Flight Training - July 2022 - 26

PREFLIGHT WEATHER
BY THOMAS A. HORNE
SQUALL LINES
LONG, STRONG, AND VIOLENT
EVERY PILOT LEARNS ABOUT COLD
fronts as part of their weather education-
but not all cold fronts are alike. Yes, cold
fronts are advancing masses of cold air
that form a boundary when they encounter
warmer air. But it's the fast-moving
ones you have you really have to watch
out for. Your " typical " cold front might
travel at 15 knots, but fast-movers can hit
groundspeeds as high as 50 knots. Imagine
what happens when all that energy slams
into 90-degree air that's been feeding
itself northward from the Gulf of Mexico
for days. Cold and warm air converge at
the front's leading edge, and when convergence
happens near the surface, there's
nowhere else for the air to go but up.
So up it goes, cooling and condensing
into dense clouds that churn with the heat
and humidity (revealed in dew points that
are 60 degrees, or more) that act as fuel for
initiating thunderstorms. And that's not all.
If the winds aloft are running parallel to
the front-and coming from the south, they
26
FLIGHT TRAINING JULY 2022
usually are-heavy rainfall can organize
into thin bands. Now we've got a situation
where long, highly energized, long-lasting
storm cells propel high-speed winds and
severe turbulence ahead of the front.
These bands are called squall lines,
and they're bad news. They can be as little
as 50 nautical miles long, or as stretch
across hundreds of miles and several
states. Even worse, they can last for hours.
Squall lines get a lot of press because
they produce very strong, damaging
straight-line winds at the surface. Pilots
unfortunate enough to encounter them can
expect all the adverse weather you'd expect
from a rocking thunderstorm-severe
turbulence, icing, hail, and lightning-all
covering ground at high speed.
Pilots can be taken by surprise if
they underestimate a squall line's speed,
but a good preflight weather briefing
will certainly mention if squall lines are
likely. Convective outlooks and mesoscale
discussions from the Storm Prediction
Center website (spc.noaa.gov) will
certainly mention their probability, as
will convective sigmets on the Aviation
Weather Center website (aviationweather.
gov). Radar imagery does a great job of
showing squall lines, so look for thin lines
of red or magenta to pick them out-either
on the Aviation Weather Center's website
under the radar imagery link, or in the air
if you're equipped with datalinked Doppler
weather radar services like SiriusXM
Aviation weather or FIS-B.
Once in the air, you should keep your
eyes peeled if a fast-moving cold front
has been advertised. Squall lines have
rain showers or distinctive low-level shelf
clouds ahead of them. They're signals of
the rowdy, rising air immediately preceding
them. If you see one, you're too close.
Turn away and come up with a plan B. It
might involve a precautionary landing.
You do not want to go in there!
tom.horne@aopa.org
THOMAS B. HAINES
http://spc.noaa.gov
Flight Training - July 2022

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