From site:  The Online Meteorology Guide is a collection of web-based instructional modules that use multimedia technology and the dynamic capabilities of the web. These resources incorporate text, colorful diagrams, animations, computer simulations, audio and video to introduce fundamental concepts in the atmospheric sciences. Selected pages link to (or will soon link to) relevant classroom activities and current weather products to reinforce topics discussed in the modules and allow the user to apply what has been learned to real-time weather data.

LearningReviews.com note:  Modules include Light and Optics, Clouds and Precipitation, Forces and Winds, Air Masses and Fronts, Weather Forecasting, Severe Storms, Hurricanes, El Nino, and the Hyrodologic Cycle (Water Cycle in elementary terms).

This website is no longer available.  As an alternative, try out SkySci for Kids or the UCAR Learning Zone for weather and climate.

KidsGeo.com provides an in-depth online textbook on the Earth’s atmospheric weather systems.  There are chapters on atmospheric temperatures, pressures, moisture, and disturbances.

From site:

Ever wondered what causes extreme, scary, even dangerous weather? Here’s a collection of online resources that discuss common, and uncommon, weather phenomena and what causes them. You’ll also find some world records in extreme weather, as well as some really handy online resources for getting the latest weather reports and forecasts.

This site is no longer available.  As an alternative, take a look at the activities on National Geographic Kids Weather site.

From site:  Welcome to the Weather Lab! Here you can test drive the tools meteorologists use every day.

Click on each tool below for more information about the tool along with instructions on building it and using it in an experiment. Print the Weather Data Sheet (PDF) to record the results of your experiment.

LearningReviews.com note:  Measurement instruments include anemometer, wind vane, barometer, rain gauge, snow gauge and thermometer.

In the Cloud Lab, learn how clouds form, the different types, what they tell us about weather, and how they help forecast weather and climate. You will classify some clouds and investigate how they change rapidly in tropical storms.

The site includes lesson and activity ideas for teachers.