Issued Sunday February 16, 2025 7:15 P.M. PST

* WINTER WEATHER ADVISORY THROUGH 10:00 A.M. PST MONDAY *

Tonight…Occasional snow. Accumulations of 1 to 3 inches possible below 4000 feet with 2 to 4 inches possible above 4000 feet. Lows in the 20s with lower 20s around 6000 feet. Light wind.

Monday…Occasional snow, decreasing in the late afternoon from the north. Accumulations of 1 to 2 inches possible below 4000 feet with 1 to 3 inches possible above 4000 feet. Highs in the lower to mid 30s with mid 20s around 6000 feet. Light wind.

Monday night…Mostly cloudy with scattered snow showers. Local accumulations of up to 1 inch possible, mainly above 3000 feet. Lows in the upper teens to mid 20s with mid teens around 6000 feet. Light northeast wind except local northeast winds 5 to 15 mph through the Purcell Trench from Samuels to Athol and across ridge tops.

Tuesday…Variable clouds with isolated snow showers. Highs in the lower to mid 30s with lower 20s around 6000 feet. Light northeast wind except local northeast winds 5 to 15 mph through the Purcell Trench from Samuels to Athol and across ridge tops.

EXTENDED OUTLOOK (WEDNESDAY THROUGH SUNDAY):

Wednesday…Snow likely. Lows in the upper single digits to upper teens with lower teens around 6000 feet. Highs in the upper 20s to lower 30s with lower 20s around 6000 feet.

Thursday…Dry and a little warmer except for a slight chance of snow showers. Lows in the 20s with lower 20s around 6000 feet. Highs in the 30s with upper 20s around 6000 feet.

Friday through Sunday…Unsettled and not as cold with a chance of valley rain and mountain snow. Lows in the 30s with upper 20s around 6000 feet. Highs in the upper 30s to mid 40s with lower 30s around 6000 feet.

In-Depth Weather Discussion for Northwest Montana/North Idaho/Northern Rockies

ISSUED 02/16/2025 8:00 P.M. MST/7:00 P.M. PST

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

Widespread, steady light snow continues across much of the region and will likely continue to do so for the next 24 hours or so before some shifts in the dynamics cause a weakening and eventual dissipation of the snowfall. Our area sits in a convergence zone of a large, cold Hudson Bay low circulating to our east across southeastern Manitoba and northern Minnesota with a weakness extending to the south and west of our area. Northwesterly upper level jet energy is passing overhead with a weakly induced surface trough across the Northern Rockies that is helping to provide a little added lift and vertical motion to keep snow ongoing. A shortwave rotating around the Hudson Bay low from the north will drop down overnight lasting into Monday morning and will help focus another period of steadier, light to occasionally moderate snowfall during this time frame before the convergence axis slips to the south of our region with colder, stable air moving into the region by later in the day on Monday. Polar air will slide into Northwest Montana by Monday afternoon and result in some gusty northeast winds in the usual areas around the Tobacco Valley near Eureka and along portions of Lake Koocanusa. By Tuesday these winds will spread south and west and begin to spill into North Idaho as well. With the winds shifting to the northeast and coming off the Continental Divide causes an overall drying and more stable atmosphere to move overhead. While not bitterly cold the air will still have a bit of a bite to it with the northeast winds remaining steady in those areas that are prone to the winds. As for the snowfall for the next 24 hours generally widespread additional totals of 2 to 4 inches are likely in the valleys with perhaps an additional 3 to 6 inches in the higher elevations. These numbers could be off by a couple of inches either way. Still snow advisories have been issued for our entire region by WFO Spokane for North Idaho and WFO Missoula for Northwest Montana. These advisories run through Monday AM/PM depending on location.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

Some significant changes appear to be headed into our region by the end of the week and next weekend which has been anticipated for a while as the MJO continues its eastward propagation across the Pacific looking at satellite like it is in Phase Space 8 and progressing into Phase Space 1 as of this writing (Phase Space 8/1 is the Western Hemisphere/Africa). At this time of year Phase Space 1 corresponds to warmer conditions and sometimes drier conditions across our region. First on Wednesday another shortwave will be progressing in from off the North Pacific and this feature looks to spread another round of light to possibly moderate snowfall region wide although temperatures will be warming some so the snow density will likely be heavier and contain more liquid in it which is actually great news for our snowpack and water supply. The downside to that is with temperatures hovering in the mid 30s and our typical snowfall intensity not being very heavy in our region which is typical, the snow will likely not stick very well at least on valley floors. After that system moves out on Wednesday night into early Thursday fairly strong height rises associated with a building upper level ridge off the West Coast will begin to all too familiar warm air advection process across our region. We may see a dry day on Thursday with warming temperatures up to near seasonal averages (which at this time of year are in the upper 30s to lower 40s in valley locations). By Friday and into next weekend stronger warm air advection looks to begin to cause adequate lift and vertical motion utilizing an anticyclonic flow of the jet stream to bring rising snow levels and at least showery if not steadier rainfall. Snow levels look to rise to near or possibly even above 5000 feet which would not be good news. At this point only minor nuisance ponding of water looks likely as the snowpack should be able to absorb much of the rain that falls but lower elevation valleys will likely see a fair amount of their snow cover disappear next weekend with high temperatures rising into the lower to possibly middle 40s if we get some wind to mix down to the surface. This will need to be watched but for now this is the most likely scenario. The good news appears to be that if the MJO continues its trek around the globe then once it migrates into Phase Space 2 we should see our temperatures drop again with a return to perhaps some snowier weather. At least the GFS model seems to think this will happen as well as the fantasy charts (and fantasy charts should ALWAYS be taken with at least a grain of salt) show a rather robust and cold upper level trough beginning to drop southward along the BC coastline at the end of February into the start of March. Should this happen, we could possibly see perhaps our heaviest snowfall of the entire season. Not going to bet on that yet but something we are watching.