Discussion: Much of the Southeast U.S. has been in a drought condition which has worsened into mid-May (Fig. 1). The dry soils have caused many days of excessive heat including daily records from Alabama to Georgia during late spring. However, a pattern change is ahead. The wetter climate forecast over the next 15 days (Fig. 2) not only ends the drought but leaves wet soils behind encouraging more convective rains (air mass thundershowers) which suppress anomalous heat risk for summer ahead.
Fig. 1: The Mid-May soil moisture assessment for the Southeast.
Fig. 2: The 15-day rainfall amount forecast using today’s 12Z GFS OP identifies excessive rains to end Southeast U.S. drought.
During the past 2 weeks Birmingham has reached 90F (or higher) on 7 occasions while Atlanta has reached at least 90 on 3 occasions. Looking ahead, due to the wet weather both Atlanta and Birmingham are commonly in the 80-85 range during the afternoon with frequent thermal collapses due to showers and thunderstorms.
The NCEP CFS V2 indicates a wet “air mass” style thundery pattern in June which suppresses heat (Fig. 3-4). The anomalous heat observed in May could have been the strongest warm anomalies for the summer season across the Southeast.
Fig. 3-4: The NCEP CFS V2 temperature anomaly and percent of normal rainfall forecast for June across the U.S. identifies the Southeast as wet suppressing heat risk.
Summary: Despite a dry or drought scenario during spring, late spring/early summer tropical rainfall can reverse drought quickly and by doing so reverse the hot bias for summer brought by dry soils to a wetter/cooler bias.