Parts of northern Illinois now face a heightened risk of dangerous severe weather Tuesday afternoon and evening, with forecasters warning that strong to intense tornadoes may be possible.

The Storm Prediction Center has upgraded much of northern and central Illinois, with areas including Will, La Salle, Bureau, Grundy and Kankakee counties, to a Moderate Risk for severe thunderstorms, a level that signals the potential for significant and widespread severe weather.

A flash flood watch through 3 a.m. Wednesday has also been called for the following counties: DuPage, eastern Will, Grundy, Kane, Kankakee, Kendall, La Salle, northern and southern Will County, most of Cook County and parts of northwest Indiana.

That could include creeks and streams rising beyond their banks and flooded roads and underpasses.

According to forecasters, thunderstorms are expected to develop late this afternoon along a boundary stretching across northern Illinois as a storm system moves northeast toward the region. Increasing warmth and humidity will fuel the atmosphere, with dew points climbing into the low to mid-60s, unusually high for early March.

Storms could begin developing by mid-afternoon, but the greatest coverage and intensity are expected from late afternoon into the evening.

If storms form as expected, they may quickly become supercells capable of producing very large hail, damaging winds, and tornadoes.

Meteorologists say the environment will strongly favor rotating storms, with powerful winds both near the ground and higher in the atmosphere. That setup could allow storms to produce hail larger than 2 inches in diameter and wind gusts over 70 mph.

The tornado threat may increase quickly during the evening as a strengthening low-level jet stream develops across Illinois. Forecasters say the corridor along and just south of the warm front in northern Illinois has the best chance of producing multiple strong tornadoes, potentially EF2 or stronger.

Storms may eventually organize into larger clusters later tonight, which could shift the main threat toward damaging winds and additional tornado potential as they move east across the Midwest.

Heavy rainfall may also accompany the storms, raising the possibility of localized flash flooding, particularly where storms repeatedly move across the same areas.

Residents are urged to closely monitor weather updates and have multiple ways to receive warnings, especially during the late afternoon and evening when the most dangerous storms could develop.