A post collapse skill that would be very useful is the ability to make accurate weather forecasts several days in advance, without depending on modern technology (weather satellites, doppler radar, etc.). Weather has a huge impact on our lives. It affects our crops, our animals, our ability to do work, our comfort, and even our very life. Weather can destroy our property, and even kill people. A knowledge of weather, and the ability to forecast it at least a day or two in advance, helps immensely in planning what we need to do and when, and in warning us when we need to prepare for possible dangerous weather events.
All weatherman jokes aside, it is possible to predict, with a fair amount of accuracy, the weather several days in advance. And you don't need modern technology to do so. A few basic instruments to monitor current conditions (temperature, humidity, wind direction & speed, and barometric pressure), along with the ability to recognize various types of cloud formations and good understanding of weather patterns, is really all you need. In fact, I've done this quite successfully.
My Meteorology Lab
Growing up I was a science geek (actually a "nerd" in those days). For Christmas during my seventh grade year, I got a Meteorology Lab as present. It came with three main pieces: 1) an outside weather station to monitor wind direction & speed, temperature, humidity, and precipitation, 2) an inside station with a barometer to measure barometric (air) pressure, along with a set of cardboard wheels that could be dialed to the current specific weather conditions and give you a basic forecast, and 3) an instruction book and cloud chart (you would use the cloud types and cloud coverage % to refine the basic forecast), along with weekly cards for recording each day's weather conditions.
I actually kept about four years with of daily records, before my equipment started to wear out and I lost interest. I couldn't make forecasts more than a few days away. But, frankly, my forecasts for 1, 2, and 3 days away were at least as accurate as the local forecasts from professionals with way more expensive equipment.
My meteorology lab and records were thrown away many years ago, but I've developed a renewed interest in the subject, and really do think it will prove a very useful skill in any post-collapse scenario. I've recently pulled out my weather books (see the resources listed below), and am looking for a weather station similar to the one I used to have.
I plan on relearning my weather forecasting skills, and understand the microclimate of the area I'm living now by daily monitoring of my local weather. A fun hobby now, an important skill later...
Resources (I have and can recommend these)
Golden Guide - Weather - This small book (4x6 inches, 160 pages) is a rather through introduction to the science of meteorology. Filled with pictures and diagrams, it explains in an easy-to-understand way, the science of the weather and weather forecasting. Appropriate for middle-schoolers through adults.
Peterson Field Guide to the Atmosphere - An extensive guide to clouds and other weather & atmospheric phenomenon, has over 400 photographs and illustrations, this book is currently out-of-print, but second-hand copies can still be readily found. A condensed version, Peterson's Clouds and Weather, is available new.
Weather: A Folding Pocket Guide to to Clouds, Storms and Weather Patterns - is a well-done, laminated fold-out chart to clouds, storms and weather patterns.
There are a wide variety of weather stations and meteorology educational kits available, with a wide range of appropriate age levels, capabilities, and prices. I haven't yet found one similar to the one I had in school, and am still looking. If you have any suggestions, please leave it in the comments section!