Posts Tagged ‘moisture’

Weather Word Wednesday : Weather

January 26th, 2011 No comments

As I got to thinking about the word I wanted to discus today, it occurred to me that the very base of what we’re talking about here, Weather, would be the perfect word to delve into!

Weather, according to Wikipedia, “is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy.” Seems pretty basic when you look at it like that! Most weather tends to occur in the troposphere, which is the layer of the atmosphere that we live in. Wikipedia goes on to say that “weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time.” And, unless you’re being specific, the term generally applies to weather on Earth.

Weather basically occurs because of density differences in temperature and moisture between different points on the earth. These differences are generally caused by the varying sun angles at any point on the earth, which varies by latitude from the tropics. The strong temperature differences between the tropics and the poles is what causes the jet stream, which is a fast flowing, narrow air current. Weather systems in the mid-latitudes, like the United States and much of Europe, is caused by instabilities of the jet stream flow. Sometimes the jet stream dips down from the poles, bringing with it cold air. Sometimes it causes a ridge that brings up warm, moist air from the tropics. All this combines to create the weather systems that get reported on each day.

Earth's Weather

Weather on Earth is complex and chaotic!

On Earth, “common weather phenomena include wind, cloud, rain, snow, fog and dust storms.” Less common events include “tornadoes, hurricanes, typhoons and ice storms.” Wind is created by differences in air pressure levels on the planet, with air flowing from regions of high pressure to low pressure. Pressure itself is caused by varying temperatures on the planet, with colder temps producing lower air pressure, and higher temps associated with high pressure systems.

The atmosphere is a hugely complex and chaotic system, where changes to one variable (temperature, pressure, moisture) can have huge effects on the weather in a particular location, or a location remote from where the variable has changed. The dynamics of weather in many cases are poorly understood, which is why long term weather forecasts are so difficult to create. As the years go by and we are able to gather more data about actual weather events, our understanding of weather and climate increase, and that leads to an increased ability to make accurate forecasts. But the weather will always surprise us, and we should be prepared for anything at any time. If you tend to venture outside your home, you should take time to understand what weather events might be headed your way!

Water Vapor Imagery

August 24th, 2010 No comments

I recently “discovered” on the local NWS website the Satellite Water Vapor Imagery data for our area, and I’m quite fascinated by it! The official description of this data is as follows:

Water vapor satellite imagery depicts moisture content in the middle and upper layers of the atmosphere. Lower level moisture is not depicted in these images. Moisture transport over large distances generally happens through the middle and upper layers of the atmosphere. Hence these images will depict moisture coming into the Southwest from the Gulf of Mexico or across Texas. Additionally, weak disturbances from the east are best tracked through water vapor imagery.

The imagery looks like this when viewed online. The is a screen capture of one frame of data:

Water Vapor Imagery

Water Vapor Imagery

Basically, what this shows is the amount of moisture that is in the upper atmosphere. This may be in the form of clouds that you see, but often it is not. Water vapor literally surrounds the earth, but is unevenly distributed due to things like oceans, lakes, rivers, deserts, arid areas, etc. For instance, in the image above, you can see a lot of water vapor coming up from the southwest into places like Arizona and New Mexico, which are traditionally dry regions. Areas like the Pacific Northwest, which are usually wet, have much less than normal. This is all due to seasonal shifts in winds and weather patterns, which change the flow of moisture around the planet. By looking at an image like this, you can get an idea of how much moisture is available in your area…moisture that could turn to rain or snow!