Derived Weather Parameters

This is an overview of all derived weather parameters and convenience Parameters. Below, each parameter is explained in more detail.

General Weather State

Weather symbol

The weather symbol is the easiest way to query an overview of the weather state.

weather_symbol_<interval>:idx

Available intervals: 20min, 30min, 1h,3h, 6h, 12h, 24h

Examples

Symbol Id (Day) Symbol Id (Night) Description
0
0
A weather code could not be determined
1
101
Clear sky
2
102
Light clouds
3
103
Partly cloudy
4
104
Cloudy
5
105
Rain
6
106
Rain and snow / sleet
7
107
Snow
8
108
Rain shower
9
109
Snow shower
10
110
Sleet shower
11
111
Light Fog
12
112
Dense fog
13
113
Freezing rain
14
114
Thunderstorms
15
115
Drizzle
16
116
Sandstorm

 

Weather Code

Weather code according to the present weather code 4677 of the international WMO Standard2 (mean for 1h, 3h, 6h, 12h, 24h)

weather_code_<interval>:idx

Weather symbol mean for 1h, 3h, 6h, 12h, 24h

  • Corresponding symbols to weather codes:

Examples

Weather Text

This parameter provides an automated text snipped describing the general weather state of the queried day. It is currently available in English, German, French and Italian.

weather_text_de:str
weather_text_en:str
weather_text_fr:str
weather_text_it:str

Example

validdate;weather_text_en:str
2019-04-08T00:00:00Z;Today after sunrise the sky will be overcast.
In the afternoon it will be mostly sunny. About 4 hours of sunshine are predicted. 
It stays very balmy with temperatures between 9°C and 16°C. 
After daybreak there is a slight northeasterly wind which shifts afterwards to a slight southerly wind. 
In the late evening the sky is partly cloudy, in the second half of the night dense mist may appear.

Visibility

This parameter returns the visibility in kilometers. You can expect foggy conditions if the visibility is less than about 1km.

visibility:<unit>

Available units: m, km

Examples

Runway Visual Range

This parameter returns the distance over which a pilot is able to see the runway surface markings at the runway margin. This parameter is used for assessing the conditions for landing and takeoff.

runway_visual_range:m
runway_visual_range:ft

Examples

Dew or Rime

This index gives you an idea whether dew or rime will occur. Dew or rime forms if the surface cools down quicker than the surrounding air, which causes condensation onto the surface at high relative humidities. Dew and rime are very sensitive to solar radiation and disappear quickly as the surface warms. Rime is the frozen version of dew.

0: neither dew nor rime, 1: dew, -1: rime

dew_or_rime:idx

Example

Fog

Check if there was any fog within the last hour or 30 minutes.

0: no fog, 1: fog event

is_fog_<interval>:idx

Available intervals: 30min, 1h

Example

  • Show if there is any fog expected during the next four days. The visibility is also shown as the two parameters contain similar information:
    https://api.meteomatics.com/__replace__0T00:00:00ZP5D:PT1H/visibility:km,is_fog_1h:idx/47.412164,9.340652/html

  • Another example as a json output for fog expectation during the next six hours:
    https://api.meteomatics.com/__replace__0T00:00:00ZPT6H:PT1H/visibility:km,is_fog_1h:idx/47.412164,9.340652/json

    {"version":"3.0","user":"api-test","dateGenerated":"2018-02-07T16:10:49Z","status":"OK","data":
    [{"parameter":"visibility:km","coordinates":[{"lat":47.4122,"lon":9.34065,"dates":
    [{"date":"2017-02-07T00:00:00Z","value":20},{"date":"2017-02-07T01:00:00Z","value":20},
    {"date":"2017-02-07T02:00:00Z","value":20},{"date":"2017-02-07T03:00:00Z","value":20},
    {"date":"2017-02-07T04:00:00Z","value":20},{"date":"2017-02-07T05:00:00Z","value":20},
    {"date":"2017-02-07T06:00:00Z","value":20}]}]},
    {"parameter":"is_fog_1h:idx","coordinates":[{"lat":47.4122,"lon":9.34065,"dates":
    [{"date":"2017-02-07T00:00:00Z","value":0},{"date":"2017-02-07T01:00:00Z","value":0},
    {"date":"2017-02-07T02:00:00Z","value":0},{"date":"2017-02-07T03:00:00Z","value":0},
    {"date":"2017-02-07T04:00:00Z","value":0},{"date":"2017-02-07T05:00:00Z","value":0},
    {"date":"2017-02-07T06:00:00Z","value":0}]}]}]}

