3/15/2024 0 Comments Wind chill chart bristolThat will probably be the subject of another blog post.įigures 7 and 8 show the hourly observations for McGrath and Prudhoe Bay respectively on January 27th and January 28th, 1989.įig. Rick is doing some checking on it since that station does not have any other wind chills lower than -92☏. There was one other instance of a sub -100☏ wind chill (-106☏ to be precise) but its reliability is in doubt. In addition to January 1989, I also downloaded hourly observations for any station that recorded an air temperature of -65☏ or colder in any year (sub -100☏ wind chills can occur with temperatures warmer than -65☏ but the amount of data was far too large so I cut it off at -65☏). Not just first place in January 1989 but possible first place all time. Therefore, when the formula changed, McGrath went from middle of the pack to 1st place. Using the old formula, it felt like -94☏. According to the New wind chill formula, it felt like -100☏. on January 27th 1989, the air temperature was a chilly -72☏ with a wind speed of 7 miles per hour. If you looked closely at Figure 5, you might have noticed the January 1989 minimum value for McGrath was -100☏. Difference in the lowest monthly wind chill value in January 1989 using the Old and the New methods. It is important to remember that the calculations were often, but not always, based on the same observation. Therefore I also downloaded all data for stations across Alaska with hourly observations in January 1989.įigure 4 shows the monthly minimum wind chill based on those observations using the Old formula in effect at the time and Figure 5 shows the monthly minimum wind chill based on the New wind chill formula. It was apparent that most North Slope stations recorded their lowest ever wind chill in January 1989. Of course the completeness of the data leaves a lot to be desired. None of the North Slope stations have ever recorded a wind chill lower than the -96☏ in January 1989 at Prudhoe Bay. I did some digging around at the NOAA hourly observation site and decided to download all data for stations on the North Slope. In addition, the New and Old windchill values are displayed. Air temperature, wind, and wind gust values are displayed. The New method also takes into account the attenuation of wind from the standard measurement height to the space that people occupy.įig 3. However, for low wind speeds, the New method produces slightly colder values since it assumes that the observer is walking at 1.5 m/s. In general, the New method's values are warmer than the Old values for most wind speeds. A comparison between the two formulas at 5☏ is shown in Figure 1. Clearly temperatures lower than -40☏ occur frequently in Alaska. The equation, however, can be used for any temperature and any wind speed. The air temperature in the original table ranged from +45☏ to -40☏. The New wind chill formula is actually an equation that was derived from a table with approximately 800 cells based on the wind tunnel experiments noted earlier. Due to some glaring shortcomings with the application of the 1945 study to human perception, a series of wind tunnel experiments were conducted and a New Wind Chill Index was formulated and implemented by the NWS in 2001. The study was not intended to determine equivalent temperatures but it was used for that purpose nonetheless and thus the Wind Chill Index (WCI) was born. The Old method was based on a study in 1945 that measured how long it took for water to freeze in various temperature and wind conditions in Antarctica. As most readers of this blog know, the formula for calculating wind chill changed in 2001 (a good description of the new formula and the rationale behind the change cane be found here).
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