When you see a pattern change coming that you've been anticipating for weeks, it's hard not to get excited. Especially when its dramatic and it leads to the potential of winter weather. A real shake-up! Having been at this business for more than 4 decades I've seen a thing or two. Trust me when I tell you, nothing is more challenging than tracking and forecasting a winter storm, especially in the central Midwest where a small deviation in path or a single degree can make the difference between 6" of snow or a cold rain.
No matter how you handle an event, you can never make people happy. Nothing is more polarizing than snow. People have a definitive love hate relationship with it. (If you're a friend of the page you all know which side of the fence I stand on). Anyway, before this winter kicks in I want you to know I give snow forecasts my undying love, passion, and effort. From time to time things don't work out due to the complexities of my trade. Just know I have high standards and do the best I can.
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Back to the topic of winter and its imminent arrival next week. As I noted earlier I'm really excited about the potential on the table for much of December starting around December 7th. However, with pattern changes and the realignment of energy, you need to be cautious of fact and what could be fiction. Here's an example of what I think is fact. It's the temperature departures off the GEFS ensembles.
Days 0-5: Still mild through next Monday.
Days 5-10: The change has arrived.
Days 10-15: The Midwest is in the freezer.
Here's another fact, a strong cross polar flow is well depicted by all models at 500mb. The massive full latitude trough is the pipeline for delivering cold to the Midwest. Count on it.
Fact or fiction, the GFS operational shows wind chills to 30 below. Is that possible?
This is harder to verify but at some point should the mother load of cold get released from the Arctic, wind chills well below zero (-15 or colder) are possible. Here's what the GEFS shows December 15th. This is interesting because ensembles are composed of many members and then averaged out. Some chills are colder than 30 below. The normal tendency for ensembles at 16 days is to reduce the amount of cold as they revert to more seasonal levels. That makes this chart at 16 days remarkable but perhaps unattainable...probably too cold.
Fact or fiction, snow (or even a snowstorm is on the way)?
This is where you need to be very careful as a forecaster. Models are notorious for spinning up storms in the period know as "fantasyland", which is anything beyond 7 days. Take the 18z operational GFS which showed this wind driven snowstorm December 14th.
Look at the snow it deposits (in fantasyland). Holy cow would I be thrilled with that!
As pretty as this looks to me, I can't really take the model seriously. All I can do is file it as a possible trend and follow up with later runs and models. I want to see this in the 5-7 day period and I want to see it on several different models. Then I can give it some respect. I would say fiction for the above depiction.
Having said that, I do think pattern changes are often accompanied by significant storms as energy is redistributed. It would not surprise me in the least if something develops somewhere in the Midwest in the period December 11-15 but I have no hard evidence yet. This looks like a pattern that's ripe for clippers. They typically produce narrow snow bands and are fast movers with 1-3" amounts. You need some luck to be in the right spot but it's still white gold. This is something to watch.
Whatever happens, there's a lot of weather on the table as December barges in the door. Roll weather...TS