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Friday, April 7, 2017

Dissecting climate trends in Minnesota month by month

Dissecting climate trends in Minnesota month by month:

Several people have asked me in recent years if our Minnesota climate is changing more in certain months of the year than others. This is difficult depending on which climate attribute you are looking at. On a statewide basis I have looked at monthly temperatures and monthly precipitation and their measured changes over the past 100 years. Taking each value I have looked at the net change in mean monthly temperature and mean monthly precipitation per decade over the past 100 years and compared this net change to the 100 year average. Here are some examples:

For temperature, the biggest change has occurred in January with the monthly mean value now (most recent decade) that is 3.7°F higher than it was a century ago. This is a 57 percent increase relative to the 100 year mean monthly value for January temperature of 6.5°F (from a statewide calculation). By most statistical criteria this is a significant change in mean monthly temperature. Another example is the change in average February temperature. It is now 5.8°F greater than it was a century ago, and this represents 48 percent of the 100-year mean value for the month of 12.1°F. Some other months with significant changes in mean temperature are:
December: +3.0°F increase
March: +4.2°F increase
November: +2.9°F increase
The month with the least change in mean temperature is July, which shows a plus 1°F or about 1 percent of the 100-year mean monthly value. Overall on a statewide basis the mean annual temperature in Minnesota has increased by 2.4°F over the past 100 years, which is about 6 percent of the 100-year mean annual temperature (40.1°F).

The pattern of temperature increase in the Twin Cities climate record is somewhat similar, but with different magnitude. For example February is the month that has increased the most in the Twin Cities Metro Area with a rise of 5.2°F.

A similar analysis for monthly precipitation shows some significant disparities of change between months on a statewide basis. Here are some of the results: October has seen an increase in total monthly precipitation of 0.52 inches, which represents 27 percent of the 100-year mean value (1.92 inches). April has seen a rise of 0.42 inches, which represents 20 percent of the 100-year mean monthly value, and December precipitation has increased by 0.27 inches, which represents 33 percent of the 100-year mean monthly value (0.81 inches). Overall on a statewide basis mean annual precipitation has increased by 2.82 inches, about 11 percent of the 100-year annual mean (25.98 inches).

For the Twin Cities, there are some different changes in precipitation. August has seen the largest change in mean monthly precipitation increasing by 1.02 inches over what it was a century ago. April monthly precipitation has increased by 0.91 inches, a value that represents nearly 43 percent of the 100-year monthly mean (2.12 inches). And September is the only month in the Twin Cities climate record that is now less than it was 100 years ago. There has been a decrease of 0.59 inches in mean September precipitation, a decline that represents 20 percent of the 100-year monthly mean value (2.90 inches). Overall the Twin Cities mean annual precipitation has increased by 3.51 inches, about 13 percent of the 100-year mean value (27.38 inches).

Clearly the pace of change in these climate attributes shows some differences depending on what month of the year is examined.

Kite Flying Time:

Though peak wind speeds in Minnesota are associated with the tornadoes and severe thunderstorms of summer, "average daily wind speeds" peak in the month of April. Most communities around the state report average wind speeds of 12 to 15 mph during this month. This makes for great kite flying weather, but also has implications for the farmer and the home gardener as exposed soils and vegetation can dry out very rapidly in the absence of adequate rainfall. The atmosphere in April can also be so dry that sometimes when combined with higher wind speeds the National Weather Service will have to issue "Red Flag Warnings" with their daily forecasts. Perhaps we don't need to worry about this as it looks like it is going to be a wetter than normal month.

Weekly Weather Potpourri:

For the first time the National Adaptation Forum is coming to Minnesota. It will be held over May 9-11 at the St Paul River Center. There will be 80 symposia and 30 working group/training sessions focusing on the practice of climate adaptation. Mayor Chris Coleman of St Paul will be a featured speaker on the first day, and a number of Minnesota scientists and citizens, along with state and local units of government will be featured. Might be worth a look for those interested in the practice of climate adaptation.

NOAA scientist recently offered a map viewer to examine the extent of sea level rise and its effect on coastal communities. It provides a tool for examining the impact in the most vulnerable areas. More information can be found at the NOAA Digital Coast web site.

Tropical Cyclone Ernie was churning off the northwest coast of Australia this week, packing wind gusts over 120 mph and producing sea waves of 30 to 35 feet. It was expected to grow stronger over the weekend but remain out to sea.

There is an interesting article in the current AGU EOS issue about the role of nitrous oxide in the atmosphere, especially in high latitudes. More study is needed to determine its potential role in future climate change.

MPR listener question:

This time of year you and your colleagues in the National Weather Service always remind us about severe weather season. When is Severe Weather Awareness Week this year?


Severe Weather Awareness Week in Minnesota will be from April 17 to April 21. There will be daily announcements that week about types of severe weather, communications protocols, and recommendations to protect yourself and your family. In addition there will be "tornado drills" on April 20th at 1:45 pm and 6:45 PM.

Twin Cities Almanac for April 7th:

The average MSP high temperature for this date is 53 degrees F (plus or minus 12 degrees F standard deviation), while the average low is 33 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for April 7th:

MSP weather records for this date include: highest daily maximum temperature of 83 degrees F in 1991; lowest daily maximum temperature of 25 degrees F in 1923 and 1936; lowest daily minimum temperature is 6 degrees F in 1936; highest daily minimum temperature of 54 degrees F in 1991; record precipitation of 1.72 inches in 1919; and a record snowfall of 8.3 inches also in 1923.

Average dew point for April 7th is 27°F; the maximum dew point on this date is 54°F in 2001; and the minimum dew point on this date is 0°F in 1936.

All-time state records for April 7th:

The state record high temperature for this date is 91 degrees F at Canby (Yellow Medicine County) in 1991. The state record low temperature for this date is -16 degrees F at Tower (St Louis County) in 1982. State record precipitation for this date is 3.52 inches at Blue Earth (Faribault County) in 2006; and record snowfall is 24.0 inches at Tower (St Louis County) in 2008.

Past Weather Features:

A rare late winter storm brought heavy snow to parts of Minnesota over April 6-8, 1923. Many central Minnesota communities reported 5 to 12 inches of snow. Though plagued by much colder temperatures, northern residents reported only traces of snow from this storm.

Following a snow storm on April 6, 1936, a polar air mass brought the coldest April 7th in state history. Over 30 Minnesota communities reported subzero morning temperatures and daytime highs barely climbed into the 20s and 30s F. It was short-live as temperatures returned to normal two days later.

April 7, 1991 was the warmest in state history, as over 60 communities reported daytime highs of 80°F or greater. Many climate stations never fell below 60 degrees F even at night, and Winona reported a balmy low temperature of 70 degrees F.


Much warmer on Saturday under mostly sunny skies. Temperatures will reach the 60s in the north, and the 70s F and 80s F in the south. More clouds on Sunday and a chance for rain and even thunderstorms by later in the day. Continued chance for rain, and even some snow in the north on Monday. Near normal temperatures again by Tuesday, then another warming trend with a chance for showers next Thursday.


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