Gloomy skies have dominated early October 2018, bringing with them cold and clammy conditions. The lack of sunshine has held down daily maximum temperatures in particular, with highs in Minnesota averaging 7-13 degrees below normal during this unusually cloudy spell. From September 25 to October 9, average high temperatures were the lowest on record at International Falls, and were among the five lowest on record at Rochester, St. Cloud, Duluth, and the Twin Cities. The same clouds that suppressed daily high temperatures also prevented the low temperatures from dropping too far, resulting in lows that have averaged just 1-3 degrees below normal.
How unusual is this cloudy weather? The period from the very end of September to early October in fact is more likely to see clear weather conditions than any other time of year . By contrast, 12 of the 15 days from September 25 to October 9, 2018 were cloudy, and none of them were clear. Solar radiation records from the U of M St. Paul Campus show that the period from September 29th to October 9th, 2018 was the least sunny on record, back to 1963. The current monthly record-holder for gloomy Octobers is 2009, which featured just one clear day all month and was also the 7th coldest October on record for the Twin Cities. Fortunately, a cold and cloudy October does not mean that November that follows will be the same. November 2009 was the 3rd warmest on record and wound up being ten degrees above normal, with eight clear days and only nine cloudy days.