Traces of snow were reported in Chicago and Rockford on October 4. A few years ago I did a post on the earliest and median dates for the first measurable snowfall of the season. Measurable means at least 0.1 inches or more. Snow flurries or traces of snow do not count since they have not been tracked closely in the historical weather records.
No real surprises for anyone who has experienced winter in Illinois. The earliest dates of measurable snow are in the late October, early November time frame. And the median dates range from late November in northern Illinois to the second half of December in southern Illinois. Even so, the dates can vary considerably between nearby sites since many of the early season snows are sporadic and not very widespread.
No doubt today (September 22) will be announced as the “first day of fall” because of the fall or autumnal equinox. However, that concept refers to the date when we get equal amounts of daylight and dark. I don’t think it was ever intended that this astronomical event would be the start of fall. In fact, this equinox would be the start of spring in the southern hemisphere. So to be fair to everyone we should call it the September equinox and leave fall out of it. 😉
Climatologists and meteorologists prefer to use calendar months to define the four seasons in the US. For example, fall would start September 1 and end on November 30. Not only is this more convenient, because you can use monthly data, but it lines up better with the typical or average temperature pattern for Illinois. Unfortunately, the meteorologists would describe this three-month period as “meteorological fall”. However, I would argue it is “climatological fall” since we are looking at long-term average to determine the season.
Heavy rains fell across the Chicago metropolitan area again today (August 22, 2014). Here is the map of rainfall amounts from our volunteer CoCoRaHS network. You will get a slightly larger and more clear image if you click on the map below. Many sites in the orange have received the average August rainfall in just 1 day. The largest total so far is from an observer in Bloomingdale in DuPage County with 5.45 inches.
Here are the reports for the morning of August 22, 2014, ranked from high to low. Most observers report between 7 and 8 am.
As impressive as this cool summer has been in Illinois, the experience here and across the Midwest stands in stark contrast to the West Coast. Here is the temperature contrast from the last full month – July (map below – click to enlarge). While the Corn Belt was 3 to 6 degrees below average in July, the West Coast and parts of the Rockies have been running 3 to 6 degrees, or more, above average.
The contrast between Chicago and Portland (OR), two of my favorite cities, show how different things have been. For July, the average high in Chicago was 79.8 degrees and the average low was 60.9 degrees. The average monthly temperature of 70.4 degrees meant that Chicago was 3.6 degrees below average.
On the other hand, the average high for July in Portland was 83.8 degrees and the average low was 59.8 degrees. As a result, their average monthly temperature of 71.8 degrees meant that Portland was 2.6 degrees above average.
Furthermore, while Chicago barely reached 90 degrees on one day in July, Portland reached or exceeded 90 degrees 7 days in July, including a reading of 99 on July 1.
The long-term average temperature for July in Chicago is 74 degrees and in Portland is 69 degrees.
It is no surprise that the NWS forecasts indicate that the heat will remain in the West for the next two weeks. However, it looks like Illinois has a good chance of seeing above-average temperatures for a change in the August 16-24 period.