Nancy,
More often, we just get snow.... just like we often just get rain
(even very heavy rain) without any thunder/lightning.... :)
True. Maybe when Daryl gets back he'll explain it to us.
I don't think I've seen him jump in on this yet...
Maybe we should look for Jim Cantore. <G>
Seriously, if you have enough lift and instability, along with charged particles in the cloud, you're going to get lightning and thunder. The
type of precipitation is determined by the air temperatures aloft, at
the mid levels, and at the ground level.
1) Below freezing at the surface, midlevels, and aloft: SNOW -- the
closer to freezing it is, may determine the difference between a heavy,
wet snow, and a dry, powdery snow.
I forget which one is better for making snow cream and a snowman with
(never mind Calvin and Hobbes with his anatomically correct creations
<G>). The dry powdery snow is best for skiing, but in the mountain
areas, a large amount of such could lead to deadly avalanches.
2) Below freezing at the surface (shallow layer), above freezing at the midlevels, and below freezing aloft: FREEZING RAIN or FREEZING DRIZZLE.
This is the most dangerous, as it puts a GLAZE on EVERYTHING -- trees,
power lines, bridges/overpasses, sidewalks, etc. Widespread downed
trees, power lines, and power outages result...sometimes for several
weeks. If more than 1/4 inch of ice accumulation is forecast, it's known
as an "ice storm". Back to back ice storms in Arkansas in 2000, had
portions of north Arkansas in the dark for 6 weeks!!
3) Below freezing at the surface (deep layer), above freezing at the
mid levels, and below freezing aloft: SLEET (also known as ice pellets).
This isn't as dangerous as freezing rain, but it can still make things slippery.
4) Above freezing at the surface, and either above or below freezing at
the midlevels and aloft: RAIN
What you mentioned is known as "VIRGA"...where the precipitation
evaporates before reaching the ground. You can still get the lightning
and thunder, but there is dry air at the low levels, and at the base of
the storm, that the precipitation dissipates on the way down. Once the
lower levels moisten up, then precipitation reaches the ground. Doppler
Radar may indicate it's raining, but surface observations note that it's
not.
Now, the first stage of a storm is known as the cumulus stage.
Moisture rises and condenses into clouds...basically, the entire storm
is composed of updrafts. Inside the cloud, particles of dust, dirt,
etc., known as condensation nuclei, attract the water droplets, which
bump into each other, and grow larger. This is known as coalesence.
Over time, the weight of the water droplets in the cloud become too
heavy to be supported and held aloft by the updrafts, so they fall,
creating a downdraft. Some thunderstorms can have as much as 500,000
tons of water or more!!
Lightning is basically a massive discharge of static electricity. In a thunderstorm, negative electrical charges buildup from the condensation
nuclei bumping into each other. These negative charges, usually at the
base of the storm, induce positive charges in the higher levels of the
storm, and on the ground for several miles around the storm. Finally,
the build up of charges becomes so great, that the air can not insulate
them from one another, and you get lightning.
All lightning can be deadly, and you never know where it'll strike
next. But, you have lightning within the thundercloud...lightning from
cloud to cloud (from one storm to another)...lightning from cloud to air
(a bolt from the blue)...and cloud to ground. Some thunderstorms can be prolific lightning producers. It only takes one lightning strike to
cause damage, injury, or death. I'm a 2 time lightning strike survivor
myself, and have nervous system as a result. The strikes were indirect,
but I still got the shock...however, I carry no electrical charge, and
can be handled safely. <G>
Each lightning bolt:
1) Is 50,000 degrees Fahrenheit (5 times hotter than the sun's surface).
2) Has 3 million volts and 300,000 amps of electricity (not even 1 amp
of electricity will kill you).
3) Is as wide as your thumb, but can be 5 miles long.
4) Can strike from 20 to 200 miles from the parent thunderstorm.
The thunder is the rapid expansion of the air in the lightning
channel. If it sounds like a sharp clap, boom, or explosion, the strike
was likely very close to you. If it sounds like a low rumble, the
storm is a few miles away. Regardless, if you hear thunder, you are
close enough to be struck by lightning...and if you're outdoors, you
need to STOP all activities IMMEDIATELY!! Lightning does NOT need to
strike twice!!
Tbe best way to remember it is "The 30-30 Rule". The first part means
that if less than 30 seconds elapses after you see lightning before you
hear thunder, you are close enough to be struck by lighnting. The second
part means that if 30 minutes has elapsed since you last heard thunder,
you can resume all normal activities.
Back to the thunderstorm itself, at this point, the storm is mature.
Heavy rain falls from the storm, causing urban and flash flooding;
especially if several thunderstorms move over the same area (known as "training", like a train repeatedly going down the tracks).
Strong winds fan out at the base of the storm, and if above 58 mph
(the criteria to class a storm as severe), it's known as downburst or
straight line winds, which can cause damage similar to an EF-0 or EF-1
tornado.
There's also lightning (some storms have very little, but others seem
to have an unending supply).
If the storm is intense enough with strong updrafts, rain droplets are
swept to the upper reaches of the storm, where temperatures are below
freezing. These super cooled water droplets freeze, and form hailstones. Depending on how strong the updraft is, the hailstone may make several
trips up and down the storm, before it becomes too heavy for the updraft
to support, and it rockets to the ground at 100 mph. Hailstones can
range from 1/4 inch diameter, to the size of a grapefruit (4 1/2 inches
in diameter). At 1 inch in diameter, it can hurt or kill you, and that's
the criteria for a severe thunderstorm. The largest hailstone ever
recorded was in South Dakota or Nebraska, at nearly 9 inches in
diameter!! If you're in an areas with large hail, you're in or near an
area where tornado development may occur.
Speaking of which, if the storm is "surface based", and there's a
turning of the winds with height, the storm may rotate. At this point,
it's known as a "supercell"...and it likely to spawn tornadoes. This
element is known as wind shear...such as southeast winds at the surface, southwest winds at the mid levels, and west winds at the upper
levels...the wind is turning with height. If the shear is extremely
strong, strong to violent, long track tornadoes, may develop. In the
case, the tornado can be a mile wide, if not bigger...and be on the
ground for hundreds of miles.
Finally, the updraft weakens. The downdraft takes over, and the
thunderstorm collapses in on itself. This is when you get intense
flooding rain, and strong downburst winds. However, the cool air left by
the storm may create an outflow boundary, where new thunderstorm
activity may form later on.
And, that's Meteorology 101 for today. :)
Daryl
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