Weather and Terrain
While no single area of the country is "best" to fly balloons, each
has its own challenges. For example, balloonists in the Great Plains
states, where the wind blows unobstructed across the wide open landscape,
are accustomed to fast landings and virtually unlimited fields in which
to touch down. Pilots along the eastern seaboard enjoy calmer landings,
but must maneuver into small fields surrounded by trees and hills. Coastal
balloonists contend with sea-breeze and fog. Mastering the skills needed
to fly in a particular geographical terrain is the learning challenge
for every aeronaut. Since balloons are so portable, and ballooning is
such a social sport, pilots travel all over the country to participate
in "meets" or rallies with other balloonists. Before launching in a
new place, smart aeronauts talk to local pilots about local conditions.
do most of their flying in the boundary layer of air close enough to
the earth's surface to be affected by it. Just as water flows around
and over rocks in a stream, so does air flow over and around obstructions
in the landscape. Balloonists learn to "hide" behind a hill or tree
line to gain calm conditions at launch, and to stay clear of rotors
a little further downwind of those same obstructions during flight.
Balloons flow with the air currents up and down riverbeds and valleys,
and around hills and buildings. Working with these local variations
is much of balloon flight planning.
Aside from terrain, the other main concern for the balloonist is weather,
specifically, wind. Ideal conditions for ballooning consist of high
pressure, moderate temperatures, and wind speeds of less than 8 m.p.h.
on the surface. While balloons can, and frequently do fly in stronger
winds at launch and at higher altitudes during flight, hitting the ground
in a wicker basket at much more than 8 m.p.h. can be an exciting experience.
While we look for calm winds on the surface, winds aloft at 3,000, 6,000
and 9,000 feet a.g.l. should be moving at least fast enough to provide
movement and some degree of steerage. At 3,000 feet, 10-20 m.p.h.is
ideal, with 5 or 10 m.p.h. more with each 3,000 feet. Higher winds aloft
might mean the risk of those speeds coming down to the surface soon
after sunrise, or surface winds not dying off during an evening flight.
Sunrise and evening? But I want to go flying at noontime, so I won't
have to get up so early. Sorry-midday is best left for glider pilots.
Balloons usually fly within two or three hours of sunrise and sunset,
when the winds are calmest and conditions most stable. During the middle
of the day, upper level pressure gradient winds mix down to the surface.
In addition, the development of thermals which the glider pilots love
can be highly dangerous for the balloonist. Balloonists try to be on
the ground no later than three hours after sunrise, and not launch more
than that amount of time before sunset. Time of year makes much less
difference than time of day. Some southwestern pilots pack their equipment
away during the hottest summer months, because it's just too unpleasant
to be outside, and hotter temperatures reduce gross lift. In New England,
pilots do just the opposite, rarely dragging out the equipment during
the harsh winters. But cold weather has a wonderful effect on balloons-fuel
lasts longer and envelope temperatures stay lower. The pilot does have
to pressurize fuel tanks with heat or nitrogen to ensure a strong flow
of fuel to the burner.
One of the most dangerous weather conditions balloonists face is thunderstorms.
During the pre-flight weather briefing, balloon pilots want radar summaries
to show thunderstorms no closer than 100 miles from the flight area.
In flight, the pilot constantly looks for changing conditions which
could signal convective activity. At the first sign of building cumulus
clouds, rapidly changing wind direction on the surface, or other such
indicators, the balloon should get on the ground as quickly as possible.
Balloonists develop the habit of being constantly on the watch for
very slight indicators of air movement. Flags, leaves and smoke are
clear wind gauges. (Another reason cold-weather flying is so enjoyable
is all the smoke indicators from people's woodstoves). During very hot
weather, pilots can judge surface wind direction by watching cows on
the ground-they usually stand facing into any slight breeze. Dust devils
mean thermals-stay on the ground.
Flight Service Stations provide good weather briefings for the most
part, but rarely are close enough to the balloonist's launch area to
be of much use at take-off time. Upon arrival at the launch site, most
pilots send up a pilot balloon (pibal) to check wind speed and direction.
The balloon must be laid out in a downwind direction for cold inflation,
and gentle surface flow can be quite different from the prevailing direction
given by Flight Service. Remember, we're talking about very light winds,
and even a 10 degree shift in direction can mean the difference between
a challenging inflation and a smooth one.