PRECIPITATION 

IN THE 

UPPER MISSISSIPPI 

RIVER BASIN 

JANUARY 1 THROUGH JULY 31 

9 9 3 

U.S. GEOLOGICAL SURVEY CIRCULAR 1120-B 
Front Cover-View of Highway 367, West Alton, Illinois, 

(Srenco Photography, St . Louis, Mo.) 

Back Cover-View of Spirit of St. Louis Airport, 

Chesterfield, Mo. (Srenco Photography, 

St . Louis, Mo.) 

Field Hydrologist making streantflow 

measurements (U.S . Geological Survey) 
PRECIPITATION IN THE


UPPER MISSISSIPPI RIVER BASIN,


JANUARY I THROUGH JULY 31, 1993


By Kenneth L. Wahl, Kevin C. Vining, and Gregg J. Wiche 

Floods in the Upper Mississippi River Basin, 1993


U.S . GEOLOGICAL SURVEY CIRCULAR 1120-B 
U.S . DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S . GEOLOGICAL SURVEY 

ROBERT M. HIRSCH, Acting Director 

UNITED STATES GOVERNMENT PRINTING OFFICE : 1993 

Free on application from


U .S . Geological Survey, Branch of Distribution


Box 25286, Denver Federal Center


Denver, CO 80225

FOREWORD 

During spring and summer 1993, record flooding inundated much of the upper Mississippi 

River Basin. The magnitude of the damages-in terms of property, disrupted business, and personal trauma-was unmatched by any other flood disaster in United States history . Property dam 

age alone is expected to exceed $10 billion. Damaged highways and submerged roads disrupted 

overland transportation throughout the flooded region. The Mississippi and the Missouri Rivers 

were closed to shipping before and after the flooding . Millions of acres of productive farmland 

remained under water for weeks during the growing season. Rills and gullies in many tilled fields 

are the result of the severe erosion that occurred throughout the Midwestern United States farmbelt. The hydrologic effects of extended rainfall throughout the upper Midwestern United States 

were severe and widespread. The banks and channels of many rivers were severely eroded, and 

sediment was deposited over large areas of the basin's flood plain. Record flows submerged many 

areas that had not been affected by previous floods. Industrial and agricultural areas were inundated, which caused concern about the transport and fate of industrial chemicals, sewage effluent, 

and agricultural chemicals in the floodwaters . The extent and duration of the flooding caused 

numerous levees to fail . One failed levee on the Raccoon River in Des Moines, Iowa, led to flooding of the city's water treatment plant. As a result, the city was without drinking water for 19 days. 

As the Nation's principal water-science agency, the U.S . Geological Survey (USGS) is in a 

unique position to provide an immediate assessment of some of the hydrological effects of the 

1993 flood. The USGS maintains a hydrologic data network and conducts extensive water 

resources investigations nationwide. Long-term data from this network and information on local 

and regional hydrology provide the basis for identifying and documenting the effects of the flooding . During the flood, the USGS provided continuous streamflow and related information to the 

National Weather Service (NWS), the U.S . Army Corps of Engineers, the Federal Emergency 

Management Agency (FEMA), and many State and local agencies as part of its role to provide 

basic information on the Nation's surface- and ground-water resources at thousands of locations 

across the United States . The NWS has used the data in forecasting floods and issuing flood warnings. The data have been used by the Corps of Engineers to operate water diversions, dams, locks, 

and levees. The FEMA and many State and local emergency management agencies have used 

USGS hydrologic data and NWS forecasts as part of the basis of their local flood-response activities . In addition, USGS hydrologists are conducting a series of investigations to document the 

effects of the flooding and to improve understanding of the related processes. The major initial 

findings from these studies will be reported in this Circular series as results become available . 

U.S. Geological Survey Circular 1120, Floods in the Upper Mississippi River Basin, 1993, 

consists of individually published chapters that will document the effects of the 1993 flooding. 

The series includes data and findings on the magnitude and frequency of peak discharges; precipi 

tation; water-quality characteristics, including nutrients and man-made contaminants ; transport of 

sediment; assessment of sediment deposited on flood plains ; effects of inundation on ground-water 

quality ; flood-discharge volume; effects of reservoir storage on flood peaks ; stream-channel scour 

at selected bridges ; extent of flood-plain inundation; and documentation of geomorphologic 

changes . 

