Droughts and pluvial cause massive socioeconomic impacts over the U.S. with an annual average cost of several billion dollars. Recently, a U.S. CLIVAR Drought Working Group was established in an effort to enhance the understanding and prediction of these extreme hydroclimate anomalies from sub-seasonal to decadal timescales. The multi-agency collaboration includes NASA, NOAA, NCAR, GFDL, Columbia University, and many other government and university scientists. These modeling centers have completed identical idealized SST forced runs using their respective AGCM's. Here the focus is on understanding the modulation and evolution of the low-level moisture bearing circulation during the warm season given its profound impact on the regional hydroclimate.

The seasonal evolution of low-level winds and their central U.S. impacts on moisture fluxes and precipitation is analyzed in the NSIPP-1 (NASA), GFS (NOAA), CAM 3.5 (NCAR), AM 2.1 (GFDL), and CCM 3 (Lamont-Columbia) idealized SST-forced AGCM integrations and supplemented with AMIP, reanalysis, and observed precipitation comparisons where available. Interesting features include varying seasonal preference for SST-influenced low-level circulation, with CAM 3.5 and AM 2.1 showing weak SST linkages, while NSIPP-1 (late summer), CCM 3 (late summer), and GFS (spring) display marked sensitivity among the varying polarities of prescribed SSTs. All 5 models show reduced (enhanced) precipitation over the northern Great Plains with coincident weakening (strengthening) of the GPLLJ (save GFS) under a cold (warm) Pacific and warm (cold) Atlantic scenario. Possible mechanisms for the SST linkages to regional U.S hydroclimate are investigated.