Weather Everywhere and Climate in the Shenandoah Valley

Kate presenting on weather in September 2014.

Kate presenting on weather in September 2014.

On December 15, 2015, Headwaters Chapter members Kate Guenther and Malcolm Cameron gave a lively presentation at the Bridgewater Public Library on the basics of weather on our planet, recording weather observations, and about climate and how it’s changing.

Kate gave an excellent PowerPoint review of how weather tries to solve the problem of the unequal heating of the earth’s surface due to the curvature of our globe. Warm air is lighter and rises, while cold air is heavier and sinks. The resulting differences in air pressure create the dynamic air flow of our winds and form low and high pressure centers. These lows and highs pull air in or push it out, respectively, and the Coriolis effect causes the air to curve to the right as it moves in the northern hemisphere. Thus, low pressure systems rotate counterclockwise and high pressure systems rotate clockwise.

An easy way to tell when we’re outside which direction the high pressure center is involves standing with your back to the wind. Rotate 30 degrees to the right and your right hand extended points to the high. For finding the low pressure center, do the same except extend your left hand as a pointer.

Cold fronts and warm fronts separate the high and low pressure centers and the changing positions of all these elements are determined by the jet stream, a fast moving wind stream at roughly 30 thousand feet altitude. The jet stream patterns shift over time and change with the seasons. Cold fronts produce low clouds and rain or thundershowers just out ahead as they move by and then higher, drier clouds after they pass. These fronts are a wedge of cold, dry air pushing under warm, moist air. Warm fronts do the opposite and the warm, moist air rides over top the cold air. They start with very high clouds moving in hundreds of miles ahead of them. As the warm front moves closer, clouds lower and steady and increasing rain is felt. After both fronts pass, the sky usually quickly clears.

cloudswithbirdKate covered cloud basics with picture examples; cirrus high clouds, alto middle level clouds and strato clouds closer to the surface. Cloud types or forms are puffy cumulus, sheet-like stratus, and nimbus rain clouds which are dark and change texture. Cumulonimbus clouds are fast rising cauliflower-like columns that form into thunderstorms with an anvil-like top when mature.

During a break, folks went outside to practice identifying clouds and pressure centers.

Malcolm Cameron finished up the class with pointers on how to setup a home weather observation routine and summarized evidence and impacts of climate change.

Malcolm has taken and recorded daily weather observations for 30 years in Rockingham County. The proper type of instruments, either old-fashioned manual thermometers and rain gauges or the remote sensor digital varieties will work. A max-min. glass tube thermometer with reset has worked well and a wedge-shaped plastic rain gauge resists cracking if the water freezes. These are inexpensive. A digital remote station can be setup as far as 300 to 500 feet from your house, but more elements measured and features offered will increase the price from about $15 up to $400 plus for station units with everything like wind speed and rain gauges. Some top of the line units offer computer software.

Proper location of instruments were covered. Thermometers must always be in the shade and not too close to houses and other sources of heat, generally at least 25 feet away. Wind gauges and rain gauges need to be well out in the open for accurate measurement.

Recording your data should be consistent in nomenclature, and observations should be taken at about the same time each day. Just before sunset works well if you only observe once a day.  If you must be away, try to get someone to fill in.  Local newspapers or airports can provide proxy data, but this can vary greatly from what occurred at your house, especially precipitation.

You have lots of options on how to use and analyze your data. The most useful are monthly total rainfall, season total snowfall and average temperatures. Data over 15 years or longer can begin to show trends.


Climate: long term weather patterns for areas and regions.

After defining climate as long term weather patterns for areas and regions, Malcolm briefly covered climate change. Climate change is becoming increasingly more obvious as the burning of fossil fuels continue and greenhouse gases like carbon dioxide and methane buildup in the atmosphere. Current global emissions of these gases equals over 47 gigatons a year. He covered many of the effects like heat waves, droughts, severe storms and more rapid melting of sea ice, glaciers and icecaps. All of the effects predicted by climate change computer models in the 1980’s have begun to happen in the years since then. Just in the last 3 or 4 years, melting and breakup of coastal glaciers in Greenland and Antarctica has increased significantly. Global average temperatures have risen 1.2 degrees Celsius since 1860, but one degree of that has been since about 1960. Carbon dioxide levels have risen from around 280 parts per million in pre-industrial times to 400 ppm today.

Malcolm related personal stories of impacts such as eroding shores and islands in the tidal Rappahannock River area where he grew up and nearly having tornadoes hit his house near Weyers Cave in April 2011. Prior to 1995, tornadoes only hit The Valley during hurricanes.

MalcolmCameronMany resources exist to study the topic, including NASA, NOAA, the National Science Foundation, and The Washington Post.

Some good news is the agreement reached this month by nearly 200 nations in Paris to set strict carbon diets in all of their future energy production, moving towards mostly clean renewables. The goal is to limit the total global temperature increase to 2 degrees Celsius.

– Malcolm Cameron, Cohort III


Click here for Dale Enterprise weather data. Dale Enterprise is just west of Harrisonburg.

The Dale Enterprise station is the oldest operating weather station in Virginia and the third oldest in the nation, and has been operated by the same family since its founding. The station is located in a farm field, “well away from buildings or hard surfaces.” As of early 2010, the station’s original thermometer remained as a back-up to an electronic temperature sensor installed in 1994. – Wikipedia