Why sometimes snow, sleet, freezing rain, etc?

Question

Why is it that precipitation under 32 degrees is sometimes light fluffy snow and sometimes crappy cold sleet/freezing rain? What atmospheric differences exist to deterine what form the precipitation will take? And how does hail fit in? Becase hail falls at temps much above 32 degrees sometimes.

Wow! I am really impressed (and educated) by the fantastic answers. I learned several things I did not know from reading these answers and looking at links. I'm torn between 3 answers for best answer so I am going to let people vote. Thanks again everyone. You really made my day.

Answer 1

Sleet, etc.
http://www.usatoday.com/weather/tg/wrisnow/wrisnow.htm

Best Overall Weather Resource Online
http://www.usatoday.com/weather/resources/basics/wworks0.htm

Hail usually occurs in the summertime when there is great turbulence along a storm front. People parachuting from airplanes or gliders have been turned into human hailstones.

Layers of air having different temperatures produce different results. You can have a warm layer over a cool layer or vice versa.

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Answer 2

a lot of times the temp at higher altitudes is warmer or colder - usually colder - so when precipitation falls it may be in different forms due to the higher altitudes temps - thats why it can snow even if it seems warm on the surface of the earth - because it may be much colder up higher


hail is kind of a different story - heat rising from the earth causes uplifting sometimes this uplifting is violent - air can rush upwards at 100 mph or more this lifts water in the air to higher altitudes where it forms ice pellets (cause remember its usually cooler up there) - these pellets fall towards earth but sometimes they are caught again and again in the uplifting movement - each time adding water and growing the ice pellets bigger - when they finally fall to earth they can be large - i think the largest hail on record was 6" or so - definitely want to go inside for that - sometimes car windshields get broken


weather is a young science - one of the youngest - we have only gathered temps from the last 180 years - we have only used accurate satelite temps from the last 30 years - thats why no one can tell you global warming is a risk - we dont know - people will try to tell you that they know the temp 100 years into the future but than why is it the weatherman cant even get the weekend weather right?

by the way a general (not always) rule of thumb is as you go up in altitude the temp drops about 2 degrees from the surface temp for every 1000' - if its 80 degrees on the surface and you go up to 2000' it will generally be 76 degrees in theory


if its 40 degrees on the surface and you go up to 8000' it will be 24 degrees there - so you can see the rain will freeze up there and become snow or ice when it falls even though its above freezing on the surface

dust in the atmosphere also is a factor on how the water forms - because water forms on the dust the shape of the dust can determine whether its fuffy snow or slush



good question

Answer 3

It all has to do with the mid-level atmospheric temperature. See when it snows, and the mid-level atmosphereic temperature is above freezing but the temp closer to the ground is at or below freezing, then the snow will become all liquid at the mid-levels atmospheric portion and then once it reaches the surface, refreeze and after a while accumulate on the ground. This usually occurs when something like warm air advection occurs, or when warmer air invades the mid and upper levels of the atmosphere.

Answer 4

It has to do with air temperatures above you. For example, if the air above you is above 32 degrees F, and it's below 32 degrees F below you, you'd get freezing rain. However, if the air is more uniformly cold from the ground up, you will more likely get the big fluffy snowflakes. Hail is a little different. Hail comes with thunderstorms, or really tall rain clouds. What happens is that these clouds have winds in them that push upwards at a good clip. These winds will take raindrops and take them up to the top of the cloud, where it freezes. The frozen drops falls and then gets pushed back up to the top of the cloud, each time accumulating another layer of ice until it gets too heavy to get pushed up further. At this point, it falls out of the cloud as hail.

Answer 5

I'm sure someone can give a better answer, but here's the gist...

Snow is crystallized ice, and is the default precipitation for below freezing. Sleet is partially melted snow, or snow mixed with rain; falling slush in essence. Freezing rain has melted and refrozen on the descent (i believe because of warm pockets / updrafts / something).

Answer 6

oh sweety you know it would take a weekend course to answer all them questions, and you being a teacher would know that, but mostly you know that wind is and the humidity plays a big part in all forms of precipitation. up drafts, down drafts, temp layers.

Answer 7

It depends on the weather

Answer 8

When cloud particles become too heavy to remain suspended in the air, they fall to the earth as precipitation. Precipitation occurs in a variety of forms; hail, rain, freezing rain, sleet or snow.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/home.rxml


Definitions of precipitation

--Rain: Falling drops of water larger than 0.02 inch in diameter. In forecasts, "rain" usually implies that the rain will fall steadily over a period of time. (See "showers" below).
---Light rain: Falls at the rate of 0.10 inch or less an hour.
---Moderate rain: Falls at the rate of 0.11 to 0.30 inch an hour.
---Heavy rain: Falls at the rate of 0.30 inch an hour or more.
---Drizzle: Falling drops of water smaller than 0.02 inch in diameter. They appear to float in air currents, but unlike fog, do fall to the ground.
---Light drizzle: Drizzle with visibility of more than 5/8 of a mile.
---Moderate drizzle: Drizzle with visibility from 5/16 to 5/8 of a mile.
---Heavy drizzle: Drizzle with visibility of less than 5/16 of a mile.
---Showers: Rain that falls intermittently over a small area. The rain from an individual shower can be heavy or light, but doesn't cover a large area or last more than an hour or so.
---Snow: Falling ice composed of crystals in complex hexagonal forms. Snow forms mainly when water vapor turns directly to ice without going through the liquid stage, a process called sublimation.
---Snowflakes: Aggregations of snow crystals.
---Snow flurries: Light showers of snow that do not cover large areas and do not fall steadily for long periods of time.
---Snow grains: Very small snow crystals. The ice equivalent of drizzle.
---Snow pellets: White, opaque ice particles that form as ice crystals fall through cloud droplets that are below freezing but still liquid (supercooled). The cloud droplets freeze to the crystals forming a lumpy mass. Scientists call snow pellets "graupel." Such pellets falling from thunderstorms are often called "soft hail."
---Sleet: Drops of rain or drizzle that freeze into ice as they fall. They are usually smaller than 0.30 inch in diameter. Official weather observations list sleet as "ice pellets." In some parts of the country "sleet" refers to a mixture of ice pellets and freezing rain.
---Freezing rain or drizzle: Falling rain or drizzle that cools below 32°F, but does not turn to ice in the air. The water is "supercooled." When the drops hit anything they instantly turn into ice.
Ice storm: A storm with large amounts of freezing rain that coats trees, power lines and roadways with ice. Often the ice is heavy enough to pull down trees and power lines.
---Hail: Falling ice in roughly round shapes at least 0.20 inch in diameter. Hail comes from thunderstorms and is larger than sleet. Hailstones form when upward moving air -- updrafts -- in a thunderstorm keep pieces of graupel from falling. Drops of supercooled water hit and freeze to the graupel, causing it to grow. When the balls of ice become too heavy for the updrafts to continue supporting them, they fall as hailstones. Sleet, in contrast, consists of raindrops that freeze on the way down.
Thunderstorm: A rain or snow shower in which there is lightning. Thunder is always caused by lightning. In general, the upward and downward winds, updrafts and downdrafts, in thunderstorms are more violent than those in ordinary showers.
Thundersnow: A thunderstorm with snow instead of rain falling on the ground.
Severe thunderstorm: A thunderstorm with winds of 57 mph or faster or hail more than 3/4 inch in diameter reaching the ground. Severe thunderstorms can also produce tornadoes.

Answer 9

ummmmm, i dont know
look at this http://en.wikipedia.org/wiki/Snow