Winter expected to blow in with early cold before warming up

Indiana will have wide temperature variations month-to-month from December through February, said Dev Niyogi, Indiana state climatologist. On average, winter temperatures should be near normal and precipitation is expected to be lower this winter.

"We expect temperatures to be colder than normal in early December," said Niyogi, a Purdue University assistant professor of agronomy and earth and atmospheric sciences. "Then, January and February could be warmer than normal, but not as warm as last year."

Typically, the average daily winter high temperature is 34 degrees in northern Indiana and 43 degrees in southern Indiana. Low readings range from 18 degrees to 25 degrees across the state. Winter precipitation ranges from 6.3 inches to 9.6 inches of rain and melted snow. Melted snow measures less than snowfall.

Although the forecast is for a drier winter, precipitation is more difficult to project than temperature, Niyogi said. El Niño tends to hold down precipitation in Indiana but doesn't play as big a role in Indiana's weather as it does in the Western and Mountain states. El Niño is a fluctuation of the ocean-atmosphere system in the tropical Pacific that affects weather worldwide.

"A new El Niño has developed in the Pacific Ocean, but it is still weak," Niyogi said.

Such weak warm-water weather events can cause dramatic weather changes, but because El Niño's effects have to travel from the Pacific and across the West Coast and the Rockies, its effect on Indiana is minimal, he said.

For this reason, forecasts need to consider additional climatic factors such as the North Atlantic Oscillation and recent hurricane activity, he said. The North Atlantic Oscillation is climatic phenomenon in the North Atlantic Ocean that controls the strength and direction of westerly winds and storm tracks in that region and affects weather on continents bordering the ocean. The oscillation is similar to the El Niño in the Pacific Ocean.

Based on climatological records, the fact that hurricane activity both in the Atlantic and Pacific oceans has been moderate this year also suggests that Indiana's early winter weather may be colder than normal, followed by a possibility of warmer than normal temperatures in January and February, Niyogi said.

In addition, wind patterns and the jet stream play major roles in Indiana's weather.

"Winds tend to work sort of like a car heater in determining temperatures," Niyogi said. "If the heater vent is directed toward one person that determines who is warm."

At the same time, the jet stream, which interacts with pressures from the North Atlantic Oscillation and El Nino, modulates Indiana's weather pattern. The jet stream location controls the influence of arctic or tropical weather events.

Because the jet stream is not static, where it's located can determine how far south arctic air penetrates in the winter, Niyogi said. If the jet stream is north of Indiana, then warmer conditions usually occur. When it's nearby, chances increase for cold weather and more snowfall in the state.

In addition, Lake Michigan influences temperature and snowfall in northern Indiana. The "lake effect" results in more snowfall for that area of the state. Greater amounts of snow on the ground keep temperatures lower because heat is reflected back into the atmosphere.

Southern Indiana tends to have warmer temperatures and less snow because the more rolling terrain and greater distance from large bodies of water mitigate jet stream and wind influences, Niyogi said.

During Indiana winters, precipitation normally falls on 29 days to 44 days. Daily snowfalls of at least 1 inch typically occur on three days in southern Indiana and as much as 16 days in the Lake Michigan snowbelt region. Total snowfall from December through February ranges from 11 inches in Evansville in southern Indiana to 50 inches in South Bend in the north.

Writer: Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu

Source: Dev Niyogi, (765) 494-6574, dniyogi@purdue.edu

Ken Scheeringa, associate state climatologist, (765) 494-8105, kens@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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Purdue Department of Agronomy

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