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Calculation of fog-point via Craddock & Pritchard method

 

T at 12 UTC (°C)
Td at 12 UTC (°C)

Mean* cloud amount (oktas) 0-2
2-4
4-6
6-8
Mean* geostrophic wind speed (kn) 0-12   13-25
* = mean of forecast values for 1800, 0000 and 0600 UTC

Calculated Tfog °C

 


Tfog - Tmin (°C) Forecast
≥ +1 Widespread fog
= 0.5 Risk for fog at end of night
= 0 Fogpatches around sunrise
-0.5 tot -1.5 Fogpatches on favorable spots
≤ -2 No fog

 
Used formula:
 

Tfog = (0.044 * t) + (0.844 * td) - 0.55 + a

(a = adjustment which depends upon the forecast cloud amount and geostrophic wind speed)

Note: to be used for calculation of radiation fog

 

Source: Forecasters' reference book - ISBN 0 86180 306 X

 

 

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