April 2004 - a Review of Weather, Temperatures, and Precipitation for the Quad State Region.


Weather Summary for April 2004


Weather Summary information is taken from the April Monthly Report of River and Flood Conditions for the Quad State Region.


April was fairly typical with daytime temperatures rising into the 60s and 70s with a few highs above 80 degrees.  Nighttime temperatures were still cool and kept daily averages near normal.  Average temperatures for the month were up to 2 degrees above normal (55 to 58 degrees).  Total precipitation for the month was, once again, below normal.  Evansville, IN was over 2.5 inches below normal for April.  Three consecutive dry months sent much of the region into the drier-than-normal category on the Palmer Drought Severity Index by the 30th. 


Cool, high pressure was in control of the region through the first week of April.  As the upper level northwest flow weakened and became more zonal, a weak storm system moved out of the Plains on the 7th to produce clouds and generally trace amounts of precipitation.  Southwest flow returned pushing several upper level systems over the region between the 10th and 13th.  Showers produced mainly light rain and total amounts during the period were less than three-quarters inch.  Surface high pressure nudged in from the Southern Plains and Gulf Coast through the 18th, allowing high temperatures to top out around 80 degrees.


On the 19th, a stronger storm system moved out of the Central Plains and by the 22nd became stalled over the lower Ohio Valley.  Showers and thunderstorms occurred daily between the 19th and the 26th across the HSA.  Many of these storms were slow moving and produced copious amounts of rain in a short amount of time.  Numerous Urban and Small Stream Flood Advisories and Flash Flood Warnings were issued.  Many of the reports were flooded roadways with several road closures.  Rain amounts during the week totaled between 1.5 and 3 inches with even isolated amounts in southeast Missouri between 4 and 6 inches.


Weak high pressure built over the region before a southwest flow return on the 29th.  Warmer and more moist air streamed up the Mississippi River Valley out ahead of an approaching storm system.  Showers and thunderstorms on the 30th produced very heavy rains and isolated flooding.  Several Urban and Small Stream Flood Advisories and Flash Flood Warnings were issued.  Total rain amounts averaged around one-half inch but there were several areas that reported between 1-2 inches.

April Temperatures Across the Quad State Region

The following table (Figure 1) displays April 2004 temperatures at five locations across the Quad State Region where this information is consistently collected. These sites are all ASOS (Automated Surface Observation System) sites located at airports, except for the Carbondale site - which is located at the Carbondale Sewage Treatment Plant.


These temperatures represent the average high and low daily temperatures for April 2004, for all days of the month, and the average temperature for the entire month. The normals are based on 30 years of temperature information from 1971 through 2000.


Range of Averages - gives the highest and lowest April average temperatures observed during the 30 year period from which the normals were calculated, 1971 through 2000.


The last column compares the April 2004 average temperature with the April average temperatures during the normal period, 1971-2000. diff is the difference in degrees between the April average temperature and the normal, while %-tile (percentile)  is the percentage of average temperatures in the normal period that were less than the 2004 April average. Note that percentile can range from zero to 100, with 50 being normal.


Figure 1. April Average Daily Temperature Summaries (Degrees F) for Several Quad State Region Locations.





Temp >








Range of






Carbondale, IL

  (well above normal)


Normal >

2004 >











max: 62.5 in 1981

min:  49.0 in 1983





Cape Girardeau, MO

 (slightly below normal)


Normal >

2004 >











max: 63.9 in 1981

min:  51.7 in 1983


   - 0.5



Evansville, IN

  (well above normal)


Normal >

2004 >











max: 61.7 in 1981

min:  50,5 in 1997





Paducah,  KY

  (above normal)


Normal >

    2004 >











max: 64.1 in 1981

min:  51.5 in 1983





Poplar Bluff, MO

  (well above normal)


Normal >

2004 >











max: 64.5 in 1981

min:  51.3 in 1983




* Range of averages is taken from the range used to calculate normals: 1971-2000.    

 This gives the highest and lowest April average temperature observed during that time.

** Two years of temperature data were missing from the normal period for Cape

 Girardeau, three years of temperature data were missing from the Poplar Bluff data.


