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.

ISSUED 02/11/2025 7:45 P.M. MST/6:45 P.M. PST

SHORT TERM (TUESDAY NIGHT THROUGH THURSDAY):

Cold, polar air is firmly in place across the region at this time with upper level northerly flow remaining across the region at 500 mb (18,000 feet). At the surface, the cold, dense air has allowed surface high pressure to settle in across the region however with a broad area of cold air at the surface the surface high is rather expansive in its coverage and without the easterly to northeasterly component to the surface pressure gradient that is often prevalent with outbreaks of polar air in our region. This is also partially due to temperatures not being much colder east of the Continental Divide as they are across our region. The potential downside to the light winds is a possible resurgence of valley freezing fog and stratus which has been steadily increasing across the region each of the last two mornings. A well established stratus and fog bank has remained in place well to our south across the Idaho and Washington Palouse region and with weak southerly low level winds anticipated overnight models are suggesting that all of the North Idaho valleys below say 4000 feet will likely be socked in by Wednesday morning. Across Northwest Montana this stratus will likely not really affect the area other than perhaps the Clark Fork River Valley where the stratus could spill into Heron and possibly extend as far south as Thompson Falls. For the remainder of the Northwest Montana valleys anticipate stratus and freezing fog to expand throughout the Kootenai Valley around Libby as well as around Lake Koocanusa up through the Tobacco Valley and south along Highway 93. All valley areas in Idaho and Montana should see at least a partial clearing of the low clouds by Wednesday afternoon but stratus is often tough to figure out. The much higher mid February sun angle will definitely help in dispersing the stratus but with fairly abundant snow cover and cold air at the surface the stratus could have other plans. By Thursday an approaching upper level trough and surface low will begin to approach the Oregon coast which will cause a slight increase in the northeasterly pressure gradient. Clouds will increase with some light northeast breezes in the typical areas. Could also begin to see some light snow develop by late afternoon or evening across Bonner County in North Idaho and along the Idaho border in Sanders County in Northwest Montana towards evening. Temperatures will moderate a bit but remain around 10 to 15 degrees below seasonal averages for mid February.

LONG TERM (THURSDAY NIGHT THROUGH TUESDAY):

Will be seeing a slow but steady pattern change across the region throughout this period likely tied to the progression of the MJO (Madden Julian Oscillation) which is currently in Phase Space 7 (The West Pacific and strongly tied to colder and snowier conditions for our region in this phase space). The MJO is forecasted to continue to propagate east into Phase Space 8 next week and then into Phase Space 1 thus completing a complete circle around the globe which is a bit surprising. At this time of year, the MJO in phase space 8 and phase space 1 (Western Hemisphere and Africa) corresponds to a warming and drying trend in our region and that is what all models are showing taking place after this weekend. The approaching shortwave on Thursday night into Friday will likely spread some light snowfall across much of the region but accumulations look very light and uneventful at this time. A bit of a break looks likely for part of Saturday, especially across Northwest Montana before a slightly further north tracking shortwave pushes into the region later Saturday into Sunday spreading more snow across the region along with continuing the airmass modification process and temperatures likely rising above freezing by Sunday across valley locations although the atmosphere as a whole will support snow down to valley floors. By Monday and Tuesday of next week upper level ridging will begin to build along or just off the West Coast which will cause the atmosphere to continue to moderate across the region resulting in temperatures returning to seasonal averages along with some lift and vertical motion through the atmosphere with chances of precipitation. Am anticipating this to result in rising snow levels with rain and snow mixed across valley locations and snow above 3,000 to 3,500 feet but these levels could be off by 500 to 1,000 feet. Either way after this cold snap comes to an end these temperatures will feel much warmer. The downside will be any liquid precipitation that does fall will likely freeze on unpaved and untreated surfaces that sit in shade all day as our ground is solidly frozen, in some cases down to over 2 feet deep. This will slowly begin to thaw over the next several weeks and month so liquid precipitation is certainly not a welcome sight at this time until the ground begins to thaw.

ISSUED 02/09/2025 7:25 P.M. MST/6:25 P.M. PST

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

Cold air continues to filter into the region with northeast winds already beginning to pick up across higher elevations in Northwest Montana as well as along portions of Lake Koocanusa and through the canyon between Libby and Troy. These winds will continue to expand further south and west overnight into the morning hours on Monday to encompass the typical areas of North Idaho through the Purcell Trench with the most noticeable winds blowing around Sandpoint as usual. While there is true arctic air east of the Continental Divide up along the Alberta/Saskatchewan and Montana border it does not look deep enough to cross the Continental Divide with polar air moving into our region rather than true arctic air and that is fine with this forecaster. Still areas that see the northeast winds will have very cold wind chill values ranging between 5 below to 25 below zero at times. The surface high associated with the arctic airmass east of the divide is not terribly strong as the cold airmass is also not extremely cold either so the winds will be lighter than if this were a bitter cold outbreak. In addition the pressure gradient will be lightening up by the afternoon hours on Monday which will also begin to see the northeast winds weaken and shift to more of an easterly direction. For those areas that do not see the wind you will have to deal with temperatures likely well below zero with the typical cold spots in Northwest Montana such as Yaak, Happys Inn, Trego and McGinnis Meadows likely dropping down to near 20 to 25 below zero. If you don’t wind the cold then there will be plenty of mid winter sunshine as well in this pattern as valley freezing fog and low clouds often take a few days of airmass modification to redevelop in these patterns. We are also getting increasingly late into the winter season for freezing fog and stratus development to last all day as the sun angle continues to get increasingly higher in the sky and daylight is increasing by over 3 minutes a day now. These factors will help take the bite out a bit of the cold weather the next few days. Great for some bluebird days up on the slopes if you can get up there.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

For most areas early Wednesday morning is looking like the coldest morning of likely the entire winter season as we are now into mid February and the rapidly increasing daylight and sun angle make it increasingly difficult for our lower elevations to remain cold. All valley locations away from larger lakes such as Pend Oreille, Priest and Koocanusa(the parts that are not frozen over) will likely drop below zero on Wednesday morning due to a combination of clear skies, light winds and a cold, dry airmass in place. A large Kamchatka low will be forcing upper level height rises across the Central Pacific which will cause ridging to become established across Alaska and also forcing the North Pacific jet to split with the southern portion of the jet under-cutting the ridge and diving to the southeast into Oregon and California with the northern branch of the jet riding over the ridge in Alaska and dropping southward into our region. The ridge is showing signs of becoming increasingly negative tilted as the southern branch of the Polar jet continues to move surface lows into the West Coast which, in turn causes the northern branch of the Polar Jet to also begin loosing its northerly component and become more northwesterly and eventually westerly. What this means for our region is a return to unsettled conditions. Snow looks likely to return by late Thursday night in North Idaho and by Friday across Northwest Montana. Amounts at this stage still do not look terribly impressive but accumulations will be likely as the airmass will be plenty cold enough to support snow……at least initially and then, well I almost would rather not even talk about what is looking increasingly likely after that. Unfortunately folks it looks like eventually a return to what we have become so familiar with this winter, the old warm air advection pattern. Temperatures will continue to climb over the weekend and by Sunday likely near to above freezing across all valley locations. And as is the case with warm air advection patterns warmer air will continue to fill in and contain the lift needed for precipitation, its just that this also will likely mean a return to snow levels rising off valley floors and with the very cold ground temperatures from the past few weeks of cold this could spell freezing rain before a transition over to rain if conditions warrant. This is still a long ways off but something that needs to be watched. There is always hope that the atmospheric profile will support cold temperatures and snow down to valley floors but the way this winter has gone……..