Warm and Dry September Continues:
The first 19 days of September have brought extraordinary warmth to the state. The average statewide temperature for this period is the 3rd warmest in history, trailing only 1931 and 1897. Most climate stations are reporting an average monthly temperature so far that is 5° to 8°F above normal. Many climate stations have reported 14-15 days with daytime temperatures in the 80s F, while climate stations in Yellow Medicine, Redwood, Lyon, and Lac Qui Parle Counties have reported 90°F. In addition, many nights have remained warm, with low temperatures in the 60s F. Dr. Kenny Blumenfeld of the Minnesota State Climatology Office offered more insights on these warm temperatures in a commentary posted on their web site this week.
Over the last 20 days the statewide average rainfall has been less than a quarter of an inch, while many individual climate stations have reported less than a tenth of an inch. Parts of northern Minnesota received significant rains over the past week with amounts ranging from 1 to 2 inches. Along the Canadian border, both International Falls and Kabetogama have received over 3 inches of rain so far this month. A few stations reported new daily rainfall records from strong thunderstorms earlier this week on September 16 and 17. Some of these records included:
2.27 inches at International Falls
2.22 inches at Baudette
2.02 inches at Kabetogama
New outlook models from the NOAA Climate Prediction Center suggest that the dry pattern may persist through most of the rest of the month. Combined with the expected warmer than normal temperatures, this may mean that we will see a return of more areas in Moderate Drought around the state by month’s end.
Thoughts on fall colors:
The time is upon us when Minnesotans love to admire the beautiful changes in color that autumn brings. For those who are new to the state, I think you will find that the fall season is perhaps the most favored one by most residents.
The color changes are progressing this month even with the unusually warm climte. Most places around the state have been reporting temperatures that are from 5 to 8 degrees F warmer than normal. There has also been a conspicuous absence of overnight lows in the 30s F, a climate signal that most vegetation responds to in addition to the rapidly changing day length. The last time northern climate stations reported morning low temperatures in the 30s F was back on September 6 and 7. Color changes occur variably around the state, starting in far northeastern counties typically around the 3rd week of September and lasting until the first few days of October, then progressing to more southerly counties where the peak color typically occurs during the first half of October. The MN-DNR web site is a good place to check the daily progress of color changes around the state. The most recent map depicts 25% to 50% color change in portions of northwestern Minnesota and some areas of northeastern Minnesota.
One further note: Friends have often remarked that these color changes seem to be more vivid to the eye than those seen in spring green-up or during the flowering times of late spring and summer. There may be a number of reasons for this, perhaps some psychological, but two meteorological ones come to mind. The fall season usually brings an increase in atmospheric transmissivity, the ability of the atmosphere to let light pass through it. Some call this cleaner air, but whatever we choose to call it, we can see more clearly across some distance. The second feature of the climate that is evident is the declining sun angle. Sunlight strikes the landscape from much lower angles and therefore there is more reflection of light off into lateral directions observed by the human eye. Recall for example, your more frequent use of the sun visor in your car when commuting early in the morning or later in the afternoon during the fall season.
Weekly Weather Potpourri:
A recent paper published in the journal Science documents the global mean temperature back 485 million years. The study shows that the global mean temperature has ranged from 52°F to 97°F. Earth’s current global mean temperature is around 59°F. The historical global temperatures are highly correlated to global mean atmospheric carbon dioxide. Most disturbing is the current pace of change in both carbon dioxide and global mean temperature.
Earlier this week (September 15-17), a storm system characterized as a near-tropical storm, dumped very heavy and record-setting amounts of rainfall on portions of North Carolina. Observers in some coastal areas (Brunswick County) reported from 8 to 19 inches of rainfall, and Wilmington reported nearly 11 inches. Many roads were flooded and or portions of roads were washed out. The NOAA National Weather Service Office in Newport/Moorhead City offers updates on the storm and damages.
The BBC reported this week that Storm Boris brought heavy rains and devastating floods to portions of the Czech Republic, Romania, and Austria. Then later in the week the storm brought 8 to 12 inches of rain to portions of northern Italy, causing widespread flooding and landslides.
MPR listener question:
Here in La Crescent (Winona County) we have recorded exactly 0.01 inches of rainfall so far this month. What is our record driest September?
Answer:
The record driest September in La Crescent was in 1998 when only 0.30 inches of rain fell. Elsewhere in Winona County, the driest September at Minnesota City was in 1952 with just 0.18 inches, and the driest September in Winona was in 1979 with just 0.24 inches of rain. I noted that the evening of September 19th this week brought nearly an inch of rainfall to La Crescent, so that will help ease the recent dryness of the landscape.
Twin Cities Almanac for September 20th:
The average MSP high temperature for this date is 71 degrees F (plus or minus 10 degrees F standard deviation), while the average low is 53 degrees F (plus or minus 9 degrees F standard deviation).
MSP Local Records for September 20th:
MSP records for this date: highest daily maximum temperature of 92 degrees F in 2022; lowest daily maximum temperature of 47 degrees F in 1875; lowest daily minimum temperature of 28 degrees F in 1962; highest daily minimum temperature of 75 degrees F in 1895, and record precipitation of 1.82 inches in 1902. There was a trace of snowfall on this date in 1927.
Average dew point for September 20th is 48°F; the maximum dew point on this date is 70°F in 1970 and the minimum dew point on this date is 22 degrees F in 1930.
All-time state records for September 20th:
The state record high temperature for this date is 99 degrees F at Fairmont (Martin County) in 1891 and at Montevideo (Chippewa County) in 1984. The state record low temperature for this date is 14 degrees F at Karlstad (Kittson County) in 1973. The state record precipitation for this date is 5.54 inches at Halstad (Norman County) in 2017. The statewide snowfall record for this date is 4.0 inches at Caribou 2S (Kittson County) in 1947.
Past Weather:
Climate observers in Kittson, Koochiching, and St Louis Counties in far northern Minnesota all reported an exceptional early season snowfall on this date in 1947. Up to 4 inches of snow fell in Kittson County.
A hard freeze ended the growing season on September 20 of 1973. Many climate stations reported morning lows in the 20s F. Observers in Kittson, Roseau, and St Louis Counties reported morning low temperatures in the teens. The afternoon high at Babbitt only reached 50°F.
Very warm temperatures prevailed across western and southern Minnesota on September 20 of 1984. Observers in 37 counties reported afternoon temperatures in the 90s F. After a morning low of 48°F, citizens of Montevideo (Chippewa County) saw the afternoon temperatures climb 51°F to reach 99°F.
Outlook:
Still warm temperatures on Saturday with slight chances for rain, then cooler for Sunday and Monday, and still chances for showers in far southern Minnesota. A warming trend will start on Wednesday of next week with mostly dry weather to follow.
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