AOPA Pilot Magazine - August 2020 - 83

conditions-especially around the Great
Lakes and New England.
It's good to remember that cold-front
weather can extend as far as 200 nautical
miles ahead of the front's position as plotted
on a surface analysis chart. Cold fronts with
intense, narrow bands of heavy precipitation bear scrutiny-in summer, these are the
kind with squall lines, strong winds, hail,
and even tornadoes. Warm front weather
can reach as far as 500 nautical miles or
more from the plotted position. That's
because the advancing warm air, being less
dense, rides up and over the cool air ahead
of it in a process called overrunning.
MATURITY AND OCCLUSION

Frontal orientations and shapes change as
a low-pressure complex ages. As central
low pressures deepen, cold fronts advance.
Where once they were oriented northeastsouthwest, two days later they may run
north-south. Warm fronts, once running in
an east-west direction, may be forced into a

northwest-southeast line as they're pushed
into the colder, denser air of a high pressure
system ahead of it. Up near the center of the
parent low, in the tight, inverted V created by
the juncture of the cold and warm fronts, is
what's sometimes called Larko's triangle-an
area likely to have the most severe weather.
But by this time, the cold front is "catching
up" to the warm front ahead of it. As it does,
the cold and warm fronts merge-like pulling a zipper-and an occluded front begins to
extend to the north. The occlusion lifts the
warm sector's air and creates what amounts
to a cold front at the surface and a warm front
aloft. Eventually, the merging of the two air
masses eliminates their differences and spells
the end of the frontal system.
TIPS AND SHORTCUTS

For your next flight, check out the following:
* Find the first three isobars in the warm
sector, just south of the low's center. The
low's future movement will often parallel
the direction of their orientation.

* Compare satellite imagery with surface
analysis charts to correlate lows and fronts.
Go to the Aviation Weather Center's website (aviationweather.gov/satellite/plot)
to see how infrared signatures give away
the locations of lows and fronts. Use the
VisFog button at top right to see how surface weather correlates. Check the AWC's
water vapor channels (under Observations,
Satellite, U.S. Regional Images) to see any
precipitation fields or moisture wrapping
around a parent low.
* In flight, you'll know you're flying
through a front if your crosswind correction is to the right of course. The strongest
crosswinds frequently happen when flying east through a cold front; the most
violent weather, too.
Just remember, you can check all the
weather you want during a preflight briefing. But once you're flying, you're the
expert.
AOPA
EMAIL tom.horne@aopa.org

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AOPA Pilot Magazine - August 2020

Table of Contents for the Digital Edition of AOPA Pilot Magazine - August 2020
