The Outlook for August and Beyond

First of all, is it really July 19th already?  As a kid I remember summers lasting almost forever, now it seems to last about two weeks.  I feel cheated.

July: So far, the statewide average temperature for July is 77.4 degrees, 1.5 degrees above normal.  The statewide average precipitation is 1.94 inches, 93 percent of normal.  Strangely, the interior of the state is experiencing near to above-normal precipitation while the edges have experienced below-normal precipitation (map below).


NWS Outlooks: The NWS has released their outlooks for August and beyond.  The big news is the possible return of El Niño. While conditions are currently neutral in the Pacific Ocean, the chance for El Niño increases to about 65 percent in the fall, and to about 70 percent during this winter. As a rule of thumb, warmer than normal temperatures are expected in winter during strong El Niño events.


The outlook for August in Illinois is for an increased chance of being warmer than normal while precipitation has equal chances of being above, below, or near-normal. The term “equal chances” means that there is no climate factors driving the conditions in one direction or another. While it’s not strictly true to call it a forecast for near-normal conditions, that is probably the best solution in these instances. For an idea of what normal temperatures and precipitation for August looks like, check out the climate normals page.  In climatology, the word “normal” refers specifically to 30-year averages updated every 10 years.



The outlook for August-September-October in Illinois is for an increased chance of being warmer than normal. Southwestern Illinois has an increased chance of being drier than normal, while the rest of the state has equal chances of being above, below, or near-normal.  Notice how the outlooks are nearly identical to the August outlook.



The outlook for November-December-January in Illinois is for an increased chance of being warmer than normal (typical El Niño winter) with equal chances of above, below, and near-normal precipitation.


Warm, Wet June for Illinois

Summary: According to preliminary data, Illinois experienced its 11th warmest and 14th wettest June on record. The statewide average temperature was 75.0 degrees, 3.1 degrees above normal. The statewide average precipitation was 6.36 inches, 2.15 inches above normal.

Precipitation: The greatest monthly total for June in Illinois was 14.58 inches at Rockford (IL-WN-8). In addition, the Rockford Airport reported 14.23 inches, their wettest June and wettest month on record. Based on radar and rain gage data, precipitation was especially heavy across northern, east-central, and southeastern Illinois with widespread amounts in the 10 to 14-inch range. Meanwhile, parts of western and southern Illinois received less than 3 inches of rain.


Here are the top 15 wettest June statewide precipitation totals since 1895. Six out of the last ten years have made the list (marked in red). That is an impressive feat for the current decade.

Rank Year Total Dep. %Norm
1 2015 9.44 5.23 224
2 1902 8.27 4.06 197
3 2010 7.71 3.5 183
4 1998 7.64 3.43 182
5 2000 7.34 3.13 174
6 1928 6.93 2.72 165
7 1993 6.85 2.64 163
8 1924 6.8 2.59 162
9 2014 6.77 2.56 161
10 2011 6.69 2.48 159
11 1945 6.65 2.44 158
12 1990 6.44 2.23 153
13 1957 6.38 2.17 152
14 2018 6.36 2.15 151
15 1947 6.33 2.12 150

Here is the June precipitation for Illinois (w/o June 2018), showing the upward trend as well as increased variability in recent decades. Over the last century, annual precipitation in Illinois has increased by about 10-15%, depending on location. As a result, we have seen more problems with flooding but fewer problems with long-term drought. More on this topic in a later blog post.



Temperatures: As noted, the statewide average temperature was 75.0 degrees, 3.1 degrees above normal. Hot weather was common during the month. Here is a map of the number of days that hit 90 degrees or higher in June. They ranged from about 3-4 days in northern Illinois to about half the month in the St. Louis area. By the end of June, the combination of high temperature and high humidity led to excessive heat warnings by the National Weather Service (NWS).


Drought: At the end of the month, the US Drought Monitor shows “abnormally dry” and “moderate drought” conditions persisting in western Illinois.


Outlook: NOAA updated their outlook for July. As before, Illinois has an increased chance of above-normal temperatures. Meanwhile, the precipitation forecast is for equal chances (EC) between above, below, and near-normal precipitation for Illinois. EC is a common forecast for summer precipitation since it largely depends on short-term, local conditions (such as the passing of a cold front), rather than large-scale patterns like El Niño. By the way, according to the June 14 NOAA ENSO alert:

ENSO-neutral is favored through Northern Hemisphere summer 2018, with the chance for El Niño increasing to 50% during fall, and ~65% during winter 2018-19.

