Editing Surface weather analysis (section)

== Mesoscale features ==
{{see also|Mesoscale meteorology}}
[[Mesoscale meteorology|Mesoscale]] features are smaller than [[synoptic scale]] systems like fronts, but larger than [[storm-scale]] systems like thunderstorms. Horizontal dimensions generally range from over ten kilometres to several hundred kilometres.<ref>Fujita, T. T., 1986. ''Mesoscale classifications: their history and their application to forecasting.'' '''Mesoscale Meteorology and Forecasting.''' American Meteorological Society, Boston, p. 18–35.</ref>

=== Dry line ===
The [[dry line]] is the boundary between dry and moist air masses east of mountain ranges with similar orientation to the [[Rocky Mountains|Rockies]], depicted at the leading edge of the [[dew point]], or moisture, gradient. Near the surface, warm moist air that is denser than warmer, dryer air wedges under the drier air in a manner similar to that of a cold front wedging under warmer air.<ref>Huaqing Cai. [http://www.atmos.ucla.edu/~caihq/pic/fig23.html Dryline cross section.] {{webarchive|url=https://web.archive.org/web/20080120180130/http://www.atmos.ucla.edu/~caihq/pic/fig23.html |date=2008-01-20 }} Retrieved on 2006-12-05.</ref> When the warm moist air wedged under the drier mass heats up, it becomes less dense and rises and sometimes forms thunderstorms.<ref>{{cite web|url=http://www.accd.edu/sac/earthsci/sgirhard/1370.090/chap3.htm|archive-url=https://web.archive.org/web/20070927000112/http://www.accd.edu/sac/earthsci/sgirhard/1370.090/chap3.htm|title=Lecture 3|archive-date=27 September 2007}}</ref> At higher altitudes, the warm moist air is less dense than the cooler, drier air and the boundary slope reverses. In the vicinity of the reversal aloft, severe weather is possible, especially when a triple point is formed with a cold front.{{Citation needed|date=December 2021}}

During daylight hours, drier air from aloft drifts down to the surface, causing an apparent movement of the dryline eastward. At night, the boundary reverts to the west as there is no longer any solar heating to help mix the lower atmosphere.<ref>Lewis D. Grasso. [https://archive.today/20130116214601/http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175/1520-0493(2000)128%3C2816:ANSODS%3E2.0.CO;2 A Numerical Simulation of Dryline Sensitivity to Soil Moisture.] Retrieved on 2007-05-10.</ref> If enough moisture converges upon the dryline,  it can be the focus of afternoon and evening thunderstorms.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=lee-trough1 Lee Trough.] {{webarchive|url=https://web.archive.org/web/20110919042152/http://amsglossary.allenpress.com/glossary/search?id=lee-trough1 |date=2011-09-19 }} Retrieved on 2006-10-22.</ref> A dry line is depicted on United States surface analyses as a brown line with scallops, or bumps, facing into the moist sector. Dry lines are one of the few surface fronts where the special shapes along the drawn boundary do not necessarily reflect the boundary's direction of motion.<ref>University of Illinois. [http://ww2010.atmos.uiuc.edu/(Gl)/guides/mtr/af/frnts/dfdef.rxml Dry Line: A Moisture Boundary.] Retrieved on 2006-10-22.</ref>

=== Outflow boundaries and squall lines ===
[[File:DangerousShelfCloud.jpg|thumb|A [[shelf cloud]] such as this one can be a sign that a [[squall]] is imminent]]

Organized areas of thunderstorm activity not only reinforce pre-existing frontal zones, but they can outrun cold fronts. This outrunning occurs in a pattern where the upper level jet splits into two streams. The resultant [[mesoscale convective system]] (MCS) forms at the point of the upper level split in the wind pattern at the area of the best low-level [[Inflow (meteorology)|inflow]]. The convection then moves east and equatorward into the warm sector, parallel to low-level thickness lines. When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge where the significant wind shifts and pressure rises.<ref>Office of the Federal Coordinator for Meteorology.[http://www.ofcm.gov/slso/pdf/slsochp2.pdf Chapter 2: Definitions.] {{webarchive|url=https://web.archive.org/web/20090506002006/http://www.ofcm.gov/slso/pdf/slsochp2.pdf |date=2009-05-06 }} Retrieved on 2006-10-22.</ref> Even weaker and less organized areas of thunderstorms will lead to locally cooler air and higher pressures, and [[Outflow boundary|outflow boundaries]] exist ahead of this type of activity, "SQLN" or "SQUALL LINE", while outflow boundaries are depicted as troughs with a label of "OUTFLOW BOUNDARY" or "OUTFLOW BNDRY".{{Citation needed|date=December 2021}}

=== Sea and land breeze fronts ===
[[File:LAKE BREEZE-en.gif|thumb|Idealized circulation pattern associated with a [[sea breeze]]]]

[[Sea breeze]] fronts occur on sunny days when the landmass warms the air above it to a temperature above the water temperature. Similar boundaries form downwind on lakes and rivers during the day, as well as offshore landmasses at night. Since the [[specific heat]] of water is so high, there is little diurnal temperature change in bodies of water, even on the sunniest days. The water temperature varies less than {{convert|1|C-change}}. By contrast, the land, with a lower specific heat, can vary several degrees in a matter of hours.<ref name=seabreeze>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=sea+breeze Sea Breeze.] {{webarchive|url=https://web.archive.org/web/20070314081147/http://amsglossary.allenpress.com/glossary/search?p=1&query=sea+breeze |date=2007-03-14 }} Retrieved on 2006-10-22.</ref>

During the afternoon, air pressure decreases over the land as the warmer air rises. The relatively cooler air over the sea rushes in to replace it.  The result is a relatively cool onshore wind. This process usually reverses at night where the water temperature is higher relative to the landmass, leading to an offshore land breeze. However, if water temperatures are colder than the land at night, the sea breeze may continue, only somewhat abated. This is typically the case along the [[California]] coast, for example.{{Citation needed|date=December 2021}}

If enough moisture exists, thunderstorms can form along sea breeze fronts that then can send out outflow boundaries. This causes chaotic wind/pressure regimes if the steering flow is weak. Like all other surface features, sea breeze fronts lie inside troughs of low pressure.{{Citation needed|date=December 2021}}