Icing Potential

Icing is absolutely critical in aviation and in-flight icing on planes are the cause of multiple near-accidents or even crashes. Consequently, it is crucial for aviation to have reliable icing forecasts predicting the expected occurrence of icing on different altitudes and allowing for early circumnavigation.

icing_potential_<level>:idx

Available levels: 1000hPa, 975hPa, 950hPa, 925hPa, 900hPa, 875hPa, 850hPa, 825hPa, 800hPa, 775hPa, 750hPa, 700hPa, 650hPa, 600hPa, 550hPa, 500hPa, 450hPa, 400hPa, 350hPa, 300hPa

Index Description
0.0-0.2 No Icing
0.2-0.4 Traces
0.4-0.6 Light
0.6-0.8 Moderate
0.8-1.0 Heavy

Examples

Slippery Road

Check if there is any chance for slippery roads within the given interval.

Probability: 

prob_slippery_road_<interval>:p
Provides the probability for slippery roads from 0-100 %.

Binary Index: 

is_slippery_road_<interval>:idx
0: no slippery road conditions, 1: slippery roads possible

Available intervals: 1h, 3h, 6h, 12h, 24h

Examples

Planetary Boundary Layer Height

The planetary boundary layer (PBL) height is determined by identifying the height, where big wind direction changes, local minima of wind speed, local maxima of temperature, high temperature increases (inversion) or high potential temperature increases occur.

pbl_height:m

Examples

Snow Line

The snow line parameter provides the height above which precipitation occurs in the form of snow. Should it be undeterminable, for example if it is below ground level, it returns -666.

snow_line:m

Examples

Freezing Level

The freezing level parameter provides the altitude where the temperature equals 0 °C. If the freezing level is below ground, the return value is -666. In case of strong convection, the height of the freezing level correlates with the size of hail observed at the surface, since it determines the melting area for falling hail.

freezing_level:m

Examples

Stratospheric Polar Vortex (SPV): Wind speed

This index provides the average wind speed at 10, 50 or 200 hPa between 60°N and 90°N and thus indicates the strength of the stratospheric polar vortex during the polar winter.
The SPV index provides a measure of the circumpolar vortex strength and indirectly relates to a risk of cooling temperatures near the surface in the northern hemisphere, if decreasing below zero.
If the index becomes negative, the vortex disruption is such that a “split" or strong “displacement" is under way, possibly weakening the jet stream in the troposphere.

polar_vortex_<level>:ms

Available levels: 200hPa, 50hPa, 10hPa

Example

Power line oscillation warning

Precipitation in the form of freezing rain or wet snow can freeze onto overland power lines. With the increase in diameter and mass come a bigger air resistance and a lower resonance frequency. Strong wind over a sufficient amount of time could then excite the conductors to oscillate near their resonance frequency (sometimes referred to as gallop) and thereby damage the lines and masts.

A power line oscillation warning for the past 24 hours can be queried with the following parameter:

power_line_oscillation_24h:idx

The warning is binary with 1 corresponding to a warning and 0 to an all clear. Not taken into account are things like constructional details of the power lines or the Joule heat emitted by active power lines.

Example

Leisure Indices

The leisure index combines different weather parameters and assesses if weather conditions are favorable for certain outdoor activities or not. The index ranges from 0 to 1, where 1 means that conditions are perfect for the queried activity at the queried point in time (i.e. the parameter is instantaneous).
The indices are based on a combination of precipitation, temperature, wind speed, wind gusts, humidity, sunshine duration, snow cover, visibility and fog.

leisure_<activity>:idx

Available activities: ballooning, bbq, beach, biking, climbing, fishing, gardening, gliding, hiking, hunting, sailing, skiing, tv

Cold Index

This index combines several weather parameters like temperature, wind speed, humidity and precipitation and assesses how favorable these weather conditions are for catching a cold. The index takes values from 1 to 100, where higher values indicate higher risks.

cold_index:idx

Examples

Windchill

Gives the wind chill in °C as defined by Wikipedia1 .

windchill:C

Examples

Apparent Temperature

The apparent temperature is a measure for the human thermal comfort. On the basis of the air temperature, the apparent temperature is computed considering effects of relative humidity, wind speed and solar radiation.

t_apparent:<unit>

Available units: C, F, K

Examples

Heat Index

The Heat Index is a parameter that describes how humidity affects the perception of warm temperatures in shaded areas. Since the human body cools itself by evaporating sweat from the skin, higher humidity attenuates the effect of this mechanism. The index is computed using air temperature and relative humidity, while for temperatures below 27°C the heat index equals air temperature. The Heat Index can be used to assess the danger of heat exhaustion and strokes when performing outdoor activities. 

