When the API composes conditions for a point, it treats every network as one population ranked by distance, age and trust. Your station competes in that ranking. To find your station on the site, see Find your station on WxAlerts.
Three things decide how it does.
Trust tier
| Tier | Network |
|---|---|
| 1 | METAR / ASOS |
| 2 | Mesonet |
| 3 | Hosted PWS |
| 4 | CWOP / APRS |
A tier is a distance penalty, not a veto. At tier 4 your station has to be more than twice as close as an ASOS to win a field. That is the honest position described in why put a station on CWOP. A back-garden console is not half as good as an ASOS, but it is not as good either, and in most of the country being twice as close is easy, because the nearest ASOS is at an airport 40 km away.
Age
Readings decay. The effective distance doubles by the two-hour mark, so an hour-old reading from 2 km beats a fresh one from 20 km, but loses to a fresh one from 3 km. Past two hours a reading is treated as history rather than current conditions and drops out entirely.
Reporting on the standard five-minute cadence keeps you comfortably inside that, with room to miss a cycle.
Dewpoint is computed, not received
A CWOP packet carries humidity and no dewpoint, where a METAR carries dewpoint and no humidity. We derive the missing half of that pair so the two networks are comparable, which means your dewpoint here comes from your humidity sensor. A humidity sensor that has drifted or died shows up as a bad dewpoint as well as a bad humidity.
The consensus check
Some stations lie, and the dangerous case is not noise. It is a stuck or
placeholder value. Firmware that sends t000 for “no reading” puts 0 °F on the
map in a Florida August, surrounded by two dozen stations reading 82.
Nothing about that reading is out of range. Per-field bounds cannot catch it, because 0 °F is a real temperature in Montana in January. What makes it wrong is its neighbors, so that is what it is checked against: the median of nearby stations. The median, not the mean, because the mean is dragged by exactly the outlier being hunted.
| Peer radius | 50 miles: close enough to share an air mass, wide enough that a rural station still finds peers |
| Margin | About 30 °F from the neighbors’ median. Deliberately loose |
| Minimum peers | 3. Two peers can be two broken ones |
| Fields checked | Temperature and dewpoint only |
The margin is loose on purpose. This exists to catch broken instruments, not disagreeing ones. A sea breeze front, a thunderstorm outflow or a valley inversion can genuinely put 15 °F between two stations a few miles apart, and all three are real weather worth showing.
Wind and rain are deliberately not checked this way. A gust front or a single cell really does put 30 mph and an inch of rain at one station and nothing at the next one over, and a consensus filter would erase precisely the severe weather we exist to report.
References
APRS specification. aprs.org/doc/APRS101.PDF; aprs.org/aprs11/
(spec-wx.txt, SSIDs.txt); aprs.org/aprs12/weather-new.txt.
CWOP and MADIS. wxqa.com for the FAQ, QC and the current servers list;
madis.ncep.noaa.gov for signup and the surface QC notes; registration at
findu.com/citizenweather/cw_form.html.
QC and validation. weather.gladstonefamily.net (Weather Quality
Reporter); MesoWest at mesowest.utah.edu.
Siting. WMO No. 8, the CIMO Guide; NWS COOP standards.
Software. weewx.com/docs; cumuluswiki.org; the Direwolf user guide and
its Weather-Station.pdf.
Sensors. The ams/ScioSense AS3935 datasheet; Sensirion SHT3x and SHT4x; Bosch BME280 and BMP390.
Communities. The groups.io APRS lists; groups.google.com/g/wxqc for CWOP
QC and weewx-user; wxforum.net; the Ecowitt and Ambient forums.