Torrential, even violent t’storms popped on the afternoon of August 6, 1905. An intense macroburst & a microburst occurred & highly-variable rainfall fell on the area. Historic rainfall occurred just west of Princeton, Indiana where the NWS (U.S. Weather Bureau at the time) Cooperative observer measured 10.50″ of rainfall in 24 hours. This continues to be the official state record for maximum 24-hour rainfall for Indiana.
Widespread severe weather with wind & hail was reported from North Dakota to Wisconsin, Michigan to as far south as northern Indiana (mill sustained +$100,000 in damage at Kokomo & that is in 1905 dollars with trees & lines down) August 4-5 as surface low & apparent cold front tracked through that region.
Front moved south, but it appears that it weakened considerably & the main surface low rapidly shot to the north-northeast. It is also likely that an outflow boundary surged out ahead of the main area of severe t’storms. Ahead of the surface cold front & likely outflow boundary was a very hot, very humid & also likely highly unstable airmass. Given the fact that the main wind fields aloft went north-northeastward with the surface low, it is likely that low-level wind fields were quite slow as front hung up over area, which would result in slow t’storm movement.
However, given likely very unstable environment & high PWATs (available water to squeeze out) in such an airmass, (& there was probably high DCAPE) there was a likely good set-up for wet downbursts, especially with that water loading (weight of the rainfall enhancing downbursts). Also, given high CAPE (instability or measure of the updraft from latent heat energy available) & perhaps some marginal bulk shear to help, some large hail occurred.
This regime continued for a few days with weak front draped over the area & multiple outflow boundaries around. On August 11, 3.36″ fell 4 miles northwest of Mt. Carmel in a short period of time.
An intense macroburst occurred betwee Odon & Elnora & southwest of Odon in the late afternoon. Press reported a scene “of utter desolation”. Thousands of acres of corn were completely destroyed by intense wind & hail, orchards were reportedly completely leveled, barns destroyed, trees snapped off & large amounts of birds were killed. No hail size was given, but given the scope of damage, even if the winds were 100 mph (which it looks like that could have been 100-110 mph) such damage, which I saw with a Benton County macroburst in 2010, points to +1.75″ hail.
The corn crop in an area of Benton County in June 2010 was completely leveled & destroyed & trees were snapped at the base. The National Weather Service storm survey team determined this to have winds of 100 mph. Hail up to softball size occurred with the storm. In eastern Gibson County, August 2012, hail up to grapefruit size & winds to 110 mph caused similar catastrophic damage to crops & major tree damage (along with much structural damage).
Residents that experienced the near Odon/Elnora macroburst reported that “it was the worst storm in a long, long time”.
Tree & barn damage was also reported west of Princeton, Indiana, near where the 10.50″ of rainfall was measured. This was probably a wet microburst.
How did such rainfall occur at Princeton?
In such situations, as seen in recent significant localized flash floods (cars were carried away in Birmingham, Alabama from localized cluster of intense t’storms last week as storm actually move northeast to southwest over the city) converging outflow boundaries, converging t’storms & training t’storms (sometimes all in one) tend to produce such extreme rainfall in these highly-unstable situations without a large-scale mechanism for such rainfall. An example of a large-scale mechanism would be the March 1997 flood or even the flood along & north of the Ohio River in April 2017 where up to near 9″ of rainfall fell in one night.
In this case, it looks as if an outflow boundary was probably the trigger & it may have been mergers of others nearby from t’storms that enhanced the rainfall.