heat_index:<unit>

Available units: C, F, K

Heat Index Description
26 - 32 °C Caution: fatigue is possible, activity could result in heat cramps
32 - 41 °C Extreme caution: heat cramps and heat exhaustion possible, activity could result in heat stroke
41 - 54 °C Danger: heat cramps and heat exhaustion are likely, heat stroke is probable
>54 °C Extreme danger: heat stroke is imminent

Examples

Humidex

The Humidex is the Canadian equivalent of the Heat Index. It also describes the effects of humidity in combination with high temperatures. The computation of this index requires air temperatures and dew point temperatures. 

humidex:<unit>

Available units: C, F, K

Heat Index Description
20 - 29 °C Little to no discomfort
30 - 39 °C Some discomfort
40 - 45 °C Great discomfort; avoid exertion
>45 °C Dangerous, heat stroke possible

Examples

Wet-bulb Temperature

The wet-bulb temperature is the lowest temperature that can be reached by direct evaporative cooling. Thereby, the release of water from a saturated surface and the water absorption capacity of the surrounding atmosphere are in equilibrium. Due to the cooling by evaporation, the wet-bulb temperature always falls below the air temperature in dependence of the relative humidity.
The difference between wet-bulb temperature and air temperature is larger if the air is drier. The wet-bulb temperature exceeds the dew point temperature, except for relative humidities of 100 %, where air temperature, wet-bulb temperature and dew point temperature coincide.

wet_bulb_t_<level>:C

Available levels: 0m, 2m, 100m, 1000hPa, 975hPa, 950hPa, 925hPa, 900hPa, 875hPa, 850hPa, 825hPa, 800hPa, 775hPa, 750hPa, 700hPa, 650hPa, 600hPa, 550hPa, 500hPa, 450hPa, 400hPa, 350hPa, 300hPa

Examples

Equivalent Potential Temperature (θe)

θe is a conserved quantity during vertical motions in the atmosphere. It is the temperature an air parcel would reach if all the water vapor condensed and its latent heat was released, while the parcel is lifted adiabatically to 1000 hPa. The concept of θe is a powerful tool in order to differentiate between different air masses, which facilitates the identification of frontal systems. Moreover, it allows the assessment of atmospheric stability. If θe decreases with height, the atmosphere is unstable and convection is favored.

theta_e_<level>:<unit>

Available levels: 2m - 10000m (continuously), 1000hPa, 975hPa, 950hPa, 925hPa, 900hPa, 875hPa, 850hPa, 825hPa, 800hPa, 775hPa, 750hPa, 700hPa, 650hPa, 600hPa, 550hPa, 500hPa, 450hPa, 400hPa, 350hPa, 300hPa, 200hPa, 50hPa, 10hPa

Available units: C, K

Examples

Lake Temperatures

Meteomatics launched its own model for computing lake temperatures. The temperatures are calculated for a vast amount of lakes within Germany, Switzerland and Austria. Historical data is available back to 2015 and a 15-day forecast is provided daily. The resolution of the temperature data is 1 hour.

The model can be accessed via: 

mm-lake-temp

The corresponding lake temperature parameter has the following identification within the API:

t_lake:C

In order to perform a query for a certain lake, the coordinates are required as input. A list of all available lakes can be fetched by applying a find station query (see Find Station). For example, the following query creates a list of all available lakes within Germany:
https://api.meteomatics.com/find_station?location=germany&source=mm-lake-temp

The query for the lake temperature must contain the coordinates, the lake temperature parameter t_lake:C and the lake model specification mm-lake-temp:

This example shows the lake temperature for Lake Constance.

Current lake temperature with 15-day forecast for Lake Constance:
https://api.meteomatics.com/__replace__0T00:00:00ZP15D:PT1H/t_lake:C/47.6124,9.37955/html?source=mm-lake-temp&on_invalid=fill_with_invalid

Precipitation

Rainfall

Check if there was any rain within the last 30 minutes or last hour.

0: no rain, 1: rain event

is_rain_<interval>:idx

Available intervals: 30min, 1h

Examples

Snowfall

Check if there was any snowfall within the last hour or last 30 minutes.

0: no snowfall, 1: snowfall event

is_snow_<interval>:idx

Available intervals: 30min, 1h

Example

Sleet

Check if there was any sleet within the last hour or last 30 minutes.

