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.)