Last year, a reader of The Farmer asked me why she regularly feels the onset of seasonal affective disorder (SAD) during the month of November. Given the type of weather that the month of November typically brings to Minnesota, this should be no surprise.

According to research by the Mayo Clinic and other institutions, SAD is strongly correlated to the loss of sunlight in the autumn and winter seasons. The reduced sunlight can affect your internal biological clock. It can reduce the serotonin level (a neurotransmitter chemical of the brain), causing mood swings and sometimes more depression. And it can also affect the level of melatonin, a chemical that plays a role in our sleep pattern and mood.

Given the researched knowledge we have to understand SAD, it should be no surprise that the type of weather which November brings to Minnesota often serves to trigger its onset.

During November in Minnesota, most places lose more than one hour of daylight, as sunrise comes later in the morning and sunset comes earlier in the afternoon. In addition, the sun elevation angle gets smaller, coming from less than 40 degrees above the horizon most of the time. These lower sun angles produce a lower quality of light.

Plus, November is historically the cloudiest month of the year in Minnesota, with more than two-thirds of the days mostly or completely cloudy all day. It is not uncommon to have November produce only three or four sunny days. So, the absence of sunlight in November is often very pronounced, often a topic of conversation in the local coffee shops.

Temperatures fall as light decreases
I think, too, that those afflicted with SAD more often notice the decline in temperature that occurs during November as well. For most parts of the state, the average daily temperature declines by 15 to 20 degrees F during the month. Temperatures have been as high as the 80s F, as they were in 1909, 1950, 1999 and 2006.

Conversely, we have also seen temperatures in the -30s F, as was the case in 1896, 1903 and 1911. It was as cold as -45°F at Pokegama Dam in Itasca County, Minn., on Nov. 30, 1896.

One more dimension of the November climate which may compound the symptoms of SAD is the constancy of the wind. For most of Minnesota, November is the second-windiest month of the year. Only April shows a higher average wind speed. It is not uncommon to have days with an average wind speed over 15 mph and gusts over 30 mph.

For November 2018, the decline in sunlight and increase in wind speed will undoubtedly be observed by all of us, but at least the temperature outlook favors a warmer-than-normal month.

Seeley is professor emeritus of climatology at the University of Minnesota.