In order to provide pilots with a better understanding of winds at the Salt Lake City International Airport (SLC), the frequency of sustained wind speeds and wind gusts of 25 knots or greater has been studied.

I created a 30-year climatology of wind speed at SLC from 5/1971 through 4/2001 by using hourly surface observations excluding special observations. The climatology consists of the frequency of sustained wind speeds and wind gusts in knots per month. A total of 24 graphs were made to illustrate the distribution of the wind per month.

The frequency of wind gusts of 25 knots or greater for the 30-year period was 2.1 percent with March having the greatest at 2.99 percent and October the least at 1.5 percent. The windiest period is from March through May and least windy from September through January with the exception of November. Since this time of year is typically a transitional period between winter and summer, higher wind gust frequencies in November and the spring seem logical.

However, the frequency of sustained wind speeds of 25 knots or greater for the 30-year period was 0.4 percent sustained wind speeds show a different result with February having the greatest at 0.62 percent and October with the least at 0.16 percent. The windiest period is from November through May with the least windiest from June through October. It seems logical that time of year with the greatest occurrence of synoptic storms would have the higher wind speeds, however, it is unclear why February has the greatest frequency of sustained wind speeds of 25 knots or greater. March has the second highest frequency and November, January, April, and May all roughly have the next highest frequency.

Convection during the summer contributes to the higher wind speeds but are relative low compared to the winter and spring. The indisputable best time of year to fly is the September and October when there is little convection and when there are few synoptic systems.

The graphics depicting the frequency of monthly wind gusts shows a tendency for the peak frequency to occur around 25 knots. Also notice that the frequency of wind gusts is greatly diminished above 30 knots.

The frequency of winds in excess of 30 knots for the 30-year appreciably decreases. Whereas the frequency of wind gusts of 25 knots or greater is 2.1 percent and sustained wind speeds of 25 knots or greater is 0.5 percent, this decreases to 0.4 percent and 0.03 percent for 31 knots or greater, respectively. When this frequency is represented in number of hourly occurrences per year, the number of occurrences with wind gusts and sustained wind speeds of 25 knots or greater is 184 and 44, respectively. For winds of 31 knots or greater, the frequency decreases to 35 and 3 hours, respectively.

Jonathan Slemmer