What is this website?

This site contains some basic verification results for selected weather elements (e.g., temperature, dew point, wind speed, etc.) from the National Digital Forecast Database (NDFD). 

How to Use This Site

The NDFD Stats Viewer User's Guide can be found here.  

Definitions of weather elements

• Apparent Temperature: The perceived temperature derived from either a combination of temperature and wind (Wind Chill) or temperature and humidity (Heat Index) for the indicated hour. When the temperature at a particular grid point falls to 50 F or less, wind chill will be used for that point for the Apparent Temperature. When the temperature at a grid point rises above 80 F, the heat index will be used for Apparent Temperature. Between 51 and 80 F, the Apparent Temperature will be the ambient air temperature.
• Ceiling: The height of the cloud base for the lowest broken or overcast cloud layer. 
• Dew Point: The dew point temperature observed at 2 meters above ground level.
• Max Relative Humidity: The highest relative humidity (%) expected for the indicated 12-hour period.
• Max Temp: Daytime maximum temperature is defined as the highest temperature observed from 7 AM to 7 PM LST. Note that maximum temperature is associated with the 24-h MOS projection from 0000 UTC, 36-h MOS projection from 1200 UTC, 48-h MOS projection from 0000 UTC, and so on.
• Min Relative Humidity: The lowest relative humidity (%) expected for the indicated 12-hour period.
• Min Temp: Nighttime minimum temperature is defined as the lowest temperature observed from 7 PM to 7 AM LST. Note that minimum temperature is associated with the 24-h MOS projection from 1200 UTC, 36-h projection from 0000 UTC, 48-h projection from 1200 UTC, and so on.
• PoP01: The likelihood, expressed as a percent, of a measurable precipitation event (1/100th of an inch or more) at a grid point during the 1-hour valid period.
• PoP12: Probability of Precipitation (PoP greater than or equal to 0.01 in) for 12-h periods, specifically, 0000-1200 UTC and 1200-0000 UTC.
• QPF01: The expected quantity of liquid precipitation accumulated over a one hour period.
• QPF06: The expected quantity of liquid precipitation accumulated over a six hourly period. A quantitative precipitation forecast (QPF) will be specified when a measurable ( 1/100th of an inch or more) precipitation type is forecast for any hour during a QPF valid period. NDFD valid periods for QPF are 6 hours long beginning and ending at 0000, 0600, 1200 and 1800 UTC. QPF includes the liquid equivalent amount for snow and ice.
• QPF24:  The expected quantity of liquid precipitation accumulated over a 24-hour period.
• Relative Humidity: The ratio, expressed as a percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. The verifying observation is computed from the ambient temperature and dew point 2 meters above ground level.
• Sfc Temp: The ambient temperature observed at 2 meters above ground level.
• Sky Cover: The amount of sky covered by opaque clouds for the indicated hour. Beginning July 2007, NDFD, gridded MOS, and the verifying observations are consistent. Prior to that time, NDFD forecasts of opaque sky cover were compared to MOS forecasts and verifying observations based on total sky cover.
• Snow Amount: The expected total accumulation of new snow during a 6 hour period. A snow accumulation grid will be specified whenever a measurable snowfall is forecast for any hour during a valid period.
• Snow24:  The expected total accumulation of new snow during a 24-hour period. A snow accumulation grid will be specified whenever a measurable snowfall is forecast for any hour during a valid period.
• Visibility: The distance at which a given standard object can be seen and identified with the unaided eye.
• Wave Height: The average height (from trough to crest) of the one-third highest waves valid for the top of the designated hour. Wave Height is a combination of wind waves and swell.
• Wind Speed: The wind speed observed at 10 meters above ground level.
• Wind Dir: The wind direction observed at 10 meters above ground level.
• Wind Gust: The maximum wind speed observed at 10 meters above ground level. Note that if an actual wind gust is not observed at a given location, the wind gust assumes the value of the sustained wind speed.