Indiana’s climate has some variations depending on where which part of the state you are at. From the lake breeze along the coast of Lake Michigan to the rolling hills of southern Indiana. This wonderful state is more diverse that what people think of it as. The geography and topography of a location has affected how warm or how much precipitation one area gets on average. Today, we will go over a series of maps showing the variation of climatological averages throughout the state in the over the past few decades.
Precipitation
Annual Precipitation Averages
The annual average precipitation total map shows the highest amounts over southern Indiana. The southern portion of the state tends to get over 45 inches of rain per year regularly. Some of the driest parts of the state is located over northeastern Indiana, generally under 35 inches of precipitation per year on average. There is roughly a 20 inch difference from driest to wettest portions of the state.
Seasonal Precipitation Averages
The trend of southern Indiana receiving more precipitation remains the case for the winter months. Some locally higher precipitation averages can be found along northern LaPorte, Porter, and Lake Counties. These counties all boarder Lake Michigan to the north and sees higher precipitation totals in the winter due to lake effect snow that affects areas in proximity near the lake. The warmer large body of water compared to the cool dry air mass of the winter months accompanied by north winds can lead to large lake effect snow amounts. This can add several inches of melted precipitation to an area’s annual precipitation totals. December and January is commonly the best months for lake effect snow to occur as the largest temperature contrast between the quickly cooling air and the slowly cooling lake water.
This map takes into account Meteorological winter, which runs from December 1st to February 28th/29th.
The trend of Spring precipitation aligns similarly to the annual precipitation average in terms of trends. Most precipitation in the south least precipitation to the north. Spring on average is the wettest season of the four seasons for much of the state and totals stay rather consistent from year to year.
This map takes into account Meteorological Spring, which runs from March 1st to May 31st.
Summer is the most unpredictable season of the four when it comes to climatological precipitation predictions. Most if not all the precipitation comes from scattered, small-scale thunderstorms that form due to daytime heating. Summer precipitation is the most inconsistent of all the four seasons despite the seasonal average from 1980-2020 having the smallest range of 2.6 inches from maximum to minimum average summer precipitation over the select period. There is no correlation between the summer precipitation map and the annual precipitation total map. The highest averages in the state tended to be centered around Cass, Clay, Fulton, Owen, Pulaski, and Putnam counties. This is due to the randomness of summertime thunderstorms that form due to daytime heating. The driest portion of the state is generally southwestern Indiana, which generally sees the most precipitation on average throughout the year.
What the key of the map makes it misleading is the fact that it is the most even in terms of rainfall the state gets near equal amount of rainfall on average. What the map doesn’t tell is the inconsistency of rainfall from year to year during the summer. Indiana saw one of their driest and wettest summers on average within a four year span. With the rainfall resulting in the flood of 2008 and the remains of Hurricane Ike resulting in tremendous rainfall. On the flip side, 2012 was one of the warmest and driest summers on record creating one of the worst droughts in the state since the 1930s. An upper level ridge from dominated the weather pattern for much of the summer and blocked any flow of moisture that would trigger thunderstorms that is normally experienced during the summer.
This map takes into account Meteorological Summer, which runs from June 1st to August 31st.
The highest amounts in the Fall can now be found in the southern portions of the state and the northeastern portion being the driest. Counties near Lake Michigan have enhanced precipitation totals due to the fact that in late fall, lake effect snow begins to develop. The contrast between cooler air temperatures and a very warm waters of Lake Michigan begin to large enough create favorable conditions for lake effect snow to fall in the month of November.
This map takes into account Meteorological Fall, which runs from September 1st to November 30th.
Temperature
Annual Average Temperature
Annually on average, the warmest part of the state tends to be in the southern portions while the coldest tends to be in the northern portions. This is because the further north in latitude the less direct the sun angle is and the less efficient the sun is of heating up a specific location. While in the further south in latitude, the more direct the sun angle is, and the more powerful the sun’s energy is for a specific spot. This explains why there is a 10°F difference between warmest average annual temperatures in the south compared to the coldest average annual temperature in the north. It may not sound like a large difference but when you take the average difference across the past 40 years of data, it is quite significant.
