Temperatures Plunge For Early Snow In Rockies/High Plains

Temperatures will quickly fall from record highs in the 90s to freezing, with significant snow accumulations expected.

Below is the Weather Prediction Centers discussion on it from this evening. 

Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Mon Sep 07 2020 Valid 00Z Tue Sep 08 2020 - 00Z Thu Sep 10 2020

...Record heat in the central High Plains this afternoon will be drastically replaced by wintry cold and significant snow over the nearby Rockies by Tuesday morning...

...Excessive heat continues the rest of today across much of the West Coast states before moderating on Tuesday... 

...Critical to extreme risk of wildfires will persist for a couple more days across much of the interior West and northern/central Rockies before the polar air mass arrives... 

A highly dramatic shift in weather conditions will sweep through the northern to central portions of the country during the next couple of days as the persistent record heat over the western U.S. to the central High Plains will be drastically replaced by a surge of extremely cold air mass from Canada for this time of the year. The most dramatic changes will transpire during the next 12 hours over the central High Plains where record high temperatures in the 90s to around 100 will plunge all the way to near freezing Tuesday morning behind an "arctic" cold front. The Dog Days of Summer this afternoon will literally turn into Old Man Winter Tuesday morning with blustery northerly winds and areas of snow squalls possible from Wyoming down into central Colorado! Snow is forecast to accumulate for 6 inches or more at many locations with highest totals reaching two feet possible on the highest elevations. Temperatures are forecast to stay in the 30s on Tuesday in these areas, which are as cold as 50 degrees below normal at the coldest spots! In addition to the cold and snow, a swath of heavy rain can be expected across the upper Midwest north of the sharp front.

The strong dynamics associated with the front will also trigger heavy rain and thunderstorms Tuesday night into Wednesday across western to central Texas. Meanwhile, much of the West Coast states will endure another afternoon of excessive heat before moderating some on Tuesday.  

Farther inland, critical to extreme risk of wildfires will persist for a couple more days across much of the interior West and northern/central Rockies before the polar air mass from Canada arrives on Tuesday. Watch out for strong gusty winds from the northeast to sweep across the region behind the "arctic front".

Near the East Coast, tropical moisture will increase the chance of rain near a stationary boundary.