The warm season of 2021 in Minnesota has been marked by persistent dry weather from the late spring through the bulk of the summer. However, since the second half of August, much of Minnesota has been closer to the main storm track, so beneficial rains have occurred. Still, with thunderstorms being the primary method of getting rain fall, the highest totals have been spotty. The St. Cloud Regional Airport picked 3.82 inches of September rain, 0.81 inches above average. That rain has mainly provided some ground moisture, but has only kept up with the average since the rains began in late August.

The table below shows the extremes of the dry period, with the biggest precipitation deficit of over seven and a half inches between the beginning of May and August 19. Since August 19, the St. Cloud Airport has 7.79 inches, nearly two and a half inches above normal, and more than an inch and a half above the total for the previous three and a half months.

During the driest part of this warm season (May 1-August 19), St. Cloud Regional Airport had only 6.03 inches of rain compared to the 13.80 inch average.

The May through September period of 2021 now ranks as the 21st driest of the 140 years on record (13.21 inches actual, 17.65 inches average), but that's significant improvement from the 9th driest May-August.

Much More Rain Just to West, Less to East and South

Other nearby areas have had substantially more rainfall. Much of Morrison, Stearns, Meeker, and Kandiyohi Counties picked up over 5 inches (red) during September (see NWS Minnesota September rainfall). St. Cloud State University had 4.60 inches of rain in September. On the other hand, Sherburne and Benton Counties got much less rain with large parts under 4 inches (light tan).

The lingering effect of the moisture shortfall can be seen in other ways. While the ground is wetter from the recent rainfall, allowing streamflow to climb back to average from the Minnesota River southward, the Mississippi River upstream of the Twin Cities is still in the lowest quarter of streamflows. Nearly all rivers and streams in the northern third of the state is still very short on flow. This is because much of west central and northern Minnesota are more than 8 inches short on precipitation for the year thus far. Some areas are more than 16 inches short. That's where the extreme drought remains, while central Minnesota is now either in moderate or severe drought. The extreme drought category (red) ended in central Minnesota when the rains of late August began. There has been further easing of the severe drought (brown) area during September (set comparison of August 31 to September 28 for Minnesota).

The recent rainfall has left only 31 percent of the near surface soil moisture to be short or very short. Still, more than 50 percent of the deeper soil moisture is still short in the state.

The more frequent rainfall did produce one batch of notable severe weather. A combination of straight-line wind damage and some brief tornadoes hit the southern Twin Cities area on the morning of September 17. Most of the thunderstorms merely produced welcome rainfall.

Warmer Than Average September Blossoms Late in Month

Temperature-wise, September in St. Cloud was warm again, but that was due to unusual warmth during the second half of the month. Each of the first 15 days of September were within 4 degrees of average. As the average temperatures cooled, however, late September produced nearly as warm conditions as seen early in the month. 5 days were at least 10 degrees warmer than average during the second half of September. The warmest highs of 89 degrees, were set on the 16th and 19th. And, there were a pair of 83-degree highs on the last two days of the month. Each came within a degree of breaking a record warm high. September 30 did in fact produce a record warm low of 60 degrees and a record warm average of 72 degrees. Overall, the 62.6 degrees average was 3.1 degrees above normal, marking the warmest September since 2015. It was the 21st warmest September of the 140 Septembers on record.

There were no 90 degree highs in September as the temperature was one degree short on the 16th and 19th. That means that St. Cloud had 20 highs of at least 90 degrees, tying 2006 and 2007 for the most since 1988. However, the two September 89's meant there were a total of 6 days falling one degree short this summer.

There was one 39 degree low during September on the 22nd. That's the closest the temperature came to freezing at the St. Cloud Airport. However, there was frost in some other parts of central Minnesota during that cool outbreak. So, the first St. Cloud frost will come later than the median date of September 26 (see average last and first frost dates from NOAA via the Minnesota State Climatology Working Group).

Better Than Average Chance for Dry Weather Late Sept-Early Oct

As noted above, the warmth was concentrated late in the month. That correlates with the finding of Professor Don Baker of the University of Minnesota. He found that the most likely time of the year for high pressure in the Northern Plains was the last week of September and the first week of October. This particular trend held up this season, so it's something to keep in mind for wedding and other outdoor plans.

    September 2021 Statistics