Defrosting Truckee’s cold spot legacy
After a very cool and wet spring, summer has arrived with a vengeance. A dome of high pressure over the region has forced afternoon temperatures in Truckee to 90 degrees, but well shy of the July 1972 record of 97 degrees.Meanwhile, the unrelenting triple-digit heat in Reno has set a new record there for consecutive days with a temperature exceeding 100 degrees.Fortunately for those of us living or visiting the Truckee-Lake Tahoe region during this western heat wave, overnight low temperatures of around 50 degrees are cool enough for comfortable sleeping without air conditioning. This dramatic diurnal swing between daily high and low temperatures is a classic feature of our high altitude climate. It is also an intricate part of why, in the contest to determine bragging rights for America’s coldest community, Truckee ranks in the top 10. New residents are usually surprised to learn that their new hometown often records more national low temperatures than just about anywhere else in the lower 48 states.
Cold honorsOut of the nearly 8,000 reporting weather stations in the U.S., Truckee often registers the lowest temperature in the nation, but not during the winter ski season as one might expect. These chilly temperatures are noteworthy because they occur from June through early October, when residents and visitors are more interested in golf, tennis and fishing. The selected criteria for cold spot status does not pertain to a community’s annual average temperature; rather it is determined by counting the number of days per year any given location recorded the lowest temperature in the nation. In that category, Truckee has a reputation as a perennial top contender. Other regional players are Mammoth Lakes and Bodie, Calif. The abandoned ghost town of Bodie, located at 8,300 in a high-elevation basin, consistently ranks as the No. 1 location with the most recorded national lows. In 2001, rangers at Bodie reported the coldest temperature in the country on 167 days, which blew away all competition nationwide. Mountain town’s lowSimilar to Bodie and Mammoth Lakes, altitude and topography are primary factors in Truckee’s elite status as a nationally recognized cold spot. Located at the Truckee Tahoe Airport, the official thermometer is situated at 5,900 feet above sea level. Since the atmosphere cools at an average lapse rate of about 3.5 degrees Fahrenheit for every 1,000 feet gained in elevation, Truckee’s average low temperatures are about 20 degrees cooler than sea level locations.
Topography also plays a vital role in this equation. On clear nights, cool air from the high mountains surrounding the airport sinks downslope and into the Martis Valley, a high-elevation basin. This dense air mass settles into the airport basin, creating a chilled microclimate. The fact that the airport thermometer is located within this cold air drainage contributes significantly to Truckee’s nippy readings. This is why the coolest temperatures are recorded at the Truckee Tahoe Airport, not at the U.S. Forest Service ranger station above town.Spring and fallTruckee records the bulk of its “coldest in the nation” readings from late spring through early fall. High pressure tends to dominate West Coast weather during the summer and autumn months. This large, semi-stationary air mass forces vigorous cold fronts to track far to the north, providing the Sierra Nevada with a mild and dry summertime climate. The air under this dome of high pressure contains very little moisture. With low levels of humidity in the air, there is nothing to trap and hold the sun’s heat. As soon as the sun sets, temperatures plummet. The same principle applies to deserts, known for scorching heat during the day followed by frigid nights.This high-pressure regime also fosters calm, windless evenings in Sierra basins, which inhibits atmospheric mixing. Without breezes to stir up the night air, the dense cooler air settles to the ground with warmer air aloft. This nocturnal inversion, known as such because air aloft is normally colder than at the surface, keeps Truckee’s average minimal morning temperatures near the airport hovering in the upper 30s during the summer. In addition, Truckee’s typically cloud-free evening sky allows accumulated daytime heat to escape rapidly back into the atmosphere, a dynamic known as radiational cooling. Another component that contributes to extreme temperature fluctuations is distance from any large body of water. Oceans and large lakes, like Tahoe, heat up and cool off slowly while land surfaces gain and lose heat much more rapidly. Truckee’s afternoon temperatures are usually significantly higher than those recorded near Lake Tahoe, but at night plunge quickly, and are often 10 degrees colder by sunrise, even more during winter.
Locals knowBecause Truckee is often the nation’s coldest spot on early summer mornings, the town’s reputation is considered a tongue-in-cheek joke among locals who enjoy the Sierra’s relatively balmy winters. Despite this chilling combination of topographic and atmospheric ingredients, the local Chamber of Commerce has little to worry about. Truckee’s frosty mornings are offset by rapid daytime heating, so its monthly average temperatures, especially in winter, are much warmer than the real cold spots in the hinterlands of Minnesota, Montana, and Wyoming.Even on summer days when it isn’t the nation’s icebox, Truckee usually is within a few degrees of America’s other famous cold cities – West Yellowstone, Mont., Stanley, Idaho, and Frazier, Colo. Just for the record, out of the last 20 years, Truckee has made the top five rankings 11 times. And three of those years, 1991, 1993 and 1994, Truckee claimed the dubious honor of coldest spot in the nation, excluding Alaska. Mark McLaughlin’s column, “Weather Window,” appears monthly in the Sierra Sun. His award-winning books, “Western Train Adventures: The Good, the Bad & the Ugly” and “Sierra Stories: Trues Tales of Tahoe, Vol. 1 & 2” are available at local bookstores. Mark, a Carnelian Bay resident, can be reached at firstname.lastname@example.org.