National Climatic Data Center, 11 October 2002

September Precipitation

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The graph to the left is a time series depicting precipitation averaged across the contiguous U.S. Based upon preliminary precipitation data, September 2002 was slightly wetter than average, ranking 74th driest (35th wettest). There has been no significant trend in mean national September precipitation over the last century, though September is one of only 3 months in 2002 which has averaged slightly more precipitation than the mean.

There was considerable regional variability in precipitation across the country. Four states in the South (Mississippi, Alabama, Tennessee and Kentucky) and one in the Southwest (New Mexico) received much above average rainfall in September, while one state (California) received much below average rainfall this month. Mississippi and Tennessee were second wettest on record for the month of September. November 2001 was the last month that Colorado received above average precipitation before this month. However, despite the wetter than average September, it will still take many months of above average or near average rainfall to alleviate the long-term drought in that state and others in the Southwest and West. Much of the above-average rainfall in the eastern half of the country was a result of Tropical Storm Isidore as it moved inland off the Gulf of Mexico on the 26th. More details on September hurricanes and tropical storms can be found here.

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In Indiana on September 20th, storms occurred ahead of a strong cold front leading to numerous reports of tornadoes and significant rainfall. At least two F2 tornadoes and one F3 tornado caused significant damage in Indiana. The path of the F3 tornado was 112 miles in length, though the tornado was not at that intensity for most of the distance. Twenty-seven separate reports of tornadoes were submitted to the Storm Prediction Center - 24 in Indiana and 3 in Ohio. Although it is not unusual for tornadoes to occur in the Midwest at this time of year, the intensity of this outbreak was fairly unusual. Where the F3 tornado passed through Marion County, damage estimates have reached $36M for that county alone. (Information courtesy of the Midwest Regional Climate Center's Climate Watch).

Earlier in the month, on Monday September 2nd, a tornado ripped through the town of Ladysmith, in northwestern Wisconsin. A few dozen injuries were reported and significant structural damage occurred in the town of 4,000 residents.

Further details on flooding and rainfall in the Southeast and parts of the Gulf Coast are given on the Atlantic hurricane page, as they relate to landfalling tropical storms in September.

Precipitation Departures

The map to the right, based on more than 500 airport stations, shows September 2002 total precipitation as a percent of the 1971-2000 station normals. Above normal precipitation generally occurred in the South through the Mississippi Valley and Tennessee/Ohio Valley regions, with more than 190% of normal precipitation falling in some areas. Parts of the Southwest also received more rainfall that normal, however, dryness extended across most of the West and Northwest where as little as 25% of normal rainfall was recorded. The Central Plains were also dry this month, with less rainfall than normal also extending into Michigan.

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Last 3 months (July-September)

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The graph to the left is a time series depicting precipitation averaged across the contiguous U.S. Based upon preliminary precipitation data, July-September 2002 was wetter than average, ranking 73rd driest (36th wettest) in the last 108 years. This belies considerable regional variability as can be seen from the maps below.

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Record dryness averaged over July-September occurred in California in 2002. Three other states in the West (OR, NV, and WA) and one in the East (NH) also received much below average precipitation while fifteen other contiguous states received significantly below average precipitation. All Gulf Coast states as well as New Mexico, Tennessee and part of the Upper Midwest and Northern Plains received above average rainfall for the July-September period, with Minnesota at a rank of 4th wettest for the 3 months, and record wetness for Mississippi. Though July was quite wet for Mississippi, much of the 3-month average rainfall came in September from Tropical Storm Isidore and is discussed below and on the Atlantic hurricane season web-page. Minnesota has received much above average rainfall in three of the last four months.

National Precipitation - October 2001-September 2002

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The graph to the left is a time series depicting precipitation averaged across the contiguous U.S. Based upon preliminary precipitation data, October 2001-September 2002 was drier than average, ranking 29th driest in the last 107 such periods. The last 3 October-September periods have averaged below the long term mean precipitation.

Record dryness occurred in 2 states (CO and AZ) averaged over the last 12 months. The pattern of state-averaged October-September precipitation can be seen in the map to the right. Twelve other states ranked in the top ten driest such periods. More information on drought analysis for these states and others can be found on NCDC's Drought Pages. Four states (MN, WI, IN and MI) received much above average rainfall for the 12-month period, with a second wettest October-September occurring in Indiana.

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Questions?

For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:

For further information on the historical climate perspective presented in this report, contact:

Catherine Godfrey NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Catherine.S.Godfrey@noaa.gov

Jay Lawrimore NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Jay.Lawrimore@noaa.gov

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