A~~4 

Acting Director 

September 8, 1993 

Foreword III 
CONTENTS 

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .III 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Precipitation, January 1 Through July 31, 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Monthly Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Daily Accumulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Distribution of July Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Analysis of Selected Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Southeastern Iowa, July 4-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

North Dakota and Minnesota, July 15-16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

FIGURES 

1 .- 2. Maps showing: 

1. Mississippi River Basin and general area of flooding streams, June through August 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

2. Dominant weather patterns over the United States for June through July 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

3. Maps showing areal distribution of total precipitation in the area of flooding in the upper Mississippi River Basin, 

January through July 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

4. Map and graphs showing monthly precipitation for January through July 1993 and 30-year monthly normals (January through July 1961-90) at 10 weather-station locations in the upper Mississippi River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

5 .-6. Graph showing: 

5. Seasonal precipitation for 1993 at 10 weather-station locations in the upper Mississippi River Basin . . . . . . . . . . . . . . . 8 

6. Precipitation for Janary through July 1993, normal precipitation for January through July 1961-90, and normal 

annual precipitation for 1961-90 at 10 weather-station locations in the upper Mississippi River Basin . . . . . . . . . . . . 8 

7. Graphs showing accumulated daily precipitation for January through July 1993 and accumulated normal daily precipitation for January through July 1961-90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

8.-11 . Maps showing : 

8 . Average weather patterns over the United States for July 4-5, 1993. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

9 . Areal distribution of rainfall for the July 4-5, 1993, storm in Iowa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

10. Average weather patterns over the United States for July 15-16, 1993. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

11 . Areal distribution of rainfall for the July 15-16, 1993, storm in North Dakota, South Dakota, and Minnesota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

TABLES 

1 . Summary of 1993 precipitation and 30-year averages (1961-90) at 10 weather-station locations in the upper 

Mississippi River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

2. Five greatest May through July precipitation totals at Bismarck, North Dakota, Cedar Rapids, Iowa, and 

Manhattan, Kansas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

3 . Maximum 1-, 3-, and 5-day rainfall totals for July 1993 at Bismarck, North Dakota, Cedar Rapids, Iowa, and 

Manhattan, Kansas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Contents V 
Precipitation in the Upper Mississippi River Basin, 

January 1 Through July 31, 1993 

By Kenneth L. Wahl, Kevin C. Vining, and Gregg J . Wiche 

Abstract 

Excessive precipitation produced severe 

flooding in a nine-State area in the upper Mississippi River Basin during spring and summer 

1993 . Following a spring that was wetter than 

average, weather patterns that persisted from 

early June through July caused the upper Midwest to be deluged with an unusually large 

amount of rainfall . Monthly precipitation data 

were examined at 10 weather-station locations in 

the flood-affected region to illustrate precipitation patterns and amounts in the flood-affected 

area. In 1993, all 10 of the selected locations 

received greater than the normal rainfall for January through June 1961-90, 8 of the 10 locations 

received more than 200 percent of the normal 

rainfall for July 1961-90, and 3 received more 

than 400 percent of the normal rainfall for July. 

(The average rainfall for any given 30-year 

period is termed the "normal" rainfall for the 

given period.) May through July 1993 was the 

wettest or nearly the wettest such period on 

record at many locations in the flooded area. Of 

the 10 locations, 6 received more rainfall in the 

first 7 months of 1993 than generally is received 

in a year. 

INTRODUCTION 

This report, one of a series that documents the 

effects of the 1993 flooding in the upper Mississippi 

River Basin, covers precipitation in the upper Missis 

sippi River Basin from January 1 through July 31, 

1993 . As of August 1993, large storms continued to 

pass through the affected area ; however, weather conditions indicate that the widespread flooding might be 

coming to an end. The floodwaters in the Mississippi 

River crested at St . Louis, Missouri, on August 1, 

while the river stages along the mainstem and on the 

principal tributary streams upstream from St . Louis 

were receding. 

This report provides a general overview of the 

unusually excessive precipitation that produced 

severe flooding in a nine-State area in the upper Mis 

sissippi River Basin (fig . 1) during spring and summer 1993 . Ageneral overview of precipitation 

during the first 7 months of 1993 is presented and is 

followed by an analysis of monthly precipitation for 

10 weather-station locations distributed throughout 

the flood-affected area . Weather patterns associated 

with two specific storm systems and the resulting 

rainfall totals are shown as examples of storms that 

occurred throughout the area. 

