Summary: After the warmest May on record the month of June was nearly as impressive ranking 3rd warmest of the past 124 years of record. The anomalous hot July already underway is likely to cause the MAY/JUN/JUL 2018 seasonal temperature anomaly to rank warmest all-time. Normally, persistent anomalous heat of this extreme is attached to a widespread drought and dry climate. Drought is present across the Southwest U.S. and into the central/south Great Plains. However, both May and June ranked in the to 40% wettest years. The May and June 500 MB anomaly patterns each indicate the same result: Unusually strong polar vortex (Fig. 1-2) across much cooler than normal ocean water southwest and south of Greenland (Fig. 3) FORCING an amplified upper ridge over southern Canada and the U.S.
Fig. 1-2: The May and June 2018 500 MB anomaly pattern identifies a stronger-than-normal polar vortex over northeast North America FORCING amplification of the U.S. upper ridge pattern.
Fig. 3: Global SSTA analysis identifies the unusual vast cooler than normal ocean surface south and southwest of Greenland having a significant influence on the upper air pattern causing U.S. climate.
Discussion: The June 2018 statewide temperature rankings provided by NOAA indicate 17 of the 48 contiguous states ranked in the MUCH ABOVE normal category (Fig. 4). Most states were within the southwest-to-central U.S. drought zone. 37 of the 48 contiguous states were warmer than normal. The not-to-distant polar vortex helped to keep the Northeast U.S. near to slightly cooler than normal.
Excessive rainfall in parts of the Midwest pushed Iowa, Indiana and Kentucky into the MUCH WETTER than normal category in June (Fig. 5). A swath of anomalous heavy rain stretched from the northern Continental Divide to the Mid-Atlantic region in June while areas to the south were near or drier than normal including the 6th driest June on record in Utah.
Fig. 4: NOAA U.S. state temperature ranks for June 2018 are indicated.
Fig. 5: NOAA U.S. state precipitation ranks for June 2018 are indicated.