Drought - July 2008
|Contents Of This Report:||
|The weather pattern during July was a
continuation of the pattern of the last several months. Generally
pressure dominated the southern half of the country while the
summer storm track dragged fronts and storm systems across the
northern states, bringing rain to the Midwest to
Northeast. The cool fronts occasionally penetrated into the
Southeast, triggering scattered
showers and thunderstorms, while the remnants of Hurricane
Dolly brought relief from
drought to parts of southern Texas and the Southwest near the
end of the month (July 29 USDM
1 USDM). Dry
weather dominated the Northwest.
July was generally drier than average across eastern Puerto Rico and parts of Hawaii, and wetter than average across most of Alaska. The persistent dryness has resulted in 3-month to 6-month rainfall deficits, below-normal streamflow, and moderate to severe drought across much of Hawaii.
The showers and thunderstorms which fell across the Southeast were not widespread or heavy enough to improve the long-term precipitation deficits. Hydrological conditions remained dry and streams (both modeled and observed), lakes, and groundwater levels were low. Soil moisture continued parched (both observed as well as modeled anomalies and percentiles, root zone percentiles, and total column layer percentiles) and a greater than average percentage of the pasture and rangeland was in poor to very poor condition. USDM statistics showed moderate to exceptional drought covering about 59% of the region by the end of July, about the same as at the end of June.
A more detailed drought discussion, provided by the NOAA Regional Climate Centers, can be found below.
According to the Southeast Regional Climate Center, drought conditions across the region changed very little during the month. Exceptional drought conditions continued to plague northwestern South Carolina and portions of western North Carolina and extreme northeastern Georgia. A broad area of severe to extreme drought continued to affect much of eastern Alabama, Georgia, South Carolina, North Carolina, and southwestern Virginia. There were many reports of severe weather across the Southeast, especially high winds, which are quite common during the month of July. July 22 was the most active day of the month with numerous reports of severe weather in North Carolina, southwestern Virginia, and portions of Georgia and Alabama.
As noted by the Southern Regional Climate Center, precipitation for the month of July was quite variable over the region, which was due in part to Hurricane Dolly. The storm slammed into the southern Texas coast as a category two hurricane on the 23rd of the month. As a result, rainfall totals were excessive, with many stations in the southernmost counties reporting anywhere from 200 to 600 percent of normal. Elsewhere, rainfall was generally below normal, particularly within southern Arkansas, eastern Texas and most of Louisiana, where totals ranged from 5-50% of normal.
Drought conditions in the region changed only slightly from June. In Tennessee, a small area of extreme drought developed along a very narrow edge of the eastern border with North Carolina. Conditions in Oklahoma improved through a small reduction in the spatial extent of exceptional drought that was present in the panhandle. In Arkansas, conditions remained abnormally dry in the southern and eastern portions of the state. In Mississippi, an area of moderate drought was added in the northern third of the state, and there was a slight expansion of moderate drought in the southwest. In total, approximately 34% of the state was experiencing moderate drought at the end of July. Only 2% of the state was still in severe drought. Northern and southwestern Louisiana showed signs of moderate and severe drought. Approximately 45% of the state was experiencing moderate conditions or worse, 24% of which was severe drought conditions. In Texas, rainfall from Hurricane Dolly essentially eradicated almost all drought conditions in the Trans Pecos Climate division. As of last month, the entire division was showing either severe or extreme drought conditions. Dolly also eradicated drought in the extreme southern tip of the state. A large portion of extreme drought still existed in the south central counties, making up over 10% of the state's area. In the east, abnormally dry conditions were replaced with moderate drought.
As explained by the Midwest Regional Climate Center, much of the central Midwest received normal to above normal rainfall during July, but an area from central Iowa through the northeastern half of Missouri into western Illinois accumulated more than twice the normal July rainfall. There was no drought on the USDM map in the Midwest region at the end of July.
As noted by the High Plains Regional Climate Center, precipitation amounts for the High Plains Region resulted in scattered areas of above average precipitation and widespread areas of well below average precipitation. Above average locations included the Nebraska Panhandle, portions of eastern Wyoming, north central South Dakota, eastern North Dakota, portions of southeastern Nebraska, and north central Kansas. Those areas had 150%-200% their normal precipitation for the month of July. The remainder of the High Plains Region experienced predominantly below average precipitation (approximately 60%) with the most extreme areas being southwestern Wyoming and the majority of Colorado (less than 50%). Roscoe, SD received 5.98 in (151.9 mm) through the month, resulting in 214% their normal precipitation for July. On the other end of both the spectrum and region were Boulder, CO and Northglenn, CO. Boulder received only 0.09 in (2.3 mm) during July, resulting in 5% of the normal for the month. Even worse was Northglenn which received no rain for the month while their normal for July is 1.71 in (43.4 mm).
Drought conditions in North Dakota rapidly expanded and intensified during July. Large areas of western and central North Dakota went from D0 (abnormally dry) and D1 (moderate drought) conditions to D3 (extreme drought) in merely a month. By the end of July, the entire state was experiencing abnormally dry or drought conditions, ranging from D0 (abnormally dry) in the eastern portions to D3 (extreme) drought in the western portions.
As summarized by the Western Regional Climate Center, temperatures throughout the West were slightly to moderately above normal except for the coastal Pacific Northwest and much of New Mexico. Portions of the Intermountain West had an extremely warm month with Denver recording their 2nd warmest July on record dating back 60 years. The final 19 days of the month in Denver equaled or exceeded 90 °F (32.2 °C) which broke their all time consecutive 90 degree day record. This record consecutive string continued into August. Cheyenne, WY, recorded just one day below normal for July. Most of Alaska had a very cool month with Anchorage recording their lowest July average maximum temperature on record and Juneau recording their second coolest July on record.
Precipitation was a predictably mixed bag for a summer month with the notable exception of very wet conditions in New Mexico due to strong monsoonal flow and the remnants of Hurricane Dolly. Cloudcroft, NM, recorded their wettest month on record with 13.33 in (339 mm) of rain and Albuquerque recorded their fourth wettest July in 93 years with 3.38 in (86 mm). Parts of Alaska were quite wet with Fairbanks measuring their fourth wettest July on record and Juneau their second wettest.
Alaska: According to National Weather Service reports (from information provided by Audrey Rubel at NOAA NWS Alaska Region Headquarters), July was wetter and cooler than normal across much of the state due to a change in the circulation pattern. The high pressure ridge that had set up across much of northern Alaska gave way to a persistent low pressure trough which allowed many weather systems to move into the state from the west with fresh intrusions of either cool, moist Bering Sea air masses or even cooler air masses from the Arctic.
As noted by the Northeast Regional Climate Center, rainfall was abundant in the northern states and near or below normal in the southern half of the region during July. The USDM issued on July 29, 2008 indicated that the southern half of New Jersey and a small portion of southern West Virginia were experiencing abnormally dry conditions. In contrast, northeastern New York, western and northern Vermont and western Massachusetts fell into the extremely moist category of the Palmer Drought Severity Index.
|A detailed review of
drought and moisture conditions is available for all contiguous U.S.
states, the nine standard regions, and
the nation (contiguous U.S.):