Illinois First Fall Freeze Climatology

Due to significant planting delays across most of the Midwest this year, I have heard many concerns about an early fall freeze and its potential effects on immature crops. Most plants experience damage from a hard freeze or “killing freeze”, which is typically designated by a daily minimum air temperature at or below 28°F. Even in normal growing seasons, an early fall freeze can cause considerable impacts and yield losses for crops. Delayed planting, as was the case this season, increases the risk of freeze damage because crops are less mature going into our normal fall freeze time.

The maps and summary below show first fall freeze dates across Illinois using temperature observations over the period 1979 to 2018. The maps show the earliest and latest fall freeze dates over this 40-year period, as well as the median date, which represents the middle value in the range of dates. The median is preferred over the mean or average, as it is less sensitive to very early or very late freeze dates. Also shown are the 10th (1 in 10 years) and 90th (9 in 10 years) fall freeze dates. All station temperature data were provided by the Midwest Regional Climate Center (https://mrcc.illinois.edu); the shaded areas between stations on the map were interpolated and do not represent actual observations.

The earliest fall freeze dates over the past 40 years range from late September in northwest and central Illinois, to early October in southern and eastern Illinois. An early freeze anomaly can be seen at the Mt. Carroll station (Carroll County), which experienced a minimum temperature of 27°F on September 7, 1988. Interestingly, the observed all-season Illinois minimum temperature record was broken earlier this year at the Mt. Carroll station (-38°F).

Tenth percentile first fall freeze dates (i.e., 1 in 10 years) range from early October in northwest and central Illinois to mid- to late October in southern and eastern Illinois.

Median first fall freeze dates range from mid- to late October in northwest and central Illinois to late October/early November in southern and northeastern Illinois. Approximately half the years between 1979 and 2018 experienced the first fall freeze before the median dates. Also, the median dates map clearly shows the effects of the developed Chicagoland area on nighttime minimum temperatures. The median first fall freeze date at Chicago Midway is 10 to 15 days later than in some of the collar counties.

Ninetieth percentile first fall freeze dates (i.e., 9 in 10 years) range from early November in northwest and central Illinois to mid- to late November in southern Illinois. Based on the 40-year climatology, one could say that there is a 90% chance that the first fall freeze on any given year will occur on or before the dates in the 90th percentile map.

Finally, the latest first fall freeze dates across the state range from mid- to late November in northwest Illinois to early to mid-December in southern Illinois.

Note that air temperatures can vary considerably on smaller or micro-scales. For example, plants near heated buildings or other development can be spared when minimum temperatures dip below the 28°F threshold in the countryside. More information and useful freeze products are provided by the Midwestern Regional Climate Center as part of their Vegetation Impact Program (https://mrcc.illinois.edu/VIP/indexFFG.html).  Higher quality, full-page maps can be accessed by clicking the following links:

10th_Percentile 90th_Percentile Earliest Latest Median

Widespread, heavy rains possible over next week in Illinois

As of April 25, the statewide average precipitation for Illinois is 2.8 inches, which is 94% of normal. However, we have several opportunities for widespread rains this week and into the weekend, according to the NWS precipitation forecast.
The first round of rain on Wednesday and Thursday has potential rainfall amounts of 1 to 2 inches across most of Illinois, along with the chance for severe weather. Continue reading “Widespread, heavy rains possible over next week in Illinois”

Wet August Wraps Up Cool, Wet Summer in Illinois

Highlights: The 12th wettest August in Illinois finishes out the 10th wettest summer on record. While August was slightly warmer than average, the summer was cooler than average. Here are the statistics.

August Statistics

The statewide average precipitation for August was 5.18 inches, 1.59 inches above average and the 12th wettest on record. The wettest area of the state was Cook County. The largest monthly total was from a CoCoRaHS site (IL-CK-100) in Cicero with 10.20 inches of precipitation.

This first map shows several areas across the state with amounts of 7 to 10 inches (oranges and reds), according to radar estimates. There were a few areas in the northwest and east-central Illinois with only 2 to 3 inches. The second map shows the departures from average, showing the many areas with 2 to 8 inches above average for the month.

IL-prcp-mpe-m2d-tot-20140901

 

Continue reading “Wet August Wraps Up Cool, Wet Summer in Illinois”

Dryness Across Northern and Central Illinois

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.

IL-prcp-mpe-030-pct-20140818

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.

IL-prcp-mpe-090-pct-20140818

 

Cool Start to August with Rain in Southern and Western Illinois

The statewide average temperature for August so far is 72 degrees, 2 degrees below average. This follows on the heels of the cool July. The NWS forecast show that the mild temperatures will continue this upcoming week with highs in the upper 70s and low 80s in northern Illinois to the low to mid 80s in central and southern Illinois. The 6-10 and 8-14 day forecasts that extend out to August 21 point towards a continuation of cooler-than-average conditions.

All in all, it should be great weather for the Illinois State Fair. I can remember many years of the State Fair being hot and humid with your choice of either dust or mud. It’s a wonder the butter cow did not melt.

