Editing Mount Washington (section)

== Climate ==
{{climate chart
| Mount Washington
|−4.1|13.6|6.44
|−2.4|14.7|6.77
|  5.0 | 20.7 | 7.67
| 17.4 | 30.4 | 7.44
| 29.8 | 41.3 | 8.18
| 39.5 | 50.4 | 8.40
| 44.0 | 54.1 | 8.77
| 43.0 | 53.3 | 8.32
| 36.1 | 47.1 | 8.03
| 24.0 | 36.4 | 9.27
| 13.3 | 28.1 | 9.85
|  1.7 | 18.4 | 7.73
| units = imperial
| float = right
| clear = both
|maxprecip = 80
| source = NOAA<ref name = "NWS Gray, ME" /> }}

The summit station of Mount Washington has an [[alpine climate]] or [[Tundra#Climatic classification|tundra climate]] ([[Köppen climate classification|Köppen]] ''ET''), although it receives an extremely high amount of precipitation, atypical for most regions with such cold weather. However, elevations just beneath treeline have a [[subarctic climate]] (Köppen ''Dfc'') which eventually transitions to a [[humid continental climate]] (Köppen ''Dfb'') near the mountain's base and the surrounding lower elevations.<ref>{{cite web |title=Mount Washington Observatory: Distance Learning |publisher=[[Mount Washington Observatory]] |url=http://www.mountwashington.org/education/distancelearning/  |access-date=2010-11-13 |archiveurl=https://web.archive.org/web/20110616021240/http://www.mountwashington.org/education/distancelearning/ |archivedate=2011-06-16 |author=MWOBS |date=2009 }}</ref>

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 Coast of the United States|Gulf region]] and the [[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 area]]s are more favorable to develop along the coastline in the winter due to the relative temperature differences between the northeastern United States and the Atlantic Ocean. With these factors combined, hurricane-force wind gusts are observed from the summit of the mountain on average of 110 days per year. These extreme winds also contribute to the mountain's very short treeline, with elevations as low as {{convert|4400|ft}} being too hostile to support any plant life more than a few inches (centimeters) in height.<ref name=avalanchecenter>{{cite web |title=Weather |website=Mount Washington Avalanche Center |url=http://www.mountwashingtonavalanchecenter.org/avalanche-safety/weather/ |access-date=2015-02-12 |archiveurl=https://web.archive.org/web/20150220150020/http://www.mountwashingtonavalanchecenter.org/avalanche-safety/weather/ |archivedate=2015-02-20 |date=2012 |author=Mount Washington Avalanche Center }}</ref><ref>{{cite web |url=https://www.nhstateparks.org/getmedia/d90d59e7-0a31-43e3-99a5-859f19f115c8/Mount-Washington-Ecology.pdf |title=Mount Washington Ecology |website=www.nhstateparks.org |access-date=2023-02-04 |date=2010-05-21 |author=Division of Parks and Recreation (New Hampshire State Parks) |archive-date=September 9, 2022 |archive-url=https://web.archive.org/web/20220909024946/https://www.nhstateparks.org/getmedia/d90d59e7-0a31-43e3-99a5-859f19f115c8/Mount-Washington-Ecology.pdf |url-status=live }}</ref>

Mount Washington once held the world record, and still holds the [[Northern Hemisphere]] and [[Western Hemisphere]] record, for directly measured surface wind speed, at {{convert|231|mi/h|km/h|0|abbr=on}}, recorded on the afternoon of April 12, 1934. A new wind speed record was discovered in 2009: on April 10, 1996, Tropical [[Cyclone Olivia]] had created a wind gust of {{convert|408|km/h|abbr=on}} at [[Barrow Island (Western Australia)|Barrow Island]] off the western coast of Australia.<ref>{{cite web |date=January 22, 2010 |title=Info note No.58 — World Record Wind Gust: 408&nbsp;km/h |publisher=World Meteorological Organization |url=https://public-old.wmo.int/en/media/news/new-world-record-wind-gust |archive-url=https://web.archive.org/web/20231218171508/https://public-old.wmo.int/en/media/news/new-world-record-wind-gust |url-status=dead |archive-date=December 18, 2023 |access-date=May 18, 2016 }}</ref>

