The river is high. Will it flood? That's a very good question to ask in the morning before a storm; and the answer today turned out to be yes. Roads were inundated, Lake Barracuda emerged from its stormwater geyser, Depot Street filled with water, Mullholland Creek popped a manhole cover, and S. Main Street near Michigan Stadium filled. West Park's new water features get a workout.
Basements have taken on water, and the full extent of storm damage is unknown yet until we get the May 26 predicted rains.
Media coverage: Detroit News, noting that this is the 6th worst flood to date; AnnArbor.com, collecting more flood photos, including those of Lake Fingerle.
A few photos, with photo credits:
Lake Barracuda, captured at Depot Street by photographer Chris Dzombak. Photo used with permission, all rights reserved. The lake is named after Barracuda Networks, which occupies the new stilt-built stay-dry construction at 201 Depot St. More photos from Chris in the Flickr set Flooding at Depot/4th.
The river seen from above, taken by Kai Petainen, used with permission. His set Huron River Flood has photos and some short video taken from Island Park downstream to the Arboretum. Kai writes for Forbes with the weblog Sisu Investor.
Map of total rainfall storm to date for this storm, from the Weather Underground, as of 1:05 a.m. Thursday. Pick "total precipitation" from the radar screen, or pop out the "1 hr precipitation" from the side in the Weather Underground Classic user interface and animate to watch storms come in.
If you're looking for data, you'll find the specific current and recent historical information from these sources.
The USGS Water Data Discovery page describes the National Water Information System which has reat time, predictive, and historical data for use.
USGS National Water Information System real-time water data for gauges in the area is measured every 15 minutes and reported with 60-90 minutes delay. Look at the gauges for the Huron River at Ann Arbor, and you'll see a graph showing current levels. It's also possible to go back and get the data as data going back as far as 120 days, and to retrieve prior years data on a daily basis.
There is also a gauge on Allen Creek which has collected data from some storms, but which is not in the National Water Information System and not always online. Allen Creek empties into the Huron River just downstream of Argo Dam, and at peak flow it can dump at least 1500 cubic feet per second into the river. I have seen data from one storm, and it looks like this can turn into 600 cubic feet per second at the next gauge, though that's only one data point.
You can look yourself at the tabular data for the river rating of the Huron River at Wall Street, which shows a level by level matching of flow vs water height. If the river is very low (300 cfs), then a sudden burst of 600 cfs will raise the level of the river by about a foot, and a burst of 1500 cfs will raise the level of the river by about two feet.
River forecasts come out routinely between 9:00 a.m. and 11:00 a.m. and if needed a second forecast goes out between 9:00 p.m. and 11:00 p.m., according to National Weather Service meteorologist Danny Costello.
For more media information about products provided by the NWS, here's a slide deck I found on the Grand Rapids NOAA site as a media briefing. It explains in one of the slides a key aspect of predictions: the weather service changes from "watch" to "warning" when a forecast probability goes up to 80% likelihood of the event occurring.
Edward Vielmetti's Wordpress weblog 
Some more storm-related stuff locally:
http://annarbor.crowdmap.com has locations of storm reports. So far there’s been reports of overflow on Swift Run (at Clark), Allen Creek (at Mulholland and Depot), Mallett’s Creek (at W Eisenhower), and Traver Creek. Traver appears to have taken out a bit of Plymouth Road, still looking for exact details on that incident, but Plymouth is closed for embankment repair.
The river looks scary and dangerous. These extreme weather conditions kept on battering the nations. Floods in Mississippi, tornadoes in Missouri and extreme heat in Texas. People wonder when will all of these end? We just have to hope and pray that everything will be better, sooner or later.