A Very Dry Two Weeks

A Very Dry Two Weeks:

It has been a very wet year across the state of Minnesota, with many climate stations already reporting total precipitation for the year-to-date that exceeds their annual normal amount. So, the recent two-week dry period (nearly total absence of significant rainfall) has been quite unusual. In fact, statewide statistics show it has been the second driest two-week period or longer for the year so far.

Statewide average precipitation low points in 2024:

January 19-February 7 average of 0.06 inches (14 days)
August 31-September 13 average of 0/08 inches (20 days)
February 16-March 19 average of 0.16 inches (33 days)

In addition, some of the lowest values of afternoon relative humidity for the growing season have been measured this week with readings in the 25 to 37 percent range. As a result, many gardens around the state have required some watering this week, along with other landscapes like golf courses. It appears that this situation will change significantly during the second half of September with more frequent chances for rain beginning next week and carrying through the balance of the month. Some of the rainfall could even be heavy, over an inch.

Weekly Weather Potpourri:

Hurricane Francine made landfall in Louisiana about 5pm on Wednesday with winds up to 100 mph. According to the Weather Channel web site, Francine continued on Thursday to bring rainfall to parts of TN, MO, and IL as remnants of its low pressure migrated north. Many parts of Louisiana reported 3 to 7 inches of rainfall from Francine, while areas around Slidell and New Orleans reported from 8 to 11 inches of rainfall.

This week the Weather Underground reported that Arizona, California, Florida, Main, and New Hampshire endured their hottest meteorological summer (June-August) in history. Overall it was the 4th hottest summer for the USA, with many cities declaring it their hottest as well. On August 6th, Deadhorse Airport in northern Alaska reported a daytime high of 89°F, the warmest temperatures ever recorded in Alaska north of 70°F latitude.

MPR listener question:

Last week you spoke about September trending warming and being more like a continuation of summer, except for the declining daylength. But it seems like as the autumn season passes we see more cloudy days and less sunshine as well. Isn’t this true?

Answer:

Yes indeed. We lose about 1.5 hours of day length in both September and October, then another hour is lost in November. But compounding this loss in daylight hours is a significant increase in cloudy days when we don’t see the sun at all. For example in the Twin Cities Metro Area the historical climate data show that we get about 10 or 11 cloudy days in September, then 14 to 15 such days in October, and 18 or 19 such days in November. No wonder, that many Minnesotans start to take a daily dozen of vitamin D during the autumn season.

Twin Cities Almanac for September 13th:

The average MSP high temperature for this date is 74 degrees F (plus or minus 9 degrees F standard deviation), while the average low is 56 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for September 13th:

MSP records for this date: highest daily maximum temperature of 95 degrees F in 1939; lowest daily maximum temperature of 51 degrees F in 1873; lowest daily minimum temperature of 33 degrees F in 1890; highest daily minimum temperature of 72 degrees F in 1939, and record precipitation of 1.29 inches in 1921. No snowfall has occurred on this date.

Average dew point for September 13th is 49°F; the maximum dew point on this date is 71°F in 1939 and the minimum dew point on this date is 22 degrees F in 1923.

All-time state records for September 13th:

The state record high temperature for this date is 100 degrees F at Redwood Falls (Redwood County) in 1939. The state record low temperature for this date is 17 degrees F at Roseau (Roseau County) in 1975. The state record precipitation for this date is 4.92 inches at Elk River (Sherburne County) in 2005. There has been no snowfall on this date.

Past Weather:

The warmest September 13th in state history was in 1939 when most climate observers reported afternoon temperatures in the 90s F. It reached 100°F at Redwood Falls. Many climate stations also reported overnight low temperatures in the 70s F, as if it was mid-July.

On September 13 of 1975 over 80 climate stations reported morning frost, essentially ending the growing season. Many communities reported morning temperatures in the 20s F, and frost was observed as far south as Windom and Caledonia. The afternoon high temperature at Tower only reached 44°F.

Over September 12-13 of 1978 slow-moving thunderstorms brought heavy rains to southeastern Minnesota, where many climate stations reported 3 to 5 inches of rain. In Rochester they received over 6 inches and many parts of the downtown were flooded. It was the second 6-inch rainstorm of the growing season (another one had cause flooding over July 5-6) which had produced a good deal of flood damage to the downtown area. As a result, flood mitigation work began to re-route the South Zumbro River on the north side of the city.

Outlook:

Continuing much warmer than normal into the weekend with a chance for showers later on Saturday and early Sunday, especially in southern counties of the state. Continued warm throughout next week but with greater chances for showers by Wednesday, and towards the end of next week.