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TitleReview of Illinois summer precipitation conditions.
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Total Pages164
Table of Contents
	Average Annual, Monthly, and Daily Distributions
		Large-Scale Patterns and Downwind Studies.
	Diurnal Distributions
	Rain Events (Storms) over Fixed Areas
		Introduction and Definitions.
		Illustrations of Storms.
		Precipitation Patterns Based on Storm Motions.
		Storm Characteristics.
	Sampling Requirements for Storm Rainfall
	Severe Rainstorms
	Relationship of Atmospheric Moisture and Precipitation
	Synoptic Weather Typing
	Pre-Rain Conditions and Forecasting
	Prediction of July-August Rainfall
	Well-Organized Lines of Cells
	Less Organized Groups of Cells
	Vertical Characteristics
		Echo Growth.
		Behavior of Echo Tops.
		Merging Echo Tops.
		Echo Volumes.
		Echo Tops and Severe Weather.
		Modeling Studies.
		Radar Reflectivity Values Aloft.
	Horizontal Cell Characteristics
		Radar Echoes.
		Motion of Cells.
	Cloud Dimensions
	Cloud Base Updrafts
	In-Cloud Characteristics
		Near the Freezing Level.
		At the —10°C Level.
	Airflow Trajectories in and around Convective Clouds
		Tracer Releases on 11 August 1972.
		Tracer Releases on 23 July 1973.
		Tracer Releases on 12 August 1973.
	Cloud Frequencies
Document Text Contents
Page 2


Review of Illinois
Summer Precipitation Conditions


Title: Review of Illinois Summer Precipitation Conditions
Abstract: This report summarizes key findings regarding all aspects of precipitation in the con-
vective season gleaned from 30 years of research at the Illinois State Water Survey. Examples of
information that dimensionalize midwestern precipitation phenomena extracted from published
papers, reports, and grant-contract studies have been included. These examples are accompanied by
extensive graphs, maps, and tables to provide a useful information document pertinent to the areas
of forecasting, modification of summer convective elements, or midwestern precipitation condi-
tions in general. As an equally important purpose, the report provides listings of nearly a hundred
supporting references that serve as a guide to more extensive information. The material covers
general climatic aspects of the state, ranging from average annual, monthly, and daily rain distri-
butions through severe rainstorms and droughts. More detailed information on relationships of
precipitation with atmospheric moisture and various weather types, on organized storms and sub-
storm entities, on vertical and horizontal characteristics of individual storm cells, and on external
and internal cloud characteristics is also included.
Reference: Changnon, Stanley A. Jr., and Floyd A. Huff. Review of Illinois Summer Precipitation
Conditions. Illinois State Water Survey, Urbana, Bulletin 64, 1980.
Indexing Terms: climatology, convection, droughts, heavy rainstorms, hydrometeorology, meso-
meteorology, radar meteorology, rainfall, synoptic weather conditions, weather modification.

Page 83

Figure 80. Percent of average network rainfall in summer
air mass storms on Little Egypt Network

Pre-Rain Conditions and Forecasting
Important studies relating to the forecasting of

warm season precipitation are ongoing (1980) as
part of three projects: OSET (Operational Seeding
Evaluation Techniques), VIN (Virginia, Illinois,
NOAA project), and PACE (Precipitation Augmen-
tation for Crops Experiment). Much of the recent
Survey research relating to forecasting of warm
season precipitation and thunderstorm conditions
was performed as a part of a multi-year project
aimed at developing a plan for a hail suppression
experiment in Illinois (Changnon and Morgan,
1976). That report and related papers present
much useful information on forecasting pre-rain
and pre-storm conditions in Illinois.

Huff and Vogel (1977) in their studies of sum-
mer droughts in Illinois present useful information
on the climatology of upper air temperatures,
humidity, and saturation depths. Their results
appear in tables 3 3 and 34 for Peoria (central Illi-
nois) and Salem (southern Illinois).

Ackerman (in Ackerman, et al., 1978) in a de-
tailed study of the atmospheric conditions prior to
summer rain in the St. Louis area presented typical
pre-rain profiles of temperature and dewpoints.
Figure 82 presents the average profiles of tempera- Figure 8 1 . Correlation patterns of synoptic types in May-September storms on East Central Illinois Network


Page 164

Schickedanz, P. T. 1973. Climatic studies of extra-area ef-
fects from seeding. PEP, Phase I, Contract 14-06-D-7197,
Technical Report 5, 5 3 p.

Schickedanz, P. T., and F. A. Huff. 1971. The design and
evaluation of raincell modification experiments. Journal
of Applied Meteorology v. 10:502-514.

Semonin, R. G. 1978. Cloud Characteristics. In Summary
of METROMEX, Volume 2: Causes of Precipitation
Anomalies, Illinois State Water Survey Bulletin 63, pp.

Semonin, Richard G. 1977. Illinois seeding opportunities
as indicated by a 1-D model. Preprint Sixth Conference
on Inadvertent and Planned Weather Modification,
Champaign-Urbana; AMS, Boston, pp. 266-269.

Semonin, R. G., D. W. Staggs, and G. E. Stout. 1962. Cloud
electrification studies in Illinois. National Science Foun-
dation G-17038, Annual Report. April, 13 p.

Stall, John B., and Floyd A. Huff. 1971. The structure of
thunderstorm rainfall. Preprint 1330, ASCE National
Water Resources Engineering Meeting, Phoenix, January,
30 p.

Stout, G. E. 1960. Observations of precipitation variability.
Transactions Illinois Academy of Science v. 5 3(1,2): 11-19.

Stout, G. E., and F. A. Huff. 1962. Studies of severe rain-
storms in Illinois. ASCE Journal of Hydraulics Division
v. 88(HY4):129-146.

Towery, N. G., and S. A. Changnon. 1970. Characteristics
of hail producing radar echoes in Illinois. Monthly Weath-
er Review v. 98(5): 346-35 3.

Vogel, J. L. 1975. Air mass storms of 10 August 1973. In
Studies of Selected Precipitation Cases from METRO-
MEX, Illinois State Water Survey Report of Investigation
81, pp. 191-231.

Vogel, J. L., and F. A. Huff. 1978. Relation between St.
Louis urban precipitation anomaly and synoptic weather
factors. Journal of Applied Meteorology v. 17:1141-1150.

Vogel, J. L., and F. A. Huff. 1977. Relation between sur-
face winds, storm movement, and rainfall. In Summary
of METROMEX Volume 1: Weather Anomalies and Im-
pacts, Illinois State Water Survey Bulletin 62, pp. 53-62.

Wilk, K. E. 1961. Research concerning analysis of severe
thunderstorms. Contract AF 19(604)-4940, Final Re-
port, December, 68 p.

Wilson, J. W., and S. A. Changnon. 1971. Illinois tornadoes.
Illinois State Water Survey Circular 103, 58 p.


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