FREQUENTLY ASKED QUESTIONS
How should I use the forecast? (limitations)The forecast data displayed by XCWeather is from a high quality numerical weather prediction model run by the United States government (GFS) and is updated every six hours. The output from this model gives forecast data in the form of a grid of points at ½ degree (~50km) intervals. XCWeather interpolates this information to give a forecast for each location. You should be aware that at this resolution the forecast will not be able to fully model topographical effects. This means that in coastal areas localised effects such as sea breezes will not be fully incorporated into the prediction, wind speeds in elevated areas will not fully account for peaks and valleys and that temperatures for smaller islands can be overly influenced by the surrounding sea. Also beware that the forecast gives average wind speed but you may well experience significantly higher gust speeds.
Please use this forecast information advisedly and utilise your knowledge of the area when making decisions. The forecast is only raw model data in human readable format, it's up to you to interpret that output. Please also note that numerical weather models are not perfect, it is normal for them to be very wrong on occasion.
For more information on interpreting numerical weather prediction information take a look at Frank Singleton's web pages.
How are the observations collected?Current weather information is taken from instruments sited at each location and barring technical difficulties should reflect the conditions on the ground at the time of the observation. Most wind speed measurements are made at a height of 10 meters above ground level.
The observation maps are updated every 30 minutes. Please note that the time stamp on the map is when the image was created which will not necessarily be the same time as the observations were taken. The actual time of each observation is clearly noted below the station name. If the observation is over 3 hours old the map arrow will be grey and the time stamp will be in red. Observations over 5 hours old are removed from the map.
We try to filter out as much erroneous data as possible but because XCWeather is totally automated the occasional rogue report will inevitably slip through. Sometimes the problem is a miss-calibrated sensor at one of the stations or else it might be a genuine mistake on the part of the observer who's submitting the reports. In any event the problems are almost always transient and correct themselves in an hour or two. If a station consistently miss-reports please let us know and we'll remove it from the map until it's fixed.
Why is the visibility forecast experimental?
The visibility forecast is from a different source to most of the information displayed on XCWeather. It's not as mature and should be considered experimental. Because of this, the visibility forecast values aren't displayed by default. If required, you will need to turn them on using the Enable button on the right-hand side of the detailed forecast page. The visibility forecast maps are also marked as experimental.
This is the only visibility forecast available to us. Therefore if it predicts mist or fog the weather symbols may show this as guidance even if the full visibility forecast is disabled.
To learn more about the visibility forecast and how it's generated you can visit the Global Visibility Guidance page of the US National Weather Service Marine Meteorology group.
The experimental status only applies to the visibility forecast. The visibility observations are not from the experimental data but are actual readings taken at each station.
Can you provide historical weather information?
Unfortunately we don't keep any historical records so we can't help with this kind of enquiry. However you could try Weather Underground who do keep some historical data.
Why are some arrows red?Red arrows show that the wind is gusting. The wind is said to be gusting if the maximum speed is 10 knots or more above the current average speed. The size of each arrow on the map is always based on the average wind speed.
Why are two wind speeds reported for the same time?Where available XCWeather will report both the average and gust wind speeds in the form 12 to 32 mph. In this example the wind is averaging 12 mph but there have been gusts to 32 mph.
My favourite station has disappeared, is there a problem?All of the data plotted by XCWeather is obtained from sources on the internet and sometimes this data is temporarily unavailable. This maybe because of problems on the internet itself (web servers crashing, internet connections going down) or because of equipment problems at the station.
In addition to transient problems, some stations are only manned during office hours so they disappear overnight and at weekends. Others are just notoriously fickle and only seem to submit reports when they feel like it.
In any event XCWeather will keep looking for the data every half an hour and automatically start plotting it as soon as it's available. Unfortunately it's rare that we can do anything to speed up this process.
Do you mind if I put a link from my site to XCWeather?Please be our guest, the more the merrier.
Can I use your images and data on my website?Please don't take the images or data from XCWeather.