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.

ISSUED 06/18/2025 9:45 P.M. MDT/8:45 P.M. PDT

SHORT TERM (WEDNESDAY NIGHT THROUGH FRIDAY):

Upper level trough passed to the north of the region on Wednesday and brought dry, breezy conditions but no precipitation and this was anticipated. A larger and colder upper level low continues to spin off of the British Columbia coastline and is also slowly working its way southward parallel to the coast line. This feature looks to be off the Washington coast by Thursday afternoon with an enhanced upper level jet stream developing overhead of our region as the thermal gradient aloft begins to tighten between higher atmospheric heights and thickness values to our south and east and lower atmospheric heights and thickness values to our north and west. The Desert Southwest will be experiencing some of the hottest temperatures of the summer the next few days which is very typical at this time of year as the continental ridge remains centered across southern Arizona and Northern Mexico. For our region the enhanced upper level jet stream will help create some increasing mid and high level cloudiness that will cause the sun to definitely become much more dim during the afternoon hours but little in the way of vertical motion through the atmosphere will not result in any precipitation Thursday. Overnight Thursday and more likely early Friday morning an approaching shortwave will ride in on the strengthening upper level jet on the southeast side of the incoming upper level low and will likely create enough mid level instability to fire off some showers and thunderstorms initially across Sanders County in Montana. As the upper level low shifts further south off the Oregon coast before beginning to swing inland the rest of the Northern Rockies will come under increasingly diffluent flow aloft along with the left exit region of the jet stream. This will cause showers and isolated thunderstorms to become more widespread across all of North Idaho and Northwest Montana. This will be very beneficial rains as our region is seeing one of the driest spring seasons in recent memory. Temperatures will drop significantly on Friday with most valley locations only rising into the 60s at best with a lot of cloud cover around and showery conditions. Even cooler conditions are likely for part of the weekend. Read below for more details.

LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY):

How wet the weekend turns out will ultimately depend on where exactly the cold upper level low sets up and moves inland along with the associated shortwaves that will be spinning around the edges of the system creating the lift and dynamics to generate the precipitation. At this time it looks like the most precipitation will fall across Northwest Montana but this could change with time. Still there is a good chance that all areas will see at least a quarter inch of rainfall and while not much, it is certainly much better than nothing at all. Many areas will likely see more than that and some areas could see as much as 2 to 3 inches of rainfall if everything comes together correctly! In addition the atmosphere will be cooling such that snow levels are looking to drop down to near 6000 feet or so. Above that elevation several inches of heavy wet snow is certainly possibly with perhaps the Whitefish Range in Lincoln County seeing up to a foot of new snow above 6500 to 7000 feet again if all comes together just right. Unsettled, cool and showery conditions will continue into Sunday as the upper level trough weakens and shifts further east but enough instability will remain for continued showery conditions and possibly some thunderstorms. By Monday a new upper level trough will begin to drop southwest across Alberta placing our region in northerly steering flow aloft and models are showing a shortwave approaching during peak daytime heating Monday afternoon. If this holds true then a pretty good chance of afternoon and evening showers and thunderstorms will occur on Monday and these could produce some heavy rain as well as small hail. Some weak lingering instability continues on Tuesday for perhaps one or two showers but by Wednesday upper level ridging will return bringing back unseasonably warm and stable conditions with a lot of sunshine returning. Long range outlooks however tend to favor above average precipitation for the next 6 to 10 and 8 to 14 days. Let’s hope this proves correct!

ISSUED 06/15/2025 8:20 P.M. MDT/7:20 P.M. PDT

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

Upper level ridging over our region with a cool upper level low spinning off the Central BC coastline is bringing a stable southwest upper level flow across our region and also helping to keep atmospheric heights and thickness values knocked down. While this still results in dry conditions and warmer than seasonal temperatures no excess temperatures either way are anticipated with this pattern the next few days. Nights will be seasonably cool in the upper 30s to upper 40s on valley floors which is typical for mid June while daytime temperatures will warm Monday a few degrees over Sunday’s highs and rise into the upper 70s to upper 80s which is around 5-7 degrees above mid June seasonal averages. Southwesterly afternoon breezes will pick up the next two afternoons as the thermal trough shifts to align with the Continental Divide as a couple of weak shortwaves rounding the BC upper level low push in. The dynamics and lift will remain north of the border so no chances for rain for our region at least through this portion of the forecast but changes are on the way. Read below for more information.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

The first part of the extended forecast period doesn’t look very exciting from a weather standpoint with a continuation of a dry and stable airmass that will result in warm, mostly sunny days and clear, pleasantly cool nights and early mornings with the dry airmass in place. There will continue to be some afternoon and evening south to southwest winds as the thermal trough remains along or just east of the Continental Divide each day and with a deepening marine influence west of the Cascades associated with higher surface pressures this will ensure that the winds remain southwesterly. By late Thursday into Friday the cool British Columbia upper level low will have begun to swing further south and also begin to approach the Washington and Oregon coastlines. This will result in a lowering of atmospheric heights across our region and also result in the steering flow becoming southerly and diffluent. With the approach of the upper level low shortwaves will move much closer to our region and when they encounter the upper level diffluence ahead of the incoming upper level low this will increase the instability and vertical motion through the atmosphere which is what we need to generate precipitation. The pattern then looks much more typical of June for next weekend with much cooler temperatures and some beneficial rains and even some high elevation snows as well. Snow levels currently look to lower to near 6000 feet so keep this in mind if you have any backcountry trips or are thinking of riding the lifts up to the summit of Schweitzer or Big Mountain. With the incoming upper level low the atmosphere will continue to cool probably faster aloft than at the surface which will help continue to generate instability and the threat of thunder so keep this in mind. Still time for things to change but with the MJO showing some amplification once again and re-emerging in Phase Space 7 which is the West Pacific this corresponds to cooler and wetter conditions for our region so let’s hope the forecast trends wetter still.