Preparation of this report required cooperation 

among many persons in many organizations. The 

authors are particularly appreciative of the coopera 

tion of State Climatologists and of persons in various 

State agencies and in the offices of the National 

Weather Service, National Oceanic and Atmospheric 

Administration, for making provisional data and 

maps available on a near real-time basis. 

PRECIPITATION, JANUARY 1-JULY 31, 

1993 

General precipitation conditions throughout 

the nine-State area of the upper Midwest for the 7-

month period ending in July are best summarized by 

the following news item from the Associated Press, 

July 17, 1993 : 

The rain, of course, was the problem. 

Although much of the spring downpour fell on 

vast undammed tracts and could not be con 

tained, the real culprit was the volume dumped 

by stalled weather systems . With the ground 

already saturated by spring rainfall, June was 

Precipitation, January 1-July 31, 1993 1 
the wettest month in the region since record 

keeping began. July has been just as soggy. 

The Associated Press statement was accurate when 

written in mid-July but proved to be conservative . 

July ended up being much soggier than June. 

Monthly Precipitation 

Annual precipitation over the nine-State area 

affected by flooding (fig. 1) generally averages 

slightly more than 30 inches but ranges from about 

16 inches in south-central North Dakota to about 40 

inches in southern Missouri. Although precipitation 

is about evenly divided between the first and last 

halves of the year, the accumulation rates are not uniform throughout the year. Normally, 45 percent of 

the annual precipitation falls between April 1 and 

July 31 ; June precipitation represents about 15 percent (2-5 inches) of the average annual precipitation 

total . 

Precipitation amounts recorded throughout the 

upper Mississippi River Basin during the first 7 

months of 1993 generally were substantially greater 

than normal (January-July 1961-90). Although 

120-

715. 

EXPLANATION 

Area of flooding streams 

-. .-Boundary of Mississippi River Basin 

April-through-July precipitation was much greater 

than normal, little evidence early in the year indicated 

that precipitation amounts in 1993 would be above 

normal. January-through-March precipitation in the 

States of the upper Mississippi River Basin was near 

normal to slightly above normal. Because precipitation for those 3 months is often in the form of snow 

and generally totals less than 6 inches of moisture, 

potential flooding caused little concern. However, 

that situation began to change in April. 

Precipitation in April and May over the area 

ranged from near normal to much greater than normal, but the areas of greatest precipitation differed 

for the 2 months. April rainfall was nearly twice the 

normal amounts in parts of Wisconsin and in Missouri but was only moderately above normal in much 

of the remainder of the flood-affected area. By contrast, May rainfall was more than twice the normal 

amounts for the month over an area that extended 

from southeastern South Dakota across Iowa to eastern Kansas. The largest storms, though, were still to 

come. 

In early June, a weather pattern (fig . 2) developed that was characterized by a strong low-pressure 

system over the Western United States and a correFigure 1 . Mississippi River Basin and general area of flooding streams, June through August 1993 (from Parrett and 

others, 1993). 

2 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993 
CANADA 

EXPLANATION 

Convergence zone ; recurrent 

thunderstorm systems 

Little rainfall ; oppressive heat 

and humidity 

H High atmospheric 

pressure area 

Figure 2. Dominant weather patterns over the United States for June through July 1993 (from National Weather Service, 

1993). 

sponding large high-pressure system positioned over 

the Southeastern United States . The jetstream dipped 

south over the Western United States and flowed 

northeasterly across the upper Midwest. A southeastern high blocked the eastward movement of storms, 

thus creating a convergence zone between the warm, 

moist flow from the Gulf of Mexico and the much 

cooler and drier air from Canada, which resulted in 

thunderstorms . This pattern persisted through most 

of June and July (National Weather Service, 1993). 

As a result, the upper Midwest within this convergence zone was deluged with rain while the Southeastern and the Eastern United States from Alabama 

to Vermont, under the influence of the high-pressure 

system, was very hot and dry. Slight movements in 

the atmospheric pattern determined the timing and 

location of the excessive rainfall throughout the 

upper Midwest. 

