Is Eighty Doable?

There's lots of chatter right now about the warmth this weekend and the potential of a maximum temperature at the airport of 80ºF on Saturday or Sunday.  That would be the earliest 80˚F on record.  The current first 80˚F was observed on March 31, 2012 [Note from Jim: This was corrected from 2021, which was an error].  After April 5, all days through the summer have record maxima at or above 80˚F.  

To do this, we'll take a look at forecasts produced by the National Weather Service National Blend of Models, or NBM.  The NBM is a system that takes forecasts from many modeling systems, puts them together in a big ensemble, and then applies statistical techniques to yield forecasts, including those of maximum and minimum temperature at locations like the Salt Lake City international airport.

The NBM forecast for the Salt Lake City airport is below.  The maximum (red) and minimum (blue) temperature forecasts for the next 10-11 days are presented in the left hand panel using box-and-whisker plots to summarize the forecasts derived from all the input model forecasts.  

Source: https://hwp-viz.gsd.esrl.noaa.gov/wave1d/?col=2&hgt=1&obs=true&fontsize=1&location=KSLC

For each day, the red box denotes the middle 50% of forecasts produced by the models. This is known as the interquartile range. For Saturday, the interquartile range of maximum temperature forecasts covers 77 to 81˚F.  A horizontal line in the box denotes the median forecast, which is right in the middle of all of the forecasts. For Saturday, the median is 79˚F.  The "whiskers", which are the thin vertical lines, denote lower and upper "extremes."  Only 10% of the forecasts are at or below the lower end of the bottom whisker and only 10% of the forecasts are at or above the upper end of the top whisker.  In this case the lower "extreme" is 76˚F and the upper extreme is 82˚F.  

Roughly half of the model-derived forecasts call for a maximum temperature at or above about 80˚F.  The other half are at or below 80˚F.  It could be that the actual median is a bit above or below 80˚F.  I can't determine this without access to more than this graph, but for the purposes of this blog post, we'll call that good enough.  

Sunday is also potentially an 80ish degree day.  The interquartile range on Sunday is 78 to 84˚F, with the median also sitting very near 80˚F.  

Source: https://hwp-viz.gsd.esrl.noaa.gov/wave1d/?col=2&hgt=1&obs=true&fontsize=1&location=KSLC

Assuming these NBM forecasts are reliable and unbiased, 80˚F would be the "over/under" for maximum on Saturday and Sunday.  

Ultimately, time will tell.  Both days look nice, although the southerly winds will be picking up on Sunday and that will raise the prospects for blowing dust.