“Many daily record low maximum temperature records are possible through Monday, especially across the Northern Great Basin/Rockies, and Northern California,” according to the NWS.
NWS Weather Prediction Center College Park MD 326 AM EDT Sun Sep 29 2019
Major winter storm to bring heavy snow and high winds to parts of the Northern Rockies…
… A strong storm over Northern High Plains will move eastward to the U.S./Canadian border in the Upper Mississippi Valley by Monday evening. The system will produce an early season winter storm over parts of the Northern Intermountain Region eastward to parts of the Northern High Plains.
The storm will produce heavy snow, strong winds, and potential blizzard conditions to the region through Sunday night/Monday morning. Winter storm warnings and advisories are in effect from the interior Pacific Northwest through to parts of the Northern High Plains. As much as 1 to 3 feet (locally more) of snow is possible, especially across Western Montana which would create dangerous to impossible travel conditions across the region.
Much below average temperatures
This system will also usher in a very cold airmass, with temperatures 15 to 30 degrees below average across much of the Northwest. Many daily record low maximum temperature records are possible through Monday, especially across the Northern Great Basin/Rockies, and Northern California.
Thanks to Ian Finlay for this link