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High Water Vapor Content and Heavy Rains

High Water Vapor Content and Heavy Rains

So far this month within the state climate observing network 30 new daily rainfall records have been set with many 4-5 inch amounts. Dew points have been above 70 degrees F on many days (approximately 100 hours at MSP), so Heat Index Values around the state have varied this week from 95°F to 107°F.

All of this water vapor has been abundant fuel for thunderstorms all month long. Over 130 climate stations report 4 or more inches of rain for the month, while at least 80 climate stations report over 5 inches. A few places have seen over 8 inches. Yet some parts of the far northern counties remain dry, with less than 1 inch of rain so far this month.

Portions of Olmsted, Dodge, Houston, and Steele Counties in southeastern Minnesota have already reported over 30 inches for the year so far and are on pace to set new annual precipitation records. For example Rochester has reported 32.72 inches of precipitation this year, through July 17th, and that is the most through July 17th in their climate record which goes back to 1886.

Weekly Weather Potpourri

NOAAfeatures a fascinating article this week about 19th Century scientist Eunice Newton Foote. She was an amateur scientist from the mid-1800s and performed experiments which validated the discovery of Earth's greenhouse effect. Her experiments comparing the temperature within cylinders filled with different gases revealed the ability of water vapor and carbonic acid gas (carbon dioxide) to raise temperature. These studies inspired her to hypothesize that Earth would have been much warmer in the past if its carbon dioxide levels were higher.

The Washington Post featured stories by the “Capitol Weather Gang” about the extensive Heat Wave gripping much of the USA this week. Many states were expecting to see the National Weather Service issue Heat Advisories and Excessive Heat Warnings, as Heat Index values soar to 100°F or greater in many areas. They also note that in many places summer minimum temperatures are on the rise.

Several news outlets including the BBC this week have featured stories about the Heat Wave encompassing the eastern half of the USA, including Minnesota, Iowa, and Nebraska. The combination of high temperatures and high dew points is pushing Heat Index values to range from 95°F to 110°F or even higher over the period from July 18-21. Many new high temperature records are expected to be set across several states. We will feel relief from the heat starting on Saturday night.

A total of 55 animal species in the UK have been displaced from their natural ranges or enabled to arrive for the first time on UK shores because of climate change over the last 10 years (2008-2018) -- as revealed in a new study. You can read more at the Journal of Applied Ecology.

MPR listener question:

If I remember correctly, July 19th is the anniversary of the hottest day in Minnesota history. Can you remind me of the Heat Index values measured that day?


Yes, though the state all-time temperature records show 114.5°F at Beardsley (Big Stone County) on July 29, 1917 and 114°F at Moorhead on July 6, 1936 there was little humidity associated with those records. The hottest days in history from a Heat Index perspective were July 19-20, 2011. Here are some of the Heat Index Records set back then:
112°F at Fergus Falls; 114°F at Winona and New Ulm; 116°F at Hallock; 117°F at St Cloud; 118°F at Red Wing and Rochester; 119°F at MSP; 121°F at Austin; 123°F at Pelican Rapids; and 134°F at Moorhead. These readings were the result of temperatures in the mid to upper 90s F with dew points in the 80s F.

Twin Cities Almanac for July 19th:

The average MSP high temperature for this date is 84 degrees F (plus or minus 8 degrees F standard deviation), while the average low is 64 degrees F (plus or minus 6 degrees F standard deviation).

MSP Local Records for July 19th:

MSP weather records for this date include: highest daily maximum temperature of 100 degrees F in 1977: lowest daily maximum temperature of 63 degrees F in 1902; lowest daily minimum temperature is 46 degrees F in 1873; highest daily minimum temperature of 79 degrees F in 1977; record precipitation of 1.75 inches in 1957; and no snow has fallen on this date.

Average dew point for July 19th is 61 degrees F, with a maximum of 82 degrees F in 2011 and a minimum of 41 degrees F in 1958

All-time state records for July 19th:

The state record high temperature for this date is 108 degrees F at Canby (Yellow Medicine County) in 1932. The state record low temperature for this date is 29 degrees F at Tower (St Louis County) in 2000. State record precipitation for this date is 8.97 inches at Fosston (Polk County) in 1909; and no snowfall has occurred on this date.

Past Weather Features:

Strong thunderstorms brought heavy rains and hail to portions of northwestern Minnesota over July 19-20, 1909. Rainfall amounts ranged from 3 to 11 inches, producing widespread flooding. Many farmers reported whole fields of wheat washed out.

July 19-24, 1934 produced six consecutive days of 100 degrees F or greater for many parts of Minnesota. The Heat Wave was devastating to crops that were already drought stressed. During this Heat Wave most of the state saw little rainfall, generally less than half an inch.

Frost up north in St Louis County on July 19, 2000. Many campers woke up to temperatures in the 30s F.


It will finally cool off to below normal temperatures over the weekend. There will be chances for showers and thunderstorms on Saturday, but mostly sunny skies Sunday and Monday. Temperatures will warm up closer to normal by Tuesday – Thursday next week, and it looks like the week will mostly be dry.

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