Imagery Type

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

Provider

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.

Model

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 organizations 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

Run selects which model run (date and time) to show. Each model is run several (e.g. 2 or 4) times a day as new weather observations are added. Thus each run is effectively a new (or modified) forecast. The YYYYMMDDHH UTC date/time stamp of a run is its effective time -- when its run started. However it takes several hours to complete, so a run is generally not available until several hours after its timestamp. E.g. for CMC, the 12:00 (YYYYMMDD12) UTC run is not available until 16:00 UTC.

The run suffixed with a  now icon is the latest, and typically most accurate -- as it incorporates the most recent data. It is thus chosen by default. (If model runs are shown but none have a  now icon, then auto-refresh is off; see Settings help page.) Some providers only provide one model run, in which case it is shown unselectable.

One way to see if a model getting "confident" about its forecast is to halt the animation controls on a fixed forecast time of interest, e.g. event time with the button, and the slider on/near the  event time tick mark. Then cycle through different model runs: if the weather starts to look consistent across the most recent several runs for the same forecast time, 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 for each run checked.)

If a future event time is not yet in range of the latest model run, the time left until it is expected to be in range will also be shown, as an Event in range in Nd Nh Nm heading in the select box (when the box is clicked/in use). The hours and minutes left until the next model run (which may or may not have the event in range) is expected to be available are usually shown as well, as a (next in Nh Nm) heading in the select box. A tool tip shows both times as well. Note that model runs are not available until several hours after their timestamps (see above). Note also that these availability times are merely estimates based on experience: future runs may actually be available sooner or later than indicated. If later, choosing the  run may result in no/broken imagery shown for a time, until that run actually does become available.

Product

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

Region and the 8 arrows to its right (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 US and any of the other regions (which are smaller and generally within it).

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.)