Today, I’m introducing the first day of the White Christmas tracker. We’ll run this every week day through Christmas Eve. It’s a daily update on the potential for snow on the ground Christmas Day using computer models.
For today’s debut and until around December 18 or so, it’s important everyone understand model forecasts more than a week into the future are very unreliable. They have not demonstrated the ability to accurately predict the weather this far out in time.
We’re showing you the models so we can see how they evolve (i.e. do they shift snowier, less snowy, or constantly flip flop?) and then, in hindsight, evaluate how well or poorly they simulated reality.
It shows substantial snow cover in places you’d expect a lot of snow: near the Canadian border, in the Rockies and around the Great Lakes. The I-95 corridor is snow-free, including Washington, D.C. and New York City, as are the South and the Pacific coast. (Strangely, Minneapolis - which just got over 10 inches of snow - seems to be in a snow hole.)
Next up, we have the CFS version 2 - this is a long-range or seasonal forecasting model. It has a product which shows you the 5-day maximum snow depth over a given time period. It includes four simulations that are generated using slightly different inputs.
For the 5 days leading up to Christmas, the four runs have a similar look to the GFS but push the snow farther south and east.
Considering available information now, I would not place the odds of having snow on the ground Christmas Day in D.C. above or below the historical average (see above) of just over 10 percent (stay tuned for a post by Ian Livingston that will provide many more details about the odds of a White Christmas in D.C.)