This nested model forecast calls for generally warmer than normal conditions
over most of North America (Figure 1). The bulk of the
continental U.S. and Canada are predicted to experience warmer than
normal seasonal average temperatures by at least 20° F. The largest
departure from normal in the U.S. is in the northern plains where
temperatures are forecast to be as much as 4-6° F above normal. Over the
continent as a whole, the largest anomaly is forecast to occur in
northern central Canada, where the temperature is predicted to exceed its
normal value by more than 6°F above normal.
These warm temperature anomalies are smaller and somewhat different in
structure than those
forecast by the COLA AGCM alone, which can
be easily seen in the Nested model minus COLA AGCM difference in the
forecast temperature anomaly (Figure 2). The warm temperature
anomaly over Canada is up to 6°F less in the nested model and over
the southern U.S. the nested model is 2°F warmer than the AGCM alone.
Precipitation
The predicted precipitation (Figure 3) is generally above normal
for the southern U.S. and Mexico and below normal for the
northern U.S. and southern Canada. The extreme values for the seasonal
average are forecast for northern California where
over 20 inches more than the normal precipitation is predicted. The
southwest U.S. and the states bordering the Gulf of Mexico are expected
to receive over five inches more than normal precipitation for the
season. Reductions in precipitation from the normal precipitation are forecast in the
maritime provinces of Canada and parts of the Canadian Rockies; however,
these anomalies are modest in magnitude (about two inches below normal
for the entire season).
Although these forecast anomalies appear
similar to those forecast by the AGCM alone,
there are important
differences between the two precipitation anomaly forecasts
(Figure 4).
The nested model forecasts two to five inches less excessive
precipitation throughout much of the western U.S. and Canada
and five to ten inches less precipitation along the Sierra Nevadas
and northern Mexico. However, in northern coastal California the nested
model forecasts a precipitation anomaly of over 20 inches, roughly
double that predicted by the AGCM alone. The nested model also tends
to forecast less anomalous precipitation over the central U.S. and
Canada.
