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Montana Weather By Season

On the previous page, this article went over the "general weather traits" in Montana - if there really is such a thing. This page of the article covers what kind of weather a visitor can expect in Montana - by season.

Summer Weather in Montana

Summer on the Big Hole River
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Montana has, by and large, beautiful summer weather. This is generally standard throughout the entire state, too. Generally, from July through September (summer in Montana), it tends to be generally dry throughout Montana, with sunshine the norm, with only a few days of clouds and light rain. Yet, despite the sunshine, temperatures are generally not too hot except during periods of heat waves.

In western Montana, look for typical summer days to run from the mid-70’s to around 90, depending where in western Montana you are and at what elevation you find yourself. Over in eastern Montana, highs will generally be a tad warmer overall, with highs in the 80’s and low 90’s. During periods of heat waves, though, temperatures throughout most of Montana can soar into the low 100’s. It is during these times that you want to escape to the higher elevations to avoid some of the heat. Temperatures cool off noticeably, though, once summer flows into September – although the days are still generally dry and sunny.

Thunderstorms occur during the summer months; however, they aren’t especially common. Generally, more thunderstorms occur in the eastern half of Montana than in the western half in the summer, although the mountains can have some fantastic lightning storms.

Moreover, many of the thunderstorms that occur in Montana during the summer, particularly over the mountainous areas, are dry thunderstorms. These are the most deadly of storms, since they produce huge amounts of lightning that spawn wildfires while not dropping any rain. These dry thunderstorms are quite common in Montana during the summer, and are the main cause of most wildfires in the state.

Another thing that needs to be remembered during the summer is that although daytime temperatures can be quite warm, night temperatures usually plummet. This is especially so in the higher elevation valleys, like the Big Hole River valley. It is common to fall below freezing in places like Wisdom and West Yellowstone, even during the height of summer when daytime high temperatures can hit 80 degrees or more. Yet, even outside of these cold spots, most nights in Montana have temperatures in the 40’s or lower 50’s.

Snow in Montana during July and August happens, but not often. Generally, if snow does happen in July or August, it only effects the higher elevations of the taller mountains in Montana. It is very rare for snow to fall in any of the major Montana cities during July or August.

This changes, though, beginning in September. Generally, the first snow of the season coats the higher mountain elevations in Montana in September. Occasionally the snow will also reach the lower elevations, although the snow will not stick around long. The nice thing about September snows is that it coincides with the changing of the colors in the mountains – making for beautiful sights.

Fall Weather in Montana

Fall Colors Along North Fork Flathead River
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Fall weather in Montana begins usually sometime in late September and will run into November. During this time, weather can be highly variable – with weeks of Indian summer weather, followed by cold rain, and then snow. During the fall, it becomes normal to see eastern Montana having colder weather than western Montana, too. The reason is because the first cold air of the season usually arrives from Canada.

Western Montana weather, beginning in the fall, also usually begins to start getting cloudy in October (although lately October seems to have been as nice as September usually is). Typically, what happens in October is a mix of sunny days followed by a week of colder temperatures under cloudy skies, with some light rain and higher elevation snow thrown in for good measure. November weather brings with it colder temperatures, more precipitation and much more cloud cover (at times, you’ll be lucky to have more than a few sunny days in November in western Montana).

Eastern Montana will also experience big temperature changes, really more so than over in western Montana as it can still occasionally get quite warm in eastern Montana in October as warm air can occasionally gets sucked up from the south. Additionally, during October the first arctic air masses from Canada generally arrive, leaving eastern Montana under cold temperatures while the western part of the state basks in relative warmth.

Out in eastern Montana, snow can fall at anytime during the fall, although it generally won’t actually start sticking and hanging around until November in most areas.

Winter Weather in Montana

An inversion in Northwest Montana
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Winter sees some extremes in Montana weather. During the winter, it is very common for the areas east of the Continental Divide to be in the deep-freeze of below zero temperatures while over in Missoula and Kalispell the temperature can be fifty degrees warmer and without a wind chill to boot.

