Heat in Delaware, July 16 to 19, 1999

Another strong and oppressive ridge of high pressure gave Delaware four days of excessive heat and humidity and in the northern part of the state five consecutive days with high temperatures in the 90s. Unlike the previous hot spell, onshore winds kept shore areas a bit cooler. High temperatures reached the 90s again on the 15th in the northern part of the state and everywhere on the 16th through the 19th. The air mass on the 15th was still relatively dry. Southwest winds continued to increase humidity levels. The combination of the temperature and humidity produced heat indices of around 100 degrees during the afternoon of the 16th and around 105 degrees during each afternoon from the 17th through the 19th. The hottest part of this air mass passed over northern parts of the Middle Atlantic States. The most oppressive conditions were experienced in the northern parts of the state and coincided with the more highly urbanized parts of New Castle County. A weak backdoor cold front moved south through the region during the evening of the 19th. While the air mass was not considerably drier on the 20th, skies were cloudy as the front stalled near the area. As a high pressure system built into New England on the 21st, some dry air briefly filtered southward. The excessive heat and the lack of rain continued to decimate non-irrigated farms across the state. The high temperatures again put a strain on electrical utilities. For the second time this month, on Monday July 19th the PJM Interconnection Association called for a 5 percent reduction in voltage from 115 p.m. EDT through 210 p.m. EDT. The highest temperatures during this hot spell were scattered from the 17th through the 19th. They included 100 degrees at the New Castle County Airport, 99 degrees in Milford (Kent County) and 94 degrees in Georgetown (Sussex County) and Salisbury, MD. Due to higher historical daily maximum temperature records, fewer daily high temperature records were set. But, the high of 100 degrees at the New Castle County Airport set a new daily record high for the 19th. It was also the first time the thermometer reached 100 degrees at the airport since June 19, 1994.