ISSUED 04/23/2025 9:00 P.M. MDT/8:00 P.M. PDT

SHORT TERM (WEDNESDAY NIGHT THROUGH FRIDAY):

Upper level ridging will remain in place across the region throughout the short-term forecast period. This will mean another night of widespread frost and freezes across valley locations throughout the region for at least one more night. Surface high pressure will begin to slide southeast from British Columbia into southern Alberta and North Central to Northwest Montana. This will create a tightening northeast surface pressure gradient across the region late tonight and peak in strength on Thursday night into early Friday before weakening by Friday afternoon. Winds for most locations will be light northeast but the typical favored regions through the Purcell Trench in North Idaho as well as along portions of Lake Koocanusa, the Highway 2 corridor between Troy and Libby and the Clark Fork River Valley between Noxon and Heron will see the strongest winds and there could be gusts up to 25 mph in these locations as well as across higher elevations especially Thursday night into around noon on Friday. Winds will quickly decrease on Friday afternoon as surface high pressure weakens and slips south. Other than a few high clouds on Friday afternoon skies will remain mainly clear and high temperatures will run around 10 degrees above late April seasonal averages with plenty of upper 60s to mid 70s away from the larger cold lake bodies of Pend Oreille and Priest Lakes. The wind will keep frost restricted Thursday night to the wind sheltered valleys while breezy locations will see low temperatures fairly mild and near 40 degrees.

LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY):

Not much to talk about in the extended forecast period. Originally it appeared that a colder upper level trough would move into the region this weekend but that system now looks to dive southeast into Northern California and Southern Oregon taking the best lift, dynamics and instability with it. A bit of an inverted trough may stretch northwest from the trough by Sunday which could provide just enough low level convergence at the surface and upper level instability for a few showers but nothing terribly exciting. A new upper level trough looks to approach from the North Pacific by Monday and lasting through Wednesday which will spread cooler temperatures and chances for mainly rain showers with any snow remaining confined to the highest elevations above 7000 feet. With our warmer temperatures mountain snow melt will increase with area creeks and streams as well as larger rivers running fast, swift and cold so be sure to be very careful if traveling outdoors to enjoy the Spring-like weather.

ISSUED 04/20/2025 5:10 P.M. MDT/4:10 P.M. PDT

SHORT TERM (SUNDAY NIGHT THROUGH TUESDAY):

After a round of rather impressive early Spring thunderstorms across North Idaho on Saturday evening another round of showers and thunderstorms is redeveloping across the region as of this writing on Sunday afternoon as another shortwave passes through the flow within the general broad, large scale upper level trough that sits across the region. While no lightning has been detected as of this writing am watching cells developing upstream across the southern portions of BC and across Central Washington and thinking that as these continue to move eastwards with the dynamics of the shortwave and jet stream coming into better play by late afternoon and into the evening hours especially, similar to Saturday will see thunderstorms begin to pop up. With the shortwave passage coming in a touch earlier this evening than Saturday evening will likely see some thunderstorms make it into Northwest Montana as well. As was the case last night thunderstorms will once again be capable of producing very heavy rains, small hail and frequent lightning. One difference however with today’s shortwave is that the overall atmosphere is colder and some of the HI-RES models are showing the potential for snow to mix in within heavier showers so don’t be surprised to see some wet flakes mix in down to the surface especially with any thunderstorms that develop. One more shortwave will slip by during the day on Monday for another rinse and repeat performance although convection on Monday may start a bit earlier and end a bit earlier as well with the greatest coverage on Monday shifting more into Northwest Montana as this region will be in better proximity to the timing of the incoming shortwave. Temperatures should rise a bit on Monday which might actually help in producing more thunderstorms with warmer temperatures at the surface while temperatures aloft remain rather chilly. By Monday night skies will clear as surface high pressure builds back in across the region with atmospheric heights and thickness slowly rising as well signaling the arrival of upper level ridging. Temperatures on Tuesday morning will be rather cold across all elevations but especially across valleys so be aware of another freeze although certainly very normal for our region at this time of year.

