Editing Weather map (section)

== Types ==
[[file:Ifr.gif|thumb|Alaskan aviation weather map]]

=== Aviation maps ===

[[Aviation]] interests have their own set of weather maps. One type of map shows where VFR (visual flight rules) are in effect and where IFR (instrument flight rules) are in effect. Weather depiction plots show [[flight ceiling|ceiling]] height (level where at least half the sky is covered with clouds) in hundreds of feet, present weather, and cloud cover.<ref>{{cite web|author=Unisys Corporation|year=2009|url=http://weather.unisys.com/surface/details.html#rule|title=Surface Data Details|access-date=2010-02-07}}</ref> Icing maps depict areas where icing can be a hazard for flying. Aviation-related maps also show areas of turbulence.<ref>{{cite web|author=Jeppesen|url=http://www.jeppesen.com/wlcs/html/wx_hazmap.html |title=Weather Help|access-date=2010-02-07|date=2008-05-06 |archive-url = https://web.archive.org/web/20080607110837/http://www.jeppesen.com/wlcs/html/wx_hazmap.html |archive-date = 2008-06-07}}</ref>

=== Constant pressure charts ===
[[file:Jetstreak.png|thumb|left|An upper-level jet streak. DIV areas are regions of divergence aloft, which usually leads to surface convergence and cyclogenesis]]

Constant pressure charts normally contain plotted values of temperature, humidity, wind, and the vertical height above sea level of the pressure surface.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=constant-pressure-chart1|author=Glossary of Meteorology|date=June 2000|title=Constant-pressure chart|publisher=[[American Meteorological Society]]|access-date=2010-02-06|archive-url=https://web.archive.org/web/20110606084509/http://amsglossary.allenpress.com/glossary/search?id=constant-pressure-chart1|archive-date=2011-06-06|url-status=dead}}</ref> They have a variety of uses. In the mountainous terrain of the western United States and Mexican Plateau, the 850 hPa pressure surface can be a more realistic depiction of the weather pattern than a standard surface analysis. Using the 850 and 700 hPa pressure surfaces, one can determine when and where warm advection (coincident with upward vertical motion) and cold advection (coincident with downward vertical motion) is occurring within the lower portions of the [[troposphere]]. Areas with small dewpoint depressions and are below freezing indicate the presence of icing conditions for aircraft.<ref name="upper">{{cite book|url=https://books.google.com/books?id=kGHFWOqyiksC&pg=PA120|pages=129–134|title=Aircraft icing: a pilot's guide|author=Terry T. Lankford|isbn=978-0-07-134139-4|publisher=McGraw-Hill Professional|year=1999}}</ref> The 500 hPa pressure surface can be used as a rough guide for the motion of many [[tropical cyclone]]s. Shallower tropical cyclones, which have experienced vertical [[wind shear]], tend to be steered by winds at the 700 hPa level.<ref>{{cite web|author=[[United States Navy]]|year=2007|url=http://www.nrlmry.navy.mil/~chu/chap4/se100.htm|archive-url=https://archive.today/20120805162928/http://www.nrlmry.navy.mil/~chu/chap4/se100.htm|url-status=dead|archive-date=August 5, 2012|title=Section 1. Influences on Tropical Cyclone Motion|access-date=2010-02-06}}</ref>

Use of the 300 and 200 hPa constant pressure charts can indicate the strength of systems in the lower troposphere, as stronger systems near the Earth's surface are reflected as stronger features at these levels of the atmosphere. Isotachs are drawn at these levels, which a lines of equal wind speed. They are helpful in finding maxima and minima in the wind pattern. Minima in the wind pattern aloft are favorable for [[tropical cyclogenesis]]. Maxima in the wind pattern at various levels of the atmosphere show locations of jet streams. Areas colder than {{convert|-40|C|F}} indicate a lack of significant icing, as long as there is no active [[thunderstorm]] activity.<ref name="upper"/>

=== Surface weather analysis ===
[[file:Streamlineanalysispacific.gif|thumb|Streamline analysis of the tropical Pacific Ocean]]
{{See also|Surface weather analysis}}

A surface weather analysis is a type of weather map that depicts positions for [[high-pressure area|high]] and [[low-pressure area]]s, as well as various types of [[synoptic scale]] systems such as [[weather fronts|frontal zones]]. Isotherms can be drawn on these maps, which are lines of equal temperature. Isotherms are drawn normally as solid lines at a preferred temperature interval.<ref name="DataAir">{{cite web|author=DataStreme Atmosphere|publisher=American Meteorological Society|url=http://www.ametsoc.org/amsedu/dstreme/learn/sample.act.html |title=Air Temperature Patterns|date=2008-04-28|access-date=2010-02-07 |archive-url = https://web.archive.org/web/20080511124504/http://www.ametsoc.org/amsedu/dstreme/learn/sample.act.html |archive-date = 2008-05-11}}</ref> They show temperature gradients, which can be useful in finding fronts, which are on the warm side of large temperature gradients. By plotting the freezing line, isotherms can be useful in determination of precipitation type. Mesoscale boundaries such as [[tropical cyclone]]s, outflow boundaries and [[squall line]]s also are analyzed on surface weather analyses.

Isobaric analysis is performed on these maps, which involves the construction of lines of equal mean [[sea level pressure]]. The innermost closed lines indicate the positions of relative maxima and minima in the pressure field. The minima are called low-pressure areas while the maxima are called [[high-pressure area]]s. Highs are often shown as H's whereas [[low-pressure area|lows]] are shown as L's. Elongated areas of low pressure, or troughs, are sometimes plotted as thick, brown dashed lines down the trough axis.<ref>{{cite web|publisher=University of Wisconsin|author=Edward J. Hopkins, Ph.D.|date=1996-06-10|url=http://www.meteor.wisc.edu/~hopkins/aos100/sfc-anl.htm|title=Surface Weather Analysis Chart|access-date=2007-05-10}}</ref> Isobars are commonly used to place surface boundaries from the [[horse latitudes]] poleward, while streamline analyses are used in the tropics.<ref>{{cite web|author=Bureau of Meteorology|url=http://www.bom.gov.au/nmoc/MSL/WeatherMap.shtml#types|title=The Weather Map|publisher=Commonwealth of Australia|year=2010|access-date=2010-02-06}}</ref> A streamline analysis is a series of arrows oriented parallel to wind, showing wind motion within a certain geographic area. "C"s depict cyclonic flow or likely areas of low pressure, while "A"s depict anticyclonic flow or likely positions of high-pressure areas.<ref>{{cite web|author=[[National Weather Service]] Forecast Office [[Honolulu, Hawaii]]|url=http://www.prh.noaa.gov/hnl/graphics/tropsl.tif|title=Pacific Streamline Analysis|publisher=Pacific Region Headquarters|date=2010-02-07|access-date=2010-02-07}}</ref> An area of confluent streamlines shows the location of [[weather front#Stationary front|shearlines]] within the tropics and subtropics.<ref name="DR"/>