Mount Washington (New Hampshire) - Climate

Climate

The summit station of Mount Washington has an alpine climate or tundra climate (Köppen ET), though warming to a subarctic climate (Köppen Dfc) with lower elevation, although it receives an extremely high amount of precipitation, atypical for most regions with such cold weather.

The weather of Mount Washington is notoriously erratic. This is partly due to the convergence of several storm tracks, mainly from the Atlantic to the south, the Gulf region and Pacific Northwest. The vertical rise of the Presidential Range, combined with its north-south orientation, makes it a significant barrier to westerly winds. Low-pressure systems are more favorable to develop along the coastline in the winter months due to the relative temperature differences between the Northeast and the Atlantic Ocean. With these factors combined, winds exceeding hurricane force occur an average of 110 days per year. From November to April, these strong winds are likely to occur during two-thirds of the days.

Mount Washington once held the world record (still the Northern Hemisphere and Western Hemisphere record) for directly measured surface wind speed, at 231 mph (372 km/h), recorded on the afternoon of April 12, 1934. Although this record was surpassed in Cyclone Olivia in 1996, this wasn't reported as official until 2010. It can still be argued that Mount Washington holds the record for the highest surface wind speed recorded 'by man'; the new Australian record was measured by an automated station while no human was present, while the Mount Washington wind gust was actually measured by a human being. Phenomena measured via satellite or radar, such as tornadoes, hurricanes, and air currents in the upper atmosphere, are not directly measured at the Earth's surface and do not compete with either of these records.

The first regular meteorological observations on Mount Washington were conducted by the U.S. Signal Service, a precursor of the National Weather Service, from 1870 to 1892. The Mount Washington station was the first of its kind in the world, setting an example followed in many other countries. For many years, the record low temperature was thought to be −47 °F (−44 °C) occurring on January 29, 1934, but upon the first in-depth examination of the data from the 19th century at NOAA's National Climatic Data Center in Asheville, North Carolina, a new record low was discovered. Mount Washington's official record low of −50 °F (−46 °C) was recorded on January 22, 1885. However, there is also hand-written evidence to suggest that an unofficial low of −59 °F (−51 °C) occurred on January 5, 1871.

On January 16, 2004, the summit weather observation registered a temperature of −43.6 °F (−42.0 °C) and sustained winds of 87.5 mph (140.8 km/h), resulting in a wind chill value of −103 °F (−75 °C) at the mountain. During a 71-hour stretch from around 3 p.m. on January 13 to around 2 p.m. on January 16, 2004, the wind chill on the summit never went above −50 °F (−46 °C). Snowstorms at the summit are routine in every month of the year, with snowfall averaging 311 inches (7.9 m) per year. Temperatures above 72 °F (22 °C) at the summit have never been recorded.

The primary summit building was designed to withstand 300 mph (480 km/h) winds; other structures are literally chained to the mountain. In addition to a number of broadcast towers, the mountain is the site of a non-profit scientific observatory reporting the weather as well as other aspects of the subarctic climate of the mountain. The extreme environment at the top of Mount Washington makes using unmanned equipment problematic. The observatory also conducts research, primarily the testing of new weather measurement devices. The Sherman Adams summit building, which houses the observatory, is closed to the public during the winter and hikers are not allowed inside the building except for emergencies and pre-arranged guided tours.

The Mount Washington Observatory reoccupied the summit in 1932 through the enthusiasm of a group of individuals who recognized the value of a scientific facility at that demanding location. The observatory's weather data have accumulated into a valuable climate record since. Temperature and humidity readings have been collected using a sling psychrometer, a simple device containing two mercury thermometers. Where most unstaffed weather stations have undergone technology upgrades, consistent use of the sling psychrometer has helped provide scientific precision to the Mount Washington climate record.

The observatory makes prominent use of the slogan "Home of the World's Worst Weather", a claim that originated with a 1940 article by Charles Brooks (the man generally given the majority of credit for creating the Mount Washington Observatory), titled "The Worst Weather In the World" (even though the article concluded that Mt Washington most likely did not have the world's worst weather).