Illustration of Orographic Precipitation
Let's look at the effect of orographic process on temperature (Please read slowly and
carefully, as every word here counts:
Example effect of orographic process on temperature:
*Note: Dew point temperature has been kept constant for the purposes of this example. Normally, dew
point temperature would be subject to change as the orographic process progresses.
1. The air at Vancouver has a temperature of __________ and a dew point of
__________.
2. Air rises and cools at the __________ Adiabatic Lapse Rate (__________
C/__________ m) until the dew point is reached (__________ m).
3. Clouds form and air continues to rise and cool at the Saturated Adiabatic Lapse
Rate __________ °C/__________ m) to the crest (__________ m).
4. At some point above __________ m, rain will fall (snow above __________ m the 0° level).
5. After moving over the crest, air temperature begins to rise (at the __________
ALR) as the air descends.
6. At Lillooet, the temperature is __________ (warmer or cooler) and __________
(drier or wetter) than it was at the equivalent elevation on the windward side.
7. The cycle is repeated on the next rise. Write it out in sentences as was done for
the first rise.
Answers
1. The air at Vancouver has a temperature of 10°C and a dew point of 5°C.
2. Air rises and cools at the Dry Adiabatic Lapse Rate (10°C/1,000m) until the dew
point is reached (500m).
3. Clouds form and air continues to rise and cool at the Saturated Adiabatic Lapse
Rate (5°C/1,000m) to the crest (2,500m).
4. At some point above 500m, rain will fall (snow above 1,500m - the 0° level).
5. After moving over the crest, air temperature begins to rise (at the DALR) as the
air descends.
6. At Lillooet, the temperature is warmer and drier than it was at the equivalent
elevation on the windward side.
7. The air at Lillooet Lk. Has a temperature of 15°C and a dew point of 5°C (see
note, at top).
Air rises and cools at the Dry Adiabatic Lapse Rate (10°C/1,000m) until the dew
point is reached (1,500m).
Clouds form and air continues to rise and cool at the Saturated Adiabatic Lapse
Rate (5°C/1,000m) to the crest (3,000m).
At some point above 1,500m, rain will fall (snow above 2,500m - the 0° level).
After moving over the crest, air temperature begins to rise (at the DALR) as the
air descends.
At Lytton, the temperature is warmer and drier than it was at the equivalent
elevation on the windward side.