Fog - the atmospheric murkiness
When the weather is calm and temperature and humidity is just right, mist forms close to the earth's surface. But why?
BBC Weather has started working with new weather service provider MeteoGroup, so you may have noticed some changes to the BBC Weather website and apps on iOS, Android and Amazon Kindle.
More information about what's changed can be found in our quick guide, but here are answers to some frequently asked questions about BBC Weather.
We've divided the FAQs into four main areas: 1. Questions about weather forecasting information, 2. Technical questions about the Weather website and online services, 3. Questions about BBC Weather on TV or radio, 4. General questions about BBC Weather.
A short spell of rain or showers have been forecast - why hasn't it rained where I am?
Showers can be especially hard to forecast. Their time or location doesn't have to be far out for the forecast not to be 100% correct on the website/app graphics/red button. Showers (including hail/thunder/snow). can be very heavy or long lasting It is also possible for showers to form into bands which can cause one area to have continuous rain.
We flag this up on the TV and video forecasts where we can give more context, and in the text on the website. If you are making plans either looking at a video forecast or the map on the website can be helpful to see if there are showers nearby. This video answers the question: Why are showers so hard to forecast?
What does % chance of precipitation i.e. rain, snow, hail, mean?
MeteoGroup uses the probability of precipitation (% chance), and this ranges from 0% (no chance at all) to 100% (it will be wet).
So what does a 20% chance of rain actually mean? It means that out of 100 situations with similar weather, it should rain on 20 of those, and not rain on 80. In a nutshell, it means that, whilst you may get some rain, it's much more likely (but not certain) to stay dry.
The probabilities are given for the location chosen, and thus are valid for that location only. As MeteoGroup forecasts take advantage of hourly updates, which include real-time information from radar, satellite, and nearby weather station observations, you may notice the probabilities changing in the short-term (next 2-3 hours).
This gives you the chance to spot when, for example, a shower may be approaching your location, as the probabilities will tend to rise.
Note that when the chance of precipitation is less that 5% it will appear grey on the website. Above 5% it will be blue.
How does % chance of precipitation relate to the weather symbol?
The weather symbol is generated by taking a number of weather measurements, and then working out the most likely weather type based on them. For "wet weather" symbols these measurements include the hourly rainfall amount as well as the % chance of rain (probability of precipitation).
In order to generate a wet weather symbol, there needs to be at least some measurable rainfall expected (over 0.1mm per hour, say) and a reasonable chance of rainfall.
This means that where very light, patchy rain or drizzle is expected, there may be occasions where the chance of seeing at least a few spots of rain is high (so a high % chance of rain), but the actual amount expected is very low (less than 0.1mm of rain in one hour).
This would be the type of weather where you feel a few spots of rain on the breeze, but it's not even enough to dampen the roads and pavements. In this case, the weather symbol would remain as a "dry" weather symbol (e.g. a cloud) but the probability of rain might be quite high.
On the other hand, in shower situations the chance of rain in an individual hour might be low - in particular as it is difficult to predict long time ahead at which particular time an isolated shower will hit a particular place. When it occurs, it can be a strong short downpour and therefore the predicted amount of precipitation is reasonable high to generate a "wet" weather symbol - despite a relatively low precipitation probability.
What does "feels like" temperature mean?
The temperatures in our forecasts represent the "air temperature" forecast - that is, the temperature that a properly shielded thermometer would record.
However, there are factors which can lead to a day "feeling" hotter or colder than this value alone might suggest. The two main factors which cause this sensation are wind speed and humidity.
Our perception of temperature comes down to how quickly, or not, our skin is cooled. In light winds and high humidity, especially with higher temperatures, any moisture on our skin will be slow to evaporate, and so the cooling will be lower.
Thus, the air may "feel" somewhat warmer than the temperature indicates. Similarly, but going the other way, a windy and dry day, especially when cold, may lead to the air "feeling" colder than the temperature may suggest.
Thus, the "feels like" temperature is designed to give an indication as to when these extra factors may combine to make the apparent temperature seem higher, or lower, than indicated. Of course, the perception of temperature is rather subjective, so these should only be taken as broad guidelines.
Hourly forecasts now go out to 14 days but quite often the details change - why?
Working with our new weather provider MeteoGroup, we are able to bring more data to our digital audiences. Like many other apps this includes hourly forecasts out to 14 days.
