Nationwide
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A low pressure system developed across the southern Great Plains by February 17 and rapidly tracked northeastward to the Ohio Valley and Northeast a day later. To the northwest of the surface low track, snowfall amounts exceeded 6 inches across northeast Kansas, northern Missouri, and north-central Illinois. In the warm sector of this storm system, severe thunderstorms with locally heavy rainfall (more than 1 inch) affected the Tennessee Valley and parts of the Lower Mississippi Valley.
Another low pressure system developed by February 21 with a similar northeastward track to the Ohio Valley. 7-day precipitation amounts, from February 15 to 21, exceeded two inches across much of the Ohio and Tennessee Valleys, Ozarks region, southeast Oklahoma, and parts of northern Texas.
Farther to the south and west, little to no rainfall occurred closer to the Gulf Coast along with the Rio Grande Valley and central to southern high Plains. During mid-February, this precipitation pattern and the primary storm track across the Ohio Valley are typical during La Nina. Although there was accumulating snow across the northern to the central Rockies and northern Cascades this past week, the drier-than-normal pattern persisted throughout most of the West. 7-day temperatures, for the week ending on February 22, averaged above normal across the East, lower Mississippi Valley, and western Gulf Coast.
Meanwhile, intrusions of Arctic air began to shift south from Canada into the northern Great Plains and upper Mississippi Valley, where weekly temperatures averaged as much as 10 degrees below normal.
The West
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Following the wet December 2021 for much of the West, a dry pattern persisted since early January. 2022 year-to-date precipitation averages less than 25 percent of normal throughout much of California and the Great Basin.
Snow water equivalent (SWE) continues to decline due to the dry pattern during January and February. SWE falls below 75 percent of average for much of the southern Cascades, Sierra Nevada Mountains, and Great Basin. Due to the persistently dry pattern since early January, a 1-category degradation was made to parts of northern California and southwest Oregon, which reflects the extreme (D3) levels of drought according to the 24-month and 2022 year-to-date Standardized Precipitation Index (SPI), soil moisture indicators, and 28-day average streamflows. Without a major pattern change during March, additional degradations may be needed for California and the Great Basin in the weeks ahead.
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A slight expansion of D3 was made to northern Wyoming to be consistent with 12 to 24-month SPIs. Recent snowfall with SWE currently running near to above average prompted a 1-category improvement to the north of Denver, Colorado.
Based on a favorable snowpack across the Clearwater and Salmon basins of central Idaho, severe (D2) was improved to moderate (D1) drought for that part of Idaho. Moderate drought (D1) was degraded to severe drought (D2) across Idaho’s Upper Snake River basin as SWE for the headwaters, or this basin is nearing the 10th percentile. 7-day precipitation amounts of more than 1 inch, liquid equivalent, prompted a 1-category improvement from extreme (D3) to severe (D2) drought across parts of south-central Montana.
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Periods of above-normal temperatures coupled with enhanced surface winds support an expansion of severe (D2) to extreme (D3) drought across southern and eastern New Mexico. These worsening conditions are also consistent with SPEI at various time scales and the depiction for western Texas.
The High Plains
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Following two weeks of worsening conditions across the central Great Plains, additional degradations were made to parts of Kansas and southern Nebraska. These degradations were supported by 30 to 120-day SPI and soil moisture indicators.
Snowfall of more than 6 inches during mid-February and favorable snow water equivalent values supported a one category improvement over the Bitterroots of western Montana. A slight reduction in exceptional drought (D4) and extreme drought (D3) was made to western and south-central Montana due to this past week’s snowfall (more than 0.5 inch, liquid equivalent) along with consideration of SWE for the season and long-term SPIs.
The South
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A sharp gradient in precipitation was observed from north to south across this region which is typical for La Nina during mid-February. 7-day precipitation amounts, from Feb 15 to 21, exceeded 2 inches across most of the northern half of Mississippi, northern two-thirds of Arkansas, southeastern Oklahoma, and northwestern Texas. A 1-category improvement was made to these areas that received the heavier rainfall.
Conversely, farther to the south, a 1-category degradation was made to parts of the Lower Mississippi Valley, western Gulf Coast, and central to southern Texas, where little to no rainfall occurred this past week. Extreme drought (D3) was added to parts of southwestern Louisiana based on 30 to 90-day SPIs and soil moisture indicators. As temperatures warm heading into March and water demand increases with vegetative growth, additional degradation may be warranted for the lower Mississippi Valley.
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Although no changes were made this week to the southern high Plains, soil moisture continues to rank in the lowest 5th percentile, consistent with much of this region being designated with D3 levels of drought. The lack of adequate soil moisture remains a major concern for the winter wheat crop across the southern Great Plains, while many counties of Oklahoma and Texas remain under a burn ban. — UNL Drought Monitor
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