The Weather Guys

As the end of October arrives, the weather in Madison becomes increasingly subject to large variations, especially when measured from one year to the next.

The city’s record high temperature on Oct. 31 is 77 degrees, recorded in 1950, while the lowest temperature for the day is 16, recorded in 1925.

In 1960, we had 1.21” of rain on Halloween, surely dampening the spirits of lots of small children. In 1926, we received 3.2” of snow as a Halloween treat. As recently as 2014, we received snow on Halloween, just 0.2”, but it stands as the only snowy Halloween in the last 30 years.

On average, the high temperature is 52 on Oct. 31 while the low is 34, usually recorded in the early morning of the day. Nearly 2/3 of the past 30 Halloweens have been completely dry and only 3 of 30 have recorded more than 0.25” of rain.

Thus, our guess is that the usual conditions for setting out on trick or treat in Madison consist of no rain and a temperature between 46 and 50. All in all, not bad.

It certainly appears that this evening’s conditions will be well above the average, with a temperature likely to be as much as 10 degrees warmer than usual and no rain. It may, in fact, be our warmest Halloween since 2008, when the high temperature was 70 in the middle of an unusual and extremely late October-early November warm spell that lasted through Election Day that year.

Am early frost speeds up the fall of the leaves and brings a quick end to the fall color. Too much wind or heavy precipitation also brings the leaves down. (Photo credit: La Crosse Tribune Archives)

The season of autumn color is beginning with tints of yellow and orange in southern Wisconsin.

Sunny days and cool nights are the key weather ingredient for brilliant fall colors. The best weather conditions are bright sunny days and cool, but not frosty, nights. A drab autumn has lots of cloudy days and warm nights.

Southern Wisconsin has had above-average nighttime temperatures. Since Sept. 22, the average minimum temperature for southern Wisconsin has been in the upper 40s.

An early frost speeds up the fall of the leaves and brings a quick end to the fall color. Many southern Wisconsin regions have not experienced frost. Of course, a lot of wind or heavy precipitation would bring the leaves down.

Leaves contain chlorophyll and are green because chlorophyll reflects green light more than other colors. Other colors are absorbed by chlorophyll for photosynthesis. During autumn, the green chlorophyll disappears, and we begin to see yellow and orange.

These colors have been in the leaves all along; we can’t see them in the summer because of the chlorophyll. The color orange comes from carotene, and the yellows from xanthophyll. The bright red and purple colors come from anthocyanin pigments, which are made from leftover glucose trapped within the leaves of some trees, such as maples. Brilliant fall colors with bright red and purple colors require conditions in which leaves can make a lot of anthocyanin pigments. These discussions are a function of the weather.

While there may have been more brilliant colors during previous falls, it is still inspiring to walk the woods of Wisconsin.