According to the National Climatic Data Center, Illinois was on the list twice for billion-dollar weather disasters in 2013. In both cases, some damages occurred elsewhere but Illinois took the brunt of the losses. These numbers are based on reports from government agencies, media reports, and insurance industry estimates.
The first was the flooding in the Chicago area in April 2013. I had posts on this event here, here, and here. This event produced an estimated $1 billion in damages and led to 4 deaths. They described it as:
A slow-moving storm system created rainfall totals of 5 to 10 inches across northern and central Illinois including the Chicago metro. This resulted in damage to many homes and businesses. There was also severe weather damage from wind and hail across Indiana and Missouri.
The second was the November 17, 2013, tornado outbreak that caused an estimated $1 billion in damages and led to 8 deaths. I wrote about it here, here, here, here, and here. They described it as:
Late-season outbreak of tornadoes and severe weather over the Ohio Valley (IL, IN, MO, OH, KY, MI) with 70 confirmed tornadoes. Most severe impacts occurred across Illinois and Indiana.
The recent rains and associated flooding in the Chicago area are reflecting the long-term pattern of wetter conditions in the region. Here are a few samples of that pattern.
First of all, northeast Illinois (Cook and several surrounding counties – see map below) has experienced a shift in precipitation over the last 120 years. This plot shows the amounts for each year as green dots, and an 11-year running average showing longer periods of dry conditions (brown) and wet conditions (green). There is a pretty remarkable shift from a drier climate between 1895 and 1965 with lots of brown, towards a wetter climate from 1966 to present where green dominates.
If you compare the average annual precipitation between the two periods, you get 32.9 inches for the earlier period and 36.8 inches for the later period. That is a 3.9 inch increase, or about 12 percent.
If you look at the 10 wettest years in the record, 8 out of the 10 came after the shift in 1965. The two exceptions were 1902 at #1 and 1954 at #10.
Of course, we have still experienced drought conditions in this later wet period, as noted in 2005 and 2012. However, the wetter years far outnumber the dry years since 1965. BTW, this pattern is not unique. I have seen this across the state.
Here is the same plot for northeast Illinois for just the month of August. The green shading comes in a little later, showing generally wetter conditions since the 1980s. What is startling is the number of very wet Augusts in the last 50 years. The two wettest were 1987 with 10.04 inches and 2007 with 10.88 inches, which is more than double the long-term average.
As this plots show, the issue is not just a shift towards a wetter period over time but a shift towards wetter extremes as well.
As of August 27, 2014, the northeast region is at 5.4 inches, 1.83 inches above average.
Here is the region used in this discussion (aka Climate Division 2). Climate divisions are regions of roughly similar climate. The advantages of a regional average are no missing data and increased statistical confidence in the resulting values. You can read more about them here.
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.
The NOAA Climate Prediction Center released their monthly outlook for September and 3-month outlooks for September and beyond. At this time, they are not expecting a repeat of last winter for Illinois.
According to them, the chance of El Niño has decreased to about 65% during the Northern Hemisphere fall and early winter. If it does show up, it is expected to a moderate to weak event. As a result, the impacts on the US and the Midwest will likely be modest at best.
September and FALL
For both September and this fall, there is an equal chance (EC) of above, below, near-average temperature and precipitation (4-panel figure below) for Illinois. The north-central US is not expected to have below-average temperatures, like it has experienced this summer. This may give crops in those areas a better chance of reaching maturity this fall.
It does look like temperatures are expected to stay above-average on the West and East Coast, as well as Alaska. Wetter-than-average conditions are expected to prevail in the southwest US, and expand into the Plains and parts of Iowa and Missouri later in the fall.
For Illinois, the current forecast is for equal chances of above, below, and near-average temperatures. Or to put it another way, they see no sign of a repeat of last winter. And they are expecting below-average precipitation in Illinois and across the Great Lakes region. It is still early in the year to lock in on this forecast so I would not cancel orders for snow blowers or salt deliveries just yet.
After a wet start to the 2014 growing season, we have seen a significant drop in rainfall across parts of northern and central Illinois in the last few weeks. Here is the 30-day rainfall as a percent of average. Areas in the orange are 25 to 75 percent of average while the areas in red are less than 25 percent of average. There are reports of soil moisture running low in some areas. On the other hand, southern Illinois has received above-average rainfall in the last 30 days.
Besides the switch from too wet to too dry in northern and central Illinois, and too much rain in southern Illinois, the other issue is that temperatures have been running about 4 degrees below average for the past 30 days. We are getting some heat this week. However, the longer-term forecasts indicate a return to cooler temperatures and more rain after this week through September 1.
If you look at the last 90 days the heavier rains in June and early July masks the recent dryness (map below). In fact, at the 90 day time scale rainfall in Illinois is generally at or above long-term average (1981-2010), as denoted by the grays and greens. This is one of the challenges of drought monitoring – sorting out short-term dryness versus long-term wetness or vice versa.