Graupel Showers

John Farley

Supporter
We had some interesting weather in the St. Louis area today. As the sun heated the surface under very cold air aloft, convection occurred. While driving in the St. Louis area today, I encountered several bursts of frozen precipitation mixed with rain. Hard to categorize it - kind of a mix of wet snow and sleet or soft hail. Probably graupel would be the best catch-all term for it. Judging from short term forecasts issued by NWS offices, weather of this type occurred over much of Illinois and eastern Missouri today - even a few lightning strikes in the Chicago area, northwest Indiana, and southeast of St. Louis.

Kind of early for frozen precipitation in this area (other than hail from summer thunderstorms, but this was different from that).
 
I've a hard time distinguishing the defintion of sleet from hail to be honest! :) As you said, graupel surely fits with what you observed today.

Interesting weather to say the least!

Pat
 
I have to post about the same happening around OUN today. Around noon, the NWS posted an update on the Norman Point Forecast page saying that very sparse sleet had been reported in the area. I assume that this was the odd flake of frozen precip that hadn't managed to thaw before hitting the ground........an unusual and very interesting occurrence.

On a side note - we've just commenced watering in our front yard at 10.30pm - in a response to the Freeze Warning that has been extended down to our area for overnight tonight. Can't wait to see how low we go!!!

God I love winter!

KR
 
Originally posted by Karen Rhoden
I have to post about the same happening around OUN today. Around noon, the NWS posted an update on the Norman Point Forecast page saying that very sparse sleet had been reported in the area. I assume that this was the odd flake of frozen precip that hadn't managed to thaw before hitting the ground........an unusual and very interesting occurrence.

On a side note - we've just commenced watering in our front yard at 10.30pm - in a response to the Freeze Warning that has been extended down to our area for overnight tonight. Can't wait to see how low we go!!!

God I love winter!

KR

Karen,

Good thing they did expand the Freeze Warning farther south, seeing how Norman mesonet is reporting 35F at 10pm! With dewpoints in the mid-upper 20s, I can't imagine we won't see 28-29 overnight, with the winds helping to keep the temp from completely bottoming out. You can really see the effects of calm winds by looking at the mesonet, as most of the coldest places are seeing calm winds, with warmer temps in those location that are seeing >5mph winds. This isn't surprising of course, but it's still cool to see nonetheless.
 
I like winter for the first three months or so...unfortunately it lasts for another 2 months or so in the northern US :)

Interesting report from OK...might have been due to dry air? Can't say for certain.

Pat
 
Around 7 PM this evening I was up in the northern part of KC and saw some very light freezing precip. I was actually quite surprised to see it. Perhaps a sign of things to come...
 
hail and sleet are completely different and form in different ways. A google search should give you good examples and diagrams. In these situations when there is very cold air aloft and some surfaces heating, small hail is common in heavier showers.
 
Originally posted by HAltschule
hail and sleet are completely different and form in different ways. A google search should give you good examples and diagrams. In these situations when there is very cold air aloft and some surfaces heating, small hail is common in heavier showers.

I see both of them as frozen rain...by definition. Which is what I was referring to. Yes the way they form is quite different, but they are both frozen rain :) I learned that from a fellow that taught me the difference between light and moderate drizzle...I'll not get into a discussion of the difference.

As far as what happened in OK and IL today, I haven't a clue! I wasn't there...so it may have been whatever one chooses to call a samall chunk of frozen precip. In any event, I'm off to dream land.

Pat
 
1. hail—Precipitation in the form of balls or irregular lumps of ice, always produced by convective clouds, nearly always cumulonimbus.

2. sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth's surface;
 
Originally posted by HAltschule
1. hail—Precipitation in the form of balls or irregular lumps of ice, always produced by convective clouds, nearly always cumulonimbus.

2. sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth's surface;

Hail -- A type of frozen precipitation formed when rain droplets are lofted high into the atmosphere by strong updrafts repeatedly, adding new layers of ice with each up-and-down trip, until it is finally heavy enough to fall to the ground. Hail accompanies strong thunderstorms and is usually a summertime phenomenon.

Frozen rain drops in other words!

No matter...it is frozen rain whether it be a hydrometeor known as sleet, or whether it be one known as hail. I'll agree the two are very different in the way they form.

Thanks for the definitions, and good night :)

Pat
 
Originally posted by Pat Lawrence+--><div class='quotetop'>QUOTE(Pat Lawrence)</div>
<!--QuoteBegin-HAltschule
1. hail—Precipitation in the form of balls or irregular lumps of ice, always produced by convective clouds, nearly always cumulonimbus.

2. sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth's surface;

Hail -- A type of frozen precipitation formed when rain droplets are lofted high into the atmosphere by strong updrafts repeatedly, adding new layers of ice with each up-and-down trip, until it is finally heavy enough to fall to the ground. Hail accompanies strong thunderstorms and is usually a summertime phenomenon.

Frozen rain drops in other words!

No matter...it is frozen rain whether it be a hydrometeor known as sleet, or whether it be one known as hail. I'll agree the two are very different in the way they form.

Thanks for the definitions, and good night :)

Pat[/b]

That's correct... They may look the same, but the processes that create hail or sleet are quite different. I have seen sleet in convective storms - but that's because the SFC temperature was 33-35F, and I was confident that there was very little in the way of an updraft, but I could be wrong. Judging by looks though, it's hard to tell the difference unless you're comparing anything larger than peas - which would likely be hail.

