How hot was it?

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Summer in Redding can be summed up in one word…HOT.  It is interesting that the higher the temperature gets the more specific people seem to get in describing it.  During the spring you might hear…”it was really nice weather this weekend the temperature was in the 70s.” But when we get weather like we are having now you start hear things like this…  “They said the official high in Redding today was 106 but….” “My car thermometer said 109”  “The sign on bank said 107”.  “I’ve got a really accurate thermometer on my patio and it said 110”. While I was working at the Redding weather office these are the things I heard every summer.  So really which one is right…probably all of them!!

The United States has weather records going back over 200 years in some areas.  Redding has records going back to 1875.  The thing you need to remember or understand is how the temperature is, or was, measured. The standard for years has been to measure the temperature at approximately 4 feet above the ground and shaded from the sun.  This was done for a long time by using weather shelters.  You have probably seen these white boxes at airports and weather stations.  The boxes were 4 feet above the ground, and were louvered to let the air move through and the doors faced north.  Inside was a set of thermometers.  The thermometer that measured the maximum or high temperature was a mercurial thermometer similar to the ones we used to use to take our temperatures.  There was a constriction at the bottom and the mercury would rise as it warmed up but could not go back down the tube when the temperature dropped.  This measured the instantaneous maximum temperature.  The 1950 and 60s saw electronics and remote sensing utilized in weather observations.  All class one observing stations (mostly airports and weather offices) has sensors in the field that transmitted to readouts in the office.  These readouts had a needle that would rise and fall as the temperature changed.  As it moved up it would push a thin wire so when the temperature dropped the wire would be left at the highest temperature of the day.  This was still and instantaneous high temperature reading. In the 1980s the temperature sensors became more sensitive and computerized with digital readouts in the office. Every time the temperature changed a tenth of a degree the readout would change. This led to the start of averaging temperature data over period of time or the end of using instantaneous readings.

The air is heated not by the sunlight passing through it, but from its contact with the surface of earth.  Dark surfaces become much hotter than lighter colored surfaces especially during summer.  During July and August in the late afternoon the air in the first couple hundred feet above the ground is boiling just like a pan of water on the stove.  The “bubbles” or thermals rise up from the surface and cooler air moves in to replace it.  The sensitive, digital readouts of the 1980s registered readings to the nearest tenth of a degree and during a hot summer afternoon they would be changing every few seconds.  This is why the data had to be averaged.

Now we move into the 1990’s. The NWS, due to budget cuts, was looking at what it could automate and decided that the weather observation program would be one of the first.  Prior to this at about 1000 locations (airports and weather office) around the U.S. there were people who  hourly, more frequently during critical weather, recorded the weather…cloud cover, visibility, temperature, humidity, wind, barometer or altimeter and weather events such as rain, snow, thunderstorms, fog…etc.  These observations were transmitted on a national data circuit for use by aviation interests and the general public.  During the mid 1990’s these people were replaced by the Automated Surface Observing System (ASOS).  There are now over 1100 ASOS in the U.S.  To assimilate all the data ASOS averages some of the elements like temperature and wind.  The temperature is now a five minute average.  Not just the hourly temperature by the maximum or high temperature.  This means if you went outside and took a temperature reading every minute for 5 minutes and got the following readings 108, 110, 108, 107, 107.  If I was to ask you the high temperature you would say 110 and if we were doing things the way we did before ASOS you would be right.  However, ASOS would show the high temperature for this period to be 108.  Redding’s temperature data has come from an ASOS system for the last 15 years.  I always felt that since ASOS had the minute by minute temperature that the highest temperature should be the highest one minute temperature, but was told the national standard would be a 5 minute average.  (I checked with the NWS before writing this and was told it is still a 5 minute average).

There are several ASOS in the north state, Redding, Red Bluff, Oroville, Mt. Shasta, and Alturas.  There are also many stations around the north state that are used to measure weather for fire danger.  These stations have an instantaneous or 1 minute average temperature.   There are also cooperative observers around the area that use thermometers that measure instantaneous readings.  So when you see a listing of high temperatures for cities around the north state remember you might be comparing apples and lemons.

One last point, it will be very hard for Redding to break its all time high of 118.  This is because of the variability of the temperature due to the thermals and the five minute averaging.  Since the ASOS was installed in Redding it has recorded a high temperature of 117.  The fire weather station at the Redding airport recorded 119 for 3 hours on the day ASOS showed 117.

So what does all this mean?  It’s August, it’s Redding, and therefore it’s hot and when it goes over 105 it’s really hot. Lastly the older I get the lower my threshold for defining hot and really hot.

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Chris Fontana, aka The Old Forecaster, started his career as a meteorologist with the National Weather Service (NWS) in Sacramento. After four years as a weather officer in the U.S. Air Force, Chris transferred to the NWS office in Redding, where he was the meteorologist in charge from 1976 until the office closed in 1996. From 1996 until his 2005 retirement, he was the meteorologist in charge of the U.S. Forest Service Predictive Service Unit. Chris and his wife Jane have been married over 40 years and he works as a window covering installer in her business, Westwood Window Coverings.

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Chris Fontana
-- a.k.a. "the Old Forecaster" -- started his career as a meteorologist with the National Weather Service (NWS) in Sacramento. After four years as a weather officer in the USAF he transferred to the NWS office in Redding. He was the meteorologist in charge of the Redding office from 1976 until it closed in 1996. From 1996 until his retirement in 2005, he was the meteorologist in charge of the USFS Predictive Service Unit. Chris and his wife Jane have been married over 40 years and he works as a window covering installer in her business, Westwood Window Coverings.
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