|LOCATING DOWNSLOPING AND|
UPSLOPE WIND USING THE MODELS
METEOROLOGIST JEFF HABY
Topography has a great influence on
Upward Vertical Velocity (UVV) and Downward Vertical Velocity (DVV). The wind
direction relative to the elevated terrain will influence the regions experiencing UVV and DVV. If a region has a
prevailing wind direction, one side of the mountain range will tend to be the
windward side and the other will
be the leeward side. The windward side will experience UVV, increasing
RH and greater chances for clouds and
precipitation. The leeward side will experience DVV, decreasing RH and lesser chances for clouds and precipitation.
Moisture transport is important. If
moisture is transported into the mountain range (i.e. flow from Pacific into
Sierra Nevadas, SE to E wind into the Rocky Mountains), precipitation will be more likely and has the potential to
Note the wind direction in a mountain region and see if you see 700 mb UVVs that are likely influenced
by upslope or downslope flow.
When the wind flow is from the west, the windward side of the Rockies
is the western side and the leeward side is the eastern side. In this case, eastern Colorado has DVV.
When the wind flow is from the east, the windward side of the Rockies
is the eastern side. In this case, eastern Colorado has UVV and clouds and precipitation are much more
likely. "Weather" not "climatology" determines which side of a mountain has UVV and DVV on a particular day.
From this, a forecaster can gain valuable information as to which areas will have enhanced UVV (due to upslope)
or enhanced DVV (due to downslope).