Rain, which is on the weather menu for Chicago today and tomorrow, and snow, which is on the ground through much of the area, will combine this weekend to create conditions that are ripe for localized flooding.
Temperatures are expected to rise into the 40s and maybe the 50s before it starts getting cooler Sunday night, and the incoming storms, which are expected to produce 1-2 inches of rain, will turn all that snow on the ground into even more water. The National Weather Service said the water equivalent of the existing snowpacks throughout the area is somewhere between 1 and 2.5 inches.
How much flooding occurs will depend a lot on just how frozen the ground is below that snow. The weather service says that frost depths are currently between 6 and 10 inches. If the ground doesn't thaw much more – and the agency thinks there will still be a "significant" amount of frozen ground – there will be a lot of water runoff looking for a low spot.
The result, the agency says, is minor flooding, with a rise in levels of local stream and rivers. None of those waterways are running especially high right now, according to the weather service.
WGN-TV meteorologist Tom Skilling says on ChicagoWeatherCenter.com that this weekend’s rains will be the heaviest in five weeks, a period that's been about as wet as it gets for this time of year. Skilling says that the rain and snow that started Jan. 27 have resulted in 6.08 inches of water equivalent precipitation at O’Hare, the most observed in 126 years and more than 2.3 times the normal amount for that period.
Still more precipitation is in the Monday forecast, with some snow flurries likely. The rest of the week looks pretty dry, but Skilling is expecting more rain over the next couple of weeks.