There is a better-than-average chance that people in Montana will have a chance to see the Aurora Borealis (Northern Lights) on Saturday and into Sunday.
The latest NOAA Space Weather forecast shows a moderate geomagnetic storm to Earth over the weekend that has the potential to produce a nice aurora on Saturday night, and possibly Sunday as well.
If skies are clear in your area, your best chance of seeing the Northern Lights is to get outside of town where there is far less "light pollution," and cast your gaze northward.
The National Weather Service notes that “in order to know whether you have a chance of seeing an aurora, you need to know the level of geomagnetic activity at the time you are viewing.” The possibility of actually seeing the Northern Lights increases with a town or city’s latitude. Great Falls notably sits at a magnetic latitude of 54.9.
While the Northern Lights are typically only seen at magnetic latitudes of around 67, NWS explains “[w]hen geomagnetic activity is very high, the aurora may be seen at mid and low latitude locations around the earth that would otherwise rarely experience the polar lights.”
However, space weather forecasts are notoriously difficult, so you'll definitely want to check for updates before you grab your camera and head out Saturday night.
Two good resources are the Space Weather Prediction Center and Soft Serve News.
The SWPC is operated by the federal National Oceanic & Atmospheric Administration; the website currently states : "A G2 (Moderate) Watch is now in effect for the 1 September, 2019 UTC-day; while the G1 (Minor) Watch remains in effect for the 31 August, 2019 UTC-day. While timing of this activity has a level of uncertainty, the current expectation is the arrival of a co-rotating interaction region (CIR) the later half of the 31 August UTC-day, followed by CH HSS onset late on 31 August and into the 1 September UTC-day."
Jim Thomas, the operator of Soft Serve News, posts frequent updates on his website to let people know how likely it is that the Northern Lights may be visible.
Thomas also notes: "Experienced Northern Lights hunters are familiar with disappointment. Predictions of when the CME cloud or a high speed solar wind stream hits the earth are not always accurate. Sometimes CME events produce much smaller displays than expected, or even none at all. Even with these uncertainties, seeing the grandeur of a powerful Aurora Borealis display may be a once in a lifetime event, so for some it's worth the gamble to try."
From September 2017:
