|
LONG RANGE FORECASTS
Atmospheric scientists have
developed various ways to give generalized outlooks of what to expect months
in advance, but these outlooks are different in important ways from ordinary
daily forecasts.
The NWS Climate Prediction
Center issues a seasonal outlook for the entire country. This outlook gives
the odds for temperature and precipitation being above average, average, or
below average during the forecast period. The forecast of above average temperature
from March through May for much of California does not mean the "warm"
areas won't have any cold outbreaks. In fact, several cold spells are possible.
But, as long as the 3-month period averages warmer than normal, the forecast
will be a success.
In general, long range
forecasts for temperature are usually more accurate than these for precipitation.
This is because temperature varies only by small increments from place to place;
it is more constant. On the other hand, precipitation is widely variable through
time and from place to place. Even in short term forecasts out to 48 hours,
precipitation forecasts are written as a probability of occurring. Therefore,
it would seem more difficult to extend a precipitation forecast out to several
months.
The accuracy of any outlook
varies both regionally and seasonally. For example, coastal areas experience
a more stabilized climate throughout the year, making it less changeable and
easier to predict.
Sometimes long range forecasts
show no extreme deviation from normal and simply use climatology. Climatology
is a 30 year mean of daily meteorological observations. In seasonal outlooks,
the average of the 30 year mean for next 90 days is used. In other words, climatology
is close to normal.
|
www.weather.gov 
