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Preliminary September climate summary

Preliminary September climate summary

Mean monthly temperature values for most southern Minnesota observers ranged from 1 to 2 degrees F warmer than normal, while several northern Minnesota communities reported monthly means that were 1 to 2 degrees F cooler than normal. The extremes for the month were 98 degrees F at Brownton (McLeod County) on the 12th and just 16 degrees F at Warroad on the 21st. Many observers reported overnight lows in the teens and 20s F and some reported new record lows (for example 19 F at Warroad on the 18th and 16 F there on the 21st were both new daily record lows). Killing frosts were widespread in nearly all areas during the month, but crops were fully mature and suffered little damage. Minnesota reported the coldest temperature in the 48 contiguous states on six days during the month.

The real story for September was the dryness due to absence of rainfall. Many observers reported measurable rainfall amounts on only 2-3 days, resulting in one of the driest Septembers in history on a statewide basis. The driest September was 1952 when the statewide average rainfall was just 0.57 inches. This year's statewide value will be close to that one. Many observers clearly reported their driest September in history, including Windom (0.30"), Moorhead (0.19"), Willmar (0.14"), Collegeville (0.08"), and Morris (0.03"). For Morris and Collegeville it was one of their driest months in history as well.

At the University of Minnesota Research and Outreach Centers located at Crookston, Morris, and Lamberton, measured stored soil moisture values in the top 5 feet of soil were at or below the all-time lowest values ever measured for the end of September. In addition the flow volume measured on many Minnesota rivers was below the historical 10th percentile, indicating extremely low water levels.

As of the end of September the U.S. Drought Monitor placed all or parts of 45 Minnesota counties in severe to extreme drought, most notably in southwestern, south-central and northwestern Minnesota. In total over 35 percent of Minnesota's landscape was designated to be in severe or extreme drought, the largest fraction of the state since the fall of 2006. The only Minnesota county not designated to be drier than normal is Cook in the far northeast.

The DNR reports very high wildfire danger ratings in many western and northwestern counties. A number of counties in northwestern and north-central Minnesota have burning restrictions in place. The National Weather Service issued a number of Red Flag Warnings during the month due to high fire danger ratings. Wild fires were reported this week near Warroad, Park Rapids, Cloquet and Little Falls.

Peak wind gusts over 40 mph were reported from a number of observers during September. Rochester reported peak winds of 55 mph on September 4-5.

Weekly Weather potpourri

From Brad Rippey, Office of the USDA Chief Economist, USA highlights for the drought-monitoring period ending on September 25 include:
-Nearly two-thirds (65.45%) of the contiguous U.S. is in drought. This is a new U.S. Drought Monitor record (January 2000 to present).
-Corn in drought stands at 84%, down from a July peak of 89%.
-Soybeans in drought are at 80%, down from a July high of 88%.
-Hay in drought continues to rise (currently 69%), due to the westward shift of the core drought area into the Plains’ major hay production areas.
-Cattle in drought continues to rise (currently 76%), due to the westward shift of the core drought area into the Plains’ major cattle areas.
-Winter wheat in drought stands at 73%. Nationally, planting is one-quarter (25%) complete. Soil moisture shortages are most acute across the northwestern half of the Plains.

NOAA is seeking citizen interested in helping to classify the intensity of historical tropical storms and hurricanes. In a project titled NOAA describes the need for citizens to analyze color-enhanced satellite images from 30 years of tropical storm monitoring. They hope to use the resulting data sets to gain a better understanding of the intensification and dissipation of tropical storms and enhance forecasting capabilities. If you want to participate in the project you can learn more about it here.

Super Typhoon Jelawat was spinning in the western Pacific Ocean this week off the east coast of Taiwan. It was producing winds of 150 mph with higher gusts, and sea wave heights near 50 feet. The storm is expected to bring high seas, strong winds and heavy rains to Kyoto, Japan this coming weekend.

The NOAA Storm Prediction Center has filed only 26 reports of tornadoes in the USA so far in September. This is less than half the historical average for September and continues the trend of low tornado numbers that started in the month of July. The record lowest year for September tornadoes in the USA was 1952 when only 1 report was filed.

An article published this week in Science provides an analysis of paleo-climates in Utah and Nevada (14,000 to 20,000 years ago) that supports the hypothesis that a stronger summer monsoon season in the desert southwest fed and maintained the massive glacial lakes that were on the landscape then. Clearly the North America weather pattern was vastly different when ice occupied much of Canada. In this wetter period the earliest settlements were established by native people in much of the desert southwest. You can read more about this study here.

MPR listener question

You mentioned the high winds observed around the state this year. But have there also been an unusual number of days with south or southeast winds?

Answer: Examining the climate of wind direction for southern Minnesota using monthly wind roses, I find that wind blows from the south to southeast direction about 20 to 30 percent of the time during the April through September period. The peak month for southeast winds is August. Taking the data from this year (2012) south to southeast winds were more frequent and stronger than average during the months of April, May, June, and July this year. The S-SE winds have been less frequent than average during August and September. The peak strength of south-southeast winds occurred in May and June as several days brought winds from that direction at peak wind speeds over 40 mph.

Twin Cities Almanac for September 28th

The average MSP high temperature for this date is 65 degrees F (plus or minus 11 degrees F standard deviation), while the average low is 45 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for September 28th

MSP weather records for this date include: highest daily maximum temperature of 91 degrees F in 1898; lowest daily maximum temperature of 43 degrees F in 1908; lowest daily minimum temperature of 26 F in 1942; highest daily minimum temperature of 64 F in 1905; and record precipitation of 1.21 inches in 1891; Record snowfall is a trace in 1907 and 1945.

Average dew point for September 28th is 44 degrees F, with a maximum of 70 degrees F in 1971 and a minimum of 24 degrees F in 1942.

All-time state records for September 28th

The state record high temperature for this date is 97 degrees F at Argyle (Marshall County) in 1952. The state record low temperature for this date is 15 degrees F at Pipestone (Pipestone County) and Tower (St Louis County) in 1899 and at Grand Rapids (Itasca County) and Alborn (St Louis County) in 1942. State record precipitation for this date is 3.65 inches at St Peter (Nicollet County) in 1901; and the state record snowfall for this date is 2.0 inches at Ada (Norman County) and Detroit Lakes (Becker County) in 1899.

Past Weather Features:

An early season snow storm crossed northern Minnesota on September 28, 1899 bringing snow from Fergus Falls to Mount Iron in the northeast. Ada, Park Rapids, Moorhead, and Detroit Lakes all received over 1 inch of new snow. Following the snow storm, temperatures plummeted into the teens F in some areas.

Thunderstorms brought heavy rain to parts of southern Minnesota on September 28, 1901. Fairmont and Winnebago received over 1.50 inches of rainfall, while St Peter received a record-setting 3.65 inches.

September of 1952 was the driest in state history. In addition over the 27th and 28th strong south winds brought unusually warm weather for so late in the season. Over 20 Minnesota communities saw the mercury reach 90 degrees F or greater over these two days. There were a number of wild fires reported that month.

September 28-29, 1965 brought thunderstorms and heavy rains to southern Minnesota. Over 2 inches of rainfall was reported in Winona, Spring Grove, Preston, Lanesboro, Austin, Caledonia, Slayton, and Bricelyn. Over 4 inches of rain fell in Harmony, producing some local street flooding. In fact Harmony reported their wettest September in history with 13.43 inches of rainfall.


Warm and dry, with plenty of sunshine to end the month of September this weekend. And warm early next week as well, with a chance for showers in the northeast. Much cooler by Thursday and Friday as a more fall-like air mass invades the region.
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