ISSUED 05/01/2024 8:25 P.M. MDT/7:25 P.M. PDT

SHORT TERM (WEDNESDAY NIGHT THROUGH FRIDAY):

Cold upper level low continues to spin around the Northern Rockies and Northwest US keeping our weather chilly and conditionally unstable with several vort maxes rotating around within the upper level low. I will add that this cold upper level trough combined with a very warm upper level ridge over the Central and Eastern US is ejecting out various shortwave disturbances into the Midwest and combining with a strong upper level jet stream which creates tremendous upper level diffluence along with a good low level jet feeding into each passing shortwave is what is triggering these rounds of strong to severe thunderstorms and tornadoes the Plains states are seeing each evening and overnight. It’s also interesting that similar to our region that area sees its greatest thunderstorm coverage during the evening and overnight hours and not during peak daytime heating which shows once again that thunderstorm development is not dependent on moisture so much as it is on instability, lift and dynamics as the models already have moisture factored into them. Back to our weather, the cold upper level trough will not move very much over the next 24 hours or so with another shortwave rotating back around the north side of the upper level low in Alberta then dropping southward overnight bringing good surface convergence and lift into Northwest Montana overnight. This will likely produce a band of snow across northeastern Lincoln County mainly along and east of Lake Koocanusa so if you live in the Tobacco Valley south towards Trego and Olney then don’t be surprised to see some snowfall overnight into the morning hours on Thursday as that shortwave pushes through. Elsewhere across Northwest Montana and North Idaho some clearing will occur again overnight and allow near to below freezing temperatures once again across most locations away from the immediate shorelines of the larger lakes of Priest and Pend Oreille. Another shortwave will drop southward during peak heating on Thursday afternoon so another day of sunshine and showers with the odd thunderstorm will be possible so keep the umbrella handy if traveling out. Temperatures will warm up a bit on Thursday from Wednesday’s chilly readings but will remain below early May seasonal averages. By Friday shortwave upper level ridging will begin to nose into the region and while we are still likely going to see a fair amount of fair weather cloud bubble up with daytime heating my gut feeling is that the upper levels of the atmosphere will be warming up faster than daytime heating will allow and thus will likely see capping develop to prevent more than perhaps one or two mainly mountain showers on Friday afternoon. Temperatures will rise further on Friday and begin to approach or reach seasonal averages.

LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY):

A very cold for early May upper level low will be approaching the West Coast at the start of this forecast period with the center of the cold core tracking southeast towards southwest Oregon and northwest California. As this occurs it will force upper level ridging to amplify across the Northern Rockies allowing for a mild, if not warm day on Saturday under increasing atmospheric heights and thicknesses but also increasing cloudiness as well. Saturday is looking rather warm with above average temperatures and likely many of our warmer valleys in Northwest Montana especially likely to hit 70 degrees or a little warmer. All other valleys should easily warm into the 60s. Will also see a tightening northeasterly gradient as a deepening surface low tracks east along the Oregon/California border with surface high pressure east of the Continental Divide in the morning before daytime heating along with the approaching upper level low cause surface pressures to reverse and drop east of the divide in the afternoon and the gradient relaxes. Some uncertainty still on the exact track of the upper level low which really only affects how much rain and mountain snow our region will receive. A further south track would result in less rain and snow along with slightly warmer temperatures while a further north track would result in a washout most likely for both Sunday and Monday along with chilly temperatures and very beneficial rains and snows. If the further north solution pans out high temperatures on Sunday and possibly Monday may not rise out of the 40s in valley locations and possibly even remain in the upper 30s. If you’re heading over to Spokane on Sunday for Bloomsday it does look wet and cold over there so be prepared. The main upper level low will scoot east by Monday night but will leave in its wake a broad upper level trough along with much lower atmospheric heights and thickness values which will result in continued cool temperatures. The atmosphere will also remain rather cold aloft and with conditional instability a daily dose of sunshine and showers will also likely persist beyond Monday with the sunniest periods of the day likely to be in the morning hours before cloud quickly bubbles up and showers develop. Overall a rather typical spring pattern here in the Northern Rockies. Some signs in the long range if you want warm and dry conditions of this occurring by the second week of May as CPC’s 8-14 day outlook is hinting at this change but we will see.

