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The Heatwave of July 1995

When most people think of weather related disasters, they tend to focus on tornadoes, hurricanes, severe thunderstorms, etc. How many would include extreme heat in that list? However, the deadliest weather related event to affect the United States was the July 1995 heat wave that baked the Midwest and parts of the east coast. Over 1000 people lost there lives due to this heat wave. On average, around 175 people die each year from heat related causes.

Time (CDT)	Temp	Dewpoint	RH	Heat Index
9 am	89	77	68%	102
10 am	96	81	62%	118
11 am	97	73	46%	109
Noon	101	73	41%	114
1 pm	102	73	40%	116
2 pm	107	72	33%	121
3 pm	108	67	27%	117
4 pm	108	65	25%	115
5 pm	108	70	30%	120
6 pm	105	73	36%	119
7 pm	101	75	44%	117
8 pm	97	77	53%	114
9 pm	92	78	64%	108
10 pm	90	79	70%	106
11 pm	89	79	72%	104

Table 1. La Crosse Airport observations for July 13, 1995.

A strong ridge of high pressure was the main cause for the July heat wave. This slow moving feature shifted into the Upper Mississippi River Valley during the early to mid part of July, allowing for a hot and humid air mass to build across the region. Abnormally wet soils to the southwest, across parts of southern Iowa, western Illinois, and Kansas and Missouri, aided the extreme conditions. Steady south to southwest winds moved across these moisture laden areas, increasing the humidity in the air as it traveled into the Upper Mississippi River Valley and Great Lake States. These high humidity values, along with high temperatures, produced heat indices above 110 degrees, and over 120 in some locations*. The main stretch for the deadly heat was from July 12th-15th, with the 13th being the hottest day. On the 13th, La Crosse's heat index topped 100 for nearly the entire day (Table 1), while the high temperature of 108 tied for the hottest on record. Rochester experienced 100 degrees or greater heat index values for the afternoon and early evening (Table 2). There have been hotter periods on record, but it was the combination of the heat and the abnormally high humidities that made this event so significant.

Time (CDT)	Temp	Dewpoint	RH	Heat Index
Noon	93	71	49%	102
1 pm	95	72	48%	105
2 pm	96	73	48%	108
3 pm	98	73	45%	110
4 pm	99	73	44%	112
5 pm	98	75	48%	113
6 pm	95	77	56%	111
7 pm	92	78	64%	108
8 pm	89	79	72%	104

Table 2. Rochester Airport observations for July 13, 1995.

July wasn't the only hot stretch during the summer of 1995, as both June and August brought stretches of 90 degree or greater high temperatures to the region. La Crosse, WI would experience 37 days of 90 degrees or better throughout the summer months, second most after the summer of 1988 (46 days).

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