The persistence of this weather pattern caused 

unusually large amounts of rain to fall over the upper 

Midwest. These large amounts and the wetter-than 

normal spring produced flooding throughout the 

upper Mississippi River Basin, including the lower 

Missouri River Basin. The rains were extraordinary 

in the areal extent and in the amounts accumulated in 

the first 7 months of the year. Precipitation for the 7 

months totaled more than 20 inches over most of the 

flood-affected area and was more than 40 inches in 

areas of northeast Kansas and east-central Iowa 

(fig. 3A). Most of the area received from 150 to 200 

percent of the 1961-90 normal total amounts for January through July (fig . 3B; Parrett and others, 1993). 

Monthly precipitation data for 1993 and the 

normal amounts for the period 1961 to 1990 are listed 

in table 1 (National Oceanic and Atmospheric Admin 

istration, 1992) and compared in figure 4 for 10 

weather-station locations in the upper Mississippi 

River Basin. These locations-Bismarck, North 

Dakota, Sioux Falls, South Dakota, Minneapolis, 

Minnesota, Des Moines and Cedar Rapids, Iowa, 

Madison, Wisconsin, Peoria, Illinois, Manhattan, 

Kansas, and Kansas City and St. Louis, Missouriare illustrative of precipitation patterns in the floodaffected area. 

The significance of the July 1993 rainfall 

totals can best be understood by examining them in 

relation to the totals for the January-through-June 

period. All 10 of the selected locations received 

Precipitation, January 1-July 31, 1993 3 
90° 

45° 

40° 

-40- Line of equal total precipitation 

for January through July 

1993-Hachures indicate 

closed areas of lesser precipitation. 

Interval 10 inches 100 200 MILES 

i I I 

A 100 200KILOMETERS

Figure 3. Areal distribution of total precipitation in the area of flooding in the upper Mississippi River Basin, January through July 

1993. A, In inches; B, In percentage of 30-year precipitation normal for January through July 1961-90 (from Parrett and others, 

1993). Data were supplied by the National Weather Service (David Miscus, National Weather Service, written commun., 1993). 

4 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993 
100° 

40° 

-200 - Line of equal total precipitation for 

January through July 1993 as 

percentage of the 30-year pre 

cipitation normal for January 

through July 1961-90-Hachures 

indicate closed areas of lesser I 

100 200MILES 

I precipitation. Interval 50 percent 100 200 KILOMETERS 

Figure 3.-Continued 

Precipitation, January I -July 31, 1993 5 
Table 1 . Summary of 1993 precipitation and 30-year averages (1961-90) at 10 weather-station locations in the upper Mississippi 

River Basin 

[in., inches . National Oceanic and Atmospheric Administration (1992) ] 

Sioux Bismarck, Des Falls, Minneapolis, North Moines, South Minnesota Dakota Iowa Dakota 

January: 

1993 (in.) . . . . . . . . . . . . . 0.29 0.70 1.25 1 .59€

Average (in.) . . . . . . . . .45 .51 .95 .96€

1993 (percent). . . . . . . 64 137 132 166€

February : 

1993 (in.) . . . . . . . . . . . . . .33 .81 .39 1 .52€

Average (in.) . . . . . . . . .43 .64 .88 1 .11€

1993 (percent). . . . . . . 77 127 44 137€

March: 

1993 (in.) . . . . . . . . . . . . . .38 2.04 1 .25 3 .22€

Average (in.) . . . . . . . . .77 1 .64 1 .94 2.33€

1993 (percent). . . . . . . 49 124 64 138€

April: 

1993 (in.) . . . . . . . . . . . . . 1 .26 2.61 1 .99 2.96 

Average (in.) . . . . . . . . 1 .67 2.52 2.42 3.36 

1993 (percent) . . . . . . . 75 104 82 88€

May: 

1993 (in.) . . . . . . . . . . . . . 2.36 8.26 4.02 7.51 

Average (in.) . . . . . . . . 2.18 3.03 3.39 3.66 

1993 (percent) . . . . . . . 108 273 119 205€

June : 

1993 (in.) . . . . . . . . . . . . . 4.57 6.43 6.28 7.68 

Average (in.) . . . . . . . . 2.72 3.40 4.05 4.46 

1993 (percent). . . . . . . 168 189 155 172€

July :€

1993 (in.) . . . . . . . . . . . . . 13 .75 7.86 5.58 9 .75€

Average (in.) . . . . . . . . 2.14 2.68 3.53 3 .78€

1993 (percent). . . . . . . 643 293 158 258€

Seven months : 

