Year to Date – Cool and Wet in Illinois

It is probably not shocking news to find out that the first 8 months of 2014 have been both cooler and wetter than average for Illinois.

The statewide average temperature for January-August was 50.8 degrees, 3.5 degrees below the 1981-2010 average and tied with 1924 as the fifth coolest on record.

The statewide average precipitation for January – August was 28.79 inches, 1.46 inches above average and the 34th wettest on record.

Here is what the precipitation departures look like through the end of August. Several areas in northeast and east-central Illinois have precipitation departures of 6 to 12 inches above average in the shades of blue, and a few areas with 12 to 16 inches above average. Areas in green are 2 to 6 inches above average. Only a few small areas in tan/beige are 2 to 4 inches below average.

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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.

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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.

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Cool Maps of the Cool July

I will admit it – ever since I was a kid I have been fascinated/obsessed with maps. It is probably why I ended up in a career in climatology since we use maps all the time.

Here are maps from the National Climatic Data Center showing how cool July was across the Midwest. The regions are called “climate divisions” and there are nine of them in Illinois. The ones in the darkest blue had their coolest July on record, with records going back to 1895. Click on the map for a larger version which shows the numbers more clearly.

You can read more about what happened in the US in July.

July Temperature Ranking. Click to enlarge. Source National Climatic Data Center.
July Temperature Ranking. Click to enlarge. Source National Climatic Data Center.

And here are the temperature departures from the 1981-2010 average.

July Temperature Departures. Click to enlarge. Source National Climatic Data Center.
July Temperature Departures. Click to enlarge. Source National Climatic Data Center.

Here is the US map for July, showing that while the Midwest was cool, the western US was experiencing record warmth.

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Click to enlarge. Source National Climatic Data Center

This temperature pattern across the United States is the result of a ridge of high pressure over the western US and a trough of low pressure over the central US throughout most of July.

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Thursday Highlights – Drought Monitor and El Nino Forecast

Here are two highlights for today:

U.S. Drought Monitor

After some concerns of dryness over the last several months in parts of Illinois, the conditions across Illinois were much wetter in the last two weeks. Rainfall totals were especially heavy south of Interstate 72 and ranged from 3 to 8 inches or more (see map below).

The U.S. Drought Monitor has removed all areas of drought in Illinois and greatly reduced the region of “abnormally dry” conditions.

AHPSPrecipitationAnalysis

Climate Prediction Center El Niño Forecast

The NOAA Climate Prediction Center issued a new El Niño Watch today, saying …

While ENSO-neutral is favored for Northern Hemisphere spring, the chances of El Niño increase during the remainder of the year, exceeding 50% by summer.

This reflects a slightly stronger chance of El Niño arriving this summer than mentioned in their post a month ago. However, they caution that there is still a great deal of uncertainty in the timing and strength of the El Niño and recognize that the skill in forecasting El Niño this early in spring is low. This is a less certain forecast than the one issued by the Australian Bureau of Meteorology earlier this week, indicating that there was a greater than 70 percent of an El Niño event by June.

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.

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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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Frost Depth in Illinois

One of the effects of this exceptionally cold winter has been that our soils have remained frozen at considerable depths. We have hourly soil temperatures under grass at 19 sites across the state at 4 and 8 inches, available through the WARM website, that give us glimpses of soil conditions.

Here are snapshots of the daily low soil temperature at 4 inches yesterday and a week ago when temperatures were much warmer. The 4-inch temperature responded to the warmer weather and showed signs of thawing before re-freezing this week. In many parts of the state, the 8-inch soil temperatures remained frozen during this period. Click on each map to enlarge.

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Soil temperatures depend on soil types, soil moisture, vegetation, snowcover, and exposure. In general, drier soils warm up and cool faster than wet soils. Both vegetation and snow can insulate the soil for air temperature extremes. I recall the morning of January 5, 1999, when we had a foot of snow on the ground and an air temperature of 25 degrees below zero. Because the winter had been mild up to that week, the soil temperature at 4 inches was 32 degrees, a difference of 57 degrees between 4 inches below ground and 5 feet above ground!

While the above site tracks temperatures at specific depths, the NOAA North Central River Forecast Center maintains a web site with observed frost-depths in Illinois and points to the north. For most of this winter, the frost depth has run in the neighborhood of 10 to 20 inches across Illinois with a few sites going deeper. Here is a screenshot of this morning’s map. While it doesn’t work on the screen shot, you can mouse-over the points on the map on the website and see the individual reports.

North Central River Forecast SoilT

Finally, Wayne Wendland, the former State Climatologist for Illinois, did a frost-depth study in Illinois using data collected from grave diggers from 1980 to 1996. He developed a network of sites across Illinois through the Illinois Cemetery Association and provided post cards that the grave diggers filled out every two weeks in winter. They noted frost depth, soil moisture, soil texture, ground cover, and exposure. The deepest observed frost depths during this period ranged from 5 inches in far southern Illinois to 30 inches in far northern Illinois. The results were published in the Transactions of the Illinois State Academy of Science (pdf).

April Already 4th Wettest on Record

Based on preliminary data, this April in Illinois is already the 4th wettest on record with 6.58 inches of precipitation. Average statewide precipitation for April is 3.77 inches. So we are already almost two inches above average.

According to the NWS forecast, more rain is expected across southern Illinois on Friday and Saturday. Therefore, it is possible that we will move up the list by the end of the month. In addition, some sites may have already reached their record for April, including the city of Chicago.

Top 5 Wettest Aprils

  1. 2011 with 7.40 inches
  2. 1957 with 7.13 inches
  3. 1927 with 6.95 inches
  4. 2013 with 6.58 inches
  5. 1944 with 6.50 inches

Precipitation Pattern Across the State

Here is how the precipitation has been distributed around the state, based on our multi-sensor precipitation product, with the actual amounts and the departures from average. Many parts of central and northern Illinois have more than double their average April precipitation (shades of purple in the second map).

April precipitation in inches for the first 24 days of the month. Click to enlarge.
April precipitation in inches for the first 24 days of the month. Click to enlarge.
April precipitation as departures from average. Click to enlarge.
April precipitation as departures from average. Click to enlarge.