Temperatures have been below normal for the past few weeks and it appears the trend will continue for the next several weeks. While the continued trend of below-normal temperatures will increase our chance of seeing a white Christmas four weeks from now, we may be ready for a warm up by then.
The ECMWF computer model is one of just a few that looks out beyond day 5. For several days now, it has been painting a bleak picture for the weather in the lower 48 in the December 8-14 timeframe. Here is a look at the overall departure from normal when it comes to the geopotential height of the atmosphere. So you’re saying “What the heck is that?” Think of this! Since colder air is more dense than warm air it causes the pressure to be lower in cold airmasses. So, geopotential heights are lower in cold airmasses and higher in warm airmasses.
Makes it easier to understand the map now, doesn’t it? I’ve drawn in the approximate location of the jet stream as well. While our temperature could be 20-30 degrees below normal, there are equal geographical spots where the temperature is 20-30 degrees above normal! In other words, there is an extreme amount of variability in the Northern Hemisphere.
While I’m only in charge of a 7 Day Forecast, let’s look at what this type of set up means for surface temperature. Scary, isn’t it? There’s a -24°F in Southwestern Wisconsin! If that came true, it would near all-time record lows for the month of December…and for any date in winter! In other words, that’s about as cold as you can ever get here in Northern Illinois and Southern Wisconsin!
Before we jump on the “THE WORLD IS GOING TO END” bandwagon, consider this: This is a model forecast. It WILL change. It WILL change considerably in the next few days. However, every day that it is consistent with this cold solution, the more believable it is.
So, get out there and shop ’til you drop Friday morning! Get your Christmas shopping done and you just might be able to brag when everyone’s out in the deep freeze before the holidays. -Eric