David

The Fall City learning garden website hosts weather information from a weather station nearby. it provides accurate weather data 24/7 for downtown Fall City and reflects typical conditions in nearby gardens.

In this article I'll explain briefly the different tabs along the top of the weather information and acquaint you with some of the lesser known measures.

Davis Vantage Pro2 +

Weather station

You can access the weather information from the Resources menu on the website (http://letusgarden.org/index.php/fclg-resources/learning-garden-weather). This weather information is also available at  http://letusgarden.org/weather/ which may display better on devices with small screens.

The landing page for the weather is the Summary heading.

The familiar dials for temperature, wind, humidity and rain are here. Each dial shows the current measurement. On the temperature dial, the blue tick indicates the low for the day and the red tick the high, while the pointer and the text below indicate the current temperature.

Wind and the rose

Probably the most interesting of the dials are the wind roses. They reflect the prevailing winds. The directions of the rose with the longest spokes show the wind direction with the greatest frequency.

The week and year wind roses condense the many readings over a day into smaller, broader samples. The wind rose provides a different picture from the wind direction graph lower on the page. For details of a wind rose see the Wikipedia article on the wind rose (http://en.wikipedia.org/wiki/Wind_rose).

Barometric pressure

Barometric pressure is the weight of the air pressing down on the Earth. Changes in barometric pressure suggest changes in the weather. Pressure changes gradually from time to time and these relatively small changes are often related to major shifts in weather patterns. Whether the trend is rising or falling gives some clues about the type of weather.  Making sense of this is a meterologist's vocation.

24-hour graphs

Below the dials are graphs of the readings over the last 24 hours. These show the trend of values and allow a comparison of different conditions, for example, a change in humidity based on wind velocity, wind direction or rain.

Generally, the information will be current because the software uploads changed values every couple of minutes. Whenever you really need to know current conditions, check the date and time under the heading at top left to ensure that the values have been recently updated. It's possible for the weather server to be down or readings delayed by a malfunction.

The Current heading

Current links to a page showing bar graphs for current, high and low values. A blue line indicates the low value and a red line the high value for the day. The green bar and the text below a graph indicate the current reading. To the right are text values for current, high and low values.

History

The pages linked by the headings for 24 hours, 7 days, 28 days and 365 days show a similar collection of graphs with historical information for the specified period, day, week, month and year.

The Almanac page shows statistical values from the station history. This station began recording weather data on January 21, 2014, so there a very limited amount of historical information.

For the gardener

Let's look at some of the measurements that concern us as gardeners.

Humidity and dew point

Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature. When the air can't "hold" all the moisture, then it condenses as dew. Here in the valley this reading is often above 90%. Relative humidity is related to temperature. For details see http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html.

If the air is gradually cooled while maintaining the moisture content constant, the relative humidity rises until it reaches 100%. This temperature, at which the moisture content saturates the air, is called the dew point. If the air is cooled further, some of the moisture will condense. For an in-depth discussion, see http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html#c5

See the graphs of temperature and dew point and compare with the graph of humidity. Here in the valley the dew point is often very close to the actual temperature and we often have dew, and with a temperature around freezing we might have frost.

Attention to humidity and dew point may alert you to conditions that encourage tomato blight.

Solar radiation

This reading indicates the amount of sunshine on the station. Plants love and need sunshine, so a reading of from 450 to 500 for several hours helps them keep growing.

UV index

The UV Index provides a forecast of the expected risk of overexposure to UV radiation from the sun. The UV Index is a useful tool for planning sun-safe outdoor activities. It is ranked on a scale from 1 to 15. It will be interesting to see how high this value can go here in the valley. When you see this value greater than 5 or so, take your sun screen, gardening hat and sun shades with you to the garden. The Environmental Protection Agency provides more information on UV index (http://www2.epa.gov/sunwise/uv-index).

Evapotranspiration (ET)

Water cycle

Water cycle

Evapotranspiration is a measure of the water lost to the atmosphere from the ground surface or plants. Think evaporation plus transpiration. A high value here may suggest you check your plants for dryness and consider whether to water them. A higher ET may correspond to wilted plants. For more information see the United States Geological Service page on the water cycle (http://ga.water.usgs.gov/edu/watercycleevapotranspiration.html).

Citizen Weather Observer program (CWOP) and Weather Underground

Information from this weather station is reported to CWOP, a program of NOAA, who compiles and analyzes data from many weather stations for long-term analysis.

Data from this station is also sent to a Weather Underground page for the learning garden (http://www.wunderground.com/personal-weather-station/dashboard?ID=KWAFALLC11), which also displays a forecast of upcoming weather conditions.

The equipment

The weather station includes precision sensors, though it is not the most professional, it is a step up from consumer level equipment. It is a Vantage Pro2 Plus from Davis Instruments. It is mounted on a pole 7 feet above ground, with wind vane and anemometer about 23 feet above ground. The siting gives a reasonably accurate picture of current conditions. And the software, called wview, collects a huge variety of data and related calculations, and uploads changes to the Internet every couple of minutes.