Las Vegas Temperatures: The Plot Thickens

June 27th, 2014 by Roy W. Spencer, Ph. D.

This is my third post on Las Vegas temperatures. Not that I wanted to do 3 posts…but I keep running into “issues” regarding the thermometer data available from NCDC.

In yesterday’s post I thought I was providing the “official” USHCN temperatures for Las Vegas, as downloaded from an NCDC web page.

But there are 2 new problems:

1) that NCDC page seems to be buggy…it gives exactly the same data for maximum, minimum, and average temperatures.

2) Las Vegas is not a USHCN station anyway.

The point of my original post was to examine Las Vegas temperatures as perceived by the public. We all know it’s hot there in July, and as my two previous posts indicated, the McCarran Airport temperatures exhibit a strong urban heat island (UHI) warming signal over time (much more warming at night than during the day). The same is probably true of the North Las Vegas airport, which is where the NWS currently reports temperatures from.

So, if a record high temperature is reported on any given day in Las Vegas, it will likely be for these unadjusted, UHI-influenced temperatures…not from NCDC-adjusted USHCN temperatures (which don’t include these stations anyway).

Since there is a strong UHI warming effect there, such record setting temperatures are pretty meaningless in a climate context. With an increasing UHI effect, we expect the frequency of temperature records broken to increase over time. (Without a spurious UHI warming effect, and no global warming, we would expect the frequency of broken records to decrease over time…with 2 years of data, there’s a 50% chance of breaking a high temperature record, with 3 years, a 33% chance, etc.)

So, the bottom line remains the same. The UHI effect has probably hopelessly corrupted urban stations like Las Vegas (as Anthony Watts also concluded in his post from yesterday). Inferring anything about global warming from new temperature records set at these stations is impossible.

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