New Climate Normals For the U.P.

New Climate Normals for the U.P.

 1) What Are Climate Normals?

    The U.S. Climate Normals are 30-year averages of many pieces of weather information collected from thousands of weather stations nationwide. As these records are updated each decade an old decade is dropped and a new one is added. Beginning this month, when you hear that a day was hotter, or colder, or rainier than normal, that “normal” will be a little different from what it was in the past. 

    When this update occurred on August 1, 2011, the averages previously determined by using data from 1971 to 2000 were dropped and the new averages were calculated by using data collected from 1981 to 2010. The general methods for calculating climate “normals” were established in the 1930s by the World Meteorological Organization (WMO), and they are still followed by the United States and many nations all over the world.

 


2) Comparison of New and Old Climate Normals

 

NWS Marquette
1971-2000 1981-2010
Maximum Temp. (°F) 48.0 49.6
Minimum Temp (°F) 29.4 30.3
Average Temp. (°F) 38.7 40.0
Precipitation (inches) 36.3 35.7
Snowfall (inches) 184.5 203.3

 

Houghton
1971-2000 1981-2010
Maximum Temp. (°F) 49.0 48.9
Minimum Temp (°F) 32.1 31.8
Average Temp. (°F) 40.6 40.4
Precipitation (inches) 33.8 27.8
Snowfall (inches) 220.8 207.7

 

Iron Mountain
1971-2000 1981-2010
Maximum Temp. (°F) 53.3 53.5
Minimum Temp (°F) 30.1 30.9
Average Temp. (°F) 41.7 42.2
Precipitation (inches) 30.0 29.7
Snowfall (inches) 63.3 58.4

 

 Ironwood 1971-2000 1981-2010
Maximum Temp. (°F) 49.7 49.6
Minimum Temp (°F) 29.2 30.3
Average Temp. (°F) 38.5 40.0
Precipitation (inches) 34.7 34.9
Snowfall (inches) 180.3 188.2

 



3) How Has the Climate Changed?

 

a) Temperature Changes

     Overall temperatures have risen with the new normals; however, some areas such as Houghton and Ironwood have actually seen maximum temperatures remain  nearly steady or decrease slightly during the spring and summer months.  Each location shown below has actually seen maximum temperatures increase during the fall and winter months.  Overnight lows are generally warmer for each location, especialy during the winter months.  The low temperatures at Houghton appear to follow a similar trend; however, overnight lows in the spring, summer and fall have actually cooled when compared with the previous normals. 

   
   
Left click to enlarge the image.

 

b) Snow Fall Total Changes

      The normal snowfall totals have increased at the National Weather Service office near Marquette as well as in the Ironwood area.  The Marquette WFO has seen the normal snowfall totals increase by 18.8 inches, while the Ironwood location has seen an increase of 7.9 inches.  Houghton and Iron Mountain have both seen snowfall totals decrease with the new normals.  The new normals at Houghton have decreased by 13.1 inches and at Iron Mountain the new normals have decreased by 4.9 inches. 

Left click to enlarge the image.

 


4) Weather Frequencies for NWS Marquette

    The following are tables for the total number of days that had a recorded high and low temperature, precipitation amount, and snowfall total that occurred in each respective range during each 30 year climate normal span. The difference represents the change in frequencies with the new set of climate normals (1981-2010).

* Note: The 1981-2010 span consists of one less day because there was one fewer leap year day during that span than between 1971 and 2000.

 a) Maximum Temperature


 Maximum TemperatureF) - Total

1971-2000 1981-2010 Difference
<10 276 222 -54
10 to 19 740 681 -59
20 to 29 1453 1453 0
30 to 39 1742 1732 -10
40 to 49 1270 1323 53
50 to 59 1293 1324 31
60 to 69 1589 1513 -76
70 to 79 1647 1695 48
80 to 89 859 906 47
>89 89 108 19

    Looking at the graph above, there has been a notable decrease in the number of daytime highs less than 20°F, as well as between 60 and 69°F. On the other hand, the number of daytime highs above 70°F has increased, as have those between 40 and 59°F. 

    The decrease in daytime highs below 20°F reveals that the 2000's had a much warmer set of high temperatures than the 1970's. The 1970's contained several cold winters, with 3 of the top 4 coldest Michigan winters between 1971-2010 falling within this decade (1977-1979).

    While the drop in high temperatures between 60 and 69°F oddly stands out among the increase for all other temperature ranges above 40°F, it actually indicates another warming trend.  A deeper look at September high temperatures shows that there has been a significant increase in the number of warmer days during the month.


 Max TempF) - Sept.

