The cold weather weâ??ve experienced the last week is unrelenting. Since last Friday, on each day, the mean temperature at the National Weather Service (NWS) near Negaunee has been in the double digits below average. Two of those days, this past Sunday and yesterday, were 21 degrees below average. Today, after a low of 10 below zero, the mean temperature will again be at least in the teens below average.
One needs to go pretty far back in the records to see a December stretch this cold. The last cold twelfth month in 2008 wound up 4.7 degrees below average. It was cold, but not near this relenting. There were only three straight days during the month where the mean temperature was in the double digits below average. At the beginning of the 21st century, December 2000 came in 5.1 degrees below average. There was a stretch of 10 consecutive days with double digit below average anomalies. From December 5-14, the mean temperature was 13.5 degrees below the long-term average for that time period. As I write this, todayâ??s official readings are not yet in the books. However, for the past six days (December 6-11), the mean temperature is running a remarkable 18 degrees below average! Today should come in at least 18 below normal, so the streak will keep going.
After today, it does appear there will be some easing of the cold over into next week. First of all, the flow aloft is in the process of becoming more westerly. Secondly, the surface winds should veer more northerly over the next 24 hours. That means moderation off Lake Superior at the NWS location. There will likely be more clouds tonight and also Friday night and that will keep nighttime lows much higher. So the string of double digit days below average could end after today.
In the long term, the cold pattern over North America is not likely to break. The pattern in the Pacific features ridging over the eastern Pacific to northern Alaska (Image 1 above). This configuration forces cold over the North Pole southward into Canada. Moving forward, the pattern if forecast to change little. In fact if anything, the forecast is looking like a more classic brutally cold pattern in the days leading up to Christmas (Image 2). Right now, it looks like we will see some moderation during the next week, but next weekend into Christmas week is looking bitter.