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. Apply Settings: When you click this button, the page will refresh with the options you selected. This will simply display the value reported by the sensor. "Measured" will NOT populate 1, 3, 6, and 24 hour data. "Standard" will populate lines rows are aligned with times corresponding to 1, 3, 6, and 24 hour data. "Full" will populate out each row with 1, 3, 6, and 24 hour data. Precip View: This will select how the calculated precipitation values fill in 1, 3, 6, and 24 hour fields in a row of data. SPECI data will have a bold timestamp and be highlighted in yellow. If the station is a federally owned ASOS/AWOS, METAR and SPECI data will be included. If "Yes" is checked, the page will only display data where the observation time stamp has between "51" and "59" in the minutes field for NWS/FAA observation platforms (to include any "SPECI" observations/data - with the date&time stamp highlighted in yellow), and between "56" and "04" for all other platforms. Hourly Data: By default, the page will display all data for a given time period. Observation Type: The page will display coded Meteorological Aerodrome Reports (METAR), and Special Reports (SPECI). Gather Historical Data: When "On" is checked, you will be able to select the starting and ending dates you are interested in getting data for (limit of 30 days). See Chart: Toggle "on" or "off" the data chart. Page Headers: Select how much of the "top" of the page you'd like to see. Number of hours: Up to 720 hours (30 days) of data can be displayed on this page. Units of measurement: toggle between "standard (with speeds in mph)", "standard (with speeds in knots)" and "metric" measurements. Mouse over Chart Headings to reveal Magnifying Glass, Then Click for ChartĬlicking the "Settings" icon will open an area where you can select different viewing parameters. Note: Data availability varies by station. 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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