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.

March 2019: A cold start to the month, with a stormy and wet finish

March 2019 will be a month remembered for an unseasonably cold start, followed by an active and wet weather pattern which resulted in a continuation of excess soil moisture, and major flooding events on many local streams and rivers.

Statewide, March ended colder and substantially wetter than the long term average.  The preliminary average statewide March temperature was 36.6°F, which is 4.7°F below the long term average.  The preliminary average statewide precipitation was 4.16 inches, which is 1.20 inches above the long term average.

Data are provisional and may change slightly over time.

Temperature

Preliminary results show that March 2019 finished with a statewide average temperature of 36.6°F which is 4.7°F below the long term average.

The first full week or March begun with a brutal Arctic outbreak in which temperature departures of 15° to 25°  below normal were common across Illinois (see map below).

During this time three stations recorded minimum temperatures of -10° or colder.  The lowest reading in the state, -12°F, occurred at the Little Red School House station (Cook County) on March 5th.

In contrast, the warmest reading in the state was 76°F, reported at a station near Dixon Spring (Pope County) on March 13th.

The map below depicts average monthly statewide temperature departures for Illinois.  March temperature departures finished below average statewide, with the coldest departures occurring across large areas of central Illinois, and in the northwest corner of the state.

Precipitation

Preliminary statewide average precipitation for March was 4.16 inches, which is 1.20 inches above the long term average.

A persistent active weather pattern along with above average precipitation were the biggest weather stories in March.  Major and historic flooding on the lower Ohio River Basin in Southern Illinois continued into the first week of March, resulting from substantial February rain events.  By the middle of the month, a strong and historic low pressure system brought heavy rain, storms, and strong wind to Illinois and the rest of the Midwest.  The heavy rains and combined regional snow melt resulted in additional widespread flooding concerns across the region.  This included a major flooding event for northern and northwest Illinois, with the Rock, Fox, and Mississippi Rivers experiencing significant crests.

The heaviest March precipitation fell across central and southern portions of the state where 4 to 6 inches were common.  Five stations in these regions reported over 6 inches of precipitation for the month.  Totals were lower in Northern Illinois with generally 1.5 to 3 inches. The lowest totals for the month occurred along the Illinois/Wisconsin border.

The highest March precipitation total of 6.41 inches was reported at a station near Jerseyville (Jersey County).

Above average March wetness led to precipitation anomalies over 100% of average for the southern two-thirds of the state, with the most impressive anomalies of 200-300% percent of average in a large area of central Illinois (see map below).

Snowfall in March did occur statewide, although it was rarely long lasting.  Storm tracks are apparent on the accumulated snowfall map, with two distinct snow maximums. One in the vicinity of the corridor from Rushville to Springfield, and a second centered near Kankakee.  In both cases 3 to 5 inches of accumulation were measured.

Spring Outlook

Soil moisture profiles across Illinois remain in the 90th percentile or higher as we head into April.  This leaves soil conditions favorable for spring runoff, and is an ever-growing concern for the agricultural community.

The National Weather Service (NWS) spring flood outlook places the entire state in its flood risk zone. Eastern and central Illinois are subject to a minor flood risk, while western, extreme northern and southern portions of the state are in a moderate flood risk zone.  Locations immediately along the banks of the Mississippi river are in a major flood risk zone.

April 2019

Looking ahead at the rest of April 2019, the Climate Prediction Center (CPC) is favoring probabilities of above average temperatures statewide.  This is a welcome change compared to April 2018, which ranked as the second coldest April in state history.  An active weather pattern looks to persist, as the April outlook favors slight probabilities of above average precipitation for the western half of the state.