Foehn Chinook Warming Rate
Model windward dry/saturated ascent then dry lee descent with supplied crest/LCL/lapse rates; explicit rainout/unsaturated descent idealization, not actual Chinook event or environmental profile fit.
Description
Foehn warming can be illustrated by dry and saturated windward ascent followed by dry lee descent.
Foehn warming can be illustrated by dry and saturated windward ascent followed by dry lee descent. Rainout and unsaturated descent are assumptions of this idealized trajectory.1
Model windward dry/saturated ascent then dry lee descent with supplied crest/LCL/lapse rates; explicit rainout/unsaturated descent idealization, not actual Chinook event or environmental profile fit.
When to use Foehn Chinook Warming Rate
Use this tool to model windward dry/saturated ascent then dry lee descent with supplied crest/LCL/lapse rates; explicit rainout/unsaturated descent idealization, not actual Chinook event or environmental profile fit.
Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.
How to use Foehn Chinook Warming Rate and understand its results
- Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.
- Enter upwindSurfaceTemperatureC, upwindHeightM, crestHeightM, leeSurfaceHeightM, suppliedWindwardLclHeightM, callerDryLapseCPerKm, callerSaturatedLapseCPerKm using the field table and calculation rules, then run the tool.
- Read modelCrestTemperatureC, modelLeeSurfaceTemperatureC, modelLeeMinusUpwindWarmingC. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| upwindSurfaceTemperatureC | Upwind surface temperature c | number | Required |
| upwindHeightM | Upwind height m | number | Required |
| crestHeightM | Crest height m | number | Required |
| leeSurfaceHeightM | Lee surface height m | number | Required |
| suppliedWindwardLclHeightM | Supplied windward lcl height m | number | Required |
| callerDryLapseCPerKm | Caller dry lapse c per km | number | Required |
| callerSaturatedLapseCPerKm | Caller saturated lapse c per km | number | Required |
Enter a crest no lower than either surface, an LCL no lower than the upwind origin and nonnegative dry/saturated lapse rates. Split ascent at the LCL and descend using the dry rate; return crest and lee temperatures and signed lee-minus-upwind warming.
crest T = upwind T − ascent lapse losses; lee T = crest T + dry lapse × descent km Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| modelCrestTemperatureC | Model crest temperature c | number |
| modelLeeSurfaceTemperatureC | Model lee surface temperature c | number |
| modelLeeMinusUpwindWarmingC | Model lee minus upwind warming c | number |
{
"input": {
"upwindSurfaceTemperatureC": 20,
"upwindHeightM": 0,
"crestHeightM": 2000,
"leeSurfaceHeightM": 0,
"suppliedWindwardLclHeightM": 1000,
"callerDryLapseCPerKm": 10,
"callerSaturatedLapseCPerKm": 5
},
"output": {
"modelCrestTemperatureC": 5,
"modelLeeSurfaceTemperatureC": 25,
"modelLeeMinusUpwindWarmingC": 5
}
}Limitations and assumptions
The supplied trajectory does not establish an actual Chinook event or reconstruct environmental temperatures.
Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Showalter Index: Estimate Showalter 850-hPa-origin parcel index via explicit supplied LCL and caller piecewise dry/moist lapse approximation; differs from supplied surface-parcel lifted index, not a full pseudoadiabatic solver or validated thunder forecast. For a complementary task, use Bora Katabatic Drainage Speed: Evaluate inviscid uniform katabatic parcel acceleration over supplied slope distance/density proxy; no friction, entrainment, sustained Bora wind prediction or safety assessment.
References
-
Foehn Chinook Warming Rate — tool.io
Similar or alternative tools
- Showalter Index
Estimate Showalter 850-hPa-origin parcel index via explicit supplied LCL and caller piecewise dry/moist lapse approximation; differs from supplied surface-parcel lifted index, not a full pseudoadiabatic solver or validated thunder forecast.
- Bora Katabatic Drainage Speed
Evaluate inviscid uniform katabatic parcel acceleration over supplied slope distance/density proxy; no friction, entrainment, sustained Bora wind prediction or safety assessment.