1993 (in.) . . . . . . . . . . . . . 22 .94 28 .71 20 .76 34.23 

Average (in.) . . . . . . . . 10 .36 14 .42 17 .16 19 .66 

1993 (percent). . . . . . . 221 199 121 174€

Annual average. . . . . . . . 15 .47 23 .86 28 .32 33 .12€

more than 100 percent of the normal precipitation for 

January through June 1961-90 (fig . 5), and 8 locations received more than 130 percent of the normal 

precipitation for that period. By the end of June, the 

soil was saturated; then came the 1993 July deluge. 

Of the 10 locations, 8 received more than 200 percent 

of the normal rainfall for July (1961-90). Only Minneapolis (158 percent) and St. Louis (131 percent) 

did not receive 200 percent of the normal rainfall in 

July. Three locations, Bismarck, Cedar Rapids, and 

Manhattan, received from about 400 to about 650 percent of the normal rainfall amounts for July. 

Total January-through-July rainfall for 1993€

for each of the 10 locations was compared to the 

1961-90 normals for the 7-month period and the 

Cedar Madison, Peoria, Manhattan, Kansas St. Louis,

Rapids, Wisconsin Illinois Kansas Missouri 

Iowa Missouri 

1 .18 1 .60 3 .55 0.98 1 .96 3.54 

1 .01 1 .07 1 .51 .81 1 .09 1 .81 

117 150 235 121 180 196 

1 .11 1 .18 1 .68 1 .12 1.28 2.75 

1 .02 1 .08 1 .42 .93 1.10 2.12 

109 109 118 120 116 130 

3.63 3.29 4.08 3.46 2 .15 3 .31 

2.32 2.17 2.91 2.36 2 .51 3 .58 

156 152 140 147 88 92 

3.86 5.33 4.89 1 .88 5 .59 6.16 

3 .19 2.86 3.77 2 .95 3 .12 3 .50 

121 186 130 64 179 176 

5 .43 3.81 3.25 10 .99 7.30 3 .94 

3 .71 3.14 3.70 4.56 5.04 3 .97 

146 121 88 241 145 99 

8.79 6 .67 5 .70 6.83 5.67 7.12 

4.55 3 .66 3 .99 5 .54 4.72 3.72 

193 182 143 123 120 191 

17 .03 9.34 10 .15 17 .56 10 .90 5.06 

4.11 3 .39 4.20 3.28 4.38 3.85 

414 276 242 535 249 131 

41 .03 31 .22 33.30 42.82 34 .91 31 .88 

19 .91 17 .37 21 .50 20.43 21 .96 22.55 

206 180 155 210 159 141 

33 .72 30.88 36 .25 33 .82 37 .62 37 .51 

annual total (fig . 6). Of the 10 locations, 6 received 

more rain in the first 7 months of 1993 than is generally received in a year, and 3 had nearly equaled their 

1961-90 normal annual rainfall total . Only Minneapolis had some reprieve; only 121 percent of normal 

and 79 percent of the annual total was received during the first 7 months. 

The National Weather Service (1993) computed statewide-average precipitation by month for 

1895 to the present . They reported that the statewide 

averages for July 1993 were among the three wettest 

years since 1895 for eight of the nine States in the 

flood-affected area. May and June were among the 

wettest months for one-third of the years that have 

elapsed since 1895 for six and eight States, respec6 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993€
W 15 

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Figure 4. Monthly precipitation for January through July 1993 and 30-year monthly normals (January through July 1961-90) 

at 10 weather-station locations in the upper Mississippi River Basin. Data were supplied by the National Weather Service. 

Precipitation, January 1-July 31, 1993 7 
tively . Rainfall totals for the 3-month period (May 

through July) were computed for this report for Bismarck, Cedar Rapids, and Manhattan and were compared to period-of-record maximums for that 3-

month period (table 2). At Bismarck and Cedar Rapids, May through July 1993 was the wettest such 

period in more than 100 years of recordkeeping . At 

Manhattan, May through July 1993 was the second 

wettest such period in 104 years of record; in 1951, 

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Figure 5. Seasonal precipitation for 1993 at 10 weather-station locations in the upper Mississippi River Basin. Data 

were supplied by the National Weather Service. 

