We're getting close enough to PyCon to look at the weather forecast. You should certainly bring at least a light jacket and gloves; bring a heavier jacket if you're not used to cold temperatures.

According to Frommer's Portable Chicago, the average temperatures in Chicago in March are a high of 44 degF / 7 degC and a low of 28 deg / -1 degC. The temperatures predicted for the week match the averages: high temperatures of about 40-50 degF / 5-10 degC, and night temperatures of around freezing. There are chances of rain on Wednesday night and on Monday, and a chance of light snow on Friday night. Winds are predicted to be moderate, so wind chill is probably not going to make things much colder.

Here's the Weather Underground link for the hotel's postal code: http://www.wunderground.com/US/IL/Des_Plaines.html