April 2019: An Active Weather Pattern and Late Season Snow!

April 2019 will be a month remembered for a continuation of an active and stormy weather pattern across Illinois, with two short lived, yet notable and uncommon late season snow events which impacted many in northern portions of the state.

The month finished noticeably wetter than average, with temperatures marginally below the long-term average. The preliminary average statewide April temperature was 52.0°F, which is 0.6°F below the long term average. The preliminary average statewide precipitation was 4.58 inches, which is 0.80 inches above the long term average.

Note: Data are provisional and may change slightly over time.

Precipitation

Preliminary statewide average precipitation for April was 4.58 inches, which is 0.80 inches above the long term average.

Precipitation in Illinois has been above average since December 2018. Preliminary data would rank this as the 7th wettest December – April period in state history. The end of April 2019 marked six months since any portion of the state has been classified as in drought, or abnormally dry by the U.S Drought Monitor..

An active spring weather pattern resulted in a majority of regions in northern, eastern, and southern portions of the state receiving over 100% of average monthly precipitation, with localized amounts approaching 200%.  Smaller regions of the state in west-central Illinois – roughly between the Mississippi and Illinois rivers are the only locations to receive near or below average precipitation for the month (see map below).

The heaviest precipitation fell in extreme southern Illinois, especially in counties bordering the Wabash and Mississippi Rivers, where 6 to 8+ inches were common (see map below).  The highest total in the state was reported at a station near Cobden (Union County) with 8.31 inches.

Heading into May, flooding remains an ongoing concern for the state, as soil moisture percentiles remain in the 90th to 95th percent range.

As of April 30th, 134 river gauges affecting Illinois were reported with crests in minor, moderate, or major flood stages. The greatest threat continues to remain along the Mississippi River. River flooding concerns were intensified by several days or heavy rains during the last week of April.

Snowfall

A majority of April snowfall came from two short lived, yet notable late season events that impacted many in northern portions of the state.

The first event on the weekend of April 13th and 14th brought widespread reports of 1 to 5 inches along a corridor extending from near Quincy, and running northeast toward Chicago and the Illinois/Wisconsin border. Several localities west and north of Chicago reported 6 to 8+ inches. Notable accumulations were measured as far south as Peoria. An accumulation of 5.4 inches at Chicago O’Hare Airport tied the record for the snowiest calendar day this late in the season.  April 16, 1961 also recorded 5.4 inches of snow.

The second snow event on April 27th brought a variety of wintry precipitation types to locations in northern Illinois, including another round of accumulating snow for many from Chicago and points north and west.  With 3.7 inches, this was the latest 2+ inch snow event on record for Rockford (Winnebago County).

The maximum monthly snowfall in Illinois was reported at a station near St. Charles (Kane County) with an impressive 13.5 inches.

Temperature

Preliminary results show that April 2019 finished with a statewide average temperature of 52.0°F which is 0.6°F below the long term average.

Despite several significant temperature swings throughout the month, which are common during springtime, statewide April temperatures finished right around the long term average. A few pockets in extreme southern Illinois reported slightly above average, and sporadic regions in northern Illinois reported slightly below the long term average.  This is a welcome change from last year,  April 2018, which ranked as the second coldest April on record.

The highest temperature in the state was recorded at a station near Jerseyville (Jersey County) with a reading of 85°F on April 23.  In contrast, the lowest temperature of 18°F was recorded at a station in Altona (Knox County) on April 1.

May 2019

Looking ahead at the rest of May 2019, the Climate Prediction Center (CPC) is favoring probabilities of above average temperatures for the southeast half of the state, with equal chances of above, near, or below average temperatures for the northwest half of the state. Unfortunately, an active weather pattern looks to persist, as the May outlook favors probabilities of above average precipitation statewide.

Late April 2019 Snow Event

4/29/2019 – A strong and considerably cold low pressure system took aim at Illinois on Saturday April 27th, bringing a large area of widespread precipitation and unseasonably cool weather to a majority of the state.  The greatest impacts were felt in Northern Illinois, where temperatures were cold enough to support a variety of wintry precipitation types. This included a late season and uncommon accumulating snow for many from Chicago and points north and west.

According to the National Weather Service, the final snowfall total at Chicago O’Hare of 2.5 inches was the latest accumulating snowfall for the city since 1989, and the latest 2+ inch single calendar day snowfall in station history. The two day period of May 1-2, 1940 saw 2.2 inches.

Typically, Chicago O’Hare can expect 1.2 inches of snow in April, with the record for the month being 11.1 inches which was set in April 1975.  To date, April 2019 has seen 7.9 inches.

The official snowfall total in Rockford of 3.7 inches was the latest accumulating snow since 1994, and ranks as the latest 2+ inch snow event on record.  Beating out April 23, 1986 with 3.8 inches, and April 23-24, 1910 with 2.5 inches.

A station in Stockton (Jo Daviess County) reported 6.0 inches of snow with this event.  See the interpolated map below of preliminary snowfall accumulation across the state. (Note: Locally higher snowfall reports were common)

Behind this system, and with the aid of fresh spring snow cover, temperatures dropped across Northern Illinois, with Rockford tying the record daily low temperature on the morning of April 28th with a reading of 28°F.

In total 26 weather stations reported temperatures below freezing on the morning of April 28th, with Stockton (Jo Daviess County) reporting the lowest weekend reading in the state with just 21°F.

