Issued Sunday March 30, 2025 7:45 P.M. MDT
Tonight…Increasing clouds and not as cold. Rain and snow showers becoming likely after midnight from Lake Koocanusa south and west with isolated to scattered rain and snow showers after midnight north and east of Lake Koocanusa. Snow level near 3000 to 3500 feet. Local snow accumulations of 1 to 2 inches possible above 4000 feet. Lows in the upper 20s to mid 30s with mid 30s around 5000 feet. Light wind except local east to northeast winds 10 to 15 mph through favored canyons and across ridge tops.
Monday…Considerable cloudiness and cooler with scattered to numerous rain and snow showers. Isalted afternoon thunderstorms possible along the Idaho border. Snow level near 3500 to 4000 feet. Local snow accumulations of up to 1 inch possible above 4500 feet. Highs in the upper 40s to mid 50s with upper 30s around 5000 feet. Light wind except gusty winds possible near heavier showers and thunderstorms.
Monday night…Mostly cloudy with scattered rain and snow showers. Snow level lowering to near 2500 to 3000 feet. Local snow accumulations of up to 1 inch possible above 3500 feet. Lows in the upper 20s to mid 30s with upper 20s around 5000 feet. Light wind except ridge top winds southwest 10 to 15 mph.
Tuesday…Variable cloudiness with scattered rain and snow showers. Snow level rising to near 3500 feet in the afternoon. Local snow accumulations of up to 1 inch possible above 5000 feet. Highs in the upper 40s to mid 50s with mid 30s around 5000 feet. South to southwest winds 10 to 15 mph with gusts to 20 mph through favored canyons, along portions of Lake Koocanusa and across ridge tops.
EXTENDED OUTLOOK (WEDNESDAY THROUGH SUNDAY):
Wednesday and Thursday…Cool and unsettled with a chance of valley rain and snow showers and mountain snow showers. Lows in the upper 20s to mid 30s with near 30 around 5000 feet. Highs in the mid 40s to lower 50s with mid 30s around 5000 feet.
Friday through Sunday…Mostly sunny, warmer days and clear, frosty nights. Lows in the mid 20s to mid 30s except warming to the lower 40s in thermal belts on slopes and hillsides by Sunday. Highs in the 50s Friday warming to the lower 60s to lower 70s by Sunday. Around 5000 feet lows in the mid 20s Friday warming to the upper 30s by Sunday. Highs in the upper 30s Friday warming to the lower 50s by Sunday.
In-Depth Weather Discussion for Northwest Montana/North Idaho/Northern Rockies
ISSUED 03/30/2025 8:05 P.M. MDT/7:05 P.M. PDT
SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):
Another pleasant and very warm early Spring day across the Northern Rockies on Sunday with most locations in North Idaho running around 5 or more degrees above the seasonal averages for the date while across Northwest Montana temperatures were closer to seasonal averages thanks to cool air advection from the east due to the placement of the surface high just east of the Continental Divide. A shortwave spinning off of the main cold upper level low off the Oregon coast will rotate north into the region overnight bringing a band of rain and snow showers with it that should largely exit into Canada by mid morning on Monday. Behind this initial shortwave some cooler air aloft along with some weak vorticity maximums should spark off at least scattered afternoon rain and snow showers with an isolated thunderstorm or two possible mainly across North Idaho although this carries low confidence given the amount of snow cover that remains across our mountains. Snow cover is a thunderstorm inhibitor to surface based convection as the cold snow cover serves to cause sinking air over the surface similar to the larger lakes of Pend Oreille and Priest due to their cold waters during the Spring months. Another weak shortwave looks to swing northward on Monday night into Tuesday but still some uncertainty in the track this wave will take. This could be one of those situations where Northwest Montana sees higher precipitation chances than North Idaho if the track if further south and east which would pull the best surface convergence and lift further east into Northwest Montana with North Idaho possibly coming under the influence of NVA (Negative Vorticity Advection) which would result in a more stable atmosphere at least during the morning hours. By Tuesday afternoon weak instability across the region will support a few afternoon rain and snow showers once again. The overall airmass will be cooling over the next 48 hours which will result in lowering snow levels eventually down to near all valley floors however not much in the way of accumulations are anticipated below 4000 feet at this time and even above 4000 feet not much more than perhaps 3 to 4 inches is anticipated.
LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):
Cool upper level trough will linger across the region at the start of the extended forecast period with shortwaves rotating around this feature helping to kick off at least scattered valley rain and snow showers with mountain snow showers along with chilly temperatures for early April but nothing unusual at all. If any heavier showers develop overnight or during the early morning hours on Wednesday or Thursday could see some brief slushy snow accumulations on valley floors in localized areas but this is far from certain at this time. A significant large scale pattern change looks to take place by next weekend that potentially could last for several days if not longer. Spring will make a serious attempt to move into the Northern Rockies as the entire North American continent looks to undergo a flip into a positive PNA pattern with a late season cold Hudson Bay low taking up residence across Eastern Canada and the Great Lakes and Northeast US while a rather large and moderately strong Western US ridge builds across the region. Temperatures will warm up beneath this set up but should remain around 10 or so degrees above seasonal averages so am not anticipating any records to be broken or even threatened at this time. Atmospheric heights and thicknesses values, while warmer than where they should be at this time of year, do not look terribly high and this will be good news to help preserve our mountain snowpack which will definitely take a hit with the warmer temperatures. The atmosphere looks very stable under this set up with plenty of sunshine during the day with only a few fair weather cumulus clouds in the afternoon hours and clear, frosty nights on valley floors. It will likely be a good time to start those Spring clean-up chores outside after our rather lackluster winter snowfall at least across lower elevations. If you are relatively new to the area a word of caution. While it will be rather warm this upcoming weekend and many stores have started to bring out plants and flowers the growing season for most of our region doesn’t even begin until the middle of May and in some of our colder pockets early June so while it may be very tempting to want to buy plants and flowers it is simply way too early at this stage as they will need to be protected in a greenhouse. Average last frost date for Sandpoint, ID is May 23rd, Priest River, ID is May 29th, Libby, MT is June 3rd just to name a few. And as a reminder all of these sites saw killing frosts in the middle of June last year so be very careful.