Saturday opens warm, humid and cloudy with a scattering of showers in the area. The rains may only affect 20 to 30 percent of the metro area, coverage likely to escalate fairly dramatically Saturday afternoon and night as the squally downpours associated with Hurricane Isaac's remnants spread north across the Chicago area. The northern extent of the heaviest rains may extend as far north as Chicago and the I-88 corridor Saturday afternoon and evening—continuing into Saturday night.
Isaac spins up damaging tornadoes Friday downstate while producing eye-catching rain tallies
Hurricanes lose their powerful winds as they move inland, but their rain-making capability continues. So does their ability to spin up tornadoes.
Both attributes were on display in downstate Illinois Friday where powerful thunderstorms in the northbound remnants of Hurricane Isaac spawned a half dozen tornadoes which touched down between waves of torrential rainfall.
An evening tornado touchdown three miles northeast of O’Fallon, Missouri Friday scattered playground equipment at a daycare center while damaging a truck and snapping trees. Other tornado touchdowns were reported at Fieldon Jersey, Carrollton and Franklin—all in downstate Illinois.
A late Friday night deluge to the east in Greenville, IL unleashed 5.63 inches of rain. Other impressive downstate rain totals through late Friday night included 3.10 inches near Woodson, 2.85 inches at Hardin and 2.54 inches at Aviston.
Driving downstate rains headed north
Scores of computer model rainfall forecasts, generated over the past four days for the Chicago area, suggest an average of 1.40 inches is possible near the city with heavier 3 to 8 inch totals from the south suburbs southward into central Illinois and Indiana. Warm season rainfall never occurs evenly. Amounts can and most often do vary widely. There's no reason to believe things will be any different in this weekend's tropical system.
Rain-free periods Saturday morning likely to fade as more widespread rainfall and possible downpours edge north
Weekend rains won’t be continuous. But the widely spaced, isolated showers to which people awake Saturday morning, are likely to pale in comparison to the more general rains and downpours which may affect parts of the metro area later Saturday into Saturday night. And with more than 2 inches of moisture predicted to be evaporated in the atmosphere as Saturday proceeds, the potential for vigorous bursts of a torrential rain over at least part of the area aren’t out of the question.
Indications are a huge spread in the amount of rain which falls is to occur from north to south across northern Illinois. The farther south one travels, the heavier the rain which is likely to fall. By the same token, rainfall in the northern suburbs toward the Wisconsin line may end up considerably lighter than over the rest of the area.
Midnight Friday night marked August’s close and the conclusion of the third hottest 3 month meteorological summer period in 142 years
Friday was August’s closing day—and a hot one too. O’Hare topped out at 92-degrees—the 45th 90-degree temperature of 2012.
It was also the final day of the three month meteorological summer season. Summer 2012 goes down in the books as the third warmest in 142 years of weather records.