Just remember that sleet falls straight down, and doesn't re-circulate through the clouds before falling (i.e. it never gets caught up in an updraft). Hail on the other hand, re-circulates (remains in the updraft) until it's too heavy to remain in the air.
 
We had some thunderstorms form last December that were slightly elevated. It most have been 20F outside. Tons of sleet were falling down for twenty minutes. If I remember correctly there was a layer of warmer air that partially melted the snow but near the surface it was COLD and it froze again.
-Scott.
 
We had a little bit of sleet this afternoon out here in Lubbock as well.

That mushy hail stuff you were talking about.... I usually get about 1 or 2 good late February thunderstorms out this way every year that puts down copious amounts of that stuff. Covers the roads to a depth of a few inches usually, it's pretty wild. You pick it up in your hand and it almost has the consistance of an old fashion snow cone (not this new shaved ice stuff).
 
Since this is an educated weather forum I'd like to maintain that rain, snow, hail, graupel and sleet are different entities. They don't all form in the same way either.

Graupel is best described as rimed over snow. It happens when snow flakes are trapped in convective clouds and spend a longer time than normal inside the cloud. Often they can clump together.
 
Amazing how something as simple as frozen water starts such a lengthy discussion. Pea-sized hail and sleet are nearly one in the same. As rdewey (and me) said the difference is in the way the two form---but they are made of the same thing, frozen water! Even the size of the two mentioned is very nearly identical :)

Pat

Ps I noticed this definition in the online AMS glossary:

ice pellets- They may be spherical, irregular, or (rarely) conical in shape. Ice pellets usually bounce when hitting hard ground and make a sound upon impact. Now internationally recognized, ice pellets includes two basically different types of precipitation, known in the United States as 1) sleet and 2) small hail.

I didn't include the differences in formation which all of us probably already know.
 
Yes indeed Pat, almost everything on this board is criticized and corrected if it is incorrect or missing something. As it was said earlier, since this is a more educational and professional board, I think accuracy is important. If I went on the stand for trial and testified that hail is the same thing (or near same thing) as sleet, I would get ripped apart by the other side.

For the sake of any Met. students on this board, it's good that we only speak the truth so they don;t get that one wrong on the exam. Live long and prosper, Pat.

PS: Pat...hail and sleet of the same size both feel the same on your head. It reminds me of my #1 blooper at the NBC station I worked at, I was outside in the sleet and wasn't wearing a hat. We had heavy sleet at the time. It hurt. So I told the viewers to make sure they brought their hats with them, unlike me, or else they'll have all those annoying little pricks hitting your head. The studio and control room were hysterical in my earpiece. I soon realized what I said and stumbled to correct myself. Glad it was the 5:15am hit and not 6:45am. Bad choice of words to describe the sleet. DOH
 
Well, since I started this whole thing (initially intended to be a report of interesting weather, not a debate over definitions), let me provide a little more information.

First, most of the NWS offices in the Illinois area described the precipitation as sleet in their reports and short-term forecasts, though one short-term forecast from LSX did mention a possiblity of pea-sized hail.

Second, I do not think yesterday's precipitation fit into any neat category, which is what made it interesting. I am quite sure it originated as snow, and the appearance of the precipitation under the clouds was consistent with that (i.e. it looked like convective snow showers or snow squalls look). At first, it seemed to be soft and produced the same kind of impact on the windshield as wet snow does, though it was heavier and made more noise than wet snow (though some of that was probably also the rain it was mixed with). When it was at its heaviest, there were definitely chunks of ice, as in sleet or very small hail (since the showers were convective, it could have been either), but even then I am not sure if it was discrete pellets or softer chunks that broke apart. I think what the bulk of it was was partially-melted snow that may have undergone some re-freezing - but all of it was mixed with rain.

FWIW, the showers formed and built up with temperatures around 50 at the surface but very cold aloft - but when the showers occurred, the surface temperature quickly dropped at least to the mid-40s as the cold air was pulled down by the downdrafts and precipitation. You can see this on the hourly temps from LSX yesterday; 50 at 1 p.m. then down to 45 at 2 p.m.

So as to the right definition, you decide. I think there was snow and either sleet or soft hail - more likely sleet - all of it mixed with rain. But most of it was not hard like sleet and hail both usually are, so graupel sounded like a good catch-all term to use.

Now, after all this, I do have one definitional question - would you consider snow pellets and graupel to be the same phenomenon, or different ones? I have always thought of graupel as partially melted and re-frozen snow, the stuff like yesterday that kind of breaks apart and often comes down partially melted, whereas snow pellets usually do not break, but of course are lighter and softer than sleet. I encounter them (snow pellets) a lot, both locally and while skiing out west (the convective snowshowers in the rockies can be quite nasty when they put down heavy bursts of snow pellets). They are definitely a different phenomenon from what happened yesterday, although I suppose some of yesterday's precipitation could have started out that way before encountering the warmer air near the surface. I have heard some people call snow pellets graupel, but have always thought of them as different phenomena - though I of course could be wrong - or maybe the definitions are just a little vague when applied to actual stuff that falls from the sky.
 
I'll agree with the report of graupel you gave earlier.

Of course I'll also wait for the "prick expert" to chime in for the definitive answer!

Pat
 
would you consider snow pellets and graupel to be the same phenomenon, or different ones?

Different. Snow pellets are made of snow. Graupel is hail (made from water). :)

In New Zealand sleet is wet snow. Nothing to do with hail/wet hail/ice pellets....
 
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