NATIONAL WEATHER SUMMARY

AUGUST 2011

1^st-6^th…Hot and humid conditions persisted across the Southern Plains and Deep South on Friday, while the rest of the nation saw multiple areas of active weather. A ridge of high pressure positioned over the southeastern corner of the US continued to bring high temperatures to the South-Central US with temperatures near 100 degrees, and heat indices 110 to 120. However, a low pressure system spinning on the coast of the Carolinas, pushed ample moisture onshore triggering heavy showers and thunderstorms across the Mid-Atlantic states. Rainfall totals associated with this system have been between half an inch to almost 5 inches, with the highest mid-day rainfall totals reported in Charlotte, North Carolina at 2.49 inches.  Meanwhile, high pressure has dominated the Northeast and Upper Great Lakes producing mostly sunny skies with a few clouds across the region.  In the central U.S., a low pressure system moved off the Central Plains into the Mid-Mississippi Valley bringing heavy rain and strong winds to the region and parts of the Ohio, Tennessee, and Upper Mississippi Valleys. Heavy downpours and strong winds were associated with these storms, with a strong wind reports Tennessee and Illinois.  To the west, a low pressure system over Montana pushed a cold front through the Northern Rockies and Northern Plains producing moderate to heavy showers. Wind gusts were reported between 30 to 70 mph. In addition, monsoon moisture in the Southwest triggered scattered showers over the Four Corners region and Central Rockies. Meanwhile, the West Coast continued to see mostly sunny and dry conditions with a few clouds.

14^th-20^th…The heaviest precipitation fell in New England as a storm moved up the eastern seaboard and rotated into the Northeast. This storm carried a significant amount of moisture that once again dumped rain on New England as some cities received several additional inches of rain to go along with the drenching precipitation from the weekend. The cold front associated with this storm pushed through the Southeast and off the coast of the Carolinas, greeting the area with very welcomed cooler air.

Unfortunately, the cool air did not reach the Southern Plains, causing Oklahoma and Texas to once again rise into the 90s and 100s. This area continue to suffer through one of the worst droughts on record. Meanwhile, the West remained warm and mostly dry, although some rain did develop in the Southwest and Intermountain West in the afternoon. The West was set for a significant warming trend later in the week with temperatures pushing into the triple digits for areas of California that have been relatively cool this Summer. The Southeast rose into the 70s, 80s, and some 90s in Florida, while the Northeast saw temperatures in the 70s. The Southern Plains would rise into the 90s and 100s, while the Southwest saw similar temperatures. The Northwest rose into the 70s.

 

 

 

 

Parts of the Midwest experienced active weather Wednesday as a weak cold front dropped southeastward through Iowa and Wisconsin toward northwestern Illinois. Showers and a few thunderstorms accompanied the front in parts of Minnesota, Wisconsin, and Iowa during the morning and afternoon hours. While some storms associated with this system had the potential to produce damaging wind and hail, no events were reported as of this afternoon. To the south, daytime heating kicked up more showers and thunderstorms in central Florida as a frontal boundary remained stationary across the Florida Panhandle, Mississippi, and southern Arkansas. Stronger storms in this region had the potential to produce damaging wind gusts. In the Plains, moist flow and increased instability over the Central High Plains created a slight risk of severe weather development during the afternoon and evening. While large hail was the main concern with storms in this region, damaging wind and a few tornadoes were also possible. Meanwhile, hot weather with triple digit temperatures continued in the Southern Plains. Eastern Oklahoma and areas of nearby northwestern Arkansas were under Excessive Heat Watches through the afternoon and evening, while Heat Advisories remained in effect for parts northeastern and southeastern Texas and much of northern Louisiana. In the West, chances of scattered showers and thunderstorms lingered over New Mexico and Arizona due to monsoon moisture. Storms in the Southwest had the potential to produce locally heavy precipitation and some minor flooding. Localized flash flooding was also possible in recent burn scar areas.

 

21^st-27^th…The Eastern U.S. saw plenty of active weather on Wednesday, while the Western US continued to be mostly sunny and dry. Hurricane Irene strengthened to a category 3 hurricane with winds between 111 to 130 mph (95 to 115 knots). Irene is positioned over the Bahama Islands, and will continue to move closer to the southeastern coast. To the north, a large low pressure system positioned over Ontario pushed a frontal boundary through the Great Lakes to the central Plains. Showers and thunderstorms developed along and ahead of this front over the Northern Appalachians to the Central Plains. The highest mid-day rainfall totals were reported in Toledo, Ohio at 1.43 inches. However, high pressure brought mostly sunny and dry conditions for the Northern Plains and Northern Rockies. In the South, ample moisture pulled onshore, which triggering heavy showers and thunderstorms across the Lower Mississippi Valley and parts of the Tennessee Valley. Rainfall totals associated with these storms have ranged from 0.35 inches to almost 1.5 inches. In addition, strong winds were reported in several areas in Arkansas and Louisiana, with wind gusts recorded at 58 mph in Monroe, Louisiana. To the west, an area of low pressure located 250 miles south of Baja California Sur pushed moisture into the Four Corners region, which kicked up scattered rain showers over the Central and Southern Rockies. At the same time, a trough off the West Coast brought light scattered showers to northern California, the Pacific Northwest, and parts of the Intermountain West.