The first regular meteorological observations on Mount Washington were conducted by the [[Signal Corps (United States Army)|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 {{convert|-47|°F|1}} occurring on January&nbsp;29, 1934, but upon the first in-depth examination of the data from the 19th century at [[National Oceanic and Atmospheric Administration|NOAA]]'s [[National Climatic Data Center]] in [[Asheville, North Carolina]], a new record low was discovered. Mount Washington's official record low of {{convert|-50|°F|1}} was recorded on January 22, 1885. The official record low daily maximum is {{convert|-28|°F|1}} on February 6, 1995.<ref name="NWS Gray, ME" /> Highs of {{convert|0|F|C K}} or below occur on 13 days annually, while lows at or below {{convert|0|F|C K}} can be expected from November 17 through April 1; from December to March, temperatures rise above freezing ({{convert|0|C|F K}}) on only 15 days.<ref name="NWS Gray, ME" />

On January 16, 2004, the summit weather observation registered a temperature of {{convert|-43.6|°F|°C|1|lk=on|abbr=on}} and sustained winds of {{convert|87.5|mph|km/h|1|abbr=on}}, resulting in a [[wind chill]] value of {{convert|-102.59|F|1}} at the mountain.<ref name="wudg">{{cite web |title=History for Mt. Washington, NH |publisher=Weather Underground |url=http://www.wunderground.com/history/airport/KMWN/2004/1/16/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA |access-date=March 8, 2008 |archive-date=June 18, 2022 |archive-url=https://web.archive.org/web/20220618012603/http://www.wunderground.com/history/airport/KMWN/2004/1/16/DailyHistory.html?req_city=NA |url-status=live }}</ref> During a 71-hour period from approximately 3&nbsp;p.m. on January&nbsp;13 to 2&nbsp;p.m. on January&nbsp;16, 2004, the wind chill on the summit never went above {{convert|-50|°F|1}}.<ref name="wudg" /> The official record high temperature at the summit is {{convert|72|°F|1}} on June 26, 2003, and August 2, 1975,<ref name="Mount Washington Normals, Means, and Extremes" /> while the official record high daily minimum is {{convert|60|°F|1}}, recorded on the latter date.<ref name="NWS Gray, ME" /> Readings of {{convert|60|°F|1}} or higher at the summit are seen an average of 13.5 days annually.<ref name=NCDCtxt />

On [[February 2023 North American cold wave|February 3&ndash;4, 2023]], overnight wind gusts of over {{Convert|100|mph|km/h}} and a temperature of {{Convert|-47|F|C|1}} combined to produce a new US record low windchill temperature of {{convert|-108|F|C|1}},<ref>{{Cite web |last=Pulver |first=Dinah Voyles |date=2023-02-04 |title=Mount Washington wind chill: New Hampshire summit fell to minus 108 F, likely lowest recorded |url=https://www.usatoday.com/story/news/weather/2023/02/04/mount-washington-wind-chill-new-hampshire-summit-minus-108-f/11185558002/ |access-date=2023-02-04 |website=USA TODAY |language=en-US |archive-date=February 4, 2023 |archive-url=https://web.archive.org/web/20230204125945/https://www.usatoday.com/story/news/weather/2023/02/04/mount-washington-wind-chill-new-hampshire-summit-minus-108-f/11185558002/ |url-status=live }}</ref> breaking the previous figure of {{Convert|-103|F|C|1}}.<ref>{{Cite web |date=2023-02-04 |title=Meteorologist describes record-breaking cold atop Mount Washington |url=https://www.wmur.com/article/meteorologist-describes-record-breaking-cold-atop-mount-washington/42763378 |access-date=2023-02-04 |website=WMUR |language=en |archive-date=February 4, 2023 |archive-url=https://web.archive.org/web/20230204125950/https://www.wmur.com/article/meteorologist-describes-record-breaking-cold-atop-mount-washington/42763378 |url-status=live }}</ref><ref>{{Cite news |last=Fadulu |first=Lola |date=2023-02-04 |title=Mount Washington set a record for coldest wind chill ever recorded at minus 108 degrees. |language=en-US |work=The New York Times |url=https://www.nytimes.com/2023/02/04/nyregion/mount-washington-cold-new-hampshire.html |access-date=2023-02-04 |issn=0362-4331 |archive-date=February 4, 2023 |archive-url=https://web.archive.org/web/20230204180255/https://www.nytimes.com/2023/02/04/nyregion/mount-washington-cold-new-hampshire.html |url-status=live }}</ref> Temperatures remained at or below -45&nbsp;°F for 13 straight hours on February 3&ndash;4, 2023, and a -47&nbsp;°F reading from the morning of February 4, 2023 was the coldest reading in 89 years, tying a previous record low observed in January 1934.<ref>
  {{cite web
  | url = https://www.mountwashington.org/experience-the-weather/observer-comments.aspx?id=59058
  | title = Brutal Cold on Mount Washington: A Weather Story
  | publisher = Mount Washington Observatory
  | accessdate = 2023-02-26}}</ref>