As this table indicates, temperatures across the Quad State Region for the month of April ranged from near normal in Cape Girardeau, Missouri - where the 2004 April average temperature was only 0.5 degree below normal, to Carbondale, Illinois - where the April 2004 average temperature was 1.5 degrees above normal. All other sites were also above normal - with Evansville, Poplar Bluff, and Paducah being 2.1, 1.0, and 0.6 degrees above normal, respectively.


Based on normal average April temperatures, April 2004 would seem to be a fairly normal month. Looking at the percentiles gives another perspective. Three of the five sites - Carbondale,  Evansville, and Poplar Bluff - were at the 70th percentile or above, meaning that in 70 percent or more of the years in the normal period, April had a cooler average temperature than in 2004. This tells us that April was unusually warm at those locations.


At the other two sites - Paducah and Cape Girardeau - the percentiles were 63 and 43, respectively. Based on percentile, temperature at Paducah was also well above normal in 2004, while only Cape Girardeau was below normal.


Why do these two perspectives lead to different conclusions? First, it should be noted that the average April temperature at a given site is not necessarily at the 50th percentile. This is because a few unusually high or low temperatures can skew the average by a large amount compared to the other readings. In this case, an examination of the actual data for the normal period indicates that this is what happened. A few years had unusually high temperatures that brought the average well above the 50th percentile.


The conclusion: April 2004 was warmer than normal at most of the locations considered.


April Precipitation Across the Quad State Region


The next table (Figure 2) displays normal precipitation and the observed precipitation for April 2004, with the Range of average April temperatures within the normal period, and the percentile of the 2004 April average based on the normal period. The historical time periods are the same as those in Figure 1: 30 years, 1971 through 2000.  Snowfall is not available from most locations except as melted snow, which is included in the total precipitation for the month, although little or no snow fall was observed at these locations in April 2004.


Note that all locations had precipitation more than one inch below normal in April, except for Poplar Bluff, Missouri - where the total precipitation was very near normal at only 0.12 inch above. Evansville was at the low extreme, with 2.57 inches below normal.


Range in Table 2 gives the highest and lowest April precipitation observed during the 30 year period from which the normals were calculated. It can be noted that all of the 2004 April observed precipitations - except for Poplar Bluff - are near the low end of these ranges - indicating a relatively dry April in 2004 at these locations.


The last column of Table 2, %-ile (percentile), indicates the percent of years within the normal period with precipitation less than the amount observed in 2004 at each location. Percentiles range from 10 in Evansville to 52 in Carbondale.


Only Poplar Bluff had precipitation above the normal value based on average temperature, although based on the percentile of 44, the precipitation was less than normal. Note that Carbondale had precipitation 1.12 inches less than the normal value, although it was slightly above normal based on percentile, at 52.


This data indicates that, on average, April 2004 was slightly drier than normal at two locations: Cape Girardeau and Paducah, about normal at two sites: Carbondale.and Poplar Bluff, and very dry at Evansville. Overall, it was a drier than normal April across the Quad State Region.


Figure 2. April Average Monthly Precipitation (inches) and April 2004 Observed Precipitation for Several Quad State Region Locations














(within normal period)





Carbondale, IL

  (near normal)


Normal >2004 >






- 1.12


   max: 11.60 in 1983

   min:    1.68 in 1981




Cape Girardeau, MO

  (below normal)


Normal > 2004 >








   max: 12.73 in 1983

   min:    1.27 in 1971




Evansville, IN

  (well below normal)


Normal >

 2004 >








   max: 11.83 in 1996

   min:    1.19 in 1992




Paducah,  KY

  (below normal)


Normal >

2004 >








   max: 14.54 in 1983

   min:    1.55 in 1986





Poplar Bluff, MO

  (near normal)


Normal >

2004 >








   max: 11.36 in 1991

   min:    1.18 in 2000



* Total precip. Includes melted snow

** Range is the highest and lowest April precipitation observed within the period used to     calculate normals: 1971-2000.

*** Missing precipitation data: One year missing from Carbondale normals, 2 years missing     from Cape Girardeau normals, and 3 years missing from Poplar Bluff normals.

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