May Climate Summary

Below are highlights of the May climatology from the National Climate Data Center. You can read the entire article here.

The weather pattern over the contiguous United States during May 2011 was a continuation of the westerly flow which dominated April, but strong troughs, ridges, and cutoff lows frequently dug into the flow this month. This was a recipe for heavy rain, violent weather, and large temperature swings across parts of the country. The main storm track kept to the northern states, bringing record and near-record precipitation to parts of the northern Rockies and northern High Plains, and helping to keep temperatures below normal across much of the West and northern Plains.

The weather was drier than normal north and south of the storm track with dryness extending across the southern tier states into Mexico as well as across much of the Canadian Prairies. Large cold fronts, with cooler-than-normal Canadian air behind them, swept across the U.S. at times, especially during the middle part of the month. By the end of the month, the Bermuda High strengthened over the southern to eastern third of the country, bringing a reinforcing shot of hot and dry weather.

The average U.S. temperature in May was 60 degrees F (15.6 degrees C), which is 1.0 degrees F (0.6 degrees C) below the long-term (1901-2000) average. Precipitation during the month was 0.34 inch (8.6 mm) above the long-term average.

Precipitation during May was above normal for much of the United States. Only the South and Southeast experienced average precipitation that was below normal. The average precipitation of 4.7 inches (119.4 mm) in the northern High Plains was a May record, 2.19 inches (56.6 mm) above the 20th century average. At the state level, average precipitation in every Gulf Coast state was below normal. Georgia had its fifth driest May, while it was sixth driest for Louisiana, eighth driest for both Mississippi and Texas, ninth driest in Florida, and the tenth driest for Alabama.

The Spring (March - May) Climate Extremes Index was elevated in 2011, primarily the result of extremes in the precipitation indicators. Wet extremes covered approximately one third of the CONUS and extremes in 1-day precipitation were the most extensive on record (1910 - present) (around 16 percent coverage across the CONUS). The number of days experiencing precipitation was also elevated covering more than one third of the CONUS. Extremes in wetness affected a large portion of the Northwest, West North Central and Northeast regions.

Dry extremes covered approximately half of the South region, which had its 9th driest spring on record. Extremes in cold maximum temperatures were abundant over the West North Central region, where the average temperature was more than 2 degrees F (1.1 degrees C) cooler than the 20th century average and was the 16th coolest such period on record.

Here is a summary of the Southeast climatology for May.

• Mean temperatures were generally above normal across the Southeast region in May. Departures from normal ranged from 1-2 degrees F (0.5-1.1 degrees C) across most of Florida, Alabama, and Georgia to 2-4 degrees F (1.1-2.2 degrees C) across the Carolinas and Virginia. In contrast, mean temperatures were 1-2 degrees F (0.5-1.1 degrees C) below normal across Puerto Rico and the U.S. Virgin Islands. Across the Southeast, there were 438 daily maximum and 197 daily high minimum temperature records tied or broken during the month. More than half of these occurred during the last week of the month as a ridge of high pressure settled over the eastern U.S. Waycross, GA recorded a maximum temperature of 104 degrees F (40 degrees C) on the 23rd of the month, making it the highest May temperature ever recorded in a record extending back to 1902. May 31st marked the earliest date in the calendar year that the temperature reached the century mark (100 degrees F) at Greenville, NC in a record extending back to 1928. It also marked only the fourth time that the temperature equaled or exceeded 90 degrees F (32.2 degrees C) in May at Cape Hatteras, NC in a record extending back to 1893. On the 26th of the month, Brunswick, GA and Norfolk, VA set records for the warmest minimum temperature for any day in May with overnight lows of 78 degrees F (25.5 degrees C) and 77 degrees F (25 degrees C), respectively. In contrast, a stretch of unseasonably cool weather resulted in over 500 daily minimum and daily low maximum temperature records either tied or broken between the 5th and 18th of the month. Athens, GA recorded a minimum temperature of 37 degrees F (2.8 degrees C) on the 5th, which tied the lowest temperature ever recorded in May since 1945.
• Precipitation in May was generally below normal across the Southeast, except for small areas in Virginia, North Carolina, and southwest Florida. In some of these areas, training thunderstorms produced prodigious rainfall totals. On the 27th of the month, over 3 inches (76.2 mm) of rain fell in less than two hours across Chapel Hill and Durham, NC, resulting in significant urban flooding. Both Puerto Rico and the U.S. Virgin Islands received above average rainfall for the month. Aibonito, PR, located in the eastern interior of the island, recorded its wettest May on record with 15.3 inches (388.6 mm) of precipitation. In contrast, monthly precipitation totals were less than 50 percent of normal across much of South Carolina, Georgia, Alabama, Florida, and eastern North Carolina. The driest locations (less than 10 percent of normal) were found across portions of the Alabama and north Florida coasts, southwestern Georgia, and eastern South Carolina. It was the second driest May in Charleston, SC and the third driest May in Columbus, GA in records extending back to 1938 and 1948, respectively. Mobile, AL recorded its third driest May on record with only 0.42 inches (10.7 mm) of precipitation, a deficit of close to 6 inches (152.4 mm). On the 18th of the month, Mount Mitchell recorded its latest snowfall in a calendar year since official records began on the mountain in 1980.
• There were 813 reports of severe weather across the Southeast in May, including six confirmed tornadoes in northern Alabama. Most of the reports occurred in two outbreaks. A series of strong storms with damaging wind and large hail tracked southeastward across the Carolinas on the 10th of the month. Numerous reports of baseball and softball-sized hail were reported in Horry County, SC and Brunswick County, NC. A line of strong storms spawned six tornadoes across northern Alabama on the 25th and 26th of the month. Four of the tornadoes were classified as EF-0 and uprooted many trees. An EF-1 tornado destroyed a small barn near the town of Springfield. The most severe tornado was an EF-2 that touched down in Colbert County southeast of Florence. This tornado tore large sections of roofing off several buildings, including the roof of a chicken barn that was tossed over 100 yards (91.4 meters). A separate cluster of strong storms on the 26th produced damaging winds, hail up to softball-size, and frequent lightning across central Georgia. According to the Georgia State Climate Office, three people died from falling trees and more than 200,000 people lost power in the Atlanta metro area.
• The lack of precipitation in May resulted in an increase in drought severity, especially across the southern tier of the region. There was an emergence of severe drought (D2) conditions across the North Carolina coast, extreme drought (D3) conditions across southern Alabama, north Florida, and southern Georgia, and exceptional drought (D4) conditions across parts of southeast Florida. Stream flow and shallow groundwater levels continued to decline across much of the region. Daily record low flows were reported in several streams across eastern sections of Georgia and North Carolina, though no water supply problems were reported. The hot, dry conditions placed stress on numerous crops across the region. The lack of moisture made it difficult to plant peanuts in Alabama and forced many farmers to replant their cotton. There were also widespread reports of heat stress to crops, as well as worm and insect problems.