The forecast for the next 14 days (through July 15) suggests that drier conditions will prevail across most of central and northern Illinois, but the southern third of Illinois has an increased chance of above-normal precipitation.




June – Warmer and Wetter in Illinois, More to Follow

Summary: The statewide average temperature for June so far is 75.3 degrees, 4.4 degrees above normal. The statewide average precipitation for June is 3.61 inches, which is about 130% above normal. However, the precipitation is spread unevenly throughout the state. Above-normal temperatures are expected to continue for July.

Temperature: Both the average high and average low for June has been above normal (maps below). The average high ranged from the low 90s around St. Louis to the upper 80s in the southern two-thirds of Illinois. The average high ranged from the upper 70s to the low 80s in the northern third of the state. The average lows ranged from the upper 50s in northeast Illinois to the 60s for the rest of the state.

Precipitation: Precipitation was highly variable across Illinois, which is fairly typical for summer months (below). There are a few areas in pink with 10 to 15 inches. Areas in shades of orange and red have precipitation amounts of 4 to 10 inches, well above normal. The largest monthly total so far is Beecher City (Effingham County) with 11.22 inches. Meanwhile, rainfall has been less plentiful in western and southern Illinois with amounts of 2 inches or less.


Outlook: More rain is expected across Illinois the next 7 days as a slow-moving low-pressure system moves across the region. The potential amounts range from nearly 3 inches in northern Illinois to about an inch in southern Illinois.


The outlook for July from the NWS says that we can expect an increased risk of above normal temperatures for July (top row of the figure). There is no indication of increased risks of either above or below-normal precipitation for July. For the period of July through September (bottom row), the southern two-thirds of Illinois has an increased chance of warmer than normal conditions. The northern third does not. There are no climate factors to indicate an increased chance of either above or below-normal precipitation during the period of July through September.




Warmest May on Record for Illinois

Temperatures: Based on preliminary data, the statewide average temperature for May in Illinois was 70.6 degrees, 7.9 degrees above normal and the warmest May on record. The old record was 69.4 degrees set back in 1962. A brief examination of daily records indicates that Springfield, Champaign, Quincy, and Carbondale all had daily mean temperatures at or above normal for each day of the month. On the other hand, Chicago, Rockford, and Peoria had a few dips into the below-normal territory but overall finished above-normal for the month. Here is the graph of daily mean temperature departures from normal for Champaign-Urbana.


“Normal” refers to the standard 1981-2010 average. For daily normals, additional smoothing is done since even a 30-year average can have some variability from one day to the next.

It was not just warm in Illinois. Here are the temperature departures from normal across the US for the month of May.


Precipitation: Based on preliminary data, the statewide average precipitation for Illinois in May was 3.98 inches, 0.62 inches below normal. Here are the monthly totals and departures from normal maps for Illinois. Click to enlarge. Areas in northern and southwestern Illinois received sizable rainfall amounts. Meanwhile, a few spots in east-central and southeastern Illinois were well below normal, and a cause for concern as we move into the summer months. The highest monthly total reported in the state was at Barrington (Cook County) with 12.69 inches. On the other hand, Effingham reported one of the lower totals in the state with 1.11 inches.

One of the key rainfall producing systems in Illinois in May was when the remains of Subtropical Storm Alberto tracked up the IL-IN  border. As noted in a previous post, the remains of tropical storms have reached Illinois in the past.


Forecast: The National Weather Service’s Climate Prediction Center released their updated outlook for June. For Illinois, we have a greater chance of seeing the above-normal temperatures continue in June. The area around Chicago has an increased chance of below-normal rainfall, which may be welcome after the wet May. The 6-10 and 8-14 days forecasts are showing Illinois with an increased chance of both warmer and drier than normal conditions for the first half of June.


Illinois to Feel Effects of Alberto

According to the National Hurricane Center, what’s left of Subtropical Storm Alberto will reach Illinois on Wednesday, bringing widespread rain to areas that are driest in the state. By the time it reaches Illinois, it will have weakened considerably with the greatest risk from flooding instead of high winds. Here is the projected path:


And here are the projected rainfall totals for the next three days with possible totals of 2 to 4 inches in the southern third of Illinois and the risk for flash flooding in some areas, according to the NWS. Meanwhile, much of rest of the state could see amounts between 0.5 to 1.5 inches. The impact in western Illinois will be minimal.


