coastal dunes are subject to winds that vary seasonally in strength
Overall (Annual) Wind Patterns
Mean monthly wind speeds recorded at Muskegon, MI,
are between 4 and 6 m/s (9-12 mph). Peak gusts greater than 22 m/s
(50 mph) have been recorded in every month of the year. The winds
are more frequently from the west than the east throughout the year.
To read the
windrose (right), look for the percentage of time (indicated by
dashed circles) that winds come from a specific direction (such
as west). Colors indicate the speeds of the winds from the indicated
directions (see color key).
is based on thirty years (1961-1990) of wind data collected in Muskegon
by the National Weather Service.
Wind speed is a defining
variable for coastal dunes. For sand to move, wind speeds must exceed
a threshold level related to sand grain size. This threshold level
is roughly 5-6 m/s for Lake Michigan dune sands. The amount of sand
movement is also related to wind speed: the volume of sand transported
by wind increases exponentially with increases in wind speed. More
sand will move in a single storm with high winds than will move
with months of wind speeds just above the threshold.
Strong winds do not automatically
produce sand movement. If surface sand grains are affected by surface
moisture, snow, ice, ground freezing, vegetation or other complicating
variables, sand movement will be greatly reduced or halted completely.
Winter winds move
sand and snow along beach (from south to north) in Hoffmaster State
Park (January 2005).
The wind direction
determines the direction of sand movement. The direction of the
strongest winds is more important than the average wind direction
or even the direction of the most frequent winds. Wind direction
is always reported as the direction the wind is coming from.
Consider the seasonal pattern of winds as measured at Muskegon,
MI. Keep in mind that the strongest winds can move the most sand,
and the sand will move according to the direction of the strongest
|Summer winds are weaker
than winds during the rest of the year. The strongest summer winds
are from the south and southwest.
|Autumn winds are strong
and show a lot of variability. Easterly winds are not as strong as
westerly winds. Strong winds from the south and north will move sand
past the dunes along the beach.
|Winter winds are also
strong. The strongest winds are from the west and northwest. There
is still potential for transport along the beach during strong north
and south winds. Some strong east winds could move sand towards the
lake where it is deposited on the coastal ice.
|Spring winds are not as
strong as autumn and winter winds. There is considerable variability
in the direction of the strongest winds.
Wind roses are
generated from Muskegon wind data (1961-1990) using WRPLOT View software
from Lakes Environmental available at www.lakes-environmental.com.