A transition from ENSO-neutral to La Niña conditions is favored during Fall 2021. However, given the lag in an atmospheric response to changes in ENSO, La Niña conditions are not considered for the October 2021 Monthly Drought Outlook.
Drought has persisted across much of the western and north-central CONUS due to above-normal temperatures and below-normal precipitation. However, there was some improvement during September across portions of the Pacific Northwest, as that region has already begun its transition into a wetter time of year and below-normal temperatures were observed in many locations.
Parts of the Southern Plains saw rapid drought development, exacerbated by above-normal temperatures, below-normal precipitation, and high winds. The Central and Northern Plains experienced a mix of deteriorating drought conditions (western High Plains Region) and improvements (eastern High Plains Region), as some heavier precipitation amounts have resulted in improved soil moisture and stream flows.
In the Midwest and Great Lakes, targeted improvements have also been observed across Minnesota and northern Iowa in recent weeks, while pockets of D1 (moderate drought) are still evident in Michigan, due to long-term, deep soil moisture depletion. Similar conditions to those in Michigan are occurring across northern New England, as long-term precipitation deficits and soil moisture depletion are evident.
The Southeast is drought-free heading into October, but some areas in the Carolinas and Virginia have teetered between abnormal dryness (D0) and moderate drought (D1) conditions in recent weeks.
Looking forward to October, heavy rainfall is predicted across parts of the Central and Southern Plains early in the period, which should curtail and reverse the ongoing flash drought across northern Texas and Oklahoma, in the Southern Region.
Toward the end of the first week of the valid period, an amplified trough is likely to build across much of the western CONUS, leading to increased chances of above-normal precipitation across much of the West, extending eastward to the Great Plains.
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However, improvements are only likely in areas that have experienced improvements to drought conditions leading up to October, with persistence likely elsewhere across the Western and High Plains Regions. Despite increased odds of above-normal temperatures across the Midwest and Northeast during October, temperatures typically play less of a role in exacerbation of drought conditions across the northern tier during the Fall season.
As such, some improvements are likely across parts of Minnesota and the western Corn Belt where precipitation odds tilt toward above-normal. Pockets of D1-D2 drought from the Central Great Lakes to the Northeast are likely to persist, with antecedent conditions being favorable enough to offset the increased potential for below-normal precipitation across the northeastern CONUS.
The Southeast is likely to remain drought-free, as the pattern is favored to remain active through the first half of October.
Time of year and climatology are likely to keep Alaska drought-free through the end of October. Ongoing D1-D3 (moderate-extreme) drought is likely to persist in Hawaii, as seasonal temperatures are expected and the state enters into a climatologically wetter time of year, despite drier signals at the monthly lead.
Drought persistence and development is likely across inland coastal areas and the eastern third of Puerto Rico due to the increased potential for suppression of tropical convection through the first half of October, above-normal temperatures, and antecedent dryness.
Forecast confidence is high for the Western Region.
- Drought conditions continue to blanket the Western Region, with 93 percent of these states experiencing moderate drought conditions (D1) or worse, and just under 60 percent of the region in extreme to exceptional drought (D3-D4).
- Parts of the Pacific Northwest have experienced modest improvements in drought conditions since the September MDO release. As the region enters into a climatologically wetter time of year, drought removal (D1) and improvements (D2-D4) are expected to continue in parts of the Pacific Northwest and the northern Rockies.
- Furthermore, troughing is forecast to amplify across the western contiguous U.S. (CONUS) from the end of the first week of the October through the middle of the month, increasing probabilities of above-normal precipitation and near- to below-normal temperatures for much of the West.
- However, for the central and southern West Coast, the Great Basin, and Four Corners, any excessive rainfall will likely not be enough to improve drought conditions, as antecedent soil moisture conditions are widespread below the 5th percentile of the climatological distribution (below the 20th percentile across the Four Corner), stream flows have begun to decline in recent weeks as the Southwest Monsoon Season has come to an end, and major reservoirs remain at record low levels.
- As such, persistence is favored for the remainder of the Western Region, as these areas will require sustained above-normal precipitation for several weeks for meaningful improvements.
Forecast confidence is moderate for the eastern High Plains Region and moderate-to-high for the western High Plains Region.
- Across the High Plains region, drought is also prevalent, with nearly 64 percent of the region currently experiencing moderate drought (D1) conditions or worse.
- Much of the eastern Dakotas have experienced improving drought conditions in recent weeks, with several locations receiving 1 to 3 inches above-normal precipitation.
- Large areas of near- to above-normal precipitation also extend southward to Kansas. This has resulted in marked improvements to soil moisture conditions across much of the region. Above-normal precipitation is expected across portions of the Central Plains, mainly across Kansas and Nebraska.
- However, increased troughing across the western CONUS during the 6-14 day period increases the potential for above-normal precipitation across the Central and Northern Plains, warranting drought removal/improvements across parts of Kansas, central and eastern Nebraska, eastern South Dakota, and extreme southeastern North Dakota.
- Farther west in the High Plains Region, despite increased chances of above-normal rainfall through the Week-2 period, well below-normal soil moisture, high wind events, and above-normal temperatures are likely to offset the potential for above-normal precipitation early in the period, warranting persistence for the remainder of the High Plains Region.
