Abrupt reversal in temperatures, but still high humidity

Abrupt reversal in temperatures, but still high humidity:

After an exceptionally cool start to the month of September when temperatures were averaging 7°F to 9°F below normal with many overnight lows in the 30s F up north, the temperature trend has abruptly reversed itself since last Friday (September 12). Many days have brought afternoon high temperatures in the 80s and even 90s F (55 reports of daily highs in the 90s F since last Friday). And some very warm nights as well, with lows in the upper 60s to low 70s F. MSP tied a record warm minimum temperature for September 15th with a reading of 72°F and at least 7 other climate stations reported record warm minimum temperatures as well.

With the forecast calling for above normal temperatures for the balance of the month, it is safe to say that this will be a warmer than normal month of September, despite the cold start to the month. BTW, the current MN-DNR Fall Color update shows that across portions of central and northern Minnesota, the fall color progress is between 25 to 50 percent towards peak values as of September 18th.

Rainfall has been highly variable for the month so far, with many northern areas reporting above normal amounts, and much of the southern part of the state reporting below normal amounts. Both Mora (Kanabec County) and Brainerd (Crow Wind County) have reported over 4 inches of rainfall so far, well above normal. But, portions of western and southern Minnesota have seen less than half an inch. Though some areas of the state are in need of more rainfall, there are no reports of drought anywhere in Minnesota currently, according to the U.S. Drought Monitor.

One feature of the Minnesota climate that has been relatively consistent so far this September is the high humidity. The majority of hourly data show that humidity levels have mostly ranged between 60 and 90 percent this month, very high for this time of year. As a consequence, many gardeners have observed more mildew, moss, molds, mushrooms, and other fungi in their yards, as well heavy dews in the morning. Drier air is expected to prevail later next week.

Weekly Weather Potpourri:

This week’s AGU-EOS Bulletin features an interesting article about communicating climate extremes as statistical anomalies (numerically) or as impactful events with serious consequences. The authors stress that communicating the impact of climate extremes is more effective when using proper geographical and historical context. Communicating this way may more likely provoke community response to adapt or help mitigate climate change.

According to a news release from the U.K. Meteorological Office, recent research on the application of machine-learning models to the task of predicting seasonal weather outlooks shows great promise. Tests run to compare the forecast accuracy of machine-learning (AI) models with that of dynamical physics based models show them to be very competitive and useful for specific geographies.

It is a busy week for the Joint Typhoon Warning Center as they track the development of three separate Tropical Storms in the Western Pacific Ocean. The most threatening of these storms may be the one named Regasa which is likely to become a strong typhoon as it strengthens over the weekend and heads towards Hong Kong. We will likely see this storm in the news next week.

New seasonal outlooks from the NOAA Climate Prediction Center favor a warmer than normal October, November, and December for at least the southern half of Minnesota. Most model estimates suggest equal chances for above or below normal precipitation during this period. A few models suggest a drier than normal pattern. 

MPR listener question:

We heard that there were a number of tornadoes in North Dakota and South Dakota last Sunday. Was there any severe weather in western Minnesota? 

Answer:

Yes, last Sunday from midday into the evening there were two reports of tornadoes in South Dakota, and 21 reports of tornadoes in North Dakota. Fortunately, they were in the rural landscape and inflicted little damage. There were also many reports of large hail in Nebraska. The storm system did not maintain continuity as it reached Minnesota, though it did bring some high winds to southwestern areas of the state. Portions of Rock and Pipestone reported strong thunderstorms with gusts up to 70 mph, and there was a loss of power in Pipestone for a time with some wind damage to rural buildings. BTW North Dakota is on a record-setting pace for tornado reports this year, upwards of 70 reports so far. 

Twin Cities Almanac for September 19th:

The average MSP high temperature for this date is 72 degrees F (plus or minus 11 degrees F standard deviation), while the average low is 53 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for September 19th:

MSP records for this date: highest daily maximum temperature of 94 degrees F in 1895; lowest daily maximum temperature of 48 degrees F in 1918; lowest daily minimum temperature of 33 degrees F in 1991; highest daily minimum temperature of 72 degrees F in 1940; and record precipitation of 2.98 inches in 1907. There was a trace of snow on this date in 1927.

Average dew point for September 19th is 51°F; the maximum dew point on this date is 72°F in 1907 and the minimum dew point on this date is 25 degrees F in 1937. 

All-time state records for September 19th:

The state record high temperature for this date is 104 degrees F at Beardsley (Big Stone County) in 1895. The state record low temperature for this date is 16 degrees F at Alborn (St Louis County) in 1929. The state record precipitation for this date is 6.56 inches at Harmony (Fillmore County) in 2019. A record 7.3 inches of snow fell at Milaca (Mille Lacs County) on this date in 1905. 

Past Weather:

July-like weather dominated Minnesota on September 19 of 1895. Over 30 climate stations reported record-setting daily high temperatures mostly in the 90s F. The afternoon temperature reached 100°F or higher in four western counties. After a morning low of 53°F the temperature rose to a high of 104°F at Beardsley (Big Stone County.

Widespread frosts were reported around Minnesota on the morning of September 19 in 1929. Frosts occurred as far south as Olmsted County, and many northern areas saw morning lows in the 20s F and afternoon high temperatures just reach the mid to upper 40s F. The frost brought an abrupt end to the agricultural growing season.

Thunderstorms brought very heavy rains and flash flooding to portions of southeastern Minnesota over September 19 of 2019. Many areas reported 3 to 5 inches of rainfall and portions of Fillmore County saw over 6 inches of rain, with some rural roads washed out. September of 2019 proved to be record-setting for many parts of southeastern Minnesota with monthly rainfall totals ranging from 9 to 12 inches. 

Outlook:

Warmer than normal temperatures over the weekend and much of next week. There will be daily chances for showers and thunderstorms cropping up at least through Tuesday of next week. After that a drier pattern is expected, but still with warmer than normal temperatures prevailing through the end of the month.