Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 27-11-2003, 10:42   #1
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,082
Images: 241
Excellent Weather Article

Sailnet has an excellent article on using Satelite immagry for weather forecasting.
www.sailnet.com/view.cfm?page=11975
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 12-07-2004, 07:22   #2
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,082
Images: 241
Jet Contrails

JET CONTRAILS & WEATHER FORECASTING:

THICK &/or LINGERING CONTRAILS - indicate changing weather and/or precipitation
DISSIPATING or NO CONTRAILS - indicate continuing and/or clearing weather.

The plume of condensed water vapor in the exhaust trailing behind high flying jet aircraft is called a “contrail” - short for condensation trail. Contrails are long white streaks of ice crystals left behind in the exhaust of flying jet aircraft. At 8 to 12 km (5-7.5 mi.) above the ground, the jet engine pulls in very cold, dry air and spews out hot, water-filled exhaust. The hot water vapour mixes with the colder surrounding air. In doing so, it expands and freezes in (1 or 2 seconds) forming a trail of ice-crystal clouds. Contrails will only form into long-lasting visible cirrus-like cloud formations when the air temperature is at -40C or lower (-40F) and the humidity level is at 70% or greater.

Contrails can provide a clue to upcoming weather. If a jet leaves no trail or a short trail; or if the trail fades quickly - it is an indication that the air is relatively dry and sinking, which suggests that fair weather is likely to continue. On the other hand, if the exhaust trails linger for an hour or more; or they spread across the entire sky - the surrounding air is probably moist and rising, foretelling the arrival of a storm in a day or two. Reading contrails gives you a glimpse as to the weather over the next 12 to 24 hours.

Sky light blue to dark blue. Bright moon. Jet contrail disappears immediately or doesn't form. all indicate: Continuing Good Weather, Clear.

Large halo circling moon or sun. Jet contrail lingers thickly before falling apart indicate: Possible Change.

FWIW
Gord
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 12-07-2004, 15:24   #3
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
Does this suggestion, change it's reliability in differing parts of the world. I mean by that, is it more reliable in say the tropical area's or southern/northern latitudes? The reason I ask, is down here in NZ, we get Large High pressure (anti_cyclone) area's, with low pressure fonts circling around them. If we happen to be in the path of the front, we will get a Southerly (cold/wet) pattern or it can bend across the country, due to our land shape and contours and become a warmer Westerly. So how does the Contrail depict that a front is coming. Or does this article explain and I should read it????
Wheels
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 14-07-2004, 08:02   #4
Registered User

Join Date: Feb 2004
Posts: 367
Images: 11
I'm not a weather expert, but reading the article the idea is that dry sinking air is stable, and warm moist air is unstable. This should hold true in most areas, northern or southern hemisphere.

However, on the extremes you could be in the tropics and have moist rising air as a normal occurence and this would not predict the coming of a disturbance. Likewise in the higher lattitudes the air is always drier so bad weather could be coming even with dissapating contrails. So, like most "rules of thumb" it is probably valid most of the time, you just have to be aware of it's short comings.
exposure is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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
Treasure Hunting Article GordMay Fishing, Recreation & Fun 2 28-09-2006 08:04
Thought you folks might be interested in this article 29cascadefixer General Sailing Forum 8 26-12-2003 20:13
Interesting Article GordMay Boat Ownership & Making a Living 0 08-08-2003 08:18
Herb - For Weather Info' GordMay Atlantic & the Caribbean 0 02-08-2003 12:59
ARTICLE ARCHIVE & EXPERT PANEL Gisle Forum News & Announcements 0 26-05-2003 22:07

Advertise Here


All times are GMT -7. The time now is 00:47.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.