some biological agents. It helps achieve surprise in the attack by making
observation of chemical and biological clouds more difficult. It reduces the need
for screening smokes.
* Clouds affect aviation activities by reducing visibility.
effects of certain types of illumination devices such as searchlights.
Cloud cover reduces ultraviolet radiation and decreases the decay rate of
Heavy clouds increase surface temperatures which is favorable
for daytime use of chemical dispersal agents. It is during heavy cloud cover
and a moderately stable atmosphere that production of smoke is most
Heavy snow or rain affects mobility, personnel, and
Heavy rain washes liquid contaminants into low areas and steambeds,
or snow makes the use of smoke unnecessary.
Extremes of temperature adversely affect tactical
operations. Wet biological agents in aerosol form survive best in moderately
Aerosols have high decay rates in low humidity; moisture
slows decay rates.
weather because the body is more sensitive to vapor and liquid under these
High temperatures increase evaporation rates of agents and
decrease the duration of effectiveness.
The reverse is true at low
The temperature has no significant effect on smoke screens generated by
hexachlorethane mixture (HC) smoke pots.
Humidity has only a slight effect
In high humidity, HC smoke pots
generate more effective smoke screens.
Humidity has the least significant
* Wind speed affects the degree of cold-windchill factor.
personnel can be reasonably comfortable at temperatures down to 0F; however,
a 15-mph wind at 5 or a 30-mph wind at 15F can cause flesh to freeze. Wind
may affect visibility by creating dense screens of blowing sand, dust, or
Wind is important in airmobile and airborne operations.
affects the accuracy of indirect-fire weapons.
Biological agents are effective at various speeds.
Downwind area coverage
increases with increased wind speed.