Data Sources

At AvnWx.com, we're pilots, too. We strive for accurate, real-time data, because no one cares about yesterday's weather. Also, because we'd rather be flying we don't want to have hard-coded data which forces us to manually update this site to keep it accurate.

However, you agree to use this website for information only. You must contact an official Weather Briefer prior to flight to make sure you have the latest weather and NOTAMs. AvnWx.com cannot guarantee fully accurate delivery of complete briefing information.

All data filters through numerous systems, each introducing possible delays. Generally, weather data is collected / calculated at regular intervals and then made available. AvnWx.com servers poll these data sources regularly, synchronizing "current" data. Your browser then polls the AvnWx.com servers to get data to be displayed.

The chart below shows our data sources, the frequency of the (planned) updates of these sources, and the frequency with which AvnWx.com polls the data source for updates.

METARs, PIREPs, TAFs, Inflight Weather Advisories (SIGMETs, AIRMETs)

These are obtained directly from the Aviation Digital Data Server (ADDS) at NCAR (National Center for Atmospheric Research). ADDS is hosted on an FAA server and pulls data from NOAA's "NOAAPort" Statellite Broadcast Network. This data (i.e., the raw METARs, PIREPs, advisories and TAFs) is not subject to copyright protection. The presentation and translation of the raw data is provided and copyrighted by AvnWx.com. Because of the experimental nature of the ADDS service, AvnWx.com cannot full-time guarantee access to the information, and should not be relied upon in lieu of officially disseminated weather forecasts and warnings.

AvnWx.com obtains updates every few minutes. You can see the time of the most recent update in menu, next to the particular weather item. At time of the update, we have the most recently available data. You're seeing the most recent information available from ADDS.

See also AvnWx.com -- About Pilot Reports

Winds and Temperatures Aloft

Winds and Temperatures Aloft forecasts are obtained from NOAA's Aviation Weather website.

The website is polled once per hour to make sure we have the latest. See also AvnWx.com -- About Forecast Winds and Temps Aloft

Rapid Refresh (RAP) Winds and Temperatures Aloft

For Full Weather Briefs, AvnWx obtains more detailed wind and temperature data directly from NOAA/NCEP RAP model output, run hourly. Rapid Refresh model consists of high-frequency (hourly) updated short-range weather model forecasts assimilating observations from

• Commercial aircraft
• Wind profilers
• Rawinsondes
• Radar reflectivity
• Surface stations and buoys
• Satellites

It requires a great deal of data crunching, and adds a few seconds to generating your Full Weather Brief, but we think it's worth it.

Temporary Flight Restrictions

Temporary Flight Restrictions are obtained directly from FAA's Graphic TFR webpage. The website is polled every 15 minutes to make sure we have the latest set of current TFRs. Details for these TFRs are then downloaded, manipulated and stored locally. See also AvnWx.com -- About Temporary Flight Restrictions

Special handling is performed for the Stadium TFR. Using published schedules for Major League Baseball and National Football League AvnWx.com displays TFR areas for upcoming games. Note that the TFR applies to "one hour before to one hour after" the game. Games are estimated to last three hours, but AvnWx.com has no way of determining the precise end of a game. Major Motor Speedway events are handled in a similar manner.

Airport/Facilities Directory

The pages displayed by AvnWx.com for the A/FD are obtained directly from the FAA. Since these are updated every 56 days, AvnWx.com gets the update also. You can check the the currency of the entry by looking at the date on the bottom of each page of the A/FD. A/FD often have runway diagrams for smaller airports, so if you don't see a full airport diagram for an airport, check its entry in the A/FD.

Procedures

Arrival, Approach, and Departure procedures are obtained directly from the FAA. FAA issues new versions every 28 days, even though the procedure itself may not have changed. Always note the date on the side of the printed procedure plate. These pages are available only from the airport's detailed page. (Right-click on a METAR symbol or Airport symbol and select Airport details..., or browse airports at maps.AvnWx.com/airport, for example maps.AvnWx.com/airport/KORD)

Surface Analysis Overlay

Surface Analysis overlay, showing warm and cold fronts, is drawn from data provided by NOAA's HPC. New data is provided approximately every three hours. AvnWx.com checks for new data every fifteen minutes, and will draw a new frontal system when new data is obtained. See AvnWx.com -- About Surface Analysis for more information.

NEXRAD Precipitation Overlay

This overlay is the NEXRAD Base Reflectivity, provided by IEM. The data is gathered by IEM and regenerated every 5 minutes. Though it is updated every 5 minutes, the base radar images are not all updated every five minutes and therefore the resulting composite may not be fully updated every 5 minutes. Use this image as merely a guide current precipitation. Turning on animation menu, will show the previous 45 minutes of radar images, pausing a few seconds at the most recent image. This is useful to see direction of weather and trends. It also helps when there appears to be a missing radar echo. Note that echos change rapidly, so use echos for general planning only. Avoid thunderstorms by at least 20 miles, and recall that cumulonimbus can grow in less than one hour.

Turning on NEXRAD will overload computers with 512M or less RAM, or computers on slow links -- you've been warned!

NEXRAD Individual Sites

For each known NEXRAD radar site, an icon is displayed. The image information is retrieved once, when initially displayed. To update the displayed information you must use the Refresh button associated with the site. Data is not automatically updated. Images (including range rings and legends) are retrieved directly from NOAA at radar.weather.gov. Image times differ based on whenever NOAA provides the update (which differs for different sites, and for different image types).

The individual sites provide you with the ability to observe echoes for the same area from different angles. This is especially useful when trying to analyze returns for anomalies. Additionally, we provide more than just current precipitation images.

NOTAMs

NOTAMs are synchronized with the FAA's NAIMES data portal (AIDAP), and include NOTAMs for domestic, international and military locations. NOTAMs which have expired are not shown.

Other

We use tables and additional algorithms for all sorts of other useful information.

• Sunrise/Sunset, Lunar Phase tables
  This is calculated algorithmically, based on the location's latitude longitude, using algorithms from NOAA and Keith Peter Burnett (bodmas.org/astronomy/riset.html)
• Magnetic deviation calculation
  With each airport, the FAA publishes a magnetic deviation, with a date that value was made. This information is visible on the detailed page for each airport. Magnetic deviation shifts over the years, and the FAA doesn't get around to updating the magnetic variations too often for the smaller airports. For this reason, AvnWx.com provides both the FAA's value, as well as a newly calculated value, based on World Magnetic Model (WMM-2005) from NGDC. These values rarely differ by more than a few degrees, but you should be aware of that your GPS or magnetic compass will disagree with the field alignment. Winds are published as True, runway heading were (mostly) magnetic when built, but may be 10+ degrees off as magnetic north has shifted. This also means that a VOR bearing may not match magnetic bearing. When AvnWx.com displays flight path information, the reported magnetic heading is based on "real"/"current" magnetic heading, which may be different than the VOR heading you need to fly.
• Density Altitude Calculation
  Density altitude is shown with METAR information, when we have sufficient current information. To calculate accurately, we need station elevation, current temperature, current dewpoint, and current barometric pressure. When the METAR does not report all information, we will not show density altitude. Details on density altitude are from Richard Shelquist's excellent set of calculators at wahiduddin.net/calc.
• Flight Path Calculation
  Flight paths are calculated along a great circle route. We're indebted to Ed Williams (williams.best.vwh.net) for providing great algorithms useful for performating these calculations.