A significant La Niña is currently underway, and is expected to continue throughout the Nov-Dec-Jan (NDJ) 2020-21 drought outlook period. In the West, CPC’s official 30-day and 90-day precipitation outlooks lean heavily on La Niña composites, which favor increased odds for below normal precipitation over portions of the southern and central thirds of the western CONUS.
New drought development is indicated over a sizable fraction of California. La Niña also boosts the odds for increased storm activity and above normal precipitation for the northern third of the Western Region.
For the High Plains Region, drought is predicted to persist, and new drought development is possible. This seems counterintuitive across the Dakotas and eastern Montana, where CPC predicts increased odds for above normal precipitation during the late autumn and early winter.
However, the benefits of increased precipitation across this area are expected to be delayed, due to frozen ground which precludes soils from being adequately recharged.
In the Southern Region, dryness and drought