The northern states saw plenty of active weather on Wednesday, while the southwestern corner of the nation saw mostly sunny skies. A strong frontal system moved through the Northwest, which contributed to widespread moderate showers and thunderstorms over the Intermountain West and Northern Rockies. Wind gusts associated with this system ranged from 30 to 50 mph. At the same time, a large low pressure system positioned over Canada pushed moderate to light rain showers to the Upper Midwest, Great Lakes, and Northeast. Wind gust reached 51 mph in Mt. Washington, New Hampshire, while rainfall totals ranged between a tenth of an inch to almost 0.40 inches. To the south, ample available moisture pushed onshore, which triggered heavy showers and thunderstorms over most of Florida and along the coast of the Gulf States. Rainfall totals reached between 0.40 inches and 0.85 inches in Florida, with the highest mid-day rainfall totals recorded in Boothville, Louisiana at 1.11 inches. Meanwhile, an upper level ridge of high pressure over the Southeast produced mostly dry conditions for the South-Central US, and eastward to the Mid-Atlantic.

To the west, high pressure over the Southwest continued to bring sunny skies for most of the West Coast and Great Basin. However, monsoon moisture triggered scattered showers and thunderstorms over parts of the Four Corners region, while a trough off the western coast brought low clouds and fog along the coasts.

Most of the precipitation were tropical in nature, as Tropical Storm Irene’s departure from the Northeast was soon followed by Tropical Storm Lee’s arrival along the central Gulf Coast. In Irene’s wake, extensive flooding struck the interior Northeast. Later, more than 10 inches of rain drenched parts of the central Gulf Coast region, triggering local flooding. Lee made landfall in southern Louisiana on the morning of September 4. Farther north and west, a strong cold front sparked some heavy showers and thunderstorms from the northern and central Plains into the western Corn Belt. Markedly cooler air trailed the front. Meanwhile, scattered showers fell across the Southwest, but the southern Plains and the Far West remained mostly dry. Due to an extended period of intense heat, weekly temperatures averaged more than 10F above normal across parts of the south-central U.S. Unusual late-season warmth also covered the Midwest and Southwest, although the heat wave broke toward week’s end.

Early in the week, Irene continued to batter the Northeast. Despite being downgraded from a hurricane to a tropical storm before reaching New York City on the morning of August 28, wind gusts on that day were clocked to 81 mph at the Blue Hill Observatory in Milton, MA; 67 mph at New York’s LaGuardia Airport; 64 mph in Providence, RI; and 63 mph in Bridgeport, CT. Meanwhile, record setting rainfall amounts for August 28 reached 5.22 inches in Newark, NJ; 4.83 inches in St. Johnsbury, VT; 4.69 inches in Albany, NY; and 4.13 inches in Mt. Pocono, PA. Wilmington, DE (6.94 inches on August 27-28), experienced its fifth-highest 2-day rainfall on record.

Record flooding affected numerous river basins from New Jersey northward. On August 28 in New Jersey, high-water marks from Hurricane Floyd in September 1999 were broken along the Millstone River at Griggstown (14.21 feet above flood stage) and Blackwells Mills (12.24 feet). Along the Passaic River at Pine Brook, NJ (5.12 feet above flood stage on August 30), the river level exceeded the highwater mark established on October 10, 1903. In Vermont, Otter Creek at Rutland climbed 9.21 feet above flood stage on August 29, easily surpassing the record of 5.45 feet set in the aftermath of a hurricane on September 22, 1938. In North Walpole, NH, the Connecticut River (3.36 feet above flood stage on August 29) climbed to its highest level since September 22, 1938. Across the south-central U.S., the list of locations reporting recordsetting number of 100-degree days continued to grow. In Texas, for example, College Station’s 1917 standard of 58 days with 100-degree heat was tied on August 31 and surpassed on September 1. Elsewhere in Texas, Del Rio experienced its 79th day of triple-digit heat (on August 30), edging its 1953 record. As far north as Kansas, Wichita’s 51st day of 100-degree heat (on September 1) topped its 1936 standard. August 28 was the hottest day on record in Austin (Camp Mabry), TX, where the high of 112°F tied the record originally set on September 5, 2000. San Antonio, TX (110F on August 28), eclipsed its monthly record of 108F originally set on August 19, 1986. Highs reached 111F in Lawton, OK (on August 28), and Childress, TX (on August 30). Late-season heat also spread into the Midwest, where Springfield, IL (99, 102, 101, and 100F), and St. Louis, MO (103, 104, 101, and 101°F), notched four consecutive daily-record highs from August 31 - September 3. The reading of 102F in Springfield represented a September record (previously, 101°F on September 1, 1984), while St. Louis tied a monthly record set on September 4, 1954, and September 1, 1984. For Springfield, it was also the hottest day since July 13, 1995. Meanwhile in Arizona, Douglas set a monthly record with a high of 104F on August 30. Finally, at week’s end, cooler air began to overspread the Plains and Midwest. However, extreme heat lingered across southern Texas, where McAllen, Harlingen, and Corpus Christi attained 106°F on September 3. In advance of a strong cold front, September 3 highs reached daily record levels in locations such as Louisville, KY (102F), and Indianapolis, IN (100F). Tropical Storm Lee made landfall on Sunday morning, September 4, near Intracoastal City, LA. At landfall, Lee’s maximum sustained winds were near 45 mph, mostly in squalls over the northern Gulf of Mexico. On September 3, prior to Lee’s arrival, a few wind gusts to near 60 mph were reported in southern Louisiana as far inland as New Orleans. A gust to 51 mph was clocked on September 3 in Gulfport, MS. In addition, a 4-foot storm surge was noted in southern Louisiana locations such as Shell Beach and Lake Pontchartrain. However, Lee’s most significant impact was heavy rain. Official September 1-5 totals reached 11.64 inches in Mobile, AL; 11.15 inches in both Gulfport and Jackson, MS; 11.05 inches in New Orleans, LA; 9.80 inches in Chattanooga, TN; and 7.97 inches in Birmingham, AL. However, much of Lee’s heavy rain fell in drought-affected areas, helping to limit flood severity.

Jim G. Munley, jr.
http://www.jimmunleywx.com