0: no sleet, 1: sleet event

is_sleet_<interval>:idx

Available intervals: 30min, 1h

Example

Wind phenomena

Bise Index

This parameter computes an index to determine whether there is a bise and its strength. The bise is usually a cold wind from North-Easterly directions in the Lake Constance area which affects local weather conditions, including those of the Swiss Plateau. It is mainly triggered by a large scale air pressure difference between a low in the South-West of the Alps and a high on the northern side of the Alps. As a rule of thumb, if the pressure difference between Geneva and Constance is less that -2 hPa and the wind direction is North-East, then bise conditions are expected. If all conditions are met the value of the index is 1 and Bise is expected, otherwise the index is 0.

bise_index:idx

Example

Foehn Index

This parameter computes an index to determine the presence, strength, and direction of the Alpine Foehn. The Foehn is usually a strong, warm, dry wind crossing the Alps from the South-East to the North, but can also move in the the opposite direction. It mainly affects alpine valleys. Usually, it is triggered by large scale air pressure differences between a high in the South of the Alps and a low in the North-West of the Alps. As a rule of thumb, if the pressure difference between Lugano and Zurich is higher than 4 hPa, Foehn conditions are expected in the northern part of the Alps. If the pressure difference is less than -4 hPa, and the wind direction is South-East to the NorthFoehn, or vice versa, then foehn conditions are expected in the southern part of the Alps.

north_foehn_index:idx

If all conditions are met for North Foehn winds to be expected, the value of the index is 1, otherwise it is 0.

Example:

south_foehn_index:idx

If all conditions are met for South Foehn winds to be expected, the value of the index is 1, otherwise it is 0.

Example:

Moehlin Jet Index

The Moehlin Jet is a south-easterly local wind that originates from the Frick Valley and is responsible for dissolving fog in the region of Basel. This is the reason why sunshine duration there clearly exceeds the one of the Swiss midlands in fall. Favoring conditions are winterly high pressure situations over Switzerland, when the midlands act as a cold air pool. If the pool is full, the cold air masses spill over and follow gravity towards Moehlin, while the air is dried and heated on the way. The index takes values of 0 and 1, where 1 indicates the presence of a Moehlin Jet.

moehlin_jet:idx

Example

Santa Ana Wind Index

This parameter computes the presence and strength of the Santa Ana Winds in southern California. These are strong and extremely dry down-slope winds that originate from the desert and descend towards coastal areas. They develop if dry, cool high-pressure air masses are prevailing in the Great Basin and low pressure over the Pacific. Typically, these events occur in fall. Due to the extremely low relative humidities, such an event provides eligible conditions for wildfires. The index takes values in the range of 0 to 1. If the index exceeds 0.6, Santa Ana Winds can be expected.

santa_ana_wind:idx

Example

Global Circulation Patterns

North Atlantic Oscillation Index

The North Atlantic Oscillation describes pressure fluctuations between the Icelandic low and the Azores high. This parameter is computed with the sea level pressures of Ponta Delgada on the Azores Islands and Reykjavík. A positive NAOI implies that increased westerlies are present, which result in cool and contrary weather conditions. If the NAOI is negative, then the westerlies are suppressed and blocking situations can occur, which are responsible for stable weather conditions. The index changes daily.

north_atlantic_oscillation:idx

Example

Southern Oscillation Index

The Southern Oscillation is the atmospheric contributor to El Niño. The oscillation describes a reversal of surface pressure over Indonesia and the eastern Pacific. This index is used as an indicator for the strength of the southern oscillation and to assess the relative strength of the trade winds. If the Index is positive, the pressure over Indonesia is higher than over the eastern Pacific. This situation is referred to as El Niño. If the index is negative, the pressure over the eastern Pacific is higher. This situation is then referred to as La Niña. If the index is equal to zero, then neutral conditions are prevailing. The index changes daily.

southern_oscillation:idx

Example

Forest Fire Risk Indices

Forest Fire Index

The Forest Fire Index estimates the risk of forest fires based on moisture information of three different soil layers. The index ranges from 0 to 1, where the risk increases for values exceeding 0.5. A value of 0 indicates low risk, while a value of 1 indicates very high risk.

forest_fire_warning:idx

Examples

Fosberg Fire Weather Index

The Fosberg fire weather index indicates the risk for bush/grass fire and ranges from 0 to 100 (continuous scale). The fire danger is evaluated according to the present weather without taking into account past weather conditions.

fosberg_fire_weather_index:idx

Examples

Drought Index

This index forecasts whether a certain location is under a drought or not. The percentiles of the deviation of the current time window from the mean of the past years is computed. The percentiles are then grouped into bins which gives the following output scale for the drought index:

Percentile 0-10 10-20 20-30 30-40 40-60 60-70 70-80 80-90 90-100
Index -4 -3 -2 -1 0 1 2 3 4
      dry ⟵   ⟶ humid     
drought_index:idx

Examples

Weather Warnings

All weather warning parameters are inspired by the descriptions of the DWD.

