Much of the western half of the lower 48 states observed above-normal average temperatures this week. The Intermountain West and Pacific Northwest experienced the largest positive temperature anomalies, where widespread temperatures averaged 5°F to 10°F above normal, with a few pockets exceeding 10°F above normal for the week as 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.
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. 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 to 5 inch 30-day precipitation deficits and predominantly above-normal temperatures. This dryness also extends to 60 to 90 days for several areas across the Southern Plains and along the Gulf Coast, warranting 1-category deteriorations in the drought depiction for many locations not receiving rainfall this week.
Midwest
Moderate rainfall over several days leading up to Oct. 18, associated with a series of storm systems over the Great Lakes, resulted in targeted improvements to portions of western and northern Michigan and eastern Ohio this week. However, most areas, particularly along the Ohio and Middle and Upper Mississippi Valleys, experienced another round of degradation this week. Short-term (30 to 60-day) SPIs are widespread D1-equivalent (moderate drought) or worse across areas seeing degradation.
Additionally, topsoil moisture continues to dry out across portions of the Ohio Valley and the Corn Belt. Deeper soil moisture remains very low also across much of the Mississippi Valley, with several soil moisture indicators (CPC Leaky Bucket, NASA SPoRT, and NASA GRACE) exhibiting large coverage of D1-equivalent (moderate drought) or worse soil moisture conditions along and west of the Mississippi River.
High Plains
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.
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. 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 SPIs.
Soil moisture is in excellent shape as well 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.
