Flooding Tuesday midday downpours over sections of the metro area not the last; building heat in coming days to establish sporadically thundery “ring of fire” pattern
The heavens opened over the city Midday Tuesday—and it won’t be the last time that happens in the days ahead. The cluster of deluge-generating cumulonimbus clouds (thunderheads) this afternoon, towered 47,000 feet into an atmosphere in which 1.50 to 2” of water is evaporated, generating concentrated radar-estimated 1 to 2” downpours which flooded sections of the metro area. These 1 hour radar rainfall estimates indicated the storms, which centered on Grant Park and downtown Chicago, proceeded out onto the lake where even heavier rains fell.
That such heavy rains can fall in such a short period of time is easy to understand when you look at these three-dimensional radar scans of the storms responsible. The storms which produce rains like today’s towering tens of thousands of feet into the atmosphere and draw moisture in from all directions, concentrating rainfall in heavy shafts of rainfall.
Tuesday’s midday storms won’t be the last. Scattered storms may develop in the afternoon heat and humidity as laid out in these forecast panels off the National Weather Service’s HRRR model—one of the high resolution computer forecast models which attempts to depict details of our weather up to 15 hours into the future. The panels we’re posting here are prediction of precipitation at 4pm, 5pm and 6 pm this evening. The showers and thunderstorms they depict may impact up to half the metro area. (Summer rains rarely fall in a homogenous or even manner. Rainfalls tend to vary widely over short distances).
The extended spell of hot weather, which may first push area temps into the 90s as early as Thursday, is to generate a multi-day streak of 90-degree and possibly hotter daytime highs Friday, Saturday and Sunday. The one variable which will have to be monitored carefully is any thunderstorm development. The cooler, rain-generated outflow can lower temps in and near t-storms.
Today’s storms produced prolific lightning. I thought you’d be interested in these lightning depictions off our in-house WeatherBug Professional database. These panels were produced immediately after the midday and early afternoon thunderstorms moved out over the lake and into northwest Indiana. Each of the arrows depicts a cloud to ground or intra-cloud lightning discharge.