2:15 PM | *Massive late weekend snowstorm for Montana and other parts of the Northern Rockies*

12Z GFS forecast map of 850 mb temperature anomalies for Sunday afternoon in the NW US with very chilly air for this time of year; courtesy NOAA, tropicaltidbits.com

Overview

It wasn’t that long ago that there was a fear in Montana’s Glacier National Park (GNP) that the Jackson Glacier was going to disappear in coming years, but that sentiment has changed dramatically recently largely due to extensive cold and snow in the latest winters. In fact, the Jackson Glacier—easily seen from the Going-To-The-Sun Highway—may have grown as much as 25% or more over the past decade. As recently as September 2018, there were posted signs within the park warning that GNP’s glaciers were expected to disappear completely by 2020, but these have been removed due to the recent change in sentiment on this warning. If this weekend’s snowstorm is any indication, the recent cold and snowy weather pattern across Montana in recent winters may certainly be an on-going phenomenon.

12Z GFS surface forecast map for Sunday afternoon in the NW US with snow shown in blue; courtesy NOAA, tropicaltidbits.com

Winter storm details

A major snowstorm will impact the northwest US this weekend which would be a big deal any time of winter, but it is especially noteworthy since it is happening at the end of September.  The bullseye region for this storm will be the western part of Montana where snowfall may be measured in feet across some higher elevation locations and winds could cause widespread power outages.  The western part of Glacier National Park, for example, could see two or three feet of snow to go along with 50-60 mph wind gusts during the height of this storm later in the weekend.  Some of the cold air associated with this storm will likely make its way eastward next week across the northern US and it could arrive in the NE US by next weekend.

Cooler air has pushed into the NW US today, but the big change in temperatures will take place this weekend in that part of the country as Arctic air spills over the Canadian border.  A combination of rain and snow is likely to develop early Saturday with a transition to all snow occurring from northwest-to-southeast on Saturday night and Sunday.  Widespread heavy snow is likely over much of northern and western Montana tomorrow night and Sunday with unseasonably cold temperatures and increasing winds. 

Total snowfall predicted by computer forecast model between and Monday with a bullseye of nearly 80 inches (see upper right); map courtesy weathermodels.com (Dr. Ryan Maua, twitter)

Initially, the most important snow accumulations will take place over the Rocky Mountain Front and nearby plains, but then it’ll expand southward by late tomorrow night and early Sunday.  Winds will pick up in intensity later tomorrow out of the northeast and power outages will be possible tomorrow night into Sunday due to tree damage.  The problem with heavy snowfall this early in the season is that many trees are still covered with leaves which will worsen the situation when heavy (wet) snow piles up.

Some computer forecast models have actually predicted several feet of snow in the highest elevations of western Montana with this upcoming major winter storm and this is a red flag certainly worthy of attention.  While this may be somewhat excessive, higher elevation regions of West Glacier can see as much as two or three feet of snow with winds potentially gusting to 60 mph.  In advance of the storm, the national park has closed the east side of the “Going-to-the-Sun” road at the Jackson Glacier Overlook. 

Some of the cold air associated with the weekend winter storm in the NW US will trek east to the NE US by next weekend; courtesy tropicaltidbits.com, ECMWF

Cold air advances to the east

While the NW US experiences a major winter storm this weekend, the NE US will continue to enjoy generally warmer-than-normal conditions as has been the case for much of the month.  In fact, temperatures at mid-week could reach the mid or upper 80’s in places like New York City and the 90’s in Philly and DC and some records may be challenged. However, some of the cold air associated with this winter storm in the NW US is likely to take a trek across the northern states next week and it could arrive in the NE US by this time next week.  Longer range outlooks suggest this may not be the only chilly air mass coming to the NE US in October.  Signs point to a second colder-than-normal air mass coming on the heels of the first one which is expected for next weekend. Thus far, frosts and freezes have been limited to the coldest spots of upstate New York and northern New England, but that could change as early as next weekend.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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