First Fall Winter Storm In October

[Kendall Smith]

A large winter weather system is expected to develop in the Northwest. This system will move east over the southern plains and the Rockies. Widespread snow and total accumalations will occur in these areas. Not only will there be snow produced by this system, a mix of rain and sleet will also form by Wednesday and Thursday, according to the precipitation model. This system will also be capable of producing very strong winds which will lead to blizzard conditions. A sharp cold-stationary frontal boundary will create very cold temperatures which will lead to dry powdery snow to bulid up on the surface. These temperature will drop below freezing(< 32.0F)  near the surface. Temps in the upper troposphere will also be below freezing including in the 850mb range, but slightly mild. This may lead to rain and sleet as I mentioned earlier in this paragraph. Lift will be present along these front where both warm and cold air masses violently crash into on another and will release a huge amount of kinetic energy which was origanally stored. This is known as Available potential energy (short for APE).  

A strong shortwave upper-mid level trough will move across the Northwest states, Rockies,  central plains, upper Midwest and into the applilations during this mid-late week. Winter storms along this trough will most like intensify as this area of deep low pressure strengthens. Barometric pressure will rapidly drop within the trough itself leading to this intense system. 

By early weekend, this winter weather system may weaken as energy slows down. The trough itself will also lose strength as it curls into a weaker low pressure system. Remnants of mix rain and snow will last for a short period.

[Roger Smith]

I can attest to how cold it is behind this system because I'm there, and it's cold (about 35 F at 4,000' in southern BC and likely going down to near 20 F tonight under clearing skies).

Noticed how there was quite a strong push of arctic air south into the Great Lakes region near the end of the latest GFS run, could be lake effect snow with that (not this current system but in about two weeks from now). 

Early cold is not a good signal for a prolonged east coast cold winter, most years with a cold October seem to sustain the cold to about Christmas-New Years then it flips to very mild. That happened in the coldest case of all (1875) as well as more recently in 1987. I did find a few similar patterns that held on a bit longer such as 1969-70 and 1976-77 (the flip was in mid-Feb there). 

We already had a heavy snow here a week ago which was probably a new early season record although I can't find stats going back very far for my location. Around Sep 28-29 we had about four inches on the ground where I live and 15-20 inches a bit higher up to our northwest (around 5500' asl there). Quite a bit of that snow has persisted through to today out of town, we can still see snow on nearby hilltops that fell then, with a bit of dusting last night added in. 

It has also been anomalously cold for several months in Finland and western Russia.