When producing these forecasts in the medium term, our provider uses weather model information which tends more towards trends in the weather, rather than a single 'deterministic' output.
The confidence in the forecast decreases as you move further into the future, and also depends on the climatology and actual weather pattern. However we believe our audiences understand that and would rather have the information, to give them the ability to see the trends over time to help them make the decisions they need to make.
Why is there sometimes a discrepancy between the day symbol, hourly information and map weather forecasts on the BBC Weather site/app?
Daily weather symbol: The daily symbol shows the most representative weather type for the whole day, or whole night, at that location. This could either be the predominant weather - that is, the weather that lasts for the longest period of time - or alternatively, the most significant weather.
It is hard to give a single weather symbol to cover a whole day as the weather can change a fair bit. So the symbol is chosen to reflect the weather that is most likely to cause impacts - for example even if it is only expected to rain for a few hours that will highlight the risk. As the day moves on this rule applies to the most impactful weather for the remainder of the day. At 6 o'clock it changes to the weather for the evening.
This does mean that if there is severe weather in the morning that clears that the day symbol may not match the remaining hourly symbols. This should be corrected at midday. For the purposes of the forecast the day covers the period from 0600 to 1800 GMT and the night from 1800 to 0600 GMT on the following day.
Hourly weather symbol: The symbol that appears for each hourly time step indicates the weather expected at or near the relevant location, around the time indicated. For example if a shower symbol appears for Wolverhampton at 1500, we are saying there is a chance of a shower in the Wolverhampton area at or close to 1500. There could be one a short distance away and it may actually occur at 1430.
There can be discrepancies seen between the maximum/minimum temperature given for the daily summary and the highest and lowest temperatures seen in the hourly breakdown. This is because the hourly value is given for "on the hour" whereas the max/min may occur between the hourly points so may be slightly higher/lower.
Maps: The weather maps are produced using MeteoGroup data once every three hours whereas the text-based data refreshes on an hourly basis, meaning the map data can often lag behind the 14-day forecast spot data.
Why does the wind symbol sometimes jump to over 40mph and turn black? Why are there no wind speeds in the 30s?
When the forecast predicts gusts of wind over 40mph, the hourly wind icon - which usually shows the sustained wind speed - will change to a black icon showing the expected wind gust speed. This black icon will help to inform you in advance of potential hazards that may shape your day, for example severe impacts on transport.
What is UTC (Coordinated Universal Time) and why is it used for Coast & Sea?
Our Coast & Sea section, including Tide Tables, uses the UTC time standard. During British Summer Time (BST), UTC is one hour behind the time observed in the UK.
You should therefore add one hour to the times shown. UTC is a safer system for displaying information for seafarers as it provides consistency all year round for all locations.
Why wasn't there a warning? Why was a warning issued when there weren't any impacts? I want more information about storm naming
National Severe Weather Warnings are issued by the Met Office. We do feed back to the Met Office but you can contact them directly via firstname.lastname@example.org
I've stored my favourite locations, but when I go to the new site they have gone. Why?
Your favourite locations can be easily added by searching for a new location and then selecting "Add to My Locations" button near the top of the page, where you will be prompted to sign in to, or register, a BBC ID account. More information can be found on the My Locations FAQs page.
We ask you to sign in to add locations because it's the best way to keep them safe and secure.
In the near future, we will continue to make improvements which will allow you to see forecast snapshots from all your favourite locations on the homepage if you are signed in.
However, you can find all your recent location searches by tapping on the search field at the top of any BBC Weather page. And you don't have to sign in/register with the BBC to see them.
Why is there missing data in the observations section and '- -' instead?
The main reason you may be seeing this symbol is that the local weather station does not collect this data. If all of the data is missing, then it is more likely that there is a fault with the weather station or the data feed to the website. This is likely to have been reported but can sometimes take a while to fix.
Something is broken on the website. Why?
We rigorously test the BBC Weather website on a variety of devices, operating systems and browsers. Many of the issues that our users face can be resolved by updating to the latest version of the browser and checking that you have the correct settings enabled.
Some antivirus/security software or administrator policies on a work computer can also interfere with expected behaviour, e.g. preventing you from changing your preferences (from Celsius to Fahrenheit, for example), on the site.
Unfortunately, due to the combination of available devices, operating systems, browsers and settings that can cause issues to appear, we cannot offer technical support on an individual basis.
