Parameters¶

The &params= URL query parameter takes one or more forecast model parameters as argument. These parameters can include some advanced syntax for filtering the data, but the basic notation specifies the forecast model parameters to be queried, such as wind or temperature.

Basic syntax¶

The basic parameter argument specifies the forecast <parameter> or more specifically selects a <model>|<parameter> pair:

&params=<param> - a model parameter name (see models page for details)

Example

In order to request an atmospheric temperature at 2m above ground, simply pass temp as an argument. The default forecast model will automatically be assumed:

&params=temp

In order to also select the source forecast model use the <model>|<param> syntax described below.

&params=<param1>,<param2>,... - an array of model parameters can be requested.

Example

To request multiple model parameters at once, simply provide an array of parameters as argument to the query:

&params=wind,wdir,temp,relh

&params=<model>|<param> - a specific forecast model is selected by preceding the parameter namy by a model delimited by a | character.

Example

The following example queries the 2m temperature from the GFS model and the 10m wind speed from the GEP (GFS ensemble) model:

&params=gfs|temp,gep|wind

Once a model is selected using this syntax, all subsequent forecast parameters in the request assume that model as default.

Example

The following query argument requests wind speed, relative humidity and temperature from the ECMWF EPS (ensemble prediction system) model:

&params=eps|wind,relh,temp

the equivalent, but more verbose request would be as follows:

&params=eps|wind,eps|relh,eps|temp

Operators¶

The basic parameter syntax can be exptended by appending operators that generate new, derived, parameters on the fly. These operators can perform various useful statistics on the forecast data, such as probabilities from forecast ensemble memberes and proximity statistics such as maximum winds within a specific range from the route being queried.

The operator syntax consist of two parts appended to the forecast parameter to be operated on: A collector method, then followed by an optional filter method: :<collector>:<filter>

Collectors¶

:<collector> - collects parameter values in the space, time, or ensemble neighbourhood of a point along the route. Supported collectors:

:members - collects values from all ensemble members in the forecast.
:<R>km - collects all values within a radial distance (radial proximity) R kilometers from route.
:<R>nm - collects all values within a radial distance (radial proximity) R nautical miles from route.

Example

The following example collects all EPS wind speeds within a 100 nautical mile proximity of the route

&params=eps|wind:100nm

Attention

time proximity collector is scheduled to be released with version 1.1

Filters¶

:<filter> - specifies a filter (a function or mapping) operating on the collected proximity values defnied by the preceding collector. Supported filters:

:max - selects the maximum value from the collected proximity or member values
:min - selects the minimum value from the collected proximity or member values
:mean - calculates the mean value from the collected proximity or member values
:frac(<threshold>) - calculates the fraction of values exceeding a value threshold, such as <10.0 or >10.0
:prob(<threshold>) - this method is equivalent to the :frac( ) operation, but the result is intended to denote probability of exceeding the argument threshold.

Example

The following example looks up the maximum wind speed in the NCEP GFS forecast within a 100 nautical mile distance from the route:

&params=gfs|wind:100nm:max

This second example collects the ensemble members in the ECMWF EPS forecast and calculates the probability of exceeding a wind speed of 20 m/s:

&params=eps|wind:members:prob(>20)

Default value¶

If no &params argument is provided, the default is going to be the wind speed from the NCEP GFS model, equivalent to setting the &params argument as follows:

&params=gfs|wind