While taking the dogs out for their daily jaunt over the equestrian trails hereabouts yesterday morning, I was fortunate enough to experience several tiny drops of rain at 7:10 AM. Rubbed a couple off the dusty car windows to be sure it was happening, it was THAT slight! It lasted for maybe 15 minutes. How tiny were the drops? Oh, maybe 500 microns in diameter, practically “drizzle-sized.” Recall this is ONLY THE BEGINNING of “stormy weather” in SE AZ, to quote a song title by Harold Arlen and Ted somebody.
What is “drizzle-sized” you ask? Well maybe you didn’t ask, but I am going to tell you anyway as part of a harangue about folks mis-indentifying drizzle occurrences. It happens a LOT even with your local TEEVEE weather presenter (can’t refer to anyone who doesn’t know what drizzle is as a “meteorologist”!)
Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter. A typical human hair is 100 microns in diameter. So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses. The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt. This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.
A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle” as “drizzle.” A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air. In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”! But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.” These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.
Since repetition is important for learning things, I have copied the two paragraphs above and have pasted them below:
Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter. A typical human hair is 100 microns in diameter. So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses. The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt. This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.
A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle” as “drizzle.” A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air. In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”! But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.” These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.
Finally, I would like to insult you by quoting from the Bill Nye the Science Guy program, one sponsored by the National Science Foundation, BTW, and his science ditty, The Water Cycle Jump: “Your brain is on vacation, if you don’t know about precipitation.”
So there.
Finally, here are the clouds that produced the drizzle as it was happening. You are looking at the west side of the Cat Mountains and you can see that those “Stratocumulus” clouds are quite low based, necessary for drizzle drops to reach the ground. However, I have to say that they were still a surprisingly great height above the ground for a drizzle drop to have reached me. That drop HAD to be much larger coming out of the base to have fallen, say 3,000 feet and reach me as drizzle sized. An alternative explanation that would go with the very sparse nature of the drops was that the clouds reached below the freezing level and a few ice crystals formed, which then grew into raindrops (bigger than 500 microns in diameter). TUS sounding doesn’t support this, but, BUT, the bank of clouds over Catalina was NOT over TUS at the time of the sounding release, so I think this is still a viable explanation.
The end.