Forecast confidence is moderate for the Midwest Region.
- Similar to the High Plains Region, areas in the Upper Midwest have benefitted in recent weeks from above-normal rainfall and improved soil moisture, which has led to improving drought conditions, mainly for parts of Minnesota and northwestern Iowa.
- However, long-term deficits remain widespread across Minnesota and the western Corn Belt. Temperatures typically become less of a factor during the Fall season in the Midwest, particularly the northernmost areas.
- During October, above-normal precipitation odds are favored for the western half of the Midwest Region, with the highest odds (greater than 40% chances) across Missouri, central and western Iowa, and southwestern Minnesota. Areas of removal (D1) and improvement (D2-D3) are mainly designated to areas that have experienced improved soil moisture conditions since the September MDO release.
- Therefore, drought improvements are forecast for much of central and southern Minnesota and the Corn Belt while persistence is likely across northwestern Minnesota.
- Farther east in Michigan, weak precipitation signals and long-term deficits warrant a status-quo, persistence forecast.
Forecast confidence is low-to-moderate for the Southern Region.
- In the Southern Region, the Southern Plains experienced rapid expansion of drought since the September 2021 MDO release.
- Above-normal temperatures, below-normal precipitation (in excess of 4 inches below-normal for some locations over the last 30 days), and high winds have led to rapid losses in topsoil moisture.
- Luckily, many areas are likely to receive 1-2 inches of above-normal precipitation during the beginning of October, with the highest precipitation totals likely in Texas.
- Despite another wave of drier than normal conditions during the next 6-14 days, wetter than normal conditions are likely to prevail for October as whole in the Southern Plains, with the highest odds (greater than 40% chance of above-normal precipitation) stretching from central Texas, northward across much of Oklahoma, and eastward to the Mississippi River, with above-normal precipitation odds diminishing eastward toward the Tennessee Valley and the Appalachians.
- Given the heavy precipitation in the beginning of the valid period, drought removal (D1) and improvement (D2-D3) is likely over much of the Southern Plains eastward to Arkansas.
- Farther west, across western portions of the Texas and Oklahoma Panhandles, persistence is likely, as temperatures are expected to be relatively seasonal and the heaviest precipitation amounts are predicted to remain farther to the east.
Forecast confidence is high for the Southeast Region.
- The Southeast is presently drought-free. However, some locations across the Carolinas and Virginia have experienced abnormally dry conditions for several months now.
- The Shenandoah Valley is one such area that has experienced a prolonged period of abnormal dryness, with some locations teetering between D0 (abnormally dry) and D1 (moderate drought) conditions for several months.
- Despite above-normal temperatures and below-normal precipitation for the northeastern portions of Virginia, near- to above-normal precipitation is favored during the first half of October, with above-normal precipitation probabilities encompassing much of the remainder of the Southeast during that same period.
- In addition, the Atlantic Hurricane season does remain a threat, as the main development region for tropical cyclones shifts back toward the West Atlantic, Caribbean, and Gulf of Mexico during October.
- Given the wet signals in the extended-range and the potential for tropical activity, the Southeast is likely to remain drought-free through the end of October.
Forecast confidence is high for the Northeast Region.
- Much of the coastal and inland areas of the Northeast have received rainfall in excess of 2 inches above-normal, with large pockets of more than 4-inch positive precipitation anomalies in the last 30 days.
- Groundwater conditions have finally started to rebound across Cape Cod, where D1 (moderate drought) was removed the week leading up to October.
- Unfortunately, the same cannot be said for areas closer to the eastern Great Lakes, northern New York, and parts of northern New England, where many locations experienced a drier-than-normal September, with 30-day precipitation deficits of 1 to 3 inches.
- Given decent antecedent soil moisture conditions and above-normal temperatures becoming less of a factor in increased evaporation rates during the Fall season, persistence is likely for remaining D1 and D2 (moderate and severe drought) areas across northern New England.
Forecast confidence is high for Alaska, high for Hawaii, and moderate-to-high for Puerto Rico.
- Some dryness has crept into the Kenai Peninsula in Alaska, which has resulted in some below-normal stream flows across the area. However, given October is climatologically a wetter and cooler time of year, and precipitation odds tilting toward above-normal during the first half of October, no drought development is likely for the Kenai Peninsula or elsewhere across Alaska.
- In Hawaii, with near-normal temperatures and climatology offsetting dry signals in the model guidance, drought persistence is likely.
- The higher elevations of Puerto Rico received some beneficial rainfall in recent weeks (greater than 4-inch positive precipitation anomalies across interior central and western parts of the island). However, precipitation deficits in excess of 2 inches have continued to mount over the eastern third of Puerto Rico, further reducing stream flows across the region.
- Despite the climatological westward shift in the main development region for tropical cyclones in the Atlantic basin during October, forecasts for outgoing longwave radiation indicate the increased potential for suppressed convection across the Caribbean during at least the first half of October.
- In addition, long-range statistical model guidance favors warmer and drier conditions to prevail. As such, drought persistence is likely in existing D1 (moderate drought) areas along the southern and northwestern coasts, with drought development likely in the eastern third of the island, abnormally dry (D0) areas adjacent to current drought areas, and on Vieques Island in Puerto Rico.