Geoscience Reference
In-Depth Information
above/below the median) (see Figures 8.7 and 8.8),
together with tables for many cities. Figure 8.8A illus-
trates the observed height field corresponding to Figure
8.7A for December 1985, showing that the pattern is
well represented on the forecast chart. Figure 8.8B and
C show that in this case, as is usual, the temperature
forecasts are more reliable than those for precipitation.
A statistical techniqe called a
canonical correlation
analysis
uses all the above information to produce long-
range outlooks. Simulated 700-mb heights, global SST
patterns, US surface temperature and precipitation for
the past year are all used to infer possible preferred
patterns. Temperature and precipitation history give
information about persistence and trends over the
year. ENSO is emphasized in this analysis but other
natural modes of variability such as the North Atlantic
Oscillation are also accounted for.
Secondary analyses which use single predictor
variables are also available and become more or less
useful than the correlation analysis under differing cir-
cumstances. The composite analysis estimates ENSO
effects by defining whether a La Niña, El Niño, or
neutral conditions are forecast for the period of interest
and then taking into account whether there is confidence
that this one phase of ENSO will exist. Another index
predicts future temperature and precipitation based on
persistence in the past ten or fifteen years. This measure
emphasizes trends and long-term regimes. A third
secondary index is a constructed analogue forecast from
soil moisture patterns.
Figure 8.8
Actual North American
weather for December 1985 (cf. Figure
8.7). Observed 700-mb contours (5 gp
dam) corresponding to Figure 8.7A, B
and C. Observed temperature (B) and
precipitation (C), corresponding to Figure
8.7B and C.
Source
: From
Monthly and Seasonal Weather
Outlook
, 40(1) (1986), Climate Analysis
Center, NOAA, Washington, DC.
