AOPA Pilot Magazine - July 2013 - 87
THE CULPRIT cutoff low at
feet, parked over the midAtlantic states. Meanwhile,
the main jet stream
the closely spaced height
contours on this
is far to the north.
Oh, no, a cutoff low!
BY THOMAS A. HORNE
And that’s what happened to the
Orlando/Mid-Atlantic migration of
“my” cutoff low. It really did follow me
home! So if you see the characteristic
signature of a cutoff low in your forecast, don’t expect much in the way of
good flying weather. It might be a good
time to review the AIM—or even better, follow the system online as it goes
through its changes and slowly makes
its way out of the area.
I WAS TAKING an intensive flight training course earlier this year, and it ended
up being a real workout. By this I mean instrument weather for much of the
nine hours I flew during the weeklong course. Ceilings as low as 100 feet.
Visibilities as low as one-quarter mile. And, yes, thunderstorms and heavy
rainshowers. It’s what you might expect for the Orlando area in the spring,
but rotten weather for a solid week?
Training done, I flew back home to Maryland—and another week of low, EMAIL email@example.com
rainy weather. I was even accused of bringing the lousy weather home with me! What
was going on here?
The answer: a cutoff low. Cutoff lows TAF CURVEBALL: WS
are low pressure centers that primarily live
The TAF for my destination airport appeared challenging
in the 700- to 500-millibar (about 10,000 to enough, with surface winds forecast out of 160 degrees at
18,000 feet) levels and are detached—cut off, six knots (16006KT), two-mile visibility in mist (2SM BR),
hence the name—from any jet stream flows. and a 300-foot overcast (OVC003). But it was the last entry
You can see them on constant pressure that really caught my attention: WS005/20040KT. What
charts, floating like islands. They live south sort of abbreviational curveball was this?
Translation: Wind shear at 500 feet, out of 200 degrees
of jet streams, and away from the steering
winds that high-speed jet streams provide. and 40 knots strong. Compare this with the languid surface
For this reason, cutoff lows hang around for winds and the ceiling, and you know that you could be very
days at a time, causing widespread adverse busy just above decision height or the minimum descent
altitude. You’d still be in the clouds, on approach, and then
weather. After a few days, they eventually
be hit with turbulence and gusts that could rob you of
move off, urged along by what little winds
airspeed and altitude at a very critical time. It’s nice to be
aloft may be present.
www.aopa.org/pilot AOPA PILOT | 87