LONG TERM (TUESDAY NIGHT THROUGH SUNDAY):

Transient shortwave upper level ridging will pass overhead on Wednesday and Thursday lasting through the first part of Friday before shifting east as the next upper level trough approaches. Wednesday through Friday look to be very pleasant mid Spring days for the Northern Rockies with afternoon high temperatures likely running a good 10 or so degrees above seasonal averages. Warmest valleys especially across Northwest Montana will likely see some lower 70s once again while most other valleys away from the influences of the larger lakes of Pend Oreille and Priest will rise into the 60s. Runoff from the mountain snowpack will increase a bit during this time but nothing that warrents any concern at this time as temperatures will only be warm for a few days before the next cool down takes shape. Another rather cold upper level trough will approach the Washington and Oregon coastline late in the day on Friday spreading increasing chances of initially rain showers into North Idaho by mid to late Friday afternoon as the initial band of surface convergence and lift moves into the region. By Saturday the main baroclinic band looks to push through the region along with lowering snow levels so anticipate a valley rain and mountain snow type of day although Northwest Montana might get somewhat shadowed out except for the Bull Lake to Clark Fork River valley from Trout Creek to the Idaho state line as is often the case with approaching Pacific systems at this time of year. Sunday currently looks like a rather typical post frontal Spring day in the Northern Rockies with cool temperatures, sunshine and blustery showers, these possibly with graupel or hail and possibly some weak thunderstorms as well. Temperatures will drop from around 10 degrees above seasonal averages on Wednesday through Friday to around 5 degrees below seasonal averages by Sunday. Overall rather typical late April weather for North Idaho and Northwest Montana!

ISSUED 04/15/2025 8:45 P.M. MDT/7:45 P.M. PDT

SHORT TERM (TUESDAY NIGHT THROUGH THURSDAY):

Beautiful day across the region on Tuesday but some dramatic and abrupt changes are in store by Wednesday. A sharp upper level trough currently pressing across British Columbia will deepen as a rather strong vort max drops down the backside of the trough and pushes south into the Northern Rockies on Wednesday. Temperatures will drop as much as 20 to 25 degrees from Tuesday to Wednesday along with fairly widespread blustery showers or steadier precipitation across Northwest Montana. Models have been consistent showing a cold enough atmosphere for precipitation to fall as snow across all elevations and with the strong dynamics and good vertical motion associated with this feature think this will be the case. While WFO Missoula has issued a Winter Weather Advisory for Northwest Montana above 3000 feet for the afternoon and evening hours on Wednesday the time of day when the precipitation occurs along with it being mid April likely makes this advisory non-applicable as experience has shown that for snow to accumulate and cause travel disruptions at this time of year snowfall would need to occur during the evening and overnight periods and this does not look likely at this time. Have also dropped high temperatures well below MOS and what models are showing as they are likely far too warm with these types of systems and past experience with these features has resulted in much colder high temperatures than would be suggested by MOS. Precipitation will wind down during the evening hours on Wednesday as the vort max and entire upper level trough descends further south and out of our region. There will likely be a period of some gusty northeast winds through the usual areas on Wednesday evening into Thursday morning but the pressure gradient looks to relax rather quickly during the day on Thursday. Should also see some warming on Thursday with more sunshine and recovering atmospheric heights and thickness values.

LONG TERM (THURSDAY NIGHT THROUGH TUESDAY):

Cold night anticipated on Thursday night into Friday morning and again on Friday night into Saturday morning as a reminder that this is still early Spring in the Northern Rockies and we are still well over a month away from the average last frost which is not until late May into early June across most locations in North Idaho and Northwest Montana. Transient upper level ridging on Friday and Saturday will give way to a progressive and active North Pacific jet stream with valley rain and mountain snow returning by late Saturday into Sunday with conditions remaining seasonably unsettled throughout the remainder of the extended forecast period. The mountain snowmelt will slow down considerably during this time with periodic showers across valley locations, good for the garden and the forests along with our water supply for the upcoming drier months ahead. Temperatures will return to seasonable readings for the time of year which is in the lower to mid 50s across valley locations for mid to late April.