September 1930 was the warmest & driest September on record for much of the eastern U.S. since 1881 or 1925.
On the periphery of this hot ridge, an strong, dynamic storm system with tropical moisture from the Pacific & Gulf. The tropics were active for weeks. For example a Category 4 hurricane devestated the Dominican Republic.
Nearly half of Iowa's 99 counties reported at least wind & hail damage with some seeing tornado damage.
Widespread straight-line wind damage was reported across Indiana, but I could only find specific damage reports from counties/towns/cities in the central & northern parts. The damage in Indiana was largely confined to trees & powerlines, while much more structural damage occurred in Illinois. Crop damage was immense, reportedly with large hail of up to +2" in diameter & damaging gusts with that hail shredded ripened crops to the ground. There are many reports of windows being broken by the driving large hail in Iowa & Michigan.
Crop damage was a big issue in Indiana, however. Many crops were flattened by the damaging wind & loss to the apple crop was reportedly "heavy". In many areas of Michigan 75% of the crop of apples & pears was downed by the severe wind gusts.
There were 14 deaths in at least 10 tornadoes. The strongest tornado appears to be the likely EF3 that struck south-southeastern Iowa's Monroe County. It appears that it was on the ground for at least 14 miles. Interestingly, a likely EF1 tornado tracked 8 miles through Monroe County on September 18th.
This was part of an active, wet weather pattern for part of the Midwest & Plains while the Southeast & East baked in heat & drought.
Prior to this outbreak, severe weather was reported in Indiana on September 14, 15, 22 & 24.
Severe weather was reported in Illinois & Iowa September 7, 12, 14, 15, 18, 19, 28 & 29. This included a tornado that tracked through southern Illinois' Jefferson & Hamilton counties on the 14th that caused $8.5 million in damage (inflation adjusted). In the northern Missouri town of Browning, a likely intense microburst caused extensive roof damage to homes & businesses (as well as trees & powerlines) on the 14th.
September 1930 pattern: