SEPTEMBER 2010 30-DAY OUTLOOK
515 PM EDT Tue. August 31, 2010
Atmospheric patterns, 700 MB and 500 MB height anomalies, statistical
data, and various models, along with observed cases from past such
months and also data from 1895-2000 were used in this forecast.
La Nina conditions developed during July and continued to develop in
August, as sea surface temperature anomalies strengthened across the
central and eastern equatorial Pacific Ocean. The subsurface heat
content continued to reflect a deep layer of below normal temperatures
east of the Date Line. In addition convection continued to be enhanced
over Indonesia and remained suppressed over the western and central
tropical Pacific. Enhanced low-level easterly winds and anomalous
upper-level westerly winds continued over the western and central
equatorial Pacific. Most models forecast that the cold episode to
continue through early 2011.

The NAO index is currently negative and is forecast to remain mostly
negative through day 14. The PNA index is currently positive and is
forecast to remain positive through the same period. The models and
ensembles are in good agreement on the 500-hpa circulation pattern
across North America for the month of September. Models indicate a
trough along or off the West coast and a weak ridge across the much of
the nation.

Below normal temperatures are forecast for the Northwest, Idaho,
northern California and adjacent areas of Nevada. Various models favor
below normal temperatures in this region. Also, this is based on
observed trends from the past month so, the pro0bability of below
normal temperatures for this area is high 60 percent. Observed trends
from the past couple of month and most models indicate above normal
temperatures are for a large area of the nation. This includes the
southern Plains, the Mississippi Valley, the Ohio and Tennessee
Valleys to the east coast except Florida where near normal
temperatures are expected. Therefore, the probability of above normal
temperatures is also high 59 percent. The remainder of the nation is
expected to be near normal with no significant deviation from
climatology.
Above normal precipitation is forecast across the northern Plains. The
probability of above normal precipitation in this area is 56 percent.
Below normal precipitation is forecast for the Ohio and Tennessee
Valleys, to the East coast except Florida where near normal
precipitation is expected. The probability of below normal
precipitation in the area is 56 percent. The remainder of the nation
is expected to be near normal with no significant deviation from
climatology.

Jim Munley Jr.
http://www.jimmunleywx.com