Thursday, July 12, 2012

U hits 100

This afternoon the temperature at our campus observing site on the William Browning Building (WBB) reach 100ºF for the first time this year.  Technically, it was 99.9ºF, but we'll round up.

Temperatures on the WBB over the past 30 days
Other sites on campus have hit 100 previously.  One is our observing site at our mountain meteorology lab at the mouth of Red Butte Canyon, which reached 100 yesterday and Tuesday.  

Another is the Natural History Museum, which also has reached 100 the past three days (it has actually exceed 100 the past two days, but I've cut the scale at 100 for entertainment purposes).

Such variability in temperature is not uncommon and can arise from a variety of factors including differences in instrumentation, siting characteristics, or local surface conditions.  Further, the WBB and Natural History Museum sites are on buildings with substantially different characteristics.

Note the difference in both the darkness of the surrounding surfaces and the exposure of the instruments.  The characteristics of these locations is substantially different than a NWS observing site at an airport or a fire-weather or SNOTEL station in the mountains.  

There is no "right" place to collect weather observations.  As I like to say, all observations are bad, but some are useful.  Airport observations are viewed as the gold standard by some meteorologists, but how many people live at airports?  Are these sites representative of conditions in the adjoining urban area?  For example, in the Salt Lake Valley during winter inversions, it can sometimes be 10ºF colder (or more) at the Salt Lake Airport than along the east bench.  In such conditions, the observing sites pictured above, while perhaps not ideal, provide more useful information for residents along the east bench than the Salt Lake City airport site.  

Urban and mountainous areas are particularly problematic for collecting representative observations.  Where would you cite an observing station in downtown Salt Lake City to collect a representative weather observations?  Gallavan center?  The north side of the LDS office building?  The south side of the LDS office building?  On the City County Building.  There is tremendous variability in weather conditions in urban and mountain areas, so there is no such thing as a representative observing site. 


  1. Great post. Such variability is fun stuff. I've noted how much lower the mins are in my yard compared to the airport. For many of our yards I think it also depends on height of thermometer, presence of trees, sprinklers, is a fence sheltering from wind, presence of concrete, etc etc So many variables the wonder of it is never ending.

  2. In a dry climate where humidity is low, surface evaporation around an observing site is one of the biggest factors especially during the evening and overnight hours. I once measured a temperature differential of 12 F (77 degrees vs 65) just after sunset over a grassy area, in a distance of less than 100 feet. I even measured it twice just to be sure, could hardly believe it.