First Half of January – Colder, Snowier than Last Year

Summary: we are halfway through January and so far the statewide average temperature is 16.5 degrees, 7.3 degrees below normal. Last year, by mid-January the average temperatures is 25.2 degrees and 1.4 degrees above normal.
The statewide average precipitation is only 0.6 inches, two-thirds of normal for the first half of January. Last year, by mid-January the average precipitation was 0.82 inches, just 0.07 inches below normal. Note that precipitation is a measure of both the rainfall and the water content of snowfall.
Snowfall has been widespread with 2 to 5 inches common in all but western Illinois. For most areas, that is near to slightly below normal. So far our snow has come from fast-moving low-pressure systems out of Canada (so-called Alberta clippers) that are noted for bringing light, fluffy snow without much water content. Last year, some areas in northern Illinois had received zero snowfall in the first half of January and many areas reported less than an inch. Continue reading “First Half of January – Colder, Snowier than Last Year”

First Half of January – Colder, Snowier than Last Year

Summary: we are halfway through January and so far the statewide average temperature is 16.5 degrees, 7.3 degrees below normal. Last year, by mid-January the average temperatures is 25.2 degrees and 1.4 degrees above normal.
The statewide average precipitation is only 0.6 inches, two-thirds of normal for the first half of January. Last year, by mid-January the average precipitation was 0.82 inches, just 0.07 inches below normal. Note that precipitation is a measure of both the rainfall and the water content of snowfall.
Snowfall has been widespread with 2 to 5 inches common in all but western Illinois. For most areas, that is near to slightly below normal. So far our snow has come from fast-moving low-pressure systems out of Canada (so-called Alberta clippers) that are noted for bringing light, fluffy snow without much water content. Last year, some areas in northern Illinois had received zero snowfall in the first half of January and many areas reported less than an inch. Continue reading “First Half of January – Colder, Snowier than Last Year”

Snowfall Changes Over Time in Illinois

The snowiest winter on record was 1978-79 with a statewide total of 44.5 inches. The winter of 2011-12 had the least amount of snow with a statewide total of 9.2 inches.
While a few stations recorded snowfall in the 1800s, our statewide snowfall records in Illinois began in 1902. There is no long-term trend in the snowfall totals; however, some decades were snowier than others, such as the 1910s, 1960s, and 1970s. In fact, the 1970s were the snowiest decade on record with an average snowfall of 27.2 inches.
Since the 1970s, snowfall amounts dropped steeply with less year to year variability for much of the 1980s and into the early 2000s. However, snowfall amounts in the last six winters have been more variable with the winter of 2013-14 being about as snowy as the late 1970s while the winters of 2011-12 and 2016-17 had the lowest and third lowest snowfall totals, respectively, for the state.
 

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Snowfall is accumulated from July 1 of the first year to June 30 of the second year. The second year is used in the plot and table (for example, 2006 refers to the 2005-2006 season). Illinois State Water Survey, 2018.

 
Continue reading “Snowfall Changes Over Time in Illinois”

Snowfall Changes Over Time in Illinois

The snowiest winter on record was 1978-79 with a statewide total of 44.5 inches. The winter of 2011-12 had the least amount of snow with a statewide total of 9.2 inches.
While a few stations recorded snowfall in the 1800s, our statewide snowfall records in Illinois began in 1902. There is no long-term trend in the snowfall totals; however, some decades were snowier than others, such as the 1910s, 1960s, and 1970s. In fact, the 1970s were the snowiest decade on record with an average snowfall of 27.2 inches.
Since the 1970s, snowfall amounts dropped steeply with less year to year variability for much of the 1980s and into the early 2000s. However, snowfall amounts in the last six winters have been more variable with the winter of 2013-14 being about as snowy as the late 1970s while the winters of 2011-12 and 2016-17 had the lowest and third lowest snowfall totals, respectively, for the state.
 

image003
Snowfall is accumulated from July 1 of the first year to June 30 of the second year. The second year is used in the plot and table (for example, 2006 refers to the 2005-2006 season). Illinois State Water Survey, 2018.

 
Continue reading “Snowfall Changes Over Time in Illinois”

Snow – Date of First Snowfall and Normals for Illinois

Date of First Snowfall

Here are 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 usually occurs around Thanksgiving. The dates move 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.
date of first snow

Continue reading “Snow – Date of First Snowfall and Normals for Illinois”

Snow – Date of First Snowfall and Normals for Illinois

Date of First Snowfall

Here are 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 usually occurs around Thanksgiving. The dates move 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.
date of first snow

Continue reading “Snow – Date of First Snowfall and Normals for Illinois”

New Outlook for December – Wetter, Colder in Illinois

The NWS released their latest outlook for December. They have Illinois with equal chances (EC) of above, below, and near-normal temperatures for the entire month. However, the day to day forecasts out to 14 days show Illinois having colder than normal temperatures on most of the days. The NWS product for weeks 3 and 4 suggest that warmer-than-normal weather will return in the second half of December. In general, I have higher confidence in the forecasts out to 14 days.
The December outlook also shows Illinois with an increased chance of being wetter than normal. This is true in the shorter range forecasts out to 14 days as well. Considering it’s December, a forecast of colder and wetter than normal conditions sure sounds like a recipe for snow. As you may recall, last December was notable for having almost no snow.
Click to enlarge.