July Review - Below Normal Temperatures and Variable Rainfall

Canadian air masses were frequent visitors to central and southeast Illinois in July.  With the exception of a week of 90+ degree heat and high humidity during the middle of the month, temperatures were frequently below normal early and late in the month.  An unusually persistent cool air mass set up over the region July 24-31, with daily temperatures averaging 5-15 degrees below normal.  Several observing sites set daily record low temperatures, and record cool highs during this stretch. Record lows started of fall on July 25 in Springfield with a low of 54. On July 28 record lows were set in Peoria (51), Springfield (48), Lincoln (48), and Effingham (48).  On July 29 record lows fell in Springfield (50) and Effingham (49).  Record cool highs occurred July 27 in Peoria (69) and Lincoln (69).  For much of the area, many days during this week were more typical of mid-September with highs in the lower 70s and lows in the lower 50s. This was quite a change from July 2012, which was the 2nd warmest month on record for the state.

July temperature departure from normal 

July 24-30 high temperature departure from normal

July 24-30 low temperature departure from normal

July temp. departure from normal

July 24-30 below normal highs

July 24-30 below normal lows


Rainfall was highly variable due to the hit-and-miss nature of summertime thunderstorms.  For the month as a whole, rainfall ended up above normal south of I-70, and gradually tapered off farther north with less than 50% of normal falling north of I-74.  Localized heavy rains fell over portions of central Illinois on July 10, when showers and thunderstorms developed ahead of a slow moving frontal boundary.  Due to very high atmospheric moisture levels the storms were very efficient rainfall producers, and with weak winds aloft the storms moved very slowly.  Rainfall rates as high as 3 inches per hour were observed.  Heaviest rains were concentrated from Sangamon through Logan and Macon counties, where 2-4 inch totals fell.  Flash flooding occurred in Logan county, and isolated thunderstorm wind damage was reported in Logan and Vermilion counties.  Another period of locally heavy rain occurred July 20-22 when a slow moving cold front interacted with a very warm and humid air mass.  Scattered slow-moving thunderstorms produced very high rainfall rates once again.  This activity primarily affected areas along and south of I-72.  As is often the case with summertime convection, some areas received heavy rains while nearby locations saw very little, which is depicted well in the event rainfall maps below.

 

July precipitation departure from normal 

July 10 heavy rain 

July 20-22 rainfall

July precip. departure from normal

July 10 rainfall

July 20-22 rainfall


The table below summarizes July 2013 precipitation 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.

Site Precipitation Departure from Normal Average Temperature Departure from Normal
Charleston

4.59"

+0.12"

73.9

-2.3
Decatur

3.56"

-0.42"

72.8

-3.7
Galesburg

2.96"

-1.42"

73.7

-0.9
Jacksonville

6.09"

+2.14"

73.7

-1.5
Lincoln

2.86"

-2.20"

72.1

-2.9
Normal

1.25"

-2.91"

72.9

-1.5
Olney

9.15"

+4.82"

73.6

-2.8
Peoria

1.79"

-2.06"

74.3

-1.2
Springfield

3.26"

-0.68"

73.9

-1.9
Urbana

3.25"

-1.45"

72.5

-2.4


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.

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

 



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