I have noticed that the average date of the first snow is a popular search term on the blog, so here is the reposting of the median dates of the first measurable snowfall of the season in Illinois. This map is based on 1971-2000 data. While it is not based on the current 1981-2010 averages, the map is still relevant for the purpose of getting an idea of the dates. Measurable snowfall means at least a tenth of an inch.
In the northern third of Illinois, the first snowfall occurred around Thanksgiving. The dates switch from November to December once you reach central Illinois (just north of a line between Quincy and Champaign). By the time you reach Carbondale, the date can be as late as December 20. From this you can see that we are by no means behind schedule this year.
Illinois was one of the coolest places to live in 2014, at least in terms of temperature, according to the recent annual report released by the National Centers for Environmental Information (NCEI). In the map below, the areas in blue show areas where the temperatures were much colder than average for the central US and eastern Canada, while the West and Alaska were much warmer than average (areas in red).
According to the latest figures, the average temperature for Illinois in 2014 was 49.5 degrees, 2.7 degrees below the 1981-2010 average, and the 6th coolest year on record for Illinois.
While tornadoes can happen any time of the year, the tornado season really starts to ramp up in March in Illinois (see plot below) and remains active through the spring and on into summer. April, May, and June are the three standout months historically. So far 2015 has been very quiet with no severe weather reported in Illinois so far, according to NOAA.
The statewide average temperature for February was 18.6 degrees. That is 12.3 degrees below the 1981-2010 average and the 7th coldest February on record. By comparison, February 2014 was 9th coldest at 19.5 degrees.
Here are some amazing statistics for Chicago. February was tied with 1875 for the coldest on record, according to the Chicago National Weather Service. The average temperature for February was 14.6 degrees, 13.1 degrees below average. In addition, it was the 10th coldest month overall on record. February snowfall in Chicago was the third largest on record with 26.8 inches, 17.7 inches above average.
Snowfall for February in Illinois was widespread and well above average. Amounts of 15 to 20 inches were common in western and northern Illinois and 10 to 15 across central Illinois and parts of far southern Illinois. This was 8 to 12 inches above average in many locations. See maps below. Click to enlarge.
Some other February snowfall totals from around the state:
Chicago Midway AP: 28.3 inches
Rockford: 14.7 inches
Peoria: 12.8 inches
Quincy Lock and Dam: 11.2 inches
Springfield: 22.6 inches
Champaign-Urbana: 12.4 inches
Bloomington-Normal: 13.0 inches
Carbondale: 6.0 inches
The statewide average precipitation (rain plus the water content of snow) for February was 1.5 inches, 0.5 inches below average. Most of the state received 1 to 2 inches of precipitation, except for far southern Illinois which got 2 to 3 inches. See the second batch of maps for precipitation and precipitation departures from average.
February 2015 is on track to being one of the coldest February’s on record for Illinois. Data through February 24 puts the statewide average at 19.4° F. This is 11.5°F below average and slightly colder than last February’s 19.4°F. Before February, this was shaping up to be a mild winter with near to above-average temperatures (see graph to the left, click to enlarge).
At this point, February 2015 is ranked as the 8th coldest on record, edging out 2014 (see table below). The NWS forecasts show that temperatures for the rest of February will be 15 to 20 degrees below average. Therefore it is possible that it could move up the ranks. I will post more on this at the end of the month.
I just heard Bing Crosby on the radio and it reminded me that it’s time to do the annual post on …
What are the historical chances of a White Christmas (defined as at least an inch of snow on the ground on Christmas Day)? The first map below the shows the odds across the state. It should come as no surprise that the highest odds are in northern Illinois. In general, the odds are about 40-60 percent in the northern third of Illinois, 20-40 percent in central Illinois, and 0-20 percent in southern Illinois.
There can be large differences between nearby sites. Snowfall is notoriously difficult to measure with the potential for two nearby sites having different results due to exposure to the sun and the wind.
After a cold November, December has been much milder this year. The latest NWS 8-14 day forecast includes December 25 and continues to show Illinois with a good chance of warmer-than-average temperatures. And today there is not much snow in Illinois (map below). Stay tuned to your local forecast as we get closer. Continue reading “Chance of a White Christmas”
The statewide average temperature for October so far in Illinois is 56.5 degrees, 1.4 degrees below average. The statewide average precipitation for October so far is 2.5 inches.
Here is the map showing how the precipitation has fallen in Illinois and surrounding states. The heaviest amounts in Illinois were the 3 to 5 inches between Interstates 70 and 74. Amounts of 1 to 3 inches were common in the northern and southern thirds of the state. The largest total so far is 8.38 inches reported at Greenfield in Greene County
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.
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.
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.