La Niña conditions have developed and are expected to continue with an 87% chance of La Niña during the Northern Hemisphere winter 2021-22. Drought continues entrenched across much of the West and Northern Plains, as well as parts of the Midwest. The West Coast and Northern Rockies also saw deterioration over the late summer months.
Conversely, the Southwest has experienced remarkable improvements to drought conditions in the months leading up to the NDJ season due to a robust North American Summer Monsoon. Entering into a climatologically wetter season for much of the West, coupled with the development of La Niña conditions, increases chances for improving drought conditions across the Pacific Northwest and Northern Rockies.
Although high soil moisture is expected to be present at the beginning of the period across portions of the Four Corners Region, a warmer and drier signal predicted across the region due to the development of La Niña increases the chance of drought redevelopment across parts of Arizona and New Mexico.
The Great Plains and Midwest represent an area of transition with drought persistence likely for western areas and improvement is possible for eastern areas. Farther to the west, given ongoing drought and lack of precipitation signals, drought persistence is favored for the Northern Plains. Farther south, above-normal temperatures and below-normal precipitation favored throughout NDJ increase odds for widespread development across the Central and Southern Plains.
Precipitation signals are near to above-normal over the Great Lakes through the season, and temperatures are expected to remain above-normal. With diminishing evaporation and evapotranspiration rates during NDJ, short-term improvements are favored for parts of the Midwest.
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Since above-normal precipitation is favored during the NDJ season across ongoing drought areas of the Northeast, improving drought conditions are most likely.
The Southeast is drought free currently. However, below normal precipitation and above normal temperatures are favored across the region due to the influence of La Niña. Therefore, chances of drought redevelopment are increased over the current dry areas in the Carolinas and drought development is likely over the central and southern Florida Peninsula.
Alaska will likely remain drought-free, entering into the winter months with a wet climatology along the southern coast. Hawaii is expected to experience at least some drought improvement as they head into a climatologically wetter time of year, coupled with predicted near to above normal precipitation.
Drought persistence is favored for Puerto Rico as the region heads into its climatologically drier season and a forecast favoring near to below normal rainfall in the outlook period.
Forecast confidence is moderate-to-high for the West.
- Drought remains entrenched across the western conterminous U.S. (CONUS), with most of the Western Region experiencing severe drought conditions (D2 or worse) according to the U.S. Drought Monitor, valid on October 20, 2021.
- Some drought improvements across the West have mainly been confined to parts of the Pacific Northwest, Northern Plains, Central Rockies and Four Corners Region, where a robust North American Monsoon (NAM) season has resulted in marked improvements to soil moisture in the months leading up to the start of the NDJ forecast period.
- Much of the West is entering into a climatologically wetter time of year, with the mean storm track shifting southward from the Pacific Northwest and into California during NDJ.
- La Niña conditions are expected to continue over the tropical Pacific Ocean in the Northern Hemisphere winter 2021-22. Given the likely continuance of La Niña over the next several months, its effects are considered for the Pacific Northwest, where wetter signals are strongest coupled with predicted heavy rainfall in near term.
- As such, broad drought improvement (D2 to D4) and removal (D1 to D2) are favored across much of the Pacific Northwest and northern California, extending eastward to Montana.
- Drought persistence is favored elsewhere across the West. Some drought development is also favored for portions of Arizona and New Mexico, as above normal temperatures and drier conditions are favored during the period.
Forecast confidence is low-to-moderate for the High Plains Region.
- Similar to the West, the northern and western portions of the High Plains Region also remain entrenched in drought, while the southern High Plains Region is experiencing more localized drought conditions.
- Much of the region has experienced a mix of improving and deteriorating conditions since the October-December SDO release last month. However, many areas still did not receive enough rainfall to offset longer-term deficits for drought-stricken areas.
- In addition, the High Plains states are entering into a climatologically dry time of year and frozen season. Given the general lack of wet signals, drought persistence is favored for much of the current drought region.
Forecast confidence is moderate to high for the Southern Region.
- In late August, Category 4 Hurricane Ida made landfall in Louisiana bringing high winds and flooding to much of eastern portions of the Southern Region (Louisiana, Mississippi, and Tennessee) during its transition into the mid-latitudes.
- A couple weeks later, leading up to the start of the OND valid period, Hurricane Nicholas made landfall in southeastern Texas near Matagorda Bay bringing heavy rainfall and flooding that extended eastward to parts of Louisiana affected by Hurricane Ida.
- However, with the development of La Niña, odds tilt toward above normal temperatures and drier conditions for NDJ. Given the antecedent wetness across much of the Lower Mississippi Valley, Louisiana and Tennessee are favored to remain drought-free through the end of January.
- Farther west in the Southern Region, however, many locations across the Southern Plains have started to dry out over the past 30-60 days. Many locations across Texas, Arkansas, and Oklahoma are experiencing 1-3 inch deficits in the last 30 days.
- However, given the warmer and drier signals in the extended and long ranges coupled with the antecedent dryness across the western and northern portions of the Southern Region, drought persistence is favored for the existing drought areas and there is an increased risk for broad drought development.
Forecast confidence is moderate for the Midwest Region
- Western and southern areas of the Midwest Region experienced marked improvements to drought conditions. However, as is the case for the Northern Plains, the precipitation was not enough to overcome longer-term (beyond 30-day) deficits.
- Wetter signals are predicted over the next two weeks for much of the Midwest, together with near to above-normal precipitation also expected during the NDJ. Additionally, evaporation and evapotranspiration rates are likely to drop off dramatically across many areas in drought in the Midwest as the NDJ season progresses.
- As such, short-term improvements (D2-D3) and removal (D1) are favored across existing drought over the region.
Forecast confidence is moderate-to-high for the Southeast Region
- Presently, the Southeast is drought-free.
- In the Carolinas, some short-term dryness has redeveloped over the region due to rainfall deficits in the last 30 days.
- La Niña conditions are expected to continue in the NDJ season, consistent with increased odds of above normal temperatures and drier conditions over the region. Therefore, drought redevelopment is expected over the current abnormally dry (D0) areas.
- The Florida peninsula is entering its dry time of year and is also a favorable season for soil moisture discharge. Drought development is likely over the central and southern Florida Peninsula where current soil moisture is below normal.
Forecast confidence is moderate-to-high for the Northeast Region.
- In the Northeast, drought is confined to a small area on Cape Cod and northern New England. Parts of northern New England are experiencing 15-20 inch deficits going back to one year ago in D2 (severe) drought areas.
- However, above-normal precipitation is favored for parts of the Northeast to varying degrees throughout NDJ. Although above-normal temperatures are favored throughout NDJ too, evaporation typically dwindles toward the end of the period.
- Conditions have also trended wetter during forecast La Niña episodes in the Northeast Region.
- Given the long-term antecedent dryness and the tilt toward above-normal precipitation, modest improvement (D2) and removal of drought are likely in the Northeast.
Forecast confidence is high for Alaska, moderate-to-high for Hawaii, and low-to-moderate for Puerto Rico.
- Forecast precipitation signals across western and southern Alaska are mixed at the monthly and seasonal timescales, with weak signals elsewhere. Near to below-normal temperatures are favored for central and eastern portions of Alaska. Meanwhile, much of the state entered its annual freeze during the NDJ period.
- Therefore, Alaska is likely to remain drought-free through the NDJ.
- Given La Niña is likely to continue during the NDJ season, parts of Hawaii are likely to experience below normal temperatures and above normal precipitation through NDJ. In addition, Hawaii is transitioning into a climatologically wetter time of year. Drought improvement (D2-D3) and removal (D1) are favored across Hawaii.
- Puerto Rico has seen a decrease in D1 (moderate) drought coverage since the October-December SDO release across the island. As the region heads into its climatologically drier season coupled with a forecast favoring near to below normal rainfall in the outlook period, drought persistence is favored for parts of southwestern Puerto Rico.
