6 replies to this topic

[ElectricSnowStorm]

Snowfall is one of the most difficult weather types to forecast, and can be very exciting when it does fall for those that like snow, and when it settles it is beautiful, the landscape becomes a wonderful new scene, many like the snow scenes even if they dont like being in it, it is a fascinating element of our weather, and very interesting on how it occurs, why, forecasting it, and the close up of the snowflakes.
So here we take a look at the most incredible snowflake photography, talk about how it snows, the causes, how it is forecast, and why snowflake type affects what we experience on the ground, im sure you have heard of the 'wrong type of snow'!

Here is the most stunning close ups of the different types of snowflakes



Thankyou to the photographer of the snowflakes
http://www.its.calte...otos/photos.htm

Please discuss snow here:

• snowflake photography
  
• why snow happens
  
• forecasting snow
  
• how different types of snow affects how we experience it on the ground

Edited by ElectricSnowStorm, 08 November 2011 - 04:39 .

[greybing]

Why do snow flakes form in the same geometric pattern,ie hexgonal is it?However many sides it is they always have I wonder if anybody knows why and can explain articulately.

[WinterSnow]

I believe it has something to do with the molecular structure of water, not a 100% certain however.

[Weather Ship]

greybing, on 08 November 2011 - 18:28 , said:

Why do snow flakes form in the same geometric pattern,ie hexgonal is it?However many sides it is they always have I wonder if anybody knows why and can explain articulately.

They don't and I don't think you will get a definitive answer to this. This may help. The source is H₂O: A Biography of Water by Philip Ball. Well worth a read.

"In the 1930s, Ukichiro Nakaya at Hokkaido University in Japan developed techniques for growing snowflakes artificially in the laboratory, allowing him to explore systematically how shape and form vary with the conditions of growth. These studies showed that, for all their variety, the 'six-petalled flowers' are just one breed of a whole menagerie of forms. Nakaya and his coworkers grew the ice crystals on a rabbit's hair suspended within a stream of moist air, in a chamber placed within a room that could be cooled to minus 30°C. The main influence on the crystal shape is the temperature, although varying the humidity of the air can also affect the shape. At around 0 to -3°C, the snowflakes are 'plates' -flat flakes of ice with hexagonal shapes. Between about -3 and -SoC, they take on a needle-like form instead. At lower temperatures down to about -22 to -25°C, plates are formed if the air is not too moist, whereas dendritic stars and other complex forms appear in more moist air. If it is colder still, prismatic crystals appear. Much the same relationships have been observed in the real atmosphere. A feeling for snow is, it seems, in large measure a feeling for coldness and humidity.
A continuing mystery about dendritic snowflakes is why all six of their branches seem to be more or less identical. The theory of dendritic growth explains why the side branches will develop at certain angles, but it contains no guarantee that they will all appear at eqUivalent places on different branches, or will grow to the same dimensions; indeed, these branching events are expected to happen at random. Yet snowflakes can present astonishing examples of coordination, as if each branch knows what the other is doing. One hypothesis is that vibrations of the crystal lattice bounce back and forth through the crystal like standing waves in an organ pipe, providing a degree of coordination and communication in the growth process. Another is that the apparent similarity of the arms is illusory, a result of the spatial constraints imposed because all the branches grow close together ar more or less the same rate. But for the present the secret of the snowflake endures".

Edited by weather ship, 09 November 2011 - 00:34 .

[ElectricSnowStorm]

greybing, on 08 November 2011 - 18:28 , said:

Why do snow flakes form in the same geometric pattern,ie hexgonal is it?However many sides it is they always have I wonder if anybody knows why and can explain articulately.

I am going to research that one, most of the snowflake shapes do come to that pattern, apart from these type that fall at the lowest temperature,

Thanks weather ship just read that very interesting.
So the coldness of the air temperature and what moisture is available for the flake to develop creates a certain type of snowflake.
Bigger flakes fall at higher temperatures, usually 32f/0c or above, the flakes can stick together as the temperature rises and form very large flakes, the dew point needs to be lower at a higher temp to have snow falling, a very low dew point and very low temp we get fine snow or powder snow.
Sometimes if there is a severe frost you can see what is called diamond dust, this is visible under bright lights at night, and is frozen moisture falling to the ground, it is the frost falling.
I think i got that right!