As mentioned earlier, this occurs due to the inability of most cold air masses to make their way over the Continental Divide. A couple of times each winter, though, the cold air is deep enough (high enough) to force its way through the mountain passes along the Continental Divide, sneaking through places like Logan Pass, Marias Pass, Rogers Pass and other low elevation passes. When this happens, western Montana, particularly northwest Montana,  can become just as cold if not colder than eastern Montana. Moreover, when this happens the cold air has a nasty tendency to hang around for quite a long time. This is due to the peculiar topography of NW Montana, the huge valleys and tall mountains trap the cold air, preventing it from being shoved out.

Western Montana during the winter receives much more snow, generally, than areas in eastern Montana. However, all areas of Montana can receive deep snows. Eastern Montana, along with the occasional deep snow, also suffers from the curse of seemingly always blowing snow.

Not surprisingly, eastern Montana also is much windier during the winter than is found in western Montana, just like during the summer months. This wind, besides making the wind chill plummet, also has a nasty tendency to blow the snow that does fall in eastern Montana all over the place. Huge drifts frequently form behind houses, barns, small hills and behind anything else that the wind can’t blow away. Snow fences along eastern Montana highways, which help to capture snow and prevent it from blowing onto the highway, are also a common sight.

How much snow falls in Montana changes, often dramatically, from year to year. The tall mountains in Montana, even those found in the eastern part of the state, often receive very substantial snow falls – generally ending the year with well over 100 inches of snowpack (snowpack = packed snow depth, not how much snow actually fell during the year. To create a 100-inch snowpack by early April usually requires well over 250 inches of snowfall during the course of the winter).

By contrast, the lower valleys in western Montana tend to avoid the deep snow that happens in the mountains. The mountains tend to draw away the moisture of big storms, leaving lighter snowfalls for the low elevation valleys. Generally, most lower valley locations in western Montana tend not to receive more than 50-70 inches of snow a year.

This changes, though, for high-elevation valleys and plateaus, like West Yellowstone and Cooke City. In these locations, substantially more snow can be expected.

Spring Weather in Montana

Lake McDonald in early May on a Calm Day
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Spring in Montana can be both a delight and a curse, all at the same time. Snow can and does fall throughout the spring in most areas of Montana, with the snowfall probability lessening as spring wears on. While June snowstorms can and have happened virtually everywhere in Montana, it is a rare for most valley locations to receive snow. Instead, the mountains will often receive snow while the valleys receive rain.

Spring is also the rainy season in Montana. During May and June, Montana tends to receive the most moisture of the year. When this moisture actually happens, it goes a long way towards preventing the torrid forest fires that so often make national news. As mentioned, most of the moisture in the valleys falls in the form of rain during the springtime.

The mountains, however, receive a mix of rain and snow. During April, mountain areas tend to receive snow as the main form of moisture. This begins to shift in May, with the low and mid-elevation mountains receiving rain while only the upper peaks of the mountains receive snow. By June, most mountain peaks tend to receive rain as well, although snow can and does happen in the mountains in June almost yearly. Additionally, June rain in the mountains has a tendency to be a cold rain, not a warm spring shower.

As spring is the rainy season in Montana and because the state is dominated by northwest Pacific flows, western Montana can be very slow to warm up following winter. In western Montana, in fact, it seems at times during May and June that summer will never arrive, with often week long events of clouds, cool air and light spring showers being the “norm.” Needless to say, this kind of weather is not something that summer dreams are made out of!

Eastern Montana, owing to its location, tends to warm up much more quickly in the spring than does western Montana. While the scorching weather of July and August rarely hits this part of the state before early-June, it does happen for brief periods during the spring. Moreover, the rain events in this area tend to be more of the heavy rain variety followed by clearing skies, unlike the steady light rain/drizzle that so often plagues western Montana for weeks on end, especially northwest Montana.

Summary

Well, that is Montana weather in a nutshell. There is much more to Montana weather, of course, than what this guide lays out. Numerous sub-zones are located within both eastern and western Montana weather zones. The sub-zones often have dramatic changes in weather than what is listed here during particular times of the year. Additionally, the mountains in Montana often create their own weather at any moment. As such, while the broad, general rules in this guide are a good rule to go by when planning a trip to Montana (such as figuring out what kinds of clothes to bring), if you plan on venturing out into the mountains, always be prepared for virtually anything. The lack of preparedness by many a visitor has caused more than a few deceased hikers, anglers and other backcountry adventurers.

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