As per reports, the meteorological agencies and local regional forecasts (including the National Weather Service in Billings and Great Falls) report that monsoonal moisture moving around an upper-level ridge across the Northern Rockies is interacting with an approaching upper-level trough and surface cold front on Sunday (23 August).

• Following initial rainfall and thunderstorm activity that tracked eastward overnight, an incoming cold front on Sunday (23 August) afternoon hours is expected to cause another round of scattered rainfall and thunderstorms across central and eastern Montana.
• Convective storm cells are capable of generating localized heavy rainfall, frequent cloud-to-ground lightning, and erratic, gusty outflow winds reaching 40 to 60 meter per hour.
• Strong pre-frontal southwesterly to westerly winds, low relative humidity (dropping near 15-20 percent), and hot daytime temperatures have prompted Red Flag Warnings across western and portions of central/south-central Montana through Sunday (23 August) evening hours.
• The affected areas include Billings, Yellowstone County, Carbon, Stillwater, Sweet Grass, Musselshell, Big Horn, Rosebud, and Custer.