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Mapping the Summer Heat Wave in Surfer

As an avid outdoorsman in Colorado, I am always making sure I know what the current local weather pattern is going to do. Whether I’m going into Rocky Mountain National Park for a day hike, attending an outdoor show at Red Rocks amphitheater, or riding in the weekly Denver Cruiser ride, I have learned over the past 17 years that the weather in my colorful state is always unpredictable! I know I need to consult the forecast to see if I need to wear a rain jacket, pack a sweatshirt, cover myself with sunscreen, or a combination of all 3 before I embark on my journey. However, the past weeks and even few months seem to change this mode of thinking. The weather has been more predictable than past years; it’s going to be hot and dry.

There has been a lot of buzz in the media lately about El Niño and the global heatwave this summer. This piqued my interest; I was curious if Colorado was experiencing the same trend locally compared to previous years’ temperatures. My mapping professional side couldn’t balk at the opportunity to create some maps that compare the summer temperatures over past years in hopes to find some obvious temperature-increasing trends.

Mapping Approach:

For this mapping project, I have decided to use Surfer to create contour maps of Colorado’s monthly average temperate in July over the past 7 years to determine if we are seeing the same heatwave trend locally as what is being reported globally. I was able to access data from the NOAA Climate Prediction Center for the maximum daily temperature for July from 2010 through 2016. I downloaded the daily data in TIF grid format and used Surfer’s Grid | Math functionality to combine all of the data into a single, monthly average for each year. The data was also converted from Fahrenheit to Celsius for easier interpretation. To do so I used these steps:

  1. After the data was downloaded, I opened Surfer 13 and clicked Grid | Math.
  2. In the Grid Math dialog, I clicked the Add Grids button.
  3. In the Open Grids dialog, I selected all of the daily temp TIFs and clicked Open.
  4. I used the following equation for the function, named the resulting grid, and clicked OK: (((A+B+C+D+E+F+G+H+I+J+K+L+M+N+O+P+Q+R+S+T+U+V+W+X+Y+Z+AA+AB)/28) * 1.8 ) + 32
  5. I repeated these steps to create average maximum temperature grids for the rest of the years of data I downloaded.


Now all of the daily data has been averaged over the month of July for their respective years, I can create contour maps in Surfer for comparison. I created a separate contour map for each year, using the same contour interval and color map so that the maps could be easily compared to one another. The maps were scaled the same and posted next to each other to see if Colorado is on the same track as the rest of the globe. The resulting contour maps are below, showing that the monthly average temperature from year-to-year varies, but it is difficult to isolate a spatial trend between the years. I definitely cannot tell that this July is hotter than any other of the years I downloaded data for.

Surfer 2D & 3D Mapping: contour map depicting average maximum temperaturesA comparison of Contour Maps from Surfer that depict the average maximum temperatures in Colorado for July 2010 - 2016.

Mapping Approach, Part 2:

Because I was not able to see a trend across Colorado for the past 7 years from the contour maps, I decided to take a look at the data from another perspective. I wanted to see if there were any spatial temperature trends by differencing the average maximum temperature for this July to the average maximum temperature for the previous 6 years. This can easily be done by, again, using Surfer’s Grid Math feature. The monthly average temperature data can be combined into a single grid that represents the average temperature for July over the previous 6 years. The difference between the July 2016 temperature data and the 6-year average temperature data can be found by subtracting the two grids from one another. This gives me a grid of the temperature departures in July 2016 from the average over the last 6 years that can be visualized using a contour map.

To create the average monthly temperature grids for the previous 6 years:

  1. I clicked Grid | Math.
  2. In the Grid Math dialog, I clicked the Add Grids button.
  3. In Open Grid dialog, I navigated to all of the monthly temp grids and clicked Open.
  4. In the Grid Math dialog, I used (A + B + C + D + E + F) / 6 for the function, named the Output Grid File, and click OK.

To difference the monthly average grid and the July 2016 temperature grid:

  1. I clicked Grid | Math.
  2. In the Grid Math dialog, I clicked the Add Grids button.
  3. In the Open Grids dialog, I navigated to the average July grid and clicked Open.
  4. I clicked the Add Grids button again.
  5. In the Open Grids dialog, I navigate to the 6-year average grid and clicked Open.
  6. I clicked Grid | Math.
  7. In the Function box I entered A- B, I named the Output Grid File, and clicked OK.

Results, Part 2:

A contour map was generated in Surfer that shows the temperature departures for this July compared to the previous 6-year average; shown below. This map shows that the temperature in July has remained relatively unchanged for most of the central mountain region (central portion of the map) and the only notable temperature increases are in the southwest portion and on the eastern planes of Colorado.

Surfer 2D & 3D mapping software: contour map showing temperature differencesA contour map showing the degree departure in July 2016 from a 6-year average of maximum temperatures in July in Colorado.


As you can see, utilizing the differencing technique from Surfer’s Grid Math feature proved to be a better analysis approach for determining what areas in Colorado are seeing the same heatwave trend that is being reported across the US and globally than comparing contour maps. Surfer is developed by Golden Software, please feel free to take a look at the free demo version and place your orders at



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Tuesday, 21 March 2023

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