The primary summit building was designed to withstand {{convert|300|mi/h|km/h|abbr=on}} winds; other structures are chained to the mountain.<ref name=backpacker>{{cite journal |date=April 2007 |title=Nature Phenomenon |journal=[[Backpacker (magazine)|Backpacker]] |page=46}}</ref> 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 creates strong winds and ice at the top of Mount Washington making the use of 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<ref name=nhstateparks>{{cite web |title=Mount Washington State Park |website=The New Hampshire Division of Parks and Recreation |url=http://www.nhstateparks.org/explore/state-parks/mount-washington-state-park.aspx |access-date=2015-02-12 |archive-url=https://web.archive.org/web/20150203131026/http://www.nhstateparks.org/explore/state-parks/mount-washington-state-park.aspx |archive-date=2015-02-03 |url-status=dead}}</ref> and hikers are not allowed inside the building except for pre-arranged guided tours.<ref name="Alan Smith">{{cite journal | title=The Mount Washington Weather Observatory - 50 Years Old| last1=Smith| first1=Alan A.| journal=Bulletin of the American Meteorological Society| volume=63 |pages=986 |number=9 |date=September 1982| doi=10.1175/1520-0477(1982)063<0986:TMWOYO>2.0.CO;2| bibcode=1982BAMS...63..986S| doi-access=free}}</ref>

In 1932, the [[Mount Washington Observatory]] was built on the summit through a group interested in and noting the worth of a research facility at that demanding location.<ref name=bruceheald1>{{cite book |last=Heald |first=Bruce D. |date=2011 |title=The Mount Washington Cog Railway: Climbing the White Mountains of New Hampshire |publisher=The History Press |isbn=978-1-60949-196-3 |page=72}}</ref> The observatory's weather data have accumulated a climate record since. Temperature and humidity readings have been collected using a [[Hygrometer|sling psychrometer]], a simple device containing two [[Mercury-in-glass thermometer|mercury thermometer]]s. 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.<ref name="ukint">{{cite web |title=Product Testing and Research Capabilities with Mount Washington Observatory |publisher=[[Mount Washington Observatory]] |url=http://www.ukintpress-conferences.com/uploads/SPMTWX13/Mainstream_Conference_d3_s1_p2_Cyrena-Marie_Briede.pdf |access-date=March 18, 2016 |author=Briede, Cyrena-Marie |archive-date=March 27, 2016 |archive-url=https://web.archive.org/web/20160327122404/http://www.ukintpress-conferences.com/uploads/SPMTWX13/Mainstream_Conference_d3_s1_p2_Cyrena-Marie_Briede.pdf |url-status=live }}</ref>

