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.

ISSUED 03/26/2025 9:05 P.M. MDT/8:05 P.M. PDT

SHORT TERM (WEDNESDAY NIGHT THROUGH FRIDAY):

Warmest day of the year thus far with many record highs set across the region. The approach of a dynamic and strong upper level and surface low well offshore has been producing some active weather over and especially west of the Cascade mountains late Wednesday afternoon and into the evening hours. As expected our area has remained very quiet throughout the day despite lots of lower level moisture and this once again shows that moisture is NOT a necessary ingredient to generate thunderstorms. The best lift, dynamic forcing, surface convergence and upper level divergence remains to the west where thunderstorms are currently firing off. Will see a shortwave rotate up into the region overnight and this is expected to trigger some elevated, forced convection across the Columbia Basin that should track northeast into our region however with the abundant mountain snowfall still remaining in our region these thunderstorms will likely not be very robust but contain the usual heavy rain, small hail, gusty winds and lightning. Snow cover is an inhibitor to thunderstorm development however these cells will be tied to elevated instability so will likely see them hold together better given their elevated nature. Colder upper level trough will begin to swing inland during the day on Thursday with cooler temperatures and actually better instability, surface convergence and vertical motion for a much better setup for showers and isolated thunderstorms. These cells will be surface based rather than of the elevated forced type that we will see overnight Wednesday. However with the much cooler airmass these thunderstorms will likely be relatively low topped with tops likely only around 30,000 to 35,000 feet at best. Snow levels will also be coming down Thursday lowering to near 5500 feet by afternoon. The cool upper level trough will continue to rotate inland on Friday further lowering snow levels down to near 4000 feet. Overall Friday looks like a cool, showery day with snow in the mountains so if you’re headed up to Schweitzer for Community Ski Day Friday plan on lower visibilities with occasional snowfall. Can’t entirely rule out an afternoon thunderstorm on Friday as there will still be some dynamics associated with the upper level low moving in but again these cells, if they develop, will be more of the garden variety. Still if you’re planning on heading up to any of our local ski resorts Thursday or Friday be sure to check if lightning is in the region. Best chances will be during the afternoon hours. Temperatures by Friday should drop down back close to seasonal averages after the past very warm days we have seen.

LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY):

Overall a progressive pattern will remain in place with the parent upper level low that will directing a zonal jet stream into our region remaining largely well offshore. Periodic shortwaves will rotate through the region each bringing better lift and dynamics to generate precipitation but no large storms are anticipated at this time. For the weekend the best day currently looks to be Sunday with the lowest chances for precipitation but a few mountain showers are possible, especially across North Idaho. Temperatures will remain close to seasonal averages through the period with occasional rain and snow in the valleys and mainly snow up in the mountains above 4,000 feet. Occasional breezy conditions will also be possible. Overall typical late March/early April weather for the Northern Rockies. Long range outlooks continue to keep our region with odds favoring below average temperatures and above average precipitation. Would not be surprised to see at least one more accumulating snowfall down to valley floors sometime in the next couple of weeks as is often the case in April. Of course the timing of the snowfall will be critical if it occurs at all as it will need to fall overnight for it to stick as the sun angle is simply too high at this time of year for accumulating snowfall in the valleys during daylight hours now.

ISSUED 03/24/2025 6:55 P.M. MDT/5:55 P.M. PDT

SHORT TERM (MONDAY NIGHT THROUGH WEDNESDAY):

A robust warm front moved across the region on Sunday night/early Monday morning, something that we rarely see in this part of the country with temperatures on a steady climb overnight along with snow levels. Our region now resides on the warmer side of the upper level jet stream with the effects of the upper level ridge and its rising heights and thickness values building across our region. These will reach peak strength on Wednesday before the ridge gets shoved off to the east as the next Eastern Pacific upper level low and associated trough push into the region. Another very mild night in store as cloud cover and a warm airmass combine to bring low temperatures closer to June averages rather than late March averages. Some areas could see their high temperatures approaching record highs for Tuesday and will include the records for some select towns across our region below. More areas are likely to at least tie if not break their records for Wednesday as many areas have some rather “soft” records that day. The cold upper level low will begin its approach on Wednesday but at this time the atmosphere, while certainly very moist, will lack any triggers and instability to generate much in the way of precipitation so Wednesday looks to largely be a dry day save for perhaps some late day showers that pop up across North Idaho. As was mentioned in Sunday evenings discussion, moisture is really not a necessary ingredient for precipitation as models have already factored atmospheric moisture into the equations when they compute instability and precipitation chances. Here are some select locations record highs for the 25th and 26th of March and the year they occurred. The current forecasted highs are also given for both days:

Location: Record highs 25th/26th: Years of occurance: Forecasted high 25th/26th:

Bonners Ferry. 70/65 1970/1965 64/69

Priest River 66/64 1966/1964 63/68

Sandpoint 64/62 2001/1997 61/66

Eureka 66/67 1999/1966 64/72

Libby 71/73 1971/1973 66/73

Thompson Falls 73/71 1960/1978 66/74

Troy 68/68 1999/1992 67/75

Trout Creek 68/67 2001/1997 65/72

LONG TERM (WEDNESDAY NIGHT THROUGH MONDAY):

Wednesday night still looks to be the most portion of this forecast period with the approach of the upper level low and our area residing squarely in the favorable northeast quadrant of the upper level low, good diffluence aloft and decent mid level instability. Should see some good nocturnal thunderstorms develop in the elevated instability that will be present. As is the case with most of our warmer season thunderstorm outbreaks these cells will not likely be tied to surface based instability as the surface is likely to remain capped through this portion of the forecast but instead will rely on the mid level instability and strong lift along with favorable jet dynamics to generate convection. Most likely outcome will be lightning, heavy rain and perhaps small hail. Things will quiet down a bit early Thursday but as the colder core of the upper level trough passes overhead will see a regeneration of showers and thunderstorms. With the much colder airmass coming into the region these surface based showers and thunderstorms will be low topped (tops will only be around 25,000 to 30,000 feet at best) and contain graupel and infrequent lightning. Snow levels will also be lowering to near 4,000 feet by afternoon with accumulating snow returning to the mountains at that time. The rest of the forecast period looks predominately unsettled with several shortwaves passing through and each one bringing its own round of rain and snow with snow levels lowering to near valley floors during the colder parts of the day and rising during peak heating off of valley floors. Temperatures after Thursday will return close to seasonal averages for late March which is near 50 in valley locations.