Next week is going to be cold around Chicago. It’s January after all, but it might not stay as cold for as long as we thought. Some signs point to a milder than average second half of the month.
First, next week’s cold air is not as cold as forecast models showed a week ago. Morning temperatures will be below average with wind chills around 0° for a few days. However, more than a week ago, models were indicating wind chills of -20 to -30°. It is common for numerical models to exaggerate temperature extremes beyond a week.
Predicting exact temperatures more than a week out is difficult, especially during big storms, so meteorologists monitor trends before reporting exact numbers (this also applies to snow forecasts) . This seems like a good time to remind you not to believe or share social media posts that show major winter storms in two weeks.
We may not be able to accurately predict an exact temperature two weeks from now, but we can have a pretty good understanding of pattern and trend changes. For this, we look to the North Atlantic Oscillation, or NAO.
The NAO is an atmospheric pattern in the North Atlantic that alternates between positive and negative phases approximately every 2 to 4 weeks. Essentially, higher and lower heights of equal pressure will trade from north to south.
When the NAO index is positive, we generally experience warmer weather in the Midwest and Eastern United States. When it is negative, we experience colder weather.
Well, ensembles of forecast models, or multiple rounds of model runs, show a shift from a negative NAO to a positive NAO by mid-January. This would mean a milder second half of the month, and perhaps a mild start to February. NOAA climate models that can forecast out to 32 days show the same trend change.
There is always a caveat in meteorology, so yes, there are also global ensemble models that suggest the NAO remains in a negative phase for a little longer. However, the majority of signs point to a positive phase, which is therefore the most likely outcome. We will monitor updates daily.
Although the next 7 to 10 days are expected to be cold, temperatures could return to the 30s or 40s soon after, bringing bad news for snow lovers.
NBC Chicago
