Weekly Weather Summary:  A record-setting heat wave gripped most areas from the Plains to the East Coast. The combination of high temperatures, oppressive humidity, and a lack of overnight cooling resulted in significant stress on humans, animals, and crops.  In contrast, cool weather prevailed in the Pacific Coast States.  Meanwhile, little or no rain fell from the southern Plains into the lower Ohio Valley.  The combination of heat and a lack of rain caused further devastation in the drought-ravaged south-central U.S. and brought the season’s first round of stress to some Midwestern crops.  The Midwest’s problems were compounded by the fact that for some corn and soybeans, the heat wave coincided with the reproductive stage of development.  Late in the week, however, beneficial rain fell across an area of emerging dryness from Iowa into the lower Great Lakes region.  Areas to the south, however, including the middle Mississippi Valley, remained dry.  Hot weather also contributed to an increase in crop stress in parts of the East.  Rain tempered the heat’s effects in some areas.  Farther west, beneficial monsoon showers dotted the Southwest.

Drought monitor: Record heat in the PlainsThe Midwest and Northeast:  Record-setting heat affected both regions for several days.  On July 18, Rochester, Minnesota, set an all-time record with a dewpoint of 83°F (previously, 82°F on July 12 and 13, 1995).  On July 19, Aberdeen, South Dakota, reported its first triple-digit heat since July 7, 2007, while Moline, Illinois, registered a 100-degree day for the first time since July 17, 2006.  Even more impressively, Rockford, Illinois (100°F on July 19), tallied its first high of 100°F or greater since July 10, 1989, while Indianapolis, IN (100°F on July 21), experienced its hottest day since August 16, 1988.  Later, record-shattering heat spread into the East.  On July 22, highs soared to 108°F in Newark, New Jersey, and downtown Baltimore, Maryland.  Newark’s former all-time record of 105°F had been set on August 9, 2001, and several earlier dates.  Downtown Baltimore’s reading missed the Maryland state record by 1°F.  All-time-record highs were also set or tied on July 22 in locations such as Virginia’s Dulles Airport (105°F; previously, 104°F on August 20, 1983, and July 16, 1988); Bridgeport, Connecticut (103°F; tied the record set on July 22, 1957); Reading, Pennsylvania (106°F; previously, 105°F on August 7, 1918); and Georgetown, Delaware (104°F; previously, 102°F on July 31, 1954, and July 6, 2010).  A July record was set in Portland, Maine (100°F on July 22), where it was the hottest day since August 2, 1975 (103°F).  In Pittsburgh, Pennsylvania (96°F on July 22), it was the hottest day since August 15, 1995.  In some locations, including Reading (102, 106, and 100°F from July 21-23), daily-record highs were set on 3 days in a row.  At the height of the heat wave, all-time records for the highest minimum temperature were set or tied in numerous locations, including Newark (86°F on July 22); Washington, D.C. (84°F on July 23 and 24); New York’s Central Park (84°F on July 22); and Scranton, Pennsylvania (80°F on July 22).  In Omaha, Nebraska, the minimum temperature remained at 80°F or higher from July 17-20, marking the second-longest such streak on record behind 8 days from July 18-25, 1934.  However, as the heat relaxed, heavy rain erupted in a few areas, especially from eastern Iowa into northern Illinois.  In particular, July 23 was the wettest day on record in Chicago, Illinois, where 6.86 inches fell (previously, 6.64 inches on September 13, 2008).

The heat wave struck at an inopportune time for crops, resulting in a broad expansion of D0A.  In Pennsylvania, the portion of the corn crop rated in very poor to poor condition jumped from 11 to 30% between July 17 and 24.  During the same period, Missouri noted an increase from 16 to 22%.  By July 24, the portion of pastures rated in very poor to poor condition stood at 62% in Pennsylvania and 53% in Maryland.  Nearly all (92%) of Pennsylvania’s topsoil moisture was rated very short to short, along with 80% in Maine, 73% in New York, 72% in Michigan, and 53% in Indiana.

