Nationwide
This week, much of the western half of the lower 48 states observed above-normal average temperatures.
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The Intermountain West and Pacific Northwest experienced the largest positive temperature anomalies, where widespread temperatures averaged 5-10 F above normal, with a few pockets exceeding 10 F above average for the week as a whole. In addition to the above-normal temperatures, precipitation was also lacking for most areas from the Central and Northern Plains westward to the Pacific Coast, warranting drought deterioration. Parts of the Four Corners and Desert Southwest were the exception to this, as an area of low pressure meandered across the Southwest before being picked up by a frontal boundary dropping southward across the central U.S. This resulted in improvements to long-term drought conditions across parts of the Four Corners, with targeted improvements in the Southern Plains.
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Across the eastern half of the lower 48, frontal boundaries associated with a couple of strong low-pressure systems in the Great Lakes brought heavy precipitation and cooler-than-normal temperatures to portions of the Great Lakes, Northeast and Southeast. Therefore, a widespread mix of improvements and deterioration was warranted in many locations where the heaviest precipitation did and did not fall.
The West
An upper-level low-pressure system, coupled with a frontal boundary dropping southward across the central U.S., resulted in a good soaking this week for many areas from southeastern California eastward to the Rio Grande Valley.
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Given the lingering precipitation associated with this area of low pressure following the climatological end to a very robust Southwest Monsoon season in late September, this was another much-needed round of precipitation to further fuel ongoing improvements to long-term drought indicators, such as groundwater and 12 to 24-month Standard Precipitation Index (SPIs). Soil moisture is also in excellent shape coming out of the monsoon season across Arizona and New Mexico.
Farther northward in the Western Region, degradation was the main story, as below-normal precipitation and above-normal average temperatures (in some cases record high temperatures for this time of year) were observed. High winds and above-normal temperatures resulted in targeted degradations across northern portions of the Intermountain West and the High Plains.
In the Pacific Northwest, degradations were also warranted, with the addition of D2 (severe drought) across the parts of the Coastal Ranges and Northern Cascades in Washington, where 28-day average stream flows have dropped into the bottom 2 percent of the historical distribution. In addition, soil moisture ranks in the bottom 5 percent climatologically, vegetation indices indicate widespread drought stress, groundwater levels are falling, and SPIs for all periods out to 120 days are D4-equivalent (exceptional drought). The Pacific Northwest is entering a climatologically wetter time of year, so precipitation will need to come soon to halt further deterioration.
The High Plains
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Despite the High Plains Region observing near to below-normal average temperatures this week, a combination of antecedent dryness, below-normal precipitation, and high winds resulted predominantly in continued degradation region-wide. The only exception was the southwestern corner of Colorado, where short and long-term drought indicators have shown continued improvement following a robust Southwest Monsoon season and a couple of additional episodes of precipitation associated with cutoff areas of low pressure in the Southwest in recent weeks.
The South
Frontal boundaries associated with a couple of strong low-pressure systems over the Great Lakes brought heavy precipitation to parts of the Red River Valley of the South, the Ozarks, and the Tennessee Valley this week.
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Farther westward toward the Rio Grande Valley, a cutoff low-pressure system became entrained into the second frontal boundary dropping southward across the central U.S. bringing heavy rainfall to parts of western and southern Texas. Improvements were generally warranted in areas receiving the heaviest rainfall (greater than 1-inch positive 7-day anomalies).
However, antecedent 30-day dryness resulted in status quo depictions for several other locations receiving near to above-normal rainfall, as surface soil moisture has rapidly declined due to widespread 3-5 inch 30-day precipitation deficits and predominantly above-normal temperatures. This dryness extends to 60-90 days for several areas across the Southern Plains and along the Gulf Coast, warranting 1-category deterioration in the drought depiction for many locations not receiving rainfall this week. — UNL Drought Monitor
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