A large pool of cool ocean water south of Greenland is reflected in the upper atmosphere by a persistent polar vortex in eastern Canada. Meanwhile a large envelope of humid subtropical air surrounds Alberto in the Southeast U.S. Yesterday, the two air masses met in the form of a back door cold front in the Baltimore area and an 8-in. rainstorm evolved in Ellicott City.

Frequent very hot days caused in-part due to drought in the Southeast through the middle third of May is about to end as wet weather suppresses anomalous heat risk ahead.

The JUN/JUL/AUG 2018 probabilistic rainfall forecast issued by NOAA/CPC may be the wettest summer outlook issued in the 23-year history of the (NOAA) long-lead forecast product.

On Monday and Tuesday of this week New Orleans set daily records of 96 and 97. The onset of extreme heat is related to the rapid transition of drier soil moisture in the Mid-South U.S. during the month of May. Well known is the relationship between large areas of soil moisture deficit to increase anomalous heat risk during the summer season. Not as well-known is the ability for the same hot weather enhancement by a rapid drier soil moisture change.