http://www.springerlink.com/content/0008xl84w0743102/fulltext.html

When La Niña is present, it strongly influences where the storms track across
the United States, and the storms track in such a way as to miss the South.
Consequently, Texas and surrounding areas (especially parts of Arizona, New
Mexico and Oklahoma) suffered severe drought, and subsequently heat waves and
wild fires in the northern spring and summer 2011. Nevertheless in spring, the
storms crossing the central Midwest were able to link up with the warm moist air
from the Gulf of Mexico, creating extra instability and buoyancy for the air
that was entrained into the storms. This led to extensive heavy rains, flooding
and tornado outbreaks. The pattern of rainfall in the spring is characteristic
of La Niña although the extreme nature of the changes is not. The intense heat
wave and “exceptional drought” continued in Texas through August. Many of these
events are described in detail on line at the NOAA National Climatic Data
Center, State of the Climate, Global Hazards site:
http://www.ncdc.noaa.gov/sotc/hazards/2010/m  (or 2011/m) where m is
the month.