What is noticeable on the map is that eastern Marion County is significantly warmer than the areas around it. This is due to a phenomenon called the Urban heat island. Areas of that are consisted of asphalt metal or are in dark in color tends to absorb heat better than grassier, rural, or residential areas. Since Marion County is the location for the central business district of Indianapolis, it tends to be warmer than the surrounding areas of equal latitude. Downtown Indianapolis consists of mostly buildings, roadways, and parking lots all these objects do a great job at absorbing energy from the sun that is transformed into heat during the daytime hours. During the nighttime hours, the high roads, buildings, and parking lots acts as a blanket for the city. As the air cools down, the extra amounts of heat absorbed is then released and returned to the atmosphere at a slower rate than surrounding areas. Generally, Indianapolis on average runs 5°F warmer than areas across the state of an equal line of latitude.
Seasonal Temperature Averages
A major difference in formatting between the seasonal precipitation and temperature map is that the temperature map is an isotherm map connected by lines of equal temperature of an specific equal interval. Weather stations across the country measures melted precipitation in hundredths of an inch. Only the most advanced weather stations in the world can measure temperature to the hundredths place in °F. Since 0.01°F is a negligible amount, the following sets of maps will be made up of five or four color code isotherms of 3°F intervals.
The trend of warmest in the south, coolest in the north takes hold for the Meteorological Winter months with a 15°F temperature range from minimum to maximum. The urban heat island can be seen on this map with extreme southeastern Boone, extreme southeastern Hamilton, eastern Hendricks, and western Marion Counties in the same isotherm of areas south of the Indianapolis metro area.
Some slight temperature moderation can be seen closer to the cost of Lake Michigan as the temperature of the areas close to the lake will be closer to the actual temperature of the lake water itself than areas further away from the lake.
This map takes into account Meteorological winter, which runs from December 1st to February 28th/29th.
Warmest regions in the spring mainly southwest Indiana, while the coldest region is northeast Indiana. Some noticeable isotherm shapes oddities can be seen in this map. The “tongue” of warmer air extending into southern Greene County may have more to do with the land to the east of it more than the land itself.
While the Indiana’s highest point is only around 1,250 feet, a region of south-central and south-eastern Indiana is quite rugged in terrain. Some of the steepest changes in elevation in the entire state is in Hoosier National Forest and surrounding areas of South-Central Indiana. There are some hilltops that are exposed to the wind and elements more than flat areas. Even with just a couple hundred feet higher in elevation can affect temperatures by a 1-2°F. Like the effects elevation change has for temperature in the Rockies, except on a much smaller scale.
This map takes into account Meteorological Spring, which runs from March 1st to May 31st.
Temperature trends from warmest to coldest remains quite consistent from the yearly average map. The warmest region on the entire map entering the 78-81°F bracket is a small section in southern Vanderburgh County. Located in southern Vanderburgh County is the city of Evansville, which has an urban heat island of its own, but not as significant as one as Indianapolis as Evansville is a much smaller city than that of Indianapolis.
This map takes into account Meteorological Summer, which runs from June 1st to August 31st.
Temperature trends from warmest to coldest remains quite consistent from the yearly average. There is a few more oddities that are found on this map. The orange circle of western Gibson, eastern Pike, and northern Warrick counties is a rural region. The reporting stations in this area experiences the opposite effect of the urban heat island. More heat is reflected due to the high amount of grass, trees, and agricultural lands in this area. To add to this, there is simply not a lot of development in this area in terms of roads or large buildings. Gibson and Pike Counties rank in the bottom third in terms of population density which means there is going to be less development there. Heat from the sun will not be absorbed as great as it would be in other parts of the state and all that heat gained during the day will be released into the atmosphere quicker overnight compared to the more developed areas.
This map takes into account Meteorological Fall, which runs from September 1st to November 30th.
Monthly Average Temperature
Here is the breakdown on temperature on a monthly basis to get a good comparison of temperature maps side by side to get a closer look at the warmest and coldest areas.
Conclusion
The state of Indiana remains relatively consistent in Climate values on a pattern’s sense year-round. A pattern can be made that coldest areas of the state tend to be also the driest parts of the state. The warmest parts of the state happens to be the wettest parts of the state as well.
The unique microclimates across the state like the areas around Lake Michigan, the hills of southern Indiana, the urban heat island, and the lack there of in the rural areas does affect the climate of the region in the grand scheme of things.
Interactive maps of all stations within the state and their annual averages:
Precipitation:
https://bsumaps.maps.arcgis.com/home/item.html?id=ab0ad0586c3044f78eeb7a531e561af8
Temperature:
https://bsumaps.maps.arcgis.com/home/item.html?id=a196b2408f9c446386d4f309d939dfd6
-CWS Forecaster: Ben Waggoner-
