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A Record Setting Day
For weatherphiles, those of us who love weather in all its varied forms, extreme or rare weather events often hold the greatest allure. Spawned by our love of statistics, one extreme event that catches our attention is the record-breaking day. The local news reports love to feature a record-setting weather day. The most frequent are temperature extremes. Whether a record hot day or record cold day, it is sure make headlines. Temperature records are kept for annual extremes, monthly extremes and daily extremes. Today wherever you are, there are record maximum and minimum for the date lurking in some data set.
If I told you that today's weather set a record for either the maximum or minimum temperature, you would likely respond with a modicum of interest. If I told you that this day broke both the daily maximum and minimum temperature record, you might exhibit degree of incredulity. How can both records be broken on the same day? Can't happen, you say. Ahhh, but it can, and, though a rare event, has happened across the United States more than a couple dozen times. I call such days: double record days.
Before I tell you how both records could be broken on the same day, I must set a couple ground rules. First, what records are we talking about? Here, I am looking at the temperature extremes of hot and cold during one specific calendar day, be it May 27 or December 2, and how the specific readings on that day in 1935 or 2003 related to the extremes measured on all of those dates over the course of the climatological station's observational history.
Second, the climatological station at which the events occurred must have a data history at least several decades long. If the data span is too short, the odds of breaking a temperature record, even both, are fairly high. For example, the first year of record-keeping sets the initial marks for both maximum and minimum temperatures. So that day doesn't count. The next year on that date, the extreme temperatures may break either the maximum or the minimum mark of the previous year, or both, or neither. As the length of record increases, the likelihood of breaking either temperature extreme decreases as does the likelihood of breaking both within the same day.
How Can Both Maximum and Minimum Records Be Set on the Same Day?
While any day can potentially set new temperature extremes for both the maximum and minimum, certain weather situations are more likely to do so. As well, certain locations have a greater likelihood to experience a double record day. In the United States, for example, most double-record days have occurred in the arid and mountainous western regions of the nation: Utah and Nevada. But Florida has registered a couple events as has Hawaii.
Many such events likely occurred on days when extremely clear, dry air and light winds dominated the day's weather. Drought might also be present. Such days allow the greatest gain and loss of radiation that affect the surface air temperature. During such days, these conditions allowed maximum solar heating which can push late afternoon temperatures to a new record high. But those conditions at night also permitted the surface's heat to rapidly escape through strong thermal radiation, allowing plummeting temperatures to exceed the record low at times.
One such occurrence happened on August 1, 1998 at the AustinBergstrom Airport in Texas. A persistent high-pressure ridge restricted winds and cloud cover, and regional drought and dry soils made the air mass extremely dry. These factors were ideal for maximum surface solar heating and nocturnal surface radiation heat loss. Dry soil encourages maximum solar heating because nearly all the incident sun's energy goes to heating the soil rather than evaporating its moisture. On this day at Bergstrom Airport, the low sunk to 65oF (18.3oC) while the high soared to 104oF (40oC).
In some cases, the passage of an extreme cold front following a period of unseasonable record warmth has dropped temperatures to record low levels. One notable event came on November 11, 1911 (or as it was written at that time: 11-11-11), and double records were set at many locations. At Oklahoma City, Oklahoma, the record high of 83oF (28.3oC) plunged to 17oF (-8.3oC). Both daily temperature records remain unbroken and untied today, 93 years later. The drop was caused by a remarkably sharp cold front passing across the central Great Plains and Midwest, and many sites saw the temperature plummet 50F degrees (28C degrees) in one hour. On the same day, Kansas City, Missouri experienced a double record day with high of 76oF (24.4oC) and low of 11oF (-11.7oC) as did Springfield, Missouri: high 80oF (26.7oC) / low 13oF (-10.6oC).
In a few other events, a late-day, severe thunderstorm that produced hail can quench record heat when icy downdraft winds fall rapidly from towering cumulonimbus. This may have been the case in Melbourne, Florida where a record hot afternoon temperature of 97oF (36.1oC) dropped to a record low of 68oF (20oC) on May 22, 1998.
An opposite weather situation can occur when record morning cold is followed by a strong, hot fohn-type wind, such as a chinook or Santa Ana, blowing across the site. Fohn winds descend from mountain ridges heating its air through compression during descent. They are known to rapidly raise air temperatures by dozens of degrees. An example occurred at Bakersfield, California on January 3, 1930. At dawning, Bakersfield residents awoke to a chilly morning low of 23oF (-5oC), which tied the date's record minimum. But a fohn wind later descended the Kern County Mountains into the San Joaquin Valley with air heated to 75oF (23.9oC). That temperature established a new January 3rd record maximum at Bakersfield.
Finally, some double records are just fortuitous. Sioux City Iowa had theirs on May 16, 1997 when a high of 91oF (32.8oC) and low of 33oF (0.6oC) were measured. On no earlier date in spring had the Sioux City record low temperature been so high, and on only one May date was the record high temperature any lower.
Along a similar vein, some sites such as Quillayute Airport near Forks, Washington, generally have a very small daily range temperature. This airport is located along the Pacific coastline, west of the Olympic Mountains, and its weather is often cloudy most of the day. As a result of the shoreline location and constant clouds, the normal temperature range is small, around 12F degrees (6.7C degrees) in winter and 20F degrees (11.1C degrees) in late summer, and its record temperatures often have a small spread. But on June 25, 2000, the daily range became much wider, and Quillayute experienced a record minimum of 40oF (4.4oC) and maximum of 81oF (27.2oC).
Double Record Days of Note
I have located over couple dozen double record days in the American weather records (most listed in Chris Burt's fabulous new book Extreme Weather). Though they must exist, I have not yet found any double-record days for Canada or any other country, but like many others in the US, they likely have occurred but are hidden in the database.
Here are some of the more interesting of the American double records.
The greatest temperature range found for a double-record day occurred at Las Vegas (Sunrise Manor site), Nevada on July 13, 1972 when the blistering record high of 119oF (48.3oC) plunged to a chilly 48oF (8.9oC): a 71F-degree (39.4C-degree) drop. In contrast the smallest range occurred at Hilo, Hawaii: only 28F degrees (15.5C degrees) separated the high of 88oF (31.1oC) and low of 60oF (15.6oC) on May 26, 2003. Interestingly, Hilo had set a double record the previous day (May 25) with a high of 90oF (32.2oC) and low of 60oF (15.6oC).
August 2002 saw six double records set across the American West: twice each at Alamosa, Colorado, and Park City, Utah. Stafford Arizona and Rapid City, South Dakota set double records that month as well. At Rapid City on the 17th, the daily records were nearly all-time monthly records as well. The low of 38oF (3.3oC) fell just one F degree (0.6C degree) shy of the month's all-time low. The high of 101oF (38.3oC) was 5F degrees (2.8C degrees) off the August record.
Cold Bay, Alaska set daily maximum and minimum records on the same day three times within a 12-month period. September 25, 2000 saw a minimum of 29oF (-1.7oC) and maximum of 58oF (14.4oC). Then on May 14, 2001 these records were observed: minimum 27oF (-2.8oC); maximum 52oF (11.1oC). And finally, on June 16, 2001, new temperature records were set for minimum 30oF (-1.1oC) and maximum 64oF (17.8oC).
Most recently, Olympia, Washington experienced a double-record day. On March 14, 2005, they had record high and low temperatures of 67oF (19.4oC) and 25oF (-3.9oC), respectively.
Note, since American weather records are still kept in Fahrenheit, I have given the records in that unit first rather than the global Celsius standard.
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