Friday, July 22, 2016

Graphics With Strange Color Schemes

Over past decades meteorologists have tended to use certain colors of contours and shading to denote the character of the fields shown. For example, moisture/precipitation fields have usually been depicted using greens for higher values and browns for lower. Temperatures have been shown in blues (cool colors for colder conditions) and reds (warmer colors for hotter conditions). For example, the standard depiction of cold fronts in blue and warm fronts in red. However, with the huge proliferation of graphics during recent years, these old approaches seem to be slip sliding away.

Graphics above are from the Tucson NWS webpage and relate to precipitation during the first third of the NWS defined monsoon calendar period from June 15 through September 30th. Upper left shows estimated rainfall for the period (June 15 through July 20) - source is unknown, but may be some combination of gauge observations and radar estimates. There is some green but low amounts are in cool colors. At lower right is percent of normal with the color scale completely reversed relative to upper left; a great way to cause some confusion.

Graphic below is also percent of normal, but for July 13 through 19. This plot uses more typical colors for dry and moist areas, and is from NWS Climate Prediction Center. The useful legend at bottom provides some quantitative information about what has been plotted and gridded. The week shown was certainly a grim one for the Southwest and most of northern Mexico.

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