Wednesday, August 24, 2011

Eventos climáticos extremos nos USA

Extreme weather patterns plaguing US

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NOAA's prediction for the next several months offers little hope for relief from drought.

A persistent weather pattern that has seared the central and eastern United States has shattered heat records for both daytime and night temperatures and left the largest swath of "exceptional" drought in the 12-year history of the US Drought Monitor. Twenty-six percent of the land mass in the lower 48 states was included in that most severe drought designation at the end of July.

But the country experienced large variations in both heat and precipitation between regions, according to the National Oceanic and Atmospheric Administration.

Almost 9,000 daily heat records were broken or tied in July, according to NOAA — including 2,755 highest maximum temperatures and 6,171 highest minimum temperatures (i.e., nighttime records). NOAA found that just by plotting the location of each record a nearly complete image of the contiguous US is visible.

The January-July period was record-dry for Texas, New Mexico and the South climate region (Arkansas, Kansas, Louisiana, Mississippi, Oklahoma and Texas). The month of July in that South region was the warmest single calendar month on record for any climate region in the US.

Texas and Oklahoma had their warmest months ever on record in July and while recording nearly their driest months on record. Oklahoma's statewide average temperature in July was the warmest monthly statewide average on record for any state during any month. Texas also set a "hottest-ever" record for June. An article in the Aug. 22 edition of Time magazine says the state has received 6.53 in (17 cm) of rain so far this year, while its annual average for 12 months is 37 in (86 cm).


The little bit of water remaining in Lake E.V. Spense lies 120 feet (37 m) away from the base of the spillway (pictured here). The town of Robert Lee, Texas, (pop. 1,020) is allotted only 200,000 gallons (760 m3) a day of the water being pumped out of Spense.AP Photo/Tony Gutierrez

As the ground dried out and water demand surged, water mains popped at record rates. Houston ordered mandatory water conservation measures after experiencing 700 main breaks a day. At least two Texas towns — Kemp and Robert Lee — found they were nearly without drinking water. Kemp's system was under a boil order after main breaks and heavy usage drained its tank. Dallas exceeded 100 degrees F (37.8 C) on 30 of the 31 days in July. The O.C. Fisher reservoir at San Angelo, Texas, dried up completely.

The trough/ridge weather pattern that slashed across the US created the second warmest May-July on record for the South climate region. In fact, 41 of the lower 48 states had above-normal, much-above-normal or a record warmest July, a shift.

Meanwhile, precipitation was much above normal for most states in the northern half of the country. Three states (Kentucky, Ohio and Michigan) had record precipitation during the February-July period. California tied for its fifth wettest July ever. Reservoirs in Southern California were filling up — at 97 percent of capacity in the case of massive Diamond Lake.

The shift in weather patterns caused had unusually cool temperatures for the Northwest and West climate regions between May and July — the coolest on record for the state of Washington. Only seven states — all west of the Rocky Mountains — had July temperatures that were near or below the 20th century average.

The globe experienced its seventh warmest July since record keeping began in 1880, NOAA reported. Neither El Niño nor La Niña conditions were present during July, according to NOAA. July’s Arctic sea ice extent was the smallest on record for that month since records began in 1979. The January-July worldwide land surface temperature was 1.40F 0.78C) above the 20th century average.

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