With scattered frost in the forecast for early Tuesday morning, the smell of wood smoke in the air, and a few early bird maple trees with color on, it certainly has the feel of autumn. Even though we have plenty of warm weather coming up, it’s a good time to review some interesting autumn weather facts for Wisconsin.
To begin with, the average date of the first 32 degree temperature in the TV-9 viewing area ranges from ar0und Sept. 10th in some northern locations to around October 1st in the far southeast part of the area. It’s as late as mid-October for southeast Wisconsin right along the balmy waters of Lake Michigan. It’s important to remember that you usually experience frost on car windshields, rooftops, and lawns sooner than an ”official” 32 degree temperature is reported. That’s because those surfaces cool off faster than the air does. Also, the “official” temperatures are measured around 6 feet off the ground. Since cold air settles, it will usually be cold enough for frost on the ground on clear autumn nights when it is around 34-35 degrees at 6 feet. For more details throughout the state check out the graphic below from the Wisconsin State Climatology Office.
Here’s a look at the average temperature across Wisconsin in the September through November period from 1971-2000. This is the average taking into account the low and high temperatures. It ranges from the low 40s in northern Wisconsin to the low 50s F in the far southeast.
Now, let’s take a look at the average autumn precipitation. You’ll notice it is on average a bit wetter in northcentral Wisconsin than other parts of the state. Perhaps this is partly because of lake effect precipitation that comes down off Lake Superior when cold north winds blow in.
The next chart shows the top 20 driest autumns in the period from 1895 2007 in terms on number of dry autumns per decade. It appears the three driest periods were in the 1940s, 1950s, and mid 1990s into the 2000s.
Finally examine the top 20 wet autumns in the period from 1895 2007 in terms on number of dry autumns per decade. The mid 1970s to mid 1980s were bar far the most frequently wet with 5 of the top 20 wet autumns occurring in that stretch.
While we can’t know for sure how autumn 2011 will rank, but it still looks like the first part of meteorological Autumn (September) will turn out overall warm and dry in Wisconsin. Don’t let the mini-cool spell we’ve just been in fool you. There is lots of shorts and t-shirts weather ahead as sunshine and highs approaching 80 are expected later this week. We don’t see any prolonged rain events right through the second full week of the month. Make the most of it!
This post was written by Tony Schumacher on September 5, 2011