Go Back   Cruiser Log World Cruising & Sailing Forums > Regional Cruising > General Marine Weather > General Weather Discussion
Cruiser Wiki

Join Cruiser Log Today

Thread Tools Search this Thread Display Modes
Old 07-31-2008, 02:13 AM   #1
Join Date: Oct 2004
Posts: 3,067

Squall lines

The precipitation downdraught associated with an individual cell tends to be concentrated towards the leading edge of the storm where the cold heavy outflow spreads out at sea level forming a small high pressure cell, a meso-high, 10 – 15 nm across. The dense air lifts the warmer, moist air in its path and may initiate a self amplifying convective complex, in which neighbouring storm cells consolidate into a towering squall line of large thunderstorm cells ranged across the prevailing wind direction. At locations in the path of the squall line the resultant line squall occurs as a sharp backing in wind direction, severe gusts, temperature drop, hail or heavy rain and possibly tornadoes. If the squall line is formed in an environment of strong mid-level winds the surface gusts may exceed 50 knots.

Squall lines vary in length, some of the longest being those which develop in a pre-frontal trough 50 -100 nm ahead of a cold front. These squall lines may be several hundred nautical miles in length and 10 – 25 nm wide moving at typically 25 knots. The pre-frontal lines form ahead of the front as upper air flow develops waves ahead of the front; downward wave flow inhibiting and upward wave flow favouring, uplift. Squall lines are a common northern Australia and north into Malaysia and Sumatra feature developing along active areas of the Inter Tropical Convergence Zone, within the feeder bands of tropical storms, along sea breeze fronts or other convergence zones and in the summer heat trough. In south-east Australia they may also be associated with fast moving winter cold fronts, producing severe winds and heavy rainfall.


During daylight hours the squall line may appear as a wall of advancing cloud with spreading cirrus plume but the most severe effects will be close to each of the numerous cumulonimbus cells. The convective complex releases a tremendous amount of latent heat and moisture which may be sufficient to generate a warm core mesoscale cyclone lasting several days.

Sea breeze fronts

In coastal areas differential diurnal heating promotes development of on-shore breezes which, during the day, grow in strength to ‘moderate breeze’ and, due to coriolis effect, begin to back. The surface wind is a resultant of the sea breeze vector and the gradient wind vector. In hot land conditions the sea breeze front, a density current, can travel 100 – 200 nm inland by midnight if not blocked or diverted by terrain.

The cool air lifts the warmer inland air and, if conditions are suitable for deep convection, a squall line may develop and propagate along the convergence line of the surface flow. Opposing sea breeze fronts, such as occur in Cape York, may cause strong convergence disturbances when they meet. Along the eastern Queensland coast, typically between September and March, storm lines of cumulonimbus up to 100 nm in length form inland in mid to late afternoon then move towards the coast, being out to sea by mid-evening. Such storm lines may be difficult to avoid if encountered unexpectedly.

MMNETSEA is offline   Reply With Quote
Old 04-24-2009, 08:06 AM   #2
Join Date: Oct 2004
Posts: 3,067

Image added
MMNETSEA is offline   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
A Squall ... Is A Squall ... Is A ... ? shamrockery General Cruising Forum 10 01-29-2010 04:37 AM
Interesting Analysis Of Piracy In Gulf Of Aden & Red Sea Trim50 Regional Piracy 13 05-28-2009 11:29 AM
Which Rope For Dock Lines? Velella General Cruising Forum 9 05-08-2007 07:58 AM

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

RV & Travel Trailer Communities

Our RV & Travel Trailer sites encompasses virtually all types of Recreational Vehicles, from brand-specific to general RV communities.

» More about our RV Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

All times are GMT. The time now is 07:40 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.0