The observatory makes prominent use of the slogan "Home of the World's Worst Weather", a claim that originated with a 1940 article in ''Appalachia'' magazine by Charles Brooks, the man generally given the majority of credit for creating the Mount Washington Observatory. The article was titled "The Worst Weather in the World" even though it concluded that Mount Washington most likely did not have the world's worst weather.<ref name="Alan Smith" /><ref>{{cite journal |last1=Brooks |first1=Charles F. |title=The worst weather in the world |journal=Appalachia |date=1940 |url=http://www.davidalbeck.com/hiking/worstweather.html |pages=194–202 |access-date=May 23, 2007 |archive-date=March 12, 2015 |archive-url=https://web.archive.org/web/20150312170015/http://www.davidalbeck.com/hiking/worstweather.html |url-status=live }}</ref>

===Image gallery===
<gallery widths="200px" heights="160px">
File:2016-09-03 14 08 03 Observation tower at the Mount Washington Observatory on Mount Washington in Sargent's Purchase Township, Coos County, New Hampshire.jpg|[[Mount Washington Observatory]]
Image:Mount Washington chained building.jpg|The original weathered [[Wood shingle|shingle]]-clad building is chained to the ground, here covered in [[hard rime|rime ice]] in early April.
Image:Mt. Washington, NH.jpg|The summit of Mount Washington is frequently obscured by clouds.
</gallery>

=== Precipitation ===
[[File:Monthly Climate Normals (1991-2020) - MOUNTWASHINGTON, NH.svg|thumb|right|Climate chart for Mount Washington]]
Due in part to its high prominence, to its situation at the confluence of two major storm tracks, and to the north–south orientation of the Presidential Range ridgeline, which it crowns, Mount Washington receives high levels of precipitation, averaging an equivalent of {{convert|91.2|in|mm|sigfig=3|abbr=on}} of rain per year,{{efn|Measurable ({{convert|0.1|in|mm|abbr=on|disp=or}}) precipitation occurs on an average 210 days annually, with 26 of those days seeing {{convert|1|in|mm|abbr=on|disp=or}} or more.}} with a record high for a calendar year of {{convert|130.14|in|mm|1|abbr=on}} in 1969<ref>{{cite web| url=http://www1.ncdc.noaa.gov/pub/data/special/maxann.pdf| title=Record Maximum Annual Precipitation by State (thru 1998)| publisher=NOAA National Centers for Environmental Information| access-date=March 29, 2016| archive-date=March 4, 2016| archive-url=https://web.archive.org/web/20160304113723/http://www1.ncdc.noaa.gov/pub/data/special/maxann.pdf| url-status=live}}</ref> and a low of {{convert|71.34|in|mm|1|abbr=on}} in 1979. Monthly precipitation has ranged from {{convert|0.75|in|mm|1|abbr=on}} in October 1947 to {{convert|28.70|in|mm|1|abbr=on}} in October 2005.<ref name="Mount Washington Normals, Means, and Extremes" /> Large amounts of precipitation often fall in a short period of time: in October 1996, a record {{convert|11.07|in|mm|1|abbr=on}} of precipitation fell during a single 24-hour period. A substantial amount of this falls as snow, with a seasonal{{efn|The snow season is defined as July 1 through June 30 of the following calendar year}} average of around {{convert|280|in|m|sigfig=2}} of snow; seasonal accumulation has ranged from {{convert|75.8|in|m|abbr=on}} in 1947–48 to {{convert|566.4|in|m|abbr=on}} in 1968–69.<ref name="NWS Gray, ME" /> The record amount of snowfall in a 24-hour period, {{convert|49.3|in|cm|1|abbr=on}}, occurred in February 1969, which is also the snowiest month on record with {{convert|172.8|in|m|abbr=on}}.<ref name="Mount Washington Normals, Means, and Extremes" />
{{Mount Washington, New Hampshire weatherbox}}
{{Graph:Weather monthly history
| table=ncei.noaa.gov/weather/Mount Washington.tab
| title=Mount Washington monthly weather statistics
}}