PRIMUS
r
880
Digital
W
eather
Radar
System
A28-1146-102-00
FederalAviation Administration (FAA) Advisory Circulars
A-14
EXTRAPOLATIONTODIFFERENT CLIMBS
Generalcomment: Severe storms are associated with an atmospheric
stratification marked by large values of moisture in low levels, relative
dryness in middle levels, and strong wind shear. It is well known that
this stratification of moisture permits excessive magnitudes of
convective instability to exist for an indefinite period until rapid
overturningof air is triggered by asuitable disturbance. Regions of the
atmosphere which are either very dry or very moist throughout
substantial depths cannot harbor great convective instability.Rather,
amore nearly neutral thermal stratification is maintained, partially
through aprocess of regular atmospheric overturning.
DDesert Areas -In desert areas, storms should be avoided on the
samebasis as described in the above paragraphs. While nonstorm
turbulencemay,in general,be expectedmore frequently overdesert
areas during daylight hours than elsewhere, THE SAME
TURBULENCE CONSIDERATIONS PREVAILIN THE VICINITY
OF THUNDERSTORMS.
DTropical-HumidClimates-Whenthe atmosphereismoistandonly
slightlyunstablethougha greatdepth,strongradarechoesmaybe
receivedfromtoweringcloudswhichdo notcontainverticalvelocities
asstrongasthosefromstormsovertheU.S.plains.Thenitisamatter
of the pilotbeing informedwithrespect tothe generalatmospheric
conditionsaccompanying storms, foritiswell knownthat
PRACTICALLY ALL GEOGRAPHICAREAS HAVING
THUNDERSTORMS AREOCCASIONALLYVISITEDBY SEVERE
ONES.
USE OF AIRBORNE RADAR
Airborne radar is avaluable tool; HOWEVER, ITS USE IS
PRINCIPALLY AS AN INDICATOROF STORM LOCATIONS FOR
AVOIDANCEPURPOSES WHILE ENROUTE.