More Heavy Rains

More Heavy Rains:

Following the abundant, and sometimes record-setting rains that started the month, this week brought more heavy rains, mostly to central and southern portions of Minnesota. Many areas reported from 1 to 2 inches, and several climate stations reported record daily rainfall amounts either on August 5th or August 6th. Some of the record daily amounts this week included:

3.50 inches at Alexandria (Douglas County)
2.82 inches at Collegeville (Stearns County)
2.81 inches at St Cloud (Stearns County)
2.51 inches at Cambridge (Isanti County)
2.41 inches at Wabasha (Wabasha County)
2.20 inches at Preston (Fillmore County)
2.03 inches at Caledonia (Houston County)

Strong thunderstorms produced severe weather in some places this week, including hail, strong winds, and some tornadoes. The National Weather Service reported on the tornado at Melrose (Stearns County) on August 3, and then also filed reports on the tornadoes in southern Minnesota on August 5th, including those close to Waseca, St James, Twin Lakes, and Janesville. All were rated EF-1, with winds ranging from 95 to 105 mph.

After the first 8 days of the month, many areas of the state already report 3 to 5 inches of rainfall so far. Historical monthly normals (averages) for total rainfall in August typically range from 3 to 4 inches. With the wet start to the month, year-to-date precipitation totals exceed 30 inches in many parts of the state, while Wells in Faribault County and Elgin in Wabasha County already report over 40 inches of precipitation for the year so far.

Weekly Weather Potpourri:

The Weather Underground web site featured several updates on Tropical Storm Debby this week as it migrated from Florida up into North Carolina. The storm spawned a number of tornadoes, but mostly produced very heavy rains and flooding in each state that it passed over. Here are some of the rainfall amounts along its path:

8-16 inches in parts of Florida (including 7.00” daily record at Bradenton)
6-14 inches in parts of Georgia (including 8.75” daily record at Glenville)
7-13 inches in parts of South Carolina ((including 8.02” daily record at Waterboro)
6-15 inches in parts of North Carolina (including 8.29” daily record at Wilmington)

For those who are curious about the daily life of a meteorologist, Sarah Keith-Lucas offers a video synopsis of her daily routine at the BBC Weather Center in London. It is especially interesting to see the various use of weather graphics and how broadcast meteorologists focus on the most important weather features of the day.

The journal Nexus features an article this week by scientists who compared some of the major heat stress indices used globally to express the severity of Heat Wave episodes. This study examined the effectiveness of six different temperature-humidity-based heat wave indices in identifying dangerous heat wave outdoor conditions, using recent heat wave events observed in Asia, Europe, and the United States as case studies. The authors found that many of these heat indices methods underestimate the true heat stress on the human body. Factors that influence the magnitude of heat stress include temperature, humidity, wind, and solar radiation. In some environments the humidity is the most critical element to consider, while in others it may be solar radiation or wind.

MPR listener question:

We have read in your book that based on historical average values of monthly precipitation June is the wettest month of the year for most places in Minnesota. After the very wet start to August here in Maple Grove (over 5 inches), we are wondering if August is the wettest month of the year for some locations in the state?

Answer:

From the nearly 300 long term climate stations in Minnesota, I can find only 7 where historical averages say that August is the wettest month of the year. These are:

Buffalo and Sain Michael in Wright County
Big Lake in Sherburne County
Chanhassen in Carver County
Hutchinson in McLeod County
Jordan in Scott County
Maple Grove in Hennepin County

Though June is most often the wettest month of the year based on historical averages, there are some locations where the wettest month of the year based on history is in July, or May, as well as August. Conversely, February is the driest month of the year for almost all locations in the state.

Twin Cities Almanac for August 9th:

The average MSP high temperature for this date is 82 degrees F (plus or minus 7 degrees F standard deviation), while the average low is 64 degrees F (plus or minus 6 degrees F standard deviation).

MSP Local Records for August 9th:

MSP records for this date: highest daily maximum temperature of 95 degrees F in 2010; lowest daily maximum temperature of 60 degrees F in 1994; lowest daily minimum temperature of 46 degrees F in 1972; highest daily minimum temperature of 76 degrees F in 2010, and record precipitation of 3.34 inches in 1914. No snowfall has occurred on this date.

Average dew point for August 9th is 59°F; the maximum dew point on this date is 79°F in 1955 and the minimum dew point on this date is 39 degrees F in 1927.

All-time state records for August 9th:

The state record high temperature for this date is 104 degrees F at Canby (Yellow Medicine County) in 1947. The state record low temperature for this date is 28 degrees F at Tower (St Louis County) in 1994. The state record precipitation for this date is 5.25 inches at Two Harbors (Lake County) in 1939. There has been no snowfall on this date.

Past Weather:

On August 9 of 1947 sixteen Minnesota communities reported record high temperatures ranging between 95°F and 104°F. The overnight temperature never dropped below 76°F at New Ulm, Marshall, and Madison.

Strong thunderstorms brought record-setting rainfalls to parts of southern and central Minnesota over August 9-10 of 1948. Many areas reported 4 to 7 inches of rainfall, flooding roads and farm fields. Some corn fields were flattened by the storms and the crop had to be harvested for silage instead of grain.

Morning frosts were reported from St Louis, Lake, and Koochiching Counties on August 9 of 1994. The afternoon high temperature at Lutsen only reached 57°F

Outlook:

Mostly sunny with much cooler than normal temperatures over the weekend. A warming trend will start a climb in temperatures up towards normal beginning on Tuesday. There will be a chance for showers returning to the state by Wednesday and Thursday