Editing Surface weather analysis (section)

=== 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}}