NOV-25 was mostly hotter/drier than normal across Central/Northeast Brazil while Argentina was temperate with patchy rain zones. In DEC-25, a pattern change is forecast. The catalyst to the pattern change is the influence on the upper air pattern of a marine heat wave (MHW) west of Chile and an evolving cool (SSTA) pool off the Central East Coast of South America

Using the National Blend of Models (NBM), the 48-hour snowfall valid today and tomorrow indicates potential for 5-10 inches across the northern Great Plains and Upper Midwest. The attendant storm moves towards James Bay midweek and strengthens causing heavy snow across Upper Michigan and Ontario with significant snow downwind the Great Lakes.

Early December is trending cold to very cold, snowy (and icy) for the Great Plains and possibly Texas eastward to the Ohio Valley to northern New England. Today's midday 12Z GFS is very aggressive with this potential scenario. The widespread and southern expanse of potential snow enhances the cold and limits moderation reaching Texas. The cold is less likely to impact the East.

Excessive rainfall with flood risk is forecast for today southwest of San Antonio and in Arkansas. Excessive rainfall with flood risk returns to Texas and the southeast Great Plains SUN/MON. The NBM 10-day rainfall forecast indicates 5-7 in. of rain just north of Dallas.