The Southeast:  Scattered showers helped to offset the effects of heat in some areas.  Rainfall was heaviest in the central Gulf Coast region and along the western slopes of the central and southern Appalachians, resulting in some modest improvements in the drought depiction.  Meanwhile, short-term dryness (D0A) began to push northeastward across the Mid-South, reaching into central Missouri and western sections of Kentucky and Tennessee.  In Arkansas, nearly two-thirds (66%) of the pastures were rated in very poor to poor condition on July 24, while topsoil moisture was 86% very short to short.  Ft. Smith, Arkansas, reported 22 consecutive days of 100°F heat (and counting) from July 5-26, shattering its previous record of 17 days in July 1934.  In the Southeast, some lingering poor crop conditions were noted on July 24.  In Alabama, for example, nearly one-third of the peanuts (32%) and cotton (33%) were rated very poor to poor.  On the same date, 37% of Georgia’s cotton was rated very poor to poor.  In Florida, concern still exists for Lake Okeechobee, which had an average surface elevation of 10.26 feet on July 26.  This level is 3.71 feet below the level observed a year earlier, on July 26, 2010.

The Central and Southern Plains:  Disastrously hot, dry conditions persisted across much of the drought region, which extended as far north as southeastern Colorado and the southern half of Kansas.  In northern Texas, Amarillo’s tally of 100°F readings reached 30 days on July 26; the former annual record of 26 days had been set in 1953.  Elsewhere in Texas, Tyler recorded 29 consecutive days (and counting) of 100-degree heat from June 28 – July 26, demolishing its record of 20 days in a row set from July 15 – August 3, 1998.  From 1995-2010, the coverage of Texas rangeland and pastures in very poor to poor condition peaked at 81% in August 1998 and 2006; on July 24, 2011, coverage stood at 91%.  The rangeland and pasture situation was nearly as bad in Oklahoma (84% very poor to poor) and Kansas (52%).  One of the region’s hardest-hit row crops was cotton, with 79% rated very poor to poor in Oklahoma and 59% in Texas.  Spotty showers dotted western and southern Texas, as well as the central and southern High Plains, but in many cases temporary drought relief was more than offset by the relentless heat.  One exception was extreme southeastern Texas, where heavy rain took a bite out of the extreme to exceptional drought.

The Southwest: A plume of tropical moisture triggered scattered monsoon showers.  Some of the most widespread rain fell from southeastern Arizona into northeastern New Mexico and southeastern Colorado.  However, only minimal changes were introduced, as the rain provided only limited and localized relief from a serious drought situation.  On July 24, USDA rated 89% of New Mexico’s rangeland and pastures in very poor to poor condition.

Puerto Rico, Hawaii, and Alaska:  No changes were introduced in Puerto Rico (no dryness or drought), Hawaii, or Alaska.  Hawaii is currently in the midst of its dry season; long-term rainfall deficits persist across portions of the central and eastern Hawaiian Islands.  Meanwhile, patchy dryness lingered across south-central and southeastern Alaska.

Looking Ahead:   During the next 5 days (July 28 – August 1), Tropical Storm Don will cross the Gulf of Mexico, contributing to late-week rainfall in the central and western Gulf Coast States.  The degree of drought relief provided by Don will depend upon the storm’s intensity, as well as the track and forward speed.  Meanwhile, the Southwestern monsoon circulation interacting with a cold front will produce widespread showers and thunderstorms from the Four Corners region into the northern Plains, Midwest, and Northeast.  Showers will increase in coverage over the Southeast, but hot, mostly dry conditions will persist from the southern Plains into the Ohio Valley and northern Mid-Atlantic region.

The CPC 6- to 10-day outlook for August 2-6 calls for hotter-than-normal weather east of a line from New Mexico to Minnesota, excluding New England, while below-normal temperatures will be confined to the northern Rockies, northern California, and the Pacific Northwest.  Meanwhile, wetter-than-normal conditions will arc across the Four Corners region, northern Plains, Midwest, Ohio Valley, and southern Mid-Atlantic States, but the remainder of the U.S. will experience near- to below-normal rainfall.