Values for 3, 6, or 24 hour precipitation are extrapolated from those reports, and are displayed hourly, or every 3, 6, or 12 hours (for 24 hour precip). Precipitation is reported in 5, 10, 15, 30, or 1 hour increments. The number of tips over the recording period results in the value displayed. Each time it fills up, the see-saw tips, and that action is recorded as 0.01 inches of precipitation. When a tipper is used, liquid precipitation (rain or melted snow) gathers in a small measuring cup that looks like a see-saw.When a weighing mechanism is used, precipitation (rain, or snow) will be stored in a bucket, and an electronic scale is used to convert the weight to a value.Precipitation (precip) can be measured 2 different ways: Using a weighing mechanism, or by using a tipper. VV: Vertical Visibility - An indefinite cloud ceiling caused by fog, rain, snow, etc.OVC: Overcast - 8/8 of the sky is covered by clouds.BKN: Broken Clouds - Between 5/8 and 7/8 of the sky is covered by clouds.SCT: Scattered Clouds - Between 3/8 and 4/8 of the sky is covered by clouds.FEW: Few Clouds - Between 1/8 and 2/8 of the sky is covered by clouds.CLR: No clouds below 12,000 feet above ground level, as detected by automatic equipment.The last 3 numbers indicate the base of that layer, above the ground x 100 feet. The first 3 letters of a cloud group describe the amount of sky coverage.Up to 3 layers (the lowest 3 layers) of clouds can be reported.
This limitation can result in "Clear" conditions being reported, when clouds are above 12,000 feet.Īt major airports, this information can be augmented by a trained observer, who can also determine heights greater than 12,000 feet. Hourly ASOS data with "Special" ObservationsĬloud height sensors can measure clouds up to 12,000 feet above the ground, when the cloud is directly above the sensor. The URL in the web browser address bar has those options "built in", so the format can be saved/bookmarked.
The following weather elements are available for viewing in a chart. If a "magnifying glass" cursor appears, it means that if you click on that heading, data for that element will load into the chart. To view charts for additional elements, using a mouse, move the cursor over the element headings. Example 2: A station that reports 4 times an hour will begin trimming data after 250 hours.After 76 hours, data will be trimmed in the chart. Example 1: A NWS ASOS reports 12 - 13 times an hour.If you require high resolution charts, the "Historical Data" option will be helpful. Therefore, data will be trimmed when it exceeds 1000 datapoints, and will then display every 2nd, 3rd, etc point. For longer duration datasets, with multiple reports per hour, this will exceed the charting capability.
The chart has a limitation where 1000 data points per element can be displayed. If a station has not reported any of those elements during the requested period, no chart will be available. The default station chart contains Temperature, Dew Point Temperature, and Relative Humidity.
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