METEOROLOGIST JEFF HABY
Many snowfalls are the result of elevated uplift. Elevated uplift is the
lifting of air in the middle and
upper levels of the atmosphere (due to
jet streak DIV). The
PBL is stable in an
elevated uplift situation.
Once snowflakes form, they have a significant distance to fall to reach the surface.
The terminal velocity of a raindrop is much greater than that of a snowflake. Therefore, a snowflake may reach the
surface well after the cloud that produced it has past away. Also, wind can easily waft snowflakes a significant
horizontal distance. This is especially true of small snowflakes that have a low density. When snow develops, the
largest snowflakes will reach the surface first followed by the smaller flakes. It can often be observed that snow
first begins heavy with large flakes then the flakes become smaller and smaller with time. This is especially true
when the mechanisms that are producing the snowfall suddenly cease or move
Clouds that produce snowfall
can dissipate rapidly and/or move downwind after producing snow. This can cause snow to be observed at the surface
while the sky is partly cloudy or clear. The stars, moon or the sun can be out while light snow is still falling.
Strong wind can blow snow well downwind from its source region. Snow falling from high elevations can be blown
several kilometers from its origin point (middle and upper level wind is generally stronger than surface wind).