Editing Atmospheric pressure (section)

== Mean sea-level pressure ==
<!-- target for redirect [[Sea level atmospheric pressure]] -->
[[File:Day5pressureforecast.png|thumb|left|Map showing atmospheric pressure in mbar or hPa]]
[[File:Mslp-jja-djf.png|thumb|15-year average mean sea-level pressure for June, July, and August (top) and December, January, and February (bottom). [[ECMWF re-analysis|ERA-15]] re-analysis.]]
[[File:Aircraft altimeter.JPG|thumb|Kollsman-type barometric aircraft [[altimeter]].]]

The ''mean sea-level pressure'' (MSLP) is the atmospheric pressure at [[mean sea level]]. This is the atmospheric pressure normally given in weather reports on radio, television, and newspapers or on the [[Internet]].{{Citation needed|date=December 2024}}

The ''[[altimeter setting]]'' in aviation is an atmospheric pressure adjustment.

Average ''sea-level pressure'' is {{cvt|1013.25|hPa|inHg mmHg}}. In aviation weather reports ([[METAR]]), [[QNH]] is transmitted around the world in hectopascals or millibars (1 hectopascal = 1 millibar). In the [[United States]], [[Canada]], and [[Japan]] altimeter setting is reported in [[inches of mercury]] (to two decimal places). The United States and Canada also report ''sea-level pressure'' SLP, which is adjusted to sea level by a different method, in the remarks section, not in the internationally transmitted part of the code, in hectopascals or millibars.<ref>[http://www.flightplanning.navcanada.ca/cgi-bin/Fore-obs/metar.cgi?NoSession=NS_Inconnu&format=dcd&Langue=anglais&Region=can&Stations=CYVR&Location= Sample METAR of CYVR] {{Webarchive|url=https://web.archive.org/web/20190525162442/https://flightplanning.navcanada.ca/cgi-bin/Fore-obs/metar.cgi?NoSession=NS_Inconnu&format=dcd&Langue=anglais&Region=can&Stations=CYVR&Location= |date=2019-05-25 }} Nav Canada</ref> However, in Canada's public weather reports, sea level pressure is instead reported in kilopascals.<ref>{{citation |url=http://www.cbc.ca/montreal/weather/s0000635.html |title=Montreal Current Weather |publisher=CBC Montreal, Canada |access-date=2014-03-30 |archive-date=2014-03-30 |archive-url=https://web.archive.org/web/20140330055543/http://www.cbc.ca/montreal/weather/s0000635.html |url-status=live }}</ref>

In the US weather code remarks, three digits are all that are transmitted; decimal points and the one or two most significant digits are omitted: {{cvt|1013.2|hPa}} is transmitted as 132; {{cvt|1000|hPa|kPa}} is transmitted as 000; 998.7{{nbsp}}hPa is transmitted as 987; etc. The highest ''sea-level pressure'' on Earth occurs in [[Siberia]], where the [[Siberian High]] often attains a ''sea-level pressure'' above {{cvt|1050|hPa|psi inHg}}, with record highs close to {{cvt|1085|hPa|psi inHg}}. The lowest measurable ''sea-level pressure'' is found at the centres of [[tropical cyclone]]s and [[tornado]]es, with a [[Atmospheric pressure#Records|record low]] of {{cvt|870|hPa|psi inHg|comma=off}}. A system transmitting the last three digits transmits the same code (800) for 1080.0 hPa as for 980.0 hPa.