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> How does it snow above 32 degrees.
BtownWxWatcher
post Nov 17 2008, 05:16 PM
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Why does it?


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AnthonyS
post Nov 17 2008, 06:11 PM
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QUOTE(NickBlizzard @ Nov 17 2008, 06:16 PM) *
Why does it?


Hi there, Nick.

The answer is pretty simple, actually. Typically temperature measurements are taken at 2 meters from the ground. The temperature at this level may be above freezing by several degrees (usually not by more than 4 or 5), but as long as most of the layer above this point is below freezing, the snowflake will not fully melt into a raindrop, and it will reach the surface.

Usually, when the temperature is above freezing, snowflakes are larger and their density per area is less than if the temperature was lower. This is because the snowflakes are "sticky" from partially melting, and other snowflakes bind to them.

Anthony


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BtownWxWatcher
post Nov 17 2008, 06:21 PM
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smile.gif Thanks.


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WeatherMatrix
post Nov 17 2008, 08:33 PM
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When I was a kid, I swear I saw it snow at 54 degrees, however I'm not sure what the recorded maximum is. Probably around 50.


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bubbles
post Nov 18 2008, 08:55 AM
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QUOTE(WeatherMatrix @ Nov 17 2008, 07:33 PM) *
When I was a kid, I swear I saw it snow at 54 degrees, however I'm not sure what the recorded maximum is. Probably around 50.


ohmy.gif at 54 degrees!! Oh yeah!!! It's 54 degrees right now! That means we have hope of getting a little snow here in Phx, AZ.
lol I wish... laugh.gif


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Removed_Member_OWSweather_*
post Nov 19 2008, 12:04 PM
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Next time it's 54 here I'll go outside and hope the marine layer of socal gives me snow.
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Removed_Member_Bl1zzard_*
post Nov 19 2008, 02:15 PM
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QUOTE(WeatherMatrix @ Nov 17 2008, 09:33 PM) *
When I was a kid, I swear I saw it snow at 54 degrees, however I'm not sure what the recorded maximum is. Probably around 50.


I've seen it snow definetely in the very high forties on at least two different occasions. It may have been higher than 50 on one of them. Those are the kind of flakes that fall like pancakes and make a *splut* sound when they hit the ground.
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Removed_Member_wfreeck_*
post Nov 19 2008, 02:27 PM
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QUOTE(AnthonyS @ Nov 17 2008, 07:11 PM) *
Hi there, Nick.

The answer is pretty simple, actually. Typically temperature measurements are taken at 2 meters from the ground. The temperature at this level may be above freezing by several degrees (usually not by more than 4 or 5), but as long as most of the layer above this point is below freezing, the snowflake will not fully melt into a raindrop, and it will reach the surface.

Usually, when the temperature is above freezing, snowflakes are larger and their density per area is less than if the temperature was lower. This is because the snowflakes are "sticky" from partially melting, and other snowflakes bind to them.

Anthony


Also, the other answer is evaporative cooling.

If there's enouigh dry air in place, air temperatures will drop to a critical point. If it drops close enough to freezing, snow will fall.

This post has been edited by wfreeck: Nov 19 2008, 02:28 PM
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AnthonyS
post Nov 19 2008, 02:54 PM
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In order to have snow at warm temperatures (40 to 50, at most) , the relative humidity at the surface must be very low, while most of the air above is moist. This is obviously extremely difficult. To see snow above 50F, the RH would have to be near 0%. At 45F, the RH would have to be less than 35% to even have a minuscule chance of seeing a stray flake. It can happen, but my first thought would be to double check the accuracy of my thermometer before I think it's snowing at such temperatures.

You can calculate the RH needed to keep a flake frozen using this equation: .

Anthony

This post has been edited by AnthonyS: Nov 19 2008, 03:00 PM


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NYCSuburbs
post Nov 19 2008, 06:02 PM
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Earlier this year in February there was rain in the morning at 33 degrees, followed by snow at 47 degrees. The moderate snow fell steady for 20 minutes and temperatures remained over 45 degrees (but it didn't accumulate.)
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AnthonyS
post Nov 19 2008, 07:30 PM
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QUOTE(NYCSuburbs @ Nov 19 2008, 07:02 PM) *
Earlier this year in February there was rain in the morning at 33 degrees, followed by snow at 47 degrees. The moderate snow fell steady for 20 minutes and temperatures remained over 45 degrees (but it didn't accumulate.)


WOW! Not only must the relative humidity been 11.5% (dew point -20F!), but somehow it sustained moderate snow for 20 minutes!

To quote Macbeth: "Never, never, never!"

If someone here can provide me with actual evidence of this, I would be delighted. Otherwise, physics and mathematics rule the day.

Anthony


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snowmonster123
post Nov 21 2008, 12:08 AM
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It was snowing big juicy flakes at 40 degrees last Easter. I live in St. Louis and have never seen such a thing before. For a minute around supper time it looked like a blizzard and actually accumalated a little though it melted very quickly after it stopped. It was some impulse snow.


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