This rainfall could be welcome in southeastern Illinois, which has been exceptionally dry in May. Here is the rainfall deficit map for May so far, showing some areas 2 to 4 inches below normal (1981-2010 average). If the forecast comes true, much of that deficit will be erased. Hopefully, the rains will fall slowly enough to soak in and help soil moisture. That has been the case in past situations such as Hurricane Isaac in 2012.


It is not that unusual for systems like this to reach Illinois and actually provide welcome relief from dry conditions. From a journal article that I wrote in 2006 about the impact of four tropical systems on the 2005 drought in Illinois,

The passage of four tropical systems alleviated drought impacts, particularly in southern and central Illinois during the 2005 growing season. The four systems were Tropical Storm Arlene, and Hurricanes Dennis, Katrina, and Rita. Several circumstances make this situation significant for Illinois. The historical tropical cyclone records indicate that while an occasional tropical system passes through Illinois, occuring in 26 years since 1851, 2005 was the first time for four such systems in one season. Timing of 4 to 6 weeks between tropical systems benefited agriculture while minimizing flooding. Tropical Storm Arlene and Hurricane Dennis also occurred relatively early in the growing season when critical moisture was needed. Aggregating the rainfall from these four events shows that they provided significant drought relief in southern and central Illinois during the 2005 growing season. Without those four systems, southern and central Illinois could have been in drought almost as severe as that in northern Illinois with 7- to 10-inch rainfall deficits instead of the observed 1- to 6-inch rainfall deficits.

From 099-14MS2611-print, Tropical Storms Reduced Drought in Illinois in 2005

For those sharp-eyed individuals, you may notice that Alberto is referred to as a subtropical storm, as opposed to a tropical storm. A good discussion of why it is a subtropical storm can be found at the Weather Channel. For us in Illinois, it really doesn’t make that much difference between the two types of storms (tropical vs subtropical) since they are no longer over warm waters by the time that reach us. In either case, they are much weaker upon arrival with the greatest risk from flooding rather than high winds.

Second Coldest April on Record in Illinois


Based on the official data, the statewide average temperature was  44.5 degrees,  8.1 degrees below normal. It was the second coldest April on record, only beaten by 43.1 degrees set in April 1907. Our statewide records go back to 1895. Normal refers to a specific benchmark, the 1981-2010 average. See the longer explanation here.

Here are the temperature departures from normal look like across the Midwest. Areas in green are 1 to 9 degrees below normal, while areas in icy blue are 9 or more degrees below normal. The lowest temperature reported in Illinois for April was -1 at both Avon and Lincoln on April 2. At the other extreme, we did reach into the 80s at times during the month. The warmest reading was 86 degrees at Kaskaskia on April 13.



The statewide average precipitation for April in Illinois was  2.37 inches,  1.41 inches below normal. In general, areas in the north and west had lower precipitation totals and were part of a larger area of below-normal precipitation that extended into Missouri, Iowa, Kansas, Nebraska, and beyond. Precipitation is the combination of both rainfall and the water content of snow.

The largest monthly total precipitation was Metropolis, home of Superman, with 6.73  inches as reported by the CoCoRaHS observer (IL-MC-2). On the other extreme, the Quincy Airport reported only 0.63 inches for the month and reflects the other low totals in the area.


Snowfall was widespread across Illinois in April, which is highly unusual. Parts of central Illinois received more snow than northwest Minnesota. Snowfall was above-normal across most of the Midwest. The largest reported monthly total in Illinois was 12.0 inches at Augusta, IL (Hancock County).




Cold Start to April in Illinois

The statewide average temperature for Illinois from April 1-11 was 35.6 degrees, 12 degrees below normal. While we are having a few days of warm weather now, we are expected to get right back into colder weather over the weekend. The NWS forecast for the next 14 days shows an overall picture of below-normal temperatures. Even so, I expect the departures from normal won’t be quite as severe as the first 10 days of April.

If you are thinking that you have never seen an April this cold, you are probably right. Here are the top ten coldest Aprils in Illinois. You have to go back to 1983 and 1982 for some really cold Aprils.

Rank Year Average Normal Departure
1 1907 43.1 52.6 -9.5
2 1926 45.2 52.6 -7.4
3 1904 45.6 52.6 -7.0
4 1950 45.8 52.6 -6.8
5 1920 45.9 52.6 -6.7
6 1961 46.6 52.6 -6.0
7 1918 46.7 52.6 -5.9
8 1983 46.8 52.6 -5.8
9 1982 47.0 52.6 -5.6
10 1928 47.4 52.6 -5.2

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