Frost

This parameter indicates if there is any frost.

frost_warning:idx
Warning Description
0 No frost
1 Frost
2 Severe Frost

Examples

Heavy Rain Warning

This parameter indicates if any heavy rain events will occur in a given time interval.

heavy_rain_warning_<interval>:idx

Available intervals: 1h, 6h

Warning Description
0 No severe rainfall
1 Heavy Rainfall
2 Severe Heavy Rainfall
3 Extreme Heavy Rainfall

Examples

Incessant Rain Warning

This parameter indicates if any incessant rain events will occur in a given time interval. A rain event is defined incessant if it lasts for at least 60 minutes.

incessant_rain_warning_<interval>:idx

Available intervals: 12h, 24h, 48h, 72h

Warning Description
0 No incessant rainfall
1 Incessant Rainfall
2 Severe Incessant Rainfall
3 Extreme Incessant Rainfall

Examples

Snow Warning

This parameter indicates if any severe snow fall will occur in a given time interval.

snow_warning_<interval>:idx

Available intervals: 1h, 6h, 12h, 24h, 48h

Warning Description
0 No severe snowfall
1 Snowfall
2 Snowfall
3 Heavy Snowfall
4 Extreme Heavy Snowfall

Examples

Wind Warning

This parameter indicates if any dangerous wind speeds will occur in a given time interval. Wind speeds are considered dangerous if they exceed 50 km/h.

wind_warning_<interval>:idx

Available intervals: 1h, 2h, 3h, 6h, 12h, 24h

Warning Description
0 No severe wind conditions
1 Wind Gusts
2 Squall
3 Severe Squall
4 Violent squall
5 Gale-Froce Winds
6 Extreme Gale-Force Winds

Examples

Thunderstorm Warning

This parameter indicates if any thunderstorms will occur in a given time interval.

tstorm_warning_<interval>:idx

Available intervals: 1h

Warning Description
0 No thunderstorms
1 Thunderstorm
2 Heavy thunderstorm
3 Severe thunderstorm
4 Severe thunderstorm with extreme squalls and heavy rainfall

Examples

Soil Moisture Index (SMI)

The soil moisture index indicates the wetness of the soil. This index is computed using the permanent wilting point and the field capacity, which both depend on the geographical location (soil type). The index is 0 if the permanent wilting point is reached and 1 at field capacity. Note that the index can exceed 1 after rainfall events. The soil moisture index is available for 4 depth levels.

soil_moisture_index_<depth>:idx

Available depths: -5cm, -15cm, -50cm, -150cm

Depth Identifier Soil Layer
-5cm 0 - 7 cm
-15cm 7 - 28 cm
-50cm 28 - 100 cm
-150cm 100 - 289 cm

Examples

Soil Moisture Deficit (SMD)

This parameter computes the difference between the actual water content of the soil and the possible water content that the soil can hold in mm. The amount of water that can be hold is called field capacity. The calculation of the SMD is mainly based on soil water information in several depths as well as other meteorological parameters. The SMD is a useful tool in order to assess prevailing soil conditions like droughts. The SMD also depends on the soil type.

soil_moisture_deficit:mm

Examples

Soil Water Content

This parameter provides the volume of water for 4 soil layers. The soil water content depends on the soil type, soil depth and the groundwater level.

volumetric_soil_water_<depth>:m3m3

Available depths: -5cm, -15cm, -50cm, -150cm

Depth Identifier Soil Layer
-5cm 0 - 7 cm
-15cm 7 - 28 cm
-50cm 28 - 100 cm
-150cm 100 - 289 cm

Examples

Soil Type

This parameter provides the soil type for any location on the globe. The index takes values from 0 to 7, where each number indicates an individual soil type.

soil_type:idx
Soil Type Description
0 Ocean/Lake
1 Coarse
2 Medium
3 Medium Fine
4 Fine
5 Very Fine
6 Organic
7 Tropical Organic

Examples

  1. Wikipedia Page of Wind Chill: http://en.wikipedia.org/wiki/Wind_chill
  2. WMO Weather Code Standard: https://www.nodc.noaa.gov/archive/arc0021/0002199/1.1/data/0-data/HTML/WMO-CODE/WMO4677.HTM

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