Advisory
Circular
.
Date
l/20/83
ACNo: O&m
Initiated by: .
A-260 CIuuyp:
i
1
HlRP(lGE. This advisory circular describes the hazards of thunderstorms to
avia- offers guidance to help prevent accidents caused by thunderstorms.
2
. -ON. Advisory Circular OO-24A, dated June 23, 1978, is canceled.
3 0 REwrEDREADINc-. Advisory Circulars OO-6& Aviation Weather,
- 00-&B, Aviation Weather Services,
o&SOA,
m Level Wind Shear.
4 . GaJERAL. We all knm hat a thur&erstorm lo&s like.
Much
has been
written
about the mechanics ti life cycles of thunderstorms. They have been studied for
- many years; and while Itllch has been learned, the studies continue because much is
not .known. Knowledge and weather radar have tiified our attitudes tclward
thunderstorins, but one rule continues to be true-w storm recognizable as a
thunderstoxnshouldbeconsideredhazardcus untilmeasurwntshave shawnittobe
safe. That means safe for you and your aircraft.
Almst ary thunderstorm can spell
disaster for the wrong canbination of aircraft and pilot.
5
ERZARDS. Athunderstormpacks
just abut
everyweatherhazard
kncmntoaviation
i&o one vicious bundle. Although thehazardsoccurinnunerous ca&inations,let
us look at the most hazardous cubination of thunderstorms, the squall line, then we
will examine the hazards individually. .
.
a. Squall Lines. A squall line'is a narrw band of active thunderstorms.
Often it develops on or ahead of a mid front in moist, unstable air, but it may
develop in unstable air far removed fran any front. !Ihe line may be too long
to
detour easily and too wide and severe to penetrate. It often oontains
steady-state
.
- thunderstorms and presents the single ~~st intense weather hazard to aircraft. It
usually forms rapidly, generally reaching maximum intensity during the late
aftem and the first few hours of darkness.
b
l !ctmwoes.
(1) Thenrostviolent~~rstoansdrawairintotheir cloud baseswith
great, vigor.
If
the incoming air
has
arry initial rotatirrg motion, it often forms
anextremelyoonclentratedv0rtex franthesurfacewellintotheclolld.
Meteomlogistshme estimatedthatwind insuch avortexcanexceed200kmts;
pressureinsidethevmt~isquiteiow. Ibe strong winds gather dust and debris
tithe lowpressuregenerates afun@-shaped
cloud
extending downward frantk
.
cucul~sbase. Ifthklod do+&
reachthesurfaoe, it is a =funnel
.claw; if ittouches
a
landsurfadb, itisa"t0mdo."
.
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