1971-2000 1981-2010 Difference
<60 294 266 -28
60 to 69 340 301 -39
>69 266 333 67

    The increase in the number of daytime highs above 70°F is a result of warmer summertime high temperatures. The chart below shows the general increase in the number of high temperatures that have reached 80°F or higher.


b) MinimumTemperature 


 Minimum TemperatureF) - Total

1971-2000 1981-2010 Difference
<-20 55 43 -12
-20 to -11 311 253 -58
-10 to -1 611 569 -42
0 to 9 932 919 -13
10 to 19 1287 1244 -43
20 to 29 1916 1983 67
30 to 39 1903 1903 0
40 to 49 1784 1816 32
50 to 59 1637 1637 0
>59 522 590 68

    As with maximum temperatures, there has been a shift of minimum temperatures to the warmer side. The largest decrease has been associated with low temperatures below 0°F, while the greatest increase has occurred with lows above 59°F.  The main cause for the decreasing and increasing trends can be found within the winter and summertime lows, respectively, which are broken down into the tables below.

   

 Minimum TemperatureF) - Dec to Feb

1971-2000 1981-2010 Difference
<-20 46 32 -14
-20 to -11 267 214 -53
-10 to -1 482 455 -27
0 to 9 612 604 -8
10 to 19 680 721 41
>19 531 591 60

    Wintertime lows have increased greatly, with number of very cold nights, <-0°F, seeing nearly a 12% reduction. Once again, by dropping the 1970's from the climate normals, 3 of the 4 coldest winters over the last 40 years were removed from the data set.


 Minimum TemperatureF) - Jun to Aug

1971-2000 1981-2010 Difference
<40 200 174 -26
40 to 49 877 863 -14
50 to 59 1226 1213 -13
>59 457 510 53

    Though not as substantial as the wintertime lows, summertime lows have also seen a marked increase.  The number of warm (>59°F) summer time lows has increased by more than 11%. 


c) Daily Precipitation

   

 Precipitation (inches) - Total

1971-2000 1981-2010 Difference
0.00 and Trace 6098 6037 -61
0.01 to 0.10 2553 2587 34
0.11 to 0.30 1231 1274 43
0.31 to 0.50 476 500 24
0.51 to 1.00 416 390 -26
1.01 to 2.00 165 151 -14
>2.00 19 18 -1

    The new climate normals show that there has been a decrease in the number of days that recorded rainfall totals greater than 0.50". Nearly all of the decrease occured during the summer months (June-August) because it is the most common time of year to see heavier rainfall, mainly from thunderstorms. On the other hand, there was an increase in the number of precipitation events with values >0.10" during the winter months. This parallels the monthly new climate normals, which show a general increase in precipitation during the winter months.

    The chart below breaks down the precipitation frequencies for the summer months of June, July and August.

 


 d) Daily Snowfall


 Snowfall (inches) - Total

1971-2000 1981-2010 Difference
0.0 and Trace 8352 8262 -90
0.1 to 1.0 1340 1314 -26
1.1 to 2.0 465 485 20
2.1 to 4.0 401 436 35
4.1 to 8.0 273 306 33
8.1 to 12.0 80 94 14
>12.0 47 60 13

    Though there are noticeable changes in snowfall amounts with the new climate normals, the combination of different measuring methods and potential observer biases over the 40 year span do not allow for a scientific analysis of these numbers. 


 5) Weather Frequencies for Houghton County Airport

    The following are tables for the total number of days that had a recorded high and low temperature that occurred in each respective temperature range during each 30 year climate normal span. The difference represents the change in frequencies with the new set of climate normals (1981-2010).  Precipitation and snowfall data is not included because precipitation amounts may or may not be reflective of true amounts because of frozen precipitation, and snowfall data is not continuously taken at the airport, respectively.

* Note: There are 50 days of missing data from this location between 1971 and 2010. However, 45 of the 50 days of missing data fall between 1981 and 2000 (February 1995 is completely missing), and therefore affect both sets of data and do not alter the results. Other missing data outside of the 1981-2000 range are as follow: September 15th and 16th, 1972; November 11th and 12th, 2001; December 5th, 2001.

 

 Maximum TemperatureF) - Total

1971-2000 1981-2010 Difference
<0 32  21  -11
0 to 9  248  196  -52
10 to 19  775  718  -57
20 to 29  1366  1359  -7
30 to 39  1848  1858  10
40 to 49  1313  1349  36
50 to 59  1313  1360  47
60 to 69  1604  1560  -44
70 to 79  1634  1705  71
>79  776  780  4

   Analysis of the data from Houghton is a little more difficult due to a moderation of climate due to its proximity to Lake Superior .  Many of the trends that were seen in the NWS Marquette data are also apparent in the Houghton data.  The main difference between the two is the slight downward trend in minimum temperatures above 40 degrees, with the largest change in that range occuring during the month of May.    


 Minimum TemperatureF) - Total

1971-2000 1981-2010 Difference
<-10  74 65  -9
-10 to -1  379  342  -37
0 to 9  976  951  -25
10 to 19  1309  1256  -53
20 to 29  1728  1806  78
30 to 39  2014  2104  90
40 to 49  1842  1837  -5
50 to 59  1887  1856  -31
>59  697  691 -6

 



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