|USING PERCENTAGES IN FORECASTS
METEOROLOGIST JEFF HABY
Percentages in forecasts can give the public a general idea of how likely precipitation is, but percentages
lack specifics and description. It is up to the meteorologist to describe the character of the precipitation.
Percentages are associated too much with gambling and guess work to many people (example: There will be a
50% chance of rain *flips a coin*).
When convective activity is possible, description words can be used
chance probabilities. These description words include numerous (replaces 70%+ chance), scattered
(replaces 40 to 60% chance),
widely scattered (replaces 20 to 30% chance), and isolated (replaces less than
20% chance). Examples, "thunderstorms will be numerous across the forecast region tomorrow, most of you will
be getting wet", "thunderstorms will be isolated tomorrow, most of you will miss the storms that develop,
but a few of you may be in the right place at the right time to see a thunderboomer." The term scattered is
a good term to use instead of (40,50 or 60% chance of rain). Scattered implies that there will be rain, but
there will also be areas that do not receive rain.
The character of the precipitation is also important to
mention: severe or non-severe, heavy or light, long duration or short duration, wintry (type of winter
precipitation) or non-wintry,
convective or stratiform, slow moving or fast moving. Whatever precipitation
character information you can sneak into your graphics or say when describing the graphics within the short
amount of time will help the viewer or client prepare for the precipitation event.