Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Visibility range of clouds
    From: Frank Reed
    Date: 2016 Aug 1, 11:12 -0700

    Bob, in your Aldebaran post earlier today you asked about visibility distance:

    "On a completely separate topic, we had tornado warnings for a community 20 miles west of my house last night.  I was looking to the west, and wondering whether the thunderclouds that triggered the warning were visible to me or below my horizon.  That will be related to the height of the clouds I am looking at, of course.  But Bowditch's Table 15 was not really designed with clouds in mind.  Are there any rules of thumb for how far away I can see clouds of various sorts?"

    The square root of height approximation is reasonably accurate even in LEO (Low Earth Orbit) but near the breaking point at that altitude. Within the denser parts of the atmosphere and especially within the troposphere, where the vast majority of clouds are found, the square root of height approximation is as accurate as most needs require. The standard distance to the horizon is somewhat greater than the straight line distance since it includes terrestrial refraction, but that matters less for higher altitudes so you can use d(n.m.) = 1.06·sqrt[h(in feet)]. Mid-level clouds are on the order of 10,000 feet high which implies they have a maximum range of visibility of 106 nautical miles, close enough to 100 miles. The tops of thunderstorms generally extend to, and often slightly above, the tropopause so you can use 40,000 feet for altitude implying a visibility range of 200 nautical miles. Of course, in order to see some portion of the storm poking above the horizon, you probably couldn't detect a storm beyond 150 miles even with perfect conditions. At this range, perfect conditions exist only in theory, and extinction in the atmosphere will normally prevent you from seeing anything. I would count 50 to 75 miles as a reasonable maximum. To emphasize, for very distant thunderstorm tops, it's not that they're beyond the horizon. Rather, they're lost in the "haze" at greater distances.

    Setting aside computation, estimating distances to clouds is a visual task beyond our natural skills --we didn't evolve for that. I find that most people can't estimate the distance to a thunderstorm to better than a factor of five. They may think 'two miles' when a storm is actually ten miles away, or vice versa. Thanks to our networked pocket supercomputers, there is now a way to "train" ourselves as observers to estimate distances to certain types of clouds, in particular fully-developed thunderstorms. Next time you see some distant thunderstorms, call up the weather radar on your smartphone. Making allowances for the usual delays, you can often determine the distance to storms within a few miles. I find that I can now estimate distances to storms far better than I could fifteen years ago (before my first portable networked device with live weather radar). There are clear practical advantages to such distant estimation skills. Don't forget that storms travel with a wide range of speeds; for one storm 20 miles may mean three hours travel time, for another it may be twenty minutes. And don't forget that storms grow as well as travel, sometimes very rapidly!

    Frank Reed

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site