User:Silver skiier07

Kenrick Westerman, May 2007 Graduate from the University of Utah with a Bachelor's of Science in Meteorology.

''My purpose as a Wikipedian is to help deepen the shallow amount of Mesoscale Meteorology information. As such, I will use this page to enlighten any visitor on the phenomenon of squall lines and their associated strong winds, contributing shear, pressure perturbations, heavy rain, and lightning. Note: this page is in final draft phase...in progress to be posted on the 'Squall Line' wikipage by 4:15 PM, April 25, 2007. =o)'' Squall Line Life Cycle

There are several forms of mesoscale meteorology, including simplistic isolated thunderstorms unrelated to advancing cold fronts, to the more complex daytime/nocturnal Mesoscale Convective System (MCS) and Mesoscale Convective Complex (MCC), to squall line thunderstorms.

Squall Line Formation

The main driving force behind squall line creation is attributed to the process of in-filling of multiple thunderstorms and/or a single area of thunderstorms expanding outward within the leading space of an advancing cold front.

Updrafts

The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an updraft, rising from ground level to the highest extend of the troposhere, condensing water and building a dark, omnious clouds to one with a noticable overshooting top and anvil (thanks to synoptic scale winds). Because of the chaotic nature of updrafts and downdrafts, pressure perturbations are important.

Pressure Perturbations

Pressure perturbations within an extent of a thunderstorm are noteworthy. With buoyancy rapid within the lower and mid-levels of a mature thunderstorm, one might believe that low pressure dominates in the mesoscale environment. However, this is not the case. With downdrafts ushering colder air from mid-levels, hitting ground and propagating away in all directions, high pressure is to be found at surface levels, usually indicative of strong (potentially damaging winds).

Wind Shear

Wind shear is an important aspect to measuring the potential of squall line severity and duration. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to turn will aid in create a leading edge lifting mechanism - the gust front. In high shear environments created by opposing low level jet winds and synoptic winds, updrafts and consequential downdrafts can be much more intense (common in supercell mesocyclones). The cold air outflow leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.

Squall Line Evolution

Updrafts

As thunderstorms fill into a distinct line, strong leading-edge updrafts - occassionally visible to a ground observer in the form of a shelf cloud, appear as an omnious sign of potential severe weather.

Beyond the strong winds because of updraft/downdraft behavior, heavy rain (and hail) is another sign of a squall line. In the winter, squall lines can occur albeit less frequently - bringing heavy snow and/or thunder and lightning - usually over inland lakes] (i.e. [[Great Lakes region).

Bow Echoes

Following the initial passage of a squall line, light to moderate stratiform precipitation is also common. A Bow echo is frequently seen on the northern and southern most reaches of squall line thunderstorms (via satellite imagery. This is where the northern and southern ends curl backwards towards the middle portions of the squall line, making a "bow" shape.  Bow echoes are frequently featured within supercell mesoscale systems.

Mesolow

The northern end of the squall line is commonly referred to as the cyclonic end, with the southern side rotating anticyclonically. Because of the coriolis force, the northern end may evolve further, creating a "comma shaped" mesolow, or may continue in a squall-like pattern.

Squall Line Dissipation

As supercell or multi-cell thunderstorms disappate because of a weak shear, poor lifting mechanisms: (e.g. considerable terrain or lack of daytime heating.  The squall line associated gust front may outrun the squall line, the synoptic scale low may fill - leading to a weaking of a cold front, or the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system.  The areas of disappating squall line thunderstorms may be regions of low CAPE, low humidity, insufficent wind shear, or poor synoptic dynamics (e.g. an upper level low filling) leading to frontolysis.

From here, a general thinning of a squall line will occur: within, winds decaying with time, outflow boundaries weakening updrafts substantially, and clouds losing their thickness.