Transcript 23.3 notes precipitation and lake effect

PRECIPITATION
DRIZZLE: small, uniform liquid droplets
RAIN: liquid droplets…larger than drizzle
SLEET: small ice pellets that
form when rain drops fall
through cold air and freeze
(frozen rain).
GLAZE: super-cooled
raindrops that freeze on
contact with solid objects;
ICE STORM
SNOW: ice crystals
remain frozen.
HAIL: hard, layered round ice pellets.
Leave cloud frozen, remain so until landing.
Causes of Precipitation
• Supercooling
– (ice process)
– Ice crystals &
supercooled water
droplets mix in cloud
tops.
– When they are large
enough, they fall.
– Most Ohio rainfall…
• Collision-coalescence
– (warm cloud process)
– Liquid droplets collide &
stick together.
– Gravity takes over when
they grow large.
– …those big, fat, warm
raindrops!
DOPPLER RADAR:
• Bounces radio waves off
rain/snow.
• Works like sonar in water!
• Tells location, direction of
movement, & intensity of
precipitation.
Lake-effect snowstorms
• Land just downwind of
the Great Lakes receive
heavy snow each winter
• Localized snows of
several feet can occur
• Buffalo, NY on Nov. 20,
2000 received its third
largest 24-h snow (25
inches)
Buffalo 2000
More key processes
• As air crosses the lake,
water evaporates and
moistens the air
• Heat is also
transferred from the
air to the lake
• As the air heats, it
becomes unstable and
begins to rise and
form cumulus clouds
Lake-effect processes
• Cumulus clouds form
about halfway across
the lake, growing in
height and intensity
closer to the lee
shoreline
• As the air crosses the
shore, it slows up
owing to more
friction
Ascent on the lee side of
the lakes
• Slowing of the winds
causes low-level
convergence with
rising motion and
further cloud
development and
precipitation on the
lee side of the lakes