Types of Precipitation Precipitation comes in two forms Precipitation comes in two forms Liquid – rain, drizzle Liquid – rain, drizzle Solid - freezing rain or drizzle Solid - freezing rain or drizzle snow snow sleet or ice pellets sleet or ice pellets snow pellets or graupel snow pellets or graupel snow grains snow grains hail hail The vertical temperature structure of the atmosphere determines whether liquid or solid precipitation will fall. The vertical temperature structure of the atmosphere determines whether liquid or solid precipitation will fall.

Rain ► Liquid drops with a diameter of 0.5 mm or more ► Most rain begins as snow high in the atmosphere that melts in the warmer air of the lower atmosphere to fall as rain.

Rain Intensity  widely spaced drops do not completely wet ground  Very Light: widely spaced drops do not completely wet ground  : produces trace to 0.10 inches/hour  Light: produces trace to 0.10 inches/hour  : produces 0.11 – 0.30 inches/hour  Moderate: produces 0.11 – 0.30 inches/hour  : produces over 0.30 inches/hour  Heavy: produces over 0.30 inches/hour

Drizzle ► precipitation in the form of liquid drops with diameters less than 0.5 mm ► reduces visibility more than light rain because there are many more drops in a shower of drizzle than in a shower of light rain

Drizzle and Rain

Heavy Drizzle vs. Heavy Rain

Question ► How are amounts of rain classified?  A. visibility limits  B. inches per hour  C. centimeters per hour

Freezing Rain or Freezing Drizzle liquid drops that fall into a layer of below freezing air close to the ground and freeze on contact liquid drops that fall into a layer of below freezing air close to the ground and freeze on contact glaze surfaces with a coating of ice glaze surfaces with a coating of ice

Freezing Rain

Why is freezing rain so dangerous?

SNOW solid white or translucent ice crystals mainly branching in hexagonal forms most precipitation forms as snow

Snowfall Intensity Very Light: Scattered flakes do not completely wet or cover the ground Light: visibility is 5/8 of a mile or more Moderate: visibility is less than 5/8 mile but not less than 5/16 of a mile Heavy: visibility is less than 5/16 of a mile

Snow

Lots of snow Snow Storm Time Lapse

Heavy snow

Sleet or Ice Pellet sleet consists of transparent or translucent pellets of ice less than 5mm in diameter usually sleet is spherical formed when snow falls through above freezing and then below freezing layers of air pellets bounce off of surfaces on contact

Sleet

Snow Pellets or Graupel white, opaque, nearly round ice particles similar to snow in structure formed when ice crystal falls through layers of water droplets that stick together to make it larger ranges in size from 2 to 5 mm in diameter often falls in a shower before or with snow when surface temperatures are very near freezing

Small Graupel

Graupel

Snow Grains very small, white, opaque particles of ice solid equivalent of drizzle and resemble snow pellets in appearance but with diameters less than 1 mm never fall in shower fall in small quantities from stratus clouds or from fog

HAIL ► round or irregular lumps of ice produced by convective clouds (cumulonimbus) ► hail has diameter greater than 5 mm ► can reach size of grapefruits ► cause significant damage to property

Hail Damage

How Hail Forms ► in thunderstorms that have tremendous updrafts and down drafts ► hailstones begin as tiny ice crystals that grow in size by accretion (adding layer after layer of ice) as they are thrown into water droplets in the storm ► storm updrafts suspend hailstones until they are too large and fall

Hail Formation

Huge Hail

Hail Damage