However, if you find that something is broken with the website, we advise you to:
Why do I see adverts when I visit the BBC Weather website?
To make sure we're offering the best value for licence fee payers, users outside of the UK have access to the international version of the BBC Weather website. The international version of the website contains advertising.
We try to make sure that the advertising is only visible to people outside the UK, but due to the way certain Internet Service Providers (ISPs) connect you to the web, your location may be detected incorrectly.
Another reason you may be seeing adverts is if you're using a VPN (Virtual Private Network) connection to a server outside of the UK. People often do this for work reasons, for example to connect to their company networks.
However, nowadays people are using VPN connections more frequently to access foreign versions of streaming websites. You can see the UK version of our website (advert-free) by disconnecting from the VPN.
If you're viewing the BBC Weather website from within the UK and you can see advertising, please use this form to let us know.
What new features are there on the website/app?
There are a host of new features on the website and app, including: 14-day forecasts, more locations, new data fields and a new interactive map. You can read more about the new features on the BBC's Internet Blog.
How can I request my town/city is added/correct an error with it? (both app and website)
Go to the 'Contact the BBC' section on the website and follow the appropriate instructions to leave comments about a town to be added or an error to be corrected.
Questions about the BBC Weather app
How can I download the BBC Weather app?
You can download the Android version from Google Play, the iOS version from the iTunes store and Amazon version from the amazon.co.uk website.
The BBC Weather app is only available to download in the UK.
If you have a question about the BBC Weather app which isn't covered above, please refer to our Apps FAQs.
How do I report a technical problem with the website or app?
We try to make sure there are as few technical problems with the apps and website as possible. We test on a wide range of devices and browsers to provide the best possible experience.
However, if you have identified an issue that is not covered by our FAQs above, please let us know.
A lot of technical issues are quite specific. We therefore ask that you provide as much detail as possible about the problem, such as:-
Why isn't my town/city on the TV weather map?
The towns and cities on the map are only there to help you find your location. If we put more town names on, it would obscure the weather information, and for this reason you will often see the locations we choose around the coast. Also it might be that by adding where you live we have to lose a temperature disc or wind arrow from somewhere else.
We do appreciate that people like to see their location on the map so aim to mix the towns and cities around from time to time.
You can find a forecast for thousands of locations on the BBC website and app (UK only). On there you will also find local video forecasts and a graphics map with more detail for your area.
I've noticed that the forecast for my region is different on TV to the forecast on the website and/or app. Why is this?
While we use the same data source across TV, radio, online and the app, the forecasts can differ slightly due to the frequency at which this data is updated, as well as the granularity of the location information.
For example, a TV or radio broadcast you see at 1pm will be prepared using the latest data we have up to that point. If you check the forecast at 2pm on the website, we may have since received an updated set of data, and as such, the forecast available online could have changed from the one you saw earlier on TV.
Similarly, the forecast for a typical UK location on the website is updated every hour. Depending on the frequency settings you have configured in the Settings menu of the app, weather information in the widget could be anything up to 12 hours behind, although you will always see a message informing you when the app last refreshed its feed. You can also manually refresh the data by tapping the refresh icon.
While we always aim to provide an accurate and consistent forecast, we choose to provide you with the most up-to-date and accurate information as soon as we receive it.
Why do you never mention my region on the TV forecasts?
Our forecasts tend to be quite short and we have to cover a large geographical area for a useful timeframe therefore it is not possible for us to mention everywhere.
For that reason sometimes we may focus a little more on the areas there are more impacts from the Weather and also talk about general regions. You can always find a detailed forecast for your area on the BBC Weather website or BBC Weather app.
How do I send in my photos of the weather?
You can upload photos to us via the Weather Watchers website
I am a teacher - where can I find resources?
You can find all the BBC Learning resources on the Bitesize website
In addition the Royal Meteorological Society website has links with resources for schools - Metlink: Weather and Climate for Schools and Teachers
Secondary Schools can also sign up to BBC News School Report to report on the weather
Can I go on a tour of the BBC Weather Centre?
There are no tours at BBC News Broadcasting House but you can find out about what tours are available across the UK on the BBC Shows and Tours website
Can I apply for work experience at BBC Weather?
All BBC work experience is organised centrally. You can find out more about it here - bbc.co.uk/careers/work-experience
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