Night Spotting
(Courtesy of Skip Voros
WD9HAS and the Milwaukee Skywarn Association)
Night time
spotting of severe weather and tornadic storms is extremely difficult,
and for the mobile spotter much more dangerous. These problems arise
because there is no continuous source of light.
For
effective night time operations, spotters must significantly increase
their situational awareness since only background lightning and power
line flashes will reveal the storms most active regions.
Arcing and flashing powers lines (called Power flashes) are
often seen as flashes of white or blue-to-green colored light
originating at ground level or low angles to the horizon. These power
flashes result from: (1) lightning and electrical surges hitting power
lines or transformers, (2) wires that are being blown around and
touching because of high winds, (3) damage debris and tornadoes
intersecting power lines, (3) heavy rains and wet snows soaking wooden
electric poles creating electrical fires. In wide spread situations
with extreme downbursts, straight-line winds or outflow gust fronts,
often whole quadrants of the horizon near ground level and almost
simultaneously, may show power flashes as a dangerous system approaches.
These same strong winds can also create a roaring sound or rushing
noise that is similar to an approaching tornado. Severe storms with
large hail can also create a similar roar or even a deep rumble.
Since there
are documented cases of tornado producing storms with little or no
lightning it is very important for the night spotter to have a good
understanding of storm structure and wind fields. This is why it’s
essential to attend storm spotter training programs. When severe winds
are forecasted, night time spotters should pay attention to how rain
drops bead-up and trail on windows and windshields, the movement of
flags on flag poles, and if winds are blowing into or out of a storm.
Any sudden or dramatic shift in direction or increase in hail size
should heighten your awareness level. Keep in mind that you will only
have a few brief instants (over several lightning flashes) to correctly
identify suspicious cloud features.
Infrequent or occasional lightning is generally useless, moderate
lightning amounts are hard on the eyes, and continuous lightning may
create a strobe affect to further distort your depth perception.
However, it can sometime provide a spectacular three dimensional view
of cloud structures. As with daytime spotting you must be within a few
miles of the active areas to accurate identify suspicious features.
If you
observe a suspicious cloud feature, watch it for several minutes. Cloud
features can change almost instantly depending on your point of view and
the light source angle, whereas wall clouds, funnels, or tornadoes will
be more constant.
Low to the
ground wind blown cloud fragments, called Scud Clouds, when
illuminated by lightning may be mistaken for a funnel or tornado. Also,
a Shelf Cloud from a side view can be mistaken for a Wall
cloud. Sometimes scud can be seen rotating around a wall cloud.
Observed for several minutes, the scud will appear to be in different
locations with succeeding flashes and can reveal cloud rotation. The
spotter must be stationary to observe this effect.
Under
darkness or poor light conditions; distant telephone poles, smoke
stacks, smoke plumes, rain shafts, rain curtains or hail shafts
silhouetted by certain light source or sun angles can also create a
funnel or tornado look-alike. When in doubt watch the event for awhile.
Finally,
most people tend to over estimate hailstone sizes, and this condition is
worse when spotting at night. When making estimates keep in mind as the
distance between you and the stone increases your accuracy decreases!
Take time to be sure
of your observations
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