ISSUED 04/28/2024 8:15 P.M. MDT/7:15 P.M. PDT

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

This forecaster apologizes for not having the forecasts updated daily as is usually done as I have been dealing with a stubborn cold that has finally left hopefully for good. A rather chilly, breezy and somewhat unsettled Spring day across the region with the best coverage of showers on Sunday restricted largely to North Idaho and extreme Northwest Montana west of the Cabinet Mountains. This is where the best instability has resided but it has been less than impressive and overall rather shallow with no lightning strikes detected in the vicinity. Another, colder upper level trough is currently starting to push onto the Washington coast and this will keep the cool, breezy and unsettled conditions continuing through the day on Monday. The cold air associated with this upper level trough will be cold enough for snow to fall down to valley floors especially beneath heavier showers that develop but any snow accumulations will either have to occur overnight and only on grassy surfaces for elevations below 4000 feet. At best a couple of inches of new snow is possible across higher elevations above 4500 feet although there is a chance of perhaps 3 to 4 inches of snow falling in the Whitefish Range of northeastern Lincoln County on Monday night into Tuesday as the upper level low begins to pull away and a shortwave drops down in northwesterly flow but there remains considerable uncertainty in this scenario playing out. At least scattered showers will continue throughout the entire short-term period across the favored upslope regions of North Idaho while Northwest Montana will depend more on timing and track of shortwave energy rotating around the upper level low. Temperatures will remain below seasonal averages for late April with widespread freezing temperatures likely by Tuesday morning if some clearing is able to take place and winds relax.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

Fairly typical May pattern will be setting up as we head into the new month on Wednesday with temperatures finally beginning to show a return to milder conditions but also with the unsettled theme continuing. Due to timing uncertainty and lingering instability each day have simply broad brushed the entire extended forecast period with “chance” wording as instability showers and weak thunderstorms are possible almost any day. Models are also still somewhat at odds with each other especially towards next weekend with some models wanting to build in an upper level ridge across the region while others want to keep the troughing remaining in place. Tough to pick out one suite or another but do tend to believe that the ridge will eventually win out but again will need to wait and see. If the ridge does eventually build in it will likely not last very long as the entire region a ridge is projected to build across the West, IF it does, is simply being forced there due to another cut-off upper level low that will be spinning just offshore. This system will eventually move into the area its simply a matter of when.

ISSUED 04/21/2024 8:35 P.M. MDT/7:35 P.M. PDT

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

Splitting shortwave that brought some rain and higher elevation snow overnight and scattered afternoon rain and snow showers on Sunday afternoon along with breezy conditions continues to shift north and east away from the region. The associated upper level low will also continue to slowly push away to the east but some lingering shallow instability associated with the cool air aloft coupled with the higher late April sun angle and warming surface temperatures will likely allow cumulus clouds to once again bubble up during daytime heating on Monday but any showers will be isolated and restricted to near the Canadian border west of Lake Koocanusa where the best instability will lay. Clearing skies overnight along with lighter winds and dry air will allow for seasonably cold overnight lows across the region for the next couple of nights. Daytime high temperatures will return to near to slightly above seasonal averages for late April on Monday then rise around 5 to 10 degrees above seasonal averages by Tuesday. Transient upper level ridging will move over the region on Tuesday and coupled with light winds will make for a rather warm early spring day in the Northern Rockies. As the ridge axis slides east during the afternoon on Tuesday an increase in mid and high level cloudiness will occur which will make for a picturesque sunset on Tuesday.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

Generally weak westerly flow on Tuesday night into Wednesday will gradually give way to more upper level troughing and unsettled conditions as we progress through the end of the week into the weekend. In fact some good news in the weather department is that models are trending slightly stronger with the incoming upper level trough and associated surface low incoming later this week into the weekend which is resulting in better chances and coverage of precipitation chances region wide. Still not seeing any widespread beneficial rains and mountain snows but any precipitation at this point will be welcome and is needed. Temperatures are likely to remain above seasonal averages through the period although if the upper level trough does move overhead with colder air aloft this will increase vertical motion and instability across the area resulting in better coverage and chances for precipitation.