Edited by ElectricSnowStorm, 08 November 2011 - 23:38 .

[ElectricSnowStorm]

http://science.howstuffworks.com/nature/climate-weather/atmospheric/question302.htm
If the temperature is 30 degrees F, why do we sometimes get snow and other times get freezing rain?

Quote

When you watch the local weather report on the evening news, you always hear the "current temperature." It­ may be, for example, 32 degrees Fahrenheit (0 degrees Celsius) outside. That is useful information, but if it is precipitating, it is only one part of the puzzle.
It turns out that the atmosphere is layered, and these layers control the form that precipitation will take. The local weather report only gives us the ground-level temperature. In order to understand sleet, snow and freezing rain, what we would need is perhaps four to six different temperature readings at different altitudes.
­Precipitation starts in the cloud as snow. As it falls, it may travel through a layer of air that has a temperature ­greater than 32 F (0 C). This layer melts the snow into rain. If the temperature at ground level is below freezing, then the water may refreeze in the air, and we get sleet. Or, if the layer of sub-freezing air at ground level is thin, the precipitation falls as rain but then freezes once it touches a freezing object on the ground.
For snow to fall, all of the layers of air that the snow falls through once it leaves the cloud must be sub-freezing.
The warm middle layers are normally caused by the movement of warm fronts or cold fronts through the area. In the Southeast, temperatures often hover around 32 F, so the form of precipitation can change all the time. In more northern areas, the temperature is well below freezing, so snow is a sure thing.

Edited by ElectricSnowStorm, 18 November 2011 - 01:34 .

[ElectricSnowStorm]

Will it be rain or snow? lets take a look at a chart,


All the layers need to be freezing to enable snow to stay as snow from the cloud where it falls, otherwise it melts through the warmer layers.

Quote

Most precipitation that reaches the ground actually begins as snow high in the atmosphere. These snow flakes develop somewhere above the freezing level where the air temperature is less than 32 F (the dashed blue line), and begin to fall toward the earth as snow. If ground temperature is above 32 F, the freezing level must be located somewhere above the ground. The falling snow passes through the freezing level into the warmer air, where it melts and changes to rain before reaching the ground.When the air temperature at the ground is less than 32 F, the precipitation begins falling as snow from the clouds.

Quote

Since it is falling into cold air, the snow does not melt on the way down and reaches the ground as snow. This is why cold air is important for there to be snow.

Quote

Once in a while, a very thin layer of warm air is found near the surface and temperatures may be several degrees above freezing. However, since the layer of warm air is so shallow, the snow reaches the ground in tact before it has a chance to melt and become rain. This is how snow falls when the surface temperatures are above freezing.
Forecast Tip:
When forecasting precipitation type, if temperatures are expected to be above freezing, then rain is most likely. If temperatures are expected to be below freezing, then forecast for snow.

The bolded bit, this is sometimes where heavy snowfall overpowers the ground and the warm thin ground layer gets cold very fast enabling snow to settle, even if temperatures are above freezing, its more important that the upper layers are freezing so the snow gets nearest to the ground as it can staying as snow, then over the hills especially would get snowfall, the lower ground having a higher temperature layer can cause sleet or wet snow with the hills getting snow, sometimes precipitation can be so heavy that the upper cold can penetrate down to the ground and cool the air further and cause snow to fall at low ground level.
At some point are post on some stuff about the layers through the atmosphere and actually show the layers using a chart and show where those layers are that we look at in the model thread(850hpa/500hpa..).
When we have a warmer layer then the snowflakes melt before they reach the ground, sometimes we can get sleet or partially melted snow called wet snow, this can leave a melting slushy mess of fun! depends what way you view that! but if freezing air is moving in after the wet snow has fallen then it would of course freeze, many times we have sleet or wet snow which then turns to snow as layers of very cold air flow move across, so we get a proper snowfall. ESS

Link to the information(quotes and charts)-http://ww2010.atmos....st/prcp/rs.rxml

Edited by ElectricSnowStorm, 18 November 2011 - 01:41 .