Species differences in germination play a crucial role in structuring annual plant communities. Germination depends upon numerous cues, including temperature and moisture, with global climate change models predicting increasing nighttime temperatures and more variable precipitation with larger, but less frequent rainstorms. Analysis of 15 years of annual weed biomass data from the Kellogg Biological Station Long Term Ecological Research Site (LTER) suggests that variation in the biomass of six common weed species between years is related to precipitation and temperature in the first week after an annual disturbance (tillage). Temperature and precipitation interacted to determine biomass for Setaria faberi (giant foxtail), Digitaria ischaemm (smooth crabgrass), and Chenopodium album (common lambsquarter). While Setaria faberi and Digitaria ischaemm biomass increased with warm, dry spring conditions, Chenopodium album biomass increased under warm, wet conditions. Likewise, biomass of Digitaria sanguinalis (hairy crabgrass) increased with warmer spring conditions but never responded to precipitation. Biomass of Abutilon theophrasti (velvetleaf) and Ambrosia artemisiifolia (common ragweed) showed no response to early season temperature or moisture conditions.  These results indicate that the composition of these annual communities is likely to be highly responsive to predicted climate shifts.