Idaho with much more activity really starting to fire off further north across South Central and Southeastern BC. This activity is being triggered by a potent shortwave dropping south southeast on the backside of a rather large upper level low spinning across Manitoba and Saskatchewan. This feature looks to be the main trigger for an active afternoon and especially into the evening and first part of the overnight period. This shortwave has a good signature for some impressive thunderstorm activity with a strong signal of a convergence/divergence couplet across North Idaho and much of Northwest Montana, plenty of instability or vertical motion(Lifted index values of -1 to -3) and some good mid level lift associated with the shortwave itself. Anticipate expanding coverage of showers and thunderstorms through the remainder of the late afternoon and evening hours with focus shifting east with time before exiting Northwest Montana sometime around dawn on Tuesday. The main effects from these showers and thunderstorms will be very heavy rains, small hail, frequent lightning and gusty, erratic winds. Most areas should see a good wetting and in some cases, soaking rain from this round of convection. With the moist and cool airmass in place behind the departing shortwave I expect most valley locations to wake up on Monday morning to a rather dull and murky start with a lot of stratus and patchy fog around but with the high June sun angle this will quickly evaporate with a nice day on Monday looking likely. Another shortwave will track a bit further north on Monday afternoon closer to the Canadian border so far northern portions of Bonner County, all of Boundary County and much of Lincoln County north of Highway 2 could see another round of isolated to widely scattered showers and thunderstorms. These will tend to fade away shortly after sunset as the upper level dynamics to keep things going will not be present with this shortwave passage and its location will be too far north to bring much into our region. By Tuesday transitory upper level ridging will build into the region and while temperatures will rebound considerably and it may even feel a bit on the humid side the atmosphere will be largely stable so little in the way of convection is currently expected for Tuesday afternoon. Could see some late day showers or thunder pop up across North Idaho along the Washington border but this is far from certain at this time.
LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):
Zonal flow will become established across the region at the start of this forecast period with weak passing shortwaves along the Canadian border helping to trigger largely diurnal patterns in showers and thunderstorms. How widespread activity will be ultimately will be determined by how far south passing shortwaves move through from Wednesday through Friday. At this time, best chances look to remain along the Canadian border with the further south you go seeing lesser chances of some much needed rainfall. By next weekend there are signs that a new Gulf of Alaska upper level low will begin to amplify a bit off the West Coast which will in turn allow the Continental Upper level ridge to build north from the Desert Southwest. This looks to initially cause a sharp drying and warming trend across our region by next weekend as atmospheric heights and thickness values rise so a return to lower 90s is likely especially across the typically hotter Northwest Montana valleys (think Troy, Libby, Thompson Falls, Plains) with other valley locations likely to rise well up into the 80s again away from the influence of the larger lakes(Priest & Pend Oreille). Beyond the weekend and into the holiday week unsettled and cooler conditions are evenly split with a hotter and drier solution so it is tough to pinpoint exactly at this time if you’re trying to plan well in advance what may happen weather wise during the holiday week.