The map of observed precipitation below from the NWS shows that rainfall has been widespread and fairly heavy in western and southern Illinois with amounts ranging from 1 inch (green) to 5 inches (red). It is lighter and more variable in northern and eastern Illinois, ranging from 0.1 inches (light blue) to 2 inches (dark green). Much of that heavy rain to the east of St. Louis fell in a part of Illinois that was dry in July.

august-mpe

Midwest Most Productive Region in the World

According to a press release from NASA …

Data from satellite sensors show that during the Northern Hemisphere’s growing season, the Midwest region of the United States boasts more photosynthetic activity than any other spot on Earth, according to NASA and university scientists.

They determined this by measuring the fluorescent glow that healthy plants give off when they grow. It is not visible to the human eye but can be picked up by special sensors on satellites. The press release has a lot more details.

If you click on the map, you can see the full version. While they don’t have any state boundaries, you can make out Lake Michigan. Based on that, it looks like one of the brightest areas is across central and northern Illinois – no surprise there.

The magnitude of fluorescence portrayed in this visualization prompted researchers to take a closer look at the productivity of the U.S. Corn Belt. The glow represents fluorescence measured from land plants in early July, over a period from 2007 to 2011. Image Credit: NASA's Goddard Space Flight Center.
The magnitude of fluorescence portrayed in this visualization prompted researchers to take a closer look at the productivity of the U.S. Corn Belt. The glow represents fluorescence measured from land plants in early July, over a period from 2007 to 2011.
Image Credit: NASA’s Goddard Space Flight Center.

Soil Temperatures in Illinois

The Illinois State Water Survey maintains a network of 19 soil temperature sites across the state that measure temperatures at 4 and 8 inches. You can look at maps for 10 am, any hour of the day, high for the day, low for the day, under sod, and under bare soil. You can find all their data at this site: http://www.isws.illinois.edu/warm/soiltemp.asp 

Here is the 4-inch soil temperature from yesterday. It’s always a day behind so that they can upload the data and do quality control checks. The data now arrive hourly. My mistake – they used to upload the data once a day and do QC but now it is more timely. As you would expect, soil temperatures change more slowly than the air temperatures.

map

 

And here is what it looked like two years ago after a record warm March. I chose April 2, 2012 for the same time of day and depth. As you can see, the soil temperatures were about 12 degrees warmer and USDA NASS reported that 5% of the corn crop had already been planted by that date.

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The Tale of Two Winters – One Dry, One Wet

We have had a remarkable contrast in the last two winters in terms of precipitation. While both winters have been relatively quiet in terms of snow (at least up until the last week), this winter has made up for it in rainfall.
Here are the January 1 to February 25 precipitation departure maps for 2012 (first figure) and 2013 (second figure) for the Midwest. Precipitation is the combination of rainfall and the water content of any snow/sleet/freezing rain events.
Areas in shades of yellow show below-average precipitation while areas in shades of green show above-average precipitation. As you can see, the widespread yellow in 2012 was replaced with widespread green in 2013. This is good news for Illinois and for the Midwest.
First two months of 2012.
First two months of 2013.

Soil Temperatures in Fall in Illinois

The Illinois Agronomy Handbook recommends that fall N applications should be done when the daily maximum bare soil temperature at 4 inches is below 50 degrees. Fall application is not recommended south of Illinois Highway 16.
The Illinois State Water Survey’s Water and Atmospheric Resource Monitoring (WARM) program has a network of 19 sites around Illinois with daily soil temperature readings at 4 and 8 inches. You can see the reports from “yesterday” on their soil temperature page. Be sure to look at the daily maximum 4-inch bare soil temperature.
As of this writing (November 4), the daily maximum 4-inch bare soil temperature is below 50 degrees in the northwest part of the state. However, it is still in the low to mid 50s across northeastern and much of central Illinois.
Of course, the soil temperature in a particular field can vary due to the temperature, soil moisture, vegetation and tillage, and even soil color.
The figure below shows the average date when the 4-inch soil temperature reached 50 degrees in the fall. In general the average date was in mid-November. However, it can vary from year to year depending on weather and soil conditions.

Average date when soil temperatures at 4 inches reach 50 degrees.Click to enlarge.

Dry October in Illinois

Precipitation

The statewide average precipitation for October in Illinois was 1.79 inches, 1.12 inches below average or 61 percent of average. That makes it the 21st driest October on record back to 1895. See map below.
Amounts of less than an inch were common in western Illinois. The driest spot for October in Illinois was Colchester (near Macomb) with 0.22 inches for the month. The wettest spot in Illinois was Lansing (south Chicago) with 5.22 inches.
Moderate to severe drought remains in western Illinois, according to the U.S. Drought Monitor. The National Weather Service has predicted above-average precipitation for November across Illinois. Combined with cooler temperatures, this should lead to improvements in that area of the state.

Temperature

The statewide average temperature for October in Illinois was 55.1 degrees, just 0.5 degrees above average. The highest temperature for October in Illinois was 92 degrees at Bentley on October 8. The lowest temperature was 23 degrees at Mt. Carroll on October 29. Most of Illinois experienced temperatures at or below freezing by the end of the month.

Snowfall

No measurable snow reported yet. I’m sure that will change in November.

October precipitation
October precipitation (inches) for 2011 in Illinois. Click to enlarge.

October precipitation departure
October precipitation departure (inches) for 2011 in Illinois. Click to enlarge.