Naked Science Forum
Life Sciences => The Environment => Topic started by: fbragy on 07/07/2005 18:43:53
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how come hail storms usually happen during spring instead of winter when temps are a lot cooler. since hail is just like ice, dont they form at freezing temp? how about snow, at what temp does it start to form?
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well i cheated and googled it, but bascially it works like this.
Come srping time, after the thaw, the ground starts to get warm. hot air is lighter, so it rises, carrying water vapor with it. The higher you go, the colder it gets, and the colder the air gets, the more moisture it gives up. So when it gets up to cloud forming hieght, the water condenses into really small droplets and forms a cloud.
Now, with more updrafts liek this, the wind in side a cloud get get pretty strong and stay pretty strong. Further more, the water vapor is warm ,and releases its own heat into the air, cuasignt he updrafts in the cloud to get strong and stay strong.
Water vapor in a cloud that gets pretty tall (liek a thuderhead) can get colder than 0 degrees celsius and yet not freeze, unless they make constact with dust or something, then they freeze.In a thundercloud, with high updraft winds and such, it doesnt take long for a dust particle to be coated with thousadns of supercold water droplets, and in REALLY strong cloud, hail can get very big. Btu eventually, the updraft cant hold it up, and it falls to the ground.
Also googled, snow is formed when the air is feezing at cloud forming altiudes, and the ground is just warm enough to lift the moisture into the air without warminng the clouds. if there is too much moisture, then it will condens,e but if conditions are just right, then the moisture will freeze into a tiny crystal. when the air gets calm, it will jsut slowly fall. or, when the air is strong, liek in a blizzard, it will just be ripped out of the cloud.
heres the hail site
http://www.ucar.edu/communications/factsheets/Hail.html
and the snow site
http://nsidc.org/snow/faq.html
wah.. i dotn get snow in hot ass texas...
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The BPRD rejected my application becuase their brain-controled by Cthulhu Rip-offs. And im sure "Sparky" is sleeping with them too, kinky little firecracker she is...
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One way to answer this is to ask why does it snow? and, why does does hail form?
Snow
As we know, MOST RAIN STARTS OFF AS SNOW (http://www.thenakedscientists.com/forum/index.php?topic=6272.msg189052#msg189052), it melts on descent when it passes through an area where the temperatures is at or greater than +4c. What is different in winter is that the snow drop may not encounter an air temperature that is = or > 4c, it will then continue to fall and land as snow.
Another difference you may notice between rain and snow is that with snow the showers appear to go on for possibly hours, but with rain a shower is (generally) over in minutes. What is also different is that with snow, more falls from showers and not from continuous snowfall. The reason is simply because the snow takes much longer to reach the ground than rain does, so by the time one shower is over snow can still be falling as the next shower begins, giving the appearance of continuous snowfall.
Hail
As you have noticed we tend to get hail in the spring (and summer) months, but what is hail? Simply put "Hail is precipitation that is formed when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere", grow by collision with supercooled water drops and there are two methods by which the hailstone grows, wet growth and dry growth.
In wet growth, the hailstone nucleus (a tiny piece of ice) is in a region where the air temperature is below freezing, but not super cold. Upon colliding with a supercooled drop the water does not immediately freeze around the nucleus.
Instead liquid water spreads across tumbling hailstones and slowly freezes. Since the process is slow, air bubbles can escape resulting in a layer of clear ice.
With dry growth, the air temperature is well below freezing and the water droplet immediately freezes as it collides with the nucleus. The air bubbles are "frozen" in place, leaving cloudy ice
The size of hailstones is determined by the strentgh of the updraft within the thunderstorm, obviously multicells will have a stronger updraft then singlecell ones and the hail falls when the thunderstorm's updraft can no longer support the weight of the ice.
Hailstone size ----- Measurement in. cm. ----- Updraft Speed mph m/s (meters per second)
bb < 1/4 < 0.64 < 24 < 11
pea 1/4 0.64 24 11
marble 1/2 1.3 35 16
dime 7/10 1.8 38 17
penny 3/4 1.9 40 18
nickel 7/8 2.2 46 21
quarter 1 2.5 49 22
half dollar 1 1/4 3.2 54 24
walnut 1 1/2 3.8 60 27
golf ball 1 3/4 4.4 64 29
hen egg 2 5.1 69 31
tennis ball 2 1/2 6.4 77 34
baseball 2 3/4 7.0 81 36
tea cup 3 7.6 84 38
grapefruit 4 10.1 98 44
softball 4 1/2 11.4 103 46