May & Spring Season Weather Summaries

May Overview

In a month that is typically associated with active severe weather, May 2015 was noted as having little in the way of organized severe weather in central and southeast Illinois.  There were a few isolated/unorganized severe weather events, along with a few moderate to heavy rain events.  Overall, temperatures averaged a few degrees above normal, with warm stretches of weather (highs in mid/upper 80s) during the 3rd-7th, and 24th-29th.  Notable cool periods saw highs only reach the lower 50s to lower 60s on the 20th and 31st, when record cool daily highs were set in a few locations.  Widespread record lows were set on the 1st, when low temperatures dropped to near the freezing mark, causing a widespread late season frost.  As far as rainfall was concerned, much of central Illinois saw wet conditions, as 100-150% of normal rainfall was reported.  Amounts quickly tapered off to the southeast, as areas south of I-70 saw closer to 75% of normal May precipitation.  Here are summaries of a couple of the more significant weather events for the month:

• May 10: A squall line tracked across central and southeast Illinois during the late afternoon and evening of May 10th.  This produced sporadic wind damage along and south of a Springfield to Davnille line.  The storms formed well ahead of an approaching cold front, feeding off of ample instability provided by temperatures in the lower 80s and dew points in the middle 60s.  Wind shear was rather weak, which led to the isolated occurrence of severe weather.  Individual cells within the line periodically strengthened, creating pockets of locally enhanced winds up to 60 MPH.  General wind speeds within the line were 40 to 50 MPH.  Some of the locations impacted with the higher wind gusts were Springfield, Mattoon, Charleston, Newton, and Danville, where tree limbs and power lines were blown down.  These storms were preceded by several days of wet weather. Parts of central Illinois received 2 to 4 inches of rain from May 5th through May 10th.
  
   
• May 29-30: A slow-moving frontal boundary interacting with a warm and humid airmass produced widespread showers and thunderstorms across the region from Friday, May 29th into Saturday, May 30th.  Totals were highest east of the Illinois River, where most locations received 1 to 2 inches.  A few corridors of heavier rain were noted just west of I-55 from Morgan to McLean county where 2-3 inch totals were common.  Isolated heaver rain developed on Saturday afternoon in Effingham county, where a few observers measured as much as 4 inches of rain and some flash flooding occurred just west of Effingham.

May Rainfall Maps

May Temperature Maps

May Climate Data

The table below summarizes May 2015 rainfall and temperature, and departure from normal for selected cities across central and southeast Illinois.  Data from Peoria and Springfield are from ASOS sites, while others are from NWS Cooperative Observers.
 

** Lincoln - 7th wettest May

Links below are the monthly climate summaries for area cities. Only the summaries for Peoria, Springfield and Lincoln are considered "official", meaning they are the station of record for their respective locations. The other summaries are "supplemental", meaning another location in the area is the official climate station for that city.

• Peoria -- Peoria International Airport
• Springfield -- Abraham Lincoln Capital Airport
• Lincoln -- Lincoln NWS office
• Champaign -- University of Illinois - Willard Airport
• Decatur -- Decatur Airport
• Lawrenceville -- Lawrenceville-Vincennes International Airport
• Mattoon -- Coles County Airport

Climate data for other area cities is available at http://www.nws.noaa.gov/climate/xmacis.php?wfo=ilx 

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Spring Season (March through May) Overview

From a climatological perspective, the spring season was typcial for central and southeast Illinois.  The season overall had near normal precipitation and temperatures.  

• March Highlights: The season started off on a winter-like note on March 1st, with 6-9 inches of snow falling southeast of a Rushville to Bloomington line, and 1-4 inches farther north.  This was the end of a winter storm which started on Feb. 28, and produced storm totals up to 1 foot in parts of east central IL.  March also saw well below normal temperatures, which averaged 3 to 5 degrees below normal.  The coldest temperatures during the month were March 5-6 when low temperatures were as cold as single digits below zero, and the average daily temperature was 25 to 30 degrees below normal. 
  
   
• April Highlights: April's average temperature was 1-2 degrees above normal for central and southeast IL.  However, the first half of the month featured well above normal temperatures, while the second half saw well below normal readings. Overnight lows dropped to near freezing on numerous occasions, keeping frosty mornings going late into the month.  Monthly rainfall was well below normal west of I-55, but amounts gradually increased farther southeast, with above normal totals reported south of I-70.  A predominant northwest flow kept severe weather well south of the region during the last half of the month, while only one day of severe storms occurred early in the month, on April 9th.  On this day a broken line of strong to severe thunderstorms developed across central Illinois during the late afternoon and evening. Due to unseasonably high dewpoints in the lower to middle 60s and increasingly strong low-level wind shear, some of the strorms began to rotate as they tracked across the area. Two tornadoes touched down in central Illinois (near Dunlap in Peoria County and near Tovey in Christian County); however these were both weak and short-lived, doing no damage.  Later in the evening as the storms moved into eastern Illinois, hail as large as 3 inches in diameter was observed near Mahomet, in Champaign County.  
   
• May Highlights: see above

Spring Rainfall Maps

Spring Temperature Maps

Spring Climate Data

The table below summarizes Spring 2015 rainfall and temperature, and departure from normal for selected cities across central and southeast Illinois.  Data from Peoria and Springfield are from ASOS sites, while others are from NWS Cooperative Observers.
 

Links below are the seasonal climate summaries for area cities. Only the summaries for Peoria, Springfield and Lincoln are considered "official", meaning they are the station of record for their respective locations. The other summaries are "supplemental", meaning another location in the area is the official climate station for that city.

• Peoria -- Peoria International Airport
• Springfield -- Abraham Lincoln Capital Airport
• Lincoln -- Lincoln NWS office
• Champaign -- University of Illinois - Willard Airport
• Decatur -- Decatur Airport
• Lawrenceville -- Lawrenceville-Vincennes International Airport
• Mattoon -- Coles County Airport

Climate data for other area cities is available at http://www.nws.noaa.gov/climate/xmacis.php?wfo=ilx