50 

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January-July 1993 

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Figure 6. Precipitation for January through July 1993, normal precipitation for January through July 1961-90, and normal average precipitation for 1961-90 at 10 weather-station 

locations in the upper Mississippi River Basin. Data were 

supplied by the National Weather Service. 

Table 2. Five greatest May-through-July precipitation 

totals at Bismarck, North Dakota, Cedar Rapids, Iowa, and 

Manhattan, Kansas 

[Totals, in inches ; record of lengths, in parentheses] 

May-through-July precipitation totals 

Bismarck 

(119 years) 

Cedar Rapids

(112 years) 

Manhattan 

(104 years) 

Year Total Year Total Year Total 

1993 20.68 1993 31.25 1951 36.73 

1914 15 .55 1969 25.44 1993 35.38 

1915 14 .15 1892 22.06 1915 28 .15 

1879 12 .91 1990 21.89 1908 25 .16 

1927 12 .02 1971 20.48 1977 22 .71 

the 3-month rainfall total was only 4 percent greater 

than that of 1993 . 

Daily Accumulations 

The rates of accumulation for 1993 daily precipitation are compared with historic values in 

figure 7. The historic values are the accumulated 

daily averages for the period 1961 to 1990 smoothed 

to pass through the month-end accumulated totals . 

The precipitation totals for January through July 1993 

at all three locations were about 200 percent of normal for January through July 1961-90, but the rates 

at which the precipitation accumulated were different 

(fig . 7). Although the rate of accumulation at Bismarck was about normal through June, a dryer-thannormal January through March caused the amount of 

precipitation received to be slightly less than normal 

until the end of June. Three large storms, June 29 

through July 1, July 15-16, and July 21-22, combined to produce the large seasonal totals . Precipitation at Manhattan followed a pattern similar to that of 

Bismarck, except that several large storms came earlier in the year. Manhattan's large seasonal total 

resulted primarily from precipitation during four distinct periods : March 29 through 31, May 7 through 

11, July 1-2, and July 18 through 22. 

The rate of accumulation of precipitation at 

Cedar Rapids was different from that at either Bismarck or Manhattan. Although large storms, such as 

that for July 4-5, contributed to the excessive moisture, the rate of accumulation was greater than normal after mid-March . Unlike Bismarck and 

Manhattan, the rate reflected the accumulation of 

many small-to-moderate precipitation amounts and 

shows the effects of widespread storms over the 

entire area. 

8 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993 
--------

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1993 daily precipitation 

1961-90 normal daily precipitation 

Jan Feb Mar Apr May June July 

1993 daily precipitation 

1961-90 normal daily precipitation 

Jan Feb Mar Apr May June July 

Jan Feb Mar Apr May June July 

Figure 7. Accumulated daily precipitation for January through 

July 1993 and accumulated normal daily precipitation for January through July 1961-90. A, Bismarck, North Dakota; B, 

Cedar Rapids, Iowa ; C, Manhattan, Kansas . Data were supplied by the National Weather Service. 

Distribution of July Precipitation 

Much of the severe flooding in the upper Mississippi River Basin in 1993 was the culmination of 

the wet spring and a series of storms in July. Daily 

rainfall totaled more than 4.00 inches at many locations in July. Thus, flooding was influenced not only 

by wet antecedent conditions and large rainfall totals, 

but also by the way July daily rainfall was distributed. Maximum 1- and 3-day rainfall totals for July 

at Bismarck, Cedar Rapids, and Manhattan are similar (table 3). Maximum 5-day rainfall totals are similar at Bismarck and Cedar Rapids, but the maximum 

5-day rainfall total at Manhattan was about 1 .6 inches 

greater than at Bismarck and Cedar Rapids (table 3). 

Based on the data in table 3, the maximum 1-day July 

rainfall totals were greater than the total normal July 

rainfall at many locations throughout the flooded area. 

Table 3. Maximum 1-, 3-, and 5-day rainfall totals for July 

1993 at Bismarck, North Dakota, Cedar Rapids, Iowa, and 

Manhattan, Kansas 

[Totals, in inches] 

Rainfall 

1-day 3-day 5-day 

Bismarck . . . . . . . . . . . . . . . . 4.32 5 .74 6.18 

Cedar Rapids . . . . . . . . . . . 4.18 5 .55 6 .01 

Manhattan. . . . . . . . . . . . . . . 4.81 5 .56 7 .70 

Analysis of Selected Storms 

Several storms in July produced large amounts 

of rainfall in the area of flooding . Two of the larger 

storms are described in detail. 

