A Wet, Stormy, and Historic May 2004

All of Southeast Michigan experienced the very wet and stormy May. The month started out wet when on the first weekend over an inch of rain fell across most of the region. The storms started on May 6th with the first of many severe weather events. In many respects, May 2004 approached or eclipsed a number of records.

May 2004 Monthly Climate Summary for:
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Detroit Metroit Airport and Flint Bishop Airport both set rainfall records for the month of May. Saginaw Tri-Cities Airport placed second for May rainfall. Rainfall at all three sites was over 5 inches above the normal for the month. The following are the monthly rainfall amounts for May 2004 at the three observation sites in Southeast Michigan:

May 2004 Rainfall
monthly rainfall and departure from normal
Detroit...   8.46" (5.41" above normal)
Flint...   8.19" (5.45" above normal)
Saginaw...   8.14" (5.25" above normal)

The following list the top five May rainfalls for the three sites. Observations from the current year are italic and highlighted in yellow.

Rainfall Records - Wettest May

In addition to ranking 1st or 2nd for May rainfall, May 2004 also placed in the top 10 for wettest month on record at each of the sites. The following list the top 10 monthly rainfalls in the climate record. Observations from the current year are italic and highlighted in yellow.

Rainfall Records - Overall Wettest Month
Rank     Detroit     Flint     Saginaw
1.8.76/July 187811.04/August 197516.16/September 1986
2.8.46/May 200410.86/September 19869.95/May 1912
3.8.33/August 19269.35/July 19929.01/August 1975
4.8.31/June 18928.68/August 19568.15/September 1945
5.8.05/May 19438.68/September 19508.14/May 2004
6.7.84/May 18928.55/July 20007.93/May 1905
7.7.83/August 19758.29/September 19857.78/October 1954
8.7.80/October 19548.19/May 20047.59/May 1908
9.7.55/July 19027.92/July 19577.49/September 1981
10.7.52/September 19867.65/September 19817.33/August 1995

May 2004 Rainfall Summary by Station

Detroit Graph of daily observations for Detroit; click on image to enlarge
  • May 2004 Precipitation:
    8.46" (5.41" above normal)

  • Wettest May on Record
    (broke old record of 8.05" set in 1943)

  • 2nd Wettest Month on Record
    (record 8.76" set in July 1878)

May 2004 daily observations for Detroit:
Text or Graphic
Monthly Summary

Flint Graph of daily observations for Flint; click on image to enlarge
  • May 2004 Precipitation:
    8.19" (5.45" above normal)

  • Wettest May on Record
    (broke old record of 7.35" set in 1945)

  • 8th Wettest Month on Record
    (record 11.04" set in August 1975)

May 2004 daily observations for Flint:
Text or Graphic
Monthly Summary

Saginaw Graph of daily observations for Saginaw; click on image to enlarge
  • May 2004 Precipitation:
    8.14" (5.25" above normal)

  • 2nd Wettest May on Record
    (record 9.95" set in 1912)

  • 5th Wettest Month on Record
    (record 16.16" set in September 1986)

May 2004 daily observations for Saginaw:
Text or Graphic


While Detroit and Flint set records for the amount of rainfall received during the entire month of May, a large portion of that rain fell during the second to last weekend in the month.

Using radar estimates and ground reports, generally 3 to 6 inches of rain fell across most of Southeast Lower Michigan between Thursday night 5/20 and Monday 5/24, with most places leaning toward the high side. Using an average of 5 inches of rain and some simple math, the following is approximately how many gallons of water fell on each county. Larger sized counties will have larger numbers since they have more surface area.

Estimated Amount of Rainfall
CountyAmount of Water
Genesee51 billion gallons
Macomb37 billion gallons
Oakland70 billion gallons
St. Clair59 billion gallons
Washtenaw57 billion gallons
Wayne49 billion gallons

Some of this water soaked into the ground. However, with the soil being already moist from rains earlier in the month, a fair percentage of this water ran directly into creeks and rivers. This should give an idea of how much water our rivers had to drain and why flooding was experienced.

Graph of river stages from the Huron River near Hamburg for May 2004; Click on image for more information With the amount of rain that fell, a number of area rivers also rose above flood stage. One of those rivers was the Huron River at Hamburg in Livingston County. Minor flooding in the middle of the month had only begun to recede when the billions of gallons of water mentioned above started falling, leading to a renewed rise in the river level and major flooding late in the month. More information about the river flooding, including pictures, is available:

Tornadoes and Severe Storms

Map of tornado touchdowns across Southeast Michigan in May 2004; Click on map to enlarge

The thunderstorms not only brought heavy rainfall, but severe weather and tornadoes too.

Southeast Michigan had 14 tornadoes during the month of May. Most were brief touchdowns with little damage. The 14 tornadoes is a record for Southeast Michigan for the month of May. The previous record belonged to May 1956 when eight tornadoes were recorded (all on one day - May 12, 1956), most of which were significant tornadoes (F2 or greater).

The following is a listing of the May 2004 tornadoes:

May 2004 Tornadoes in Southeast Michigan
DateLocation Fujita Damage ScaleMap Reference
5/13West of Owosso F0#1
5/14West of Saginaw F1#2
5/146 miles North of North Branch F0#3
5/14Near Brockway F0#4
5/14Near Croswell F0#5
5/22Near Arthur F0#6
5/22Near Burt and Birch Run F0#7
5/22Southwest of Owosso F0#8
5/22West of Fostoria F1#9
5/22Northeast of Deckerville F0#10
5/23South of Montrose F0#11
5/23Mt. Morris F0#12
5/23East of Yale F0#13
5/31Port Huron F1#14

During the month of May, the National Weather Service in White Lake has issued 84 severe thunderstorm or tornado warnings (90 so far for the season). Looking back at the warning database, dating back to 1986, no other May (or spring season) has had more warnings. Statistics show that the May of 2000 previously had the most warnings issued with 53. The spring of 1998 (January 1 through May 31) previously had the most warnings issued with 62.

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