Imagery Type

The following controls in the prediction page GUI area are used to choose what type of imagery to show:

Provider selects the overall weather service provider. This controls not only the type of imagery (forecast vs. satellite), but also what models, model runs, products, and regions are available, as different providers have different offerings. Most providers are focused on only one or a few continents; hence they are grouped that way.

Product selects which product to show, e.g. cloud cover, temperature, wind etc. Total cloud cover or its equivalent is generally the default/first product.

Region and the 8 arrows beneath it (or the numeric keypad buttons, if active) select which region to show. The arrows move roughly in the direction indicated. Note that different providers/products/etc. have different regions, and they are rarely due-north/south/east/west of each other, nor of consistent size. The arrows may thus not always be reciprocal; e.g. moving southeast and then northwest may not always return to the same region (or even be allowed). An arrow with no region reasonably adjacent in that direction from the current region will be disabled (greyed out).

Note that some regions may only be accessible via the select box and not the arrows; e.g. in the NWS forecasts provider, moving to/from Contiguous United States and any of the other regions (which are smaller and generally within it).

Model selects which forecast model to show. A forecast model is a statistical tool, run by complex software, which is used to generate the forecast maps. Various weather agencies have developed different models, and their forecasts often differ -- so check multiple models where possible. Some providers only offer one model, so it is unselectable for them. Satellite providers do not use any models, as they are showing observations not forecasts.

Model run selects which model run to show. Each model is run several times a day as new weather information is added, to update the forecasts. The run suffixed (latest) is typically the most accurate -- as it incorporates the most recent data -- and thus is chosen by default. (If model runs are offered but none say (latest), then auto-refresh is off; see Settings help page.)

One way to see if a model getting "confident" about its forecast is to halt the display on a fixed forecast time of interest (e.g. event time), and choose different model runs: if the weather starts to look consistent across the most recent several runs for the same forecast time (as set by imagery slider), then the model is more sure of its predictions. (Be sure that the selected forecast time is in range of all model runs being checked: the image timestamp below the slider should stay the same.)

The hours and minutes left until the next model run is expected to be available is usually shown as well, as (next in Nh Nm). Note that this is merely a fixed estimate based on experience: the next run may actually be available sooner or later than this. If later, choosing (latest) may result in no imagery shown for a period of time, until the next run actually does become available.

Cascading options

If a used-car website were to have two select boxes for car make and model, the available model options would likely change based on the make selected -- i.e. the car make selection "cascades" down to the car model options.

Similarly on this site, Provider, Model, Product, and Region selections cascade downstream in that order. This means that selecting the provider will change the available models, products, and regions; selecting the model will change the available products and regions but not providers; etc. The interface will attempt to preserve downstream selections when their available options change due to an upstream selection, but this may not always be possible. In such cases, another upstream selection may need to be made to restore or change downstream available options.

Default provider/region

Some maps have one or more default providers and regions defined, which are selected if none are set in the URL (no #... anchor info) on initial page load. These defaults (especially region) are defined to best fit the prediction map; e.g. a prediction that mostly occurs over the eastern US might have CMC and Eastern United States defined as its default. (The procedure to set default regions is automated and does not always select the best region, however.)

Since the preferred/"best" provider might not have the longest forecast range, alternate defaults may also be defined, which will be selected if the event time is out of range of the most-preferred provider. For example, many US predictions have Wetterzentrale forecasts / North America as a secondary default for a more-preferred default of CMC / Eastern United States: the former is lower-resolution but longer-range, the latter is higher-resolution but shorter-range. On such maps, the provider and region may thus change from one default to another on a later visit, when the event time becomes in range of the more-preferred provider. (This only happens if no URL-storable GUI element has been user-changed, i.e. there is no #... URL anchor. See the Bookmarks section on the Overview help page.)