Southeastern Iowa, July 4-5 

The storm of July 4-5 produced copious 

amounts of rainfall and added to the flooding over 

southeastern Iowa. This storm was only one in a 

series that passed over Iowa and other areas of the 

upper Mississippi River Basin during June and July. 

Average weather conditions over the Central 

United States during the July 4-5 storm are depicted 

in figure 8. A large high-pressure system was positioned over the Southeastern United States while an 

area of warm, moist air flowed into the Midwestern 

United States as a result of the circulation around the 

southeastern high and the low-pressure system in 

southern Canada. Furthermore, a stationary front 

Precipitation, January 1-,July 31, 1993 9 
EXPLANATION 

Area of precipitation 

Area of moist air- Dew point greater 

than 60 degrees Fahrenheit 

Cold front 

L Low atmoshperic pressure 

rJ-r-ti Stationary front area 

-Bi~smarok Wind direction arrow and weather- H High atmoshperic pressure 

station location area 

Figure 8. Average weather patterns over the United States for July 4-5, 1993. Data were supplied by the National 

Weather Service . 

extended from northern Missouri across southeastern 

Iowa to southern Wisconsin, and a series of cold 

fronts rotated cyclonically around the low into western Iowa. The dense air behind each cold front lifted 

the lighter warm air ahead of it, and as each front collided into the warm air over Iowa, thunderstorms 

formed. Rain fell over much of Iowa, southern Minnesota, and southern Wisconsin. Aiding the production of rain was a strong area of vorticity in the 

middle atmosphere (about 18,000 feet above sea 

level), which created additional lift for thunderstorm 

development . (Vorticity is an incipient storm that 

contains enhanced cyclonic spin and associated 

upward motion.) This area of vorticity began over 

Kansas and Nebraska just to the west of the cold 

front in western Iowa and proceeded over Iowa from 

the southwest. The jetstream that passed directly 

over Iowa from southwest to northeast also aided the 

production of rain and created what is called the 

chimney effect in which strong winds in the upper 

atmosphere blow across the region of thunderstorm 

development. The effect of the winds was to evacuate air from the top of thunderstorms, which created 

an updraft . Thus, more warm, moist air was then 

drawn up into the thunderstorms, and copious 

amounts of rain were produced. As the storm moved 

northeastward at about 10 to 20 miles per hour, new 

thunderstorms formed to the southwest of the original 

thunderstorms and passed over the same areas, thus 

adding to the large rainfall totals. 

Rain from the July 4-5 storm fell across Iowa; 

one-third of the State received more than 2 inches 

total (fig . 9). The greatest amounts of rain fell in the 

south- and east-central parts of the State. Rainfall 

totals from the storm exceeded 4 inches in a 50- to 

100-mile-wide band from Lamoni to Cedar Rapids 

and Dubuque. The occurrence of many storms in the 

span of a few days led to the extensive and severe 

flooding throughout much of Iowa, most notably in 

Des Moines and Cedar Rapids and along the mainstem of the Mississippi River. 

10 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993 
North Dakota and Minnesota, July 15-16 

During July 15-16, 1993, thunderstorms that 

produced large amounts of rain moved slowly from 

western North Dakota to west-central Minnesota. 

Urban and stream flooding were considerable along 

this path. Meteorological conditions that caused 

these rains were part of the overall pattern responsible for heavy rains in the upper Midwest throughout 

the summer. 

Average weather patterns over the North-Central United States during the July 15-16 storm are 

depicted in figure 10. A warm front extended across 

northern South Dakota while an area of warm, moist 

air was drawn over the front on southerly winds of 5 

to 15 miles per hour by a developing low-pressure 

system over Montana. Thunderstorms formed in 

south-central North Dakota by late evening of July 

14 and produced moderate amounts of rain before the 

storms moved quickly towards the northeast . However, the weather patterns that produced heavy rainfall remained in place. 

EXPLANATION 

-7 -Line of equal rainfall for 

July 4-5, 1993-Interval 

1 inch 

Figure 9. Areal distribution of rainfall for the July 4-5, 1993, 

storm in Iowa. Data were supplied by the National Weather 

Service . 

o . 

