Ticker for June 13, 2007

                
MESONET TICKER ... MESONET TICKER ... MESONET TICKER ... MESONET TICKER ...
June 13, 2007      June 13, 2007      June 13, 2007      June 13, 2007



A Climate Signal You Can Use

Monday's Ticker dealt with the "duh" factor that wet summer months
tend to be cooler. Yesterday, we saw that one month's temperatures
can't really tell you much about the next month's precip.

Today, we have something that you can use (and forecasters often do!).
Today's correlations show the relationship between one month's
temperature and the previous month's precip:



In contrast to the values shown yesterday (which rarely exceeded a
magnitude of 0.1), today's correlations range far from zero, especially
during the summer months. What does this mean? Well, it means that
for most of the year, one month's precip does indeed have an impact
on the next month's temperature. August is most sensitive of all,
with correlations approaching 0.5.

Practically, what this means is that antecedent precip is a useful
predictor (but certainly not the only one) of summertime climate.
Physically, what's happening is a "memory" effect of moisture in
the soils. For instance, wet soils cause more of the sun's energy
to be used for evaporation, keeping sensible heating (i.e., temps)
down. This relationship weakens somewhat during spring and fall, but
it's still there, barely.

The winter months are the only months with essentially no correlation,
testifying to the synoptically-driven nature of just about every day,
and the small amounts of sunlight to partition.