Nationwide
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A long wave trough resulted in seasonal to below-normal temperatures across the western third of the contiguous U.S. (CONUS).
A ridge of high pressure dominated the eastern two-thirds of the CONUS, leading to above-normal temperatures, with the highest positive anomalies across the Northern Plains and Midwest. Despite the amplified ridge in the East, early in the week, an upper-level low-pressure system drifted slowly northward from the Southeast to the Great Lakes, bringing unsettled weather and keeping many areas across the Southeast and Ohio Valley wet.
A coastal low-pressure system along the coastal Carolinas brought some additional precipitation to coastal and inland areas of the Carolinas, leading to mixed reductions and expansion in coverage of abnormal dryness across the Carolinas and Virginia. In the Northeast, little to no precipitation fell and above-normal temperatures, coupled with long-term deficits, led to degradation and expansion of abnormally dry and severe drought areas across Upstate New York and New England.
This week, the Northern Plains and Upper Midwest experienced some of the largest positive temperature anomalies (8-10°F above normal). However, a strong surface low-pressure system brought heavy rainfall across the Dakotas and northern Minnesota, leading to broad 1-category improvements. In the wake of this storm system, a surface low-pressure system developed in the lee of the Rockies over the Southern Plains, dropping several inches of rainfall, further improving drought conditions (1-category improvements) in areas affected by the recent rapid onset and intensification of drought during September. This low-pressure system moved across the Midwest later in the week, leading to further improvements across portions of the western Corn Belt due to heavy rainfall. Areas that missed out on the rainfall over the Great Plains experienced worsening conditions due to above-normal temperatures and high winds, increasing longwave evaporation and leading to increased soil moisture loss.
An active storm track in the West, associated with a longwave trough, resulted in improving conditions along with fringe drought areas in the Pacific Northwest and the Four Corners, where antecedent wetness leading up to this week resulted in more immediate improvements. Given the intensity and duration of drought across the remainder of the West, more precipitation will be needed to warrant more meaningful improvements.
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The West
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This week, an active storm track across the western U.S. brought seasonal to cooler than normal temperatures and beneficial precipitation to much of the region. Improvements were mainly limited to portions of the Pacific Northwest and Four Corners due to improving soil moisture conditions.
This precipitation was on the heels of an active Southwest Monsoon season for the Four Corners region, so reduced evaporative demand coupled with above-normal precipitation led to immediate improvements. For much of the remainder of the West, more precipitation is needed to recharge soil moisture and increase groundwater levels, stream flows, and reservoir levels.
The only minor degradations of drought in the Western Region were in southeastern New Mexico and western Montana, where above-normal temperatures and high evaporative demand warranted expansion of D0 (abnormally dry) and D3 (extreme drought) areas, respectively.
The High Plains
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Similar to the Southern Plains, much of the High Plains region is susceptible to extended periods of above-normal temperatures and high winds.
In areas where little to no rain fell, these conditions helped to further degrade ongoing drought east of the Front Range across portions of Colorado, Wyoming, Kansas, and Nebraska, where many areas have seen drastic deterioration in topsoil moisture in recent weeks.
Farther north over the Dakotas, a strong low-pressure system brought widespread heavy rainfall over the weekend. Several areas received more than 2 inches of rain, with localized areas of more than 4 inches. This warranted 1-category improvements across large portions of the Dakotas. However, improvements were targeted in nature due to the longer-term deficits and above-normal temperatures increasing the evaporative demand and slowing soil recharge.
Farther south in the High Plains Region, surface low pressure developed late in the period in the wake of the system farther north and moved north-northeastward across the central U.S. Rainfall from this system mainly fell over drought-free areas of eastern Kansas before moving into the Midwest and Great Lakes. However, some locations did receive meaningful rainfall; enough to warrant 1-category improvements in northeastern and southeastern corners of the state.
Another storm system began propagating across the western U.S. on the final day of the period (Monday-Tuesday), bringing precipitation in various forms to the eastern Rockies. However, given the intensity of drought in the higher-terrain areas of the High Plains Region, the late arrival of precipitation did little to warrant any improvements this week, given the duration and intensity of drought in those areas.
The South
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Ahead of a long-wave trough across the western U.S., an area of low pressure developed over the Southern Plains, bringing with it much-needed precipitation to areas affected by the rapid onset of drought conditions in recent weeks. This has helped improve conditions, mainly across parts of Oklahoma, where many locations received 2-3 inches of rainfall (greater than 1 inch positive weekly anomalies).
Unfortunately, many locations outside of Oklahoma in the Southern Region continued to see further degradation and expansion of drought conditions in, and adjacent to, areas where the rains did not fall or were insufficient. Worsening conditions were observed across Texas and the Ark-La-Tex region was exacerbated by above-normal temperatures and high winds leading to increased evaporation and evapotranspiration rates. — UNL Drought Monitor
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