EXPLANATION 

Area of precipitation 

Area of moist air-Dew point greater 

than 60 degrees Fahrenheit 

A	 Cold front 

Warm front 

Fargo Wind direction arrow and weather- High atmoshperic pressure 

station location area 

Figure 10. Average weather patterns over the United States for July 15-16, 1993. Data were supplied by the National 

Weather Service . 

Precipitation, January 1-luly 31, 1993 1 1 
A cold front entered North Dakota from Montana during the morning of July 15 and increased 

atmospheric instability. A series of vorticity maxima 

(incipient storms) at 18,000 feet above sea level also 

approached North Dakota from the southwest and 

provided additional lift and cyclonic motion for the 

formation of thunderstorms . By midafternoon of July 

15, all the above conditions-moist air, frontal boundaries, vorticity maxima-collided over Bismarck. 

Thunderstorms formed and produced large amounts 

of rain and considerable flooding. The storms moved 

slowly towards the east at only 10 to 15 miles per 

hour, which permitted large amounts of rain to fall . 

The continued flow of moisture from the south over 

the warm front and the lifting caused by the western 

cold front maintained the large rainfalls. Intense rain 

continued along a 50-mile-wide path from Bismarck 

95° 

a 

to Fargo, North Dakota, and into west-central Minnesota during the early hours of July 16. Rainfall 

reports of 4 to 7 inches were common along this path 

(fig . 11) . Bismarck had a record 24-hour rainfall 

total of 5 .27 inches by the afternoon of July 16. Officially, the greatest rainfall total from North Dakota 

was 7.25 inches at Jamestown. The greatest rainfall 

observed in Minnesota was an unofficial total of 7 .50 

inches at Callaway. 

SUMMARY 

Excessive precipitation during April through 

July produced severe flooding in a nine-State area in 

the upper Mississippi River Basin during spring and 

summer 1993. Precipitation in May was more than 

twice the normal (1961-90) amount over an area that 

90' 

EXPLANATION 

-Line of equal rainfall for July 15-16, 

1993-Interval 1 inch 

0 100	 200 MILES 

J 

0 200 KILOMETERS 

Figure 11 . Areal distribution of rainfall for the July 15-16, 1993, storm in North Dakota, South Dakota, and Minnesota . Data 

were supplied by the National Weather Service . 

1 2 Precipitation in the Upper Mississippi River Basin, January 1 through July 31, 1993 
extended from southeastern South Dakota across 

Iowa to eastern Kansas . In early June, weather patterns combined to produce a convergence zone over 

the upper Midwest between the warm, moist air from 

the Gulf of Mexico and the much cooler, drier air 

from Canada. These weather patterns persisted until 

the end of July. As a result, the upper Midwest was 

deluged with rain while the Southeastern and the Eastern United States, under the influence of a high-pressure system, was hot and dry. The persistence of this 

weather pattern caused unusually excessive rains that, 

together with the wetter-than-normal spring, produced severe flooding throughout the region. 

Monthly precipitation data at 10 weather-station locations in the flood-affected area were used to 

illustrate precipitation patterns and amounts. In 

1993, all 10 of the selected locations received greater 

than the normal (1961-90) precipitation for January 

through June, 8 received more than 200 percent of 

the normal July rainfall; and 3 received from about 

400 to about 650 percent of the normal rainfall for 

July. May through July 1993 was the wettest or 

u .s . c .P .6 .1993-342-389 :8oo16 

nearly the wettest such period on record at many locations in the flooded area. Of the 10 locations, 6 

received more rain in the first 7 months of 1993 than 

is generally received in a year. 

REFERENCES 

Parrett, Charles, Melcher, N.B ., and James, R.W., Jr ., 

1993, Flood discharges in the Upper Mississippi 

River Basin, in Floods in the Upper Mississippi 

River Basin, 1993: U.S . Geological Survey Circular 

1120-A, 14 p. 

National Oceanic and Atmospheric Administration, 1992, 

Daily normals of temperature, precipitation, and heating and cooling degree days, 1961-90-By State: 

National Oceanic and Atmospheric Administration 

Climatography of the United States 84, [variously 

paged] . 

National Weather Service, 1993, Update on Midwestern 

floods-Heat and drought in the East: Special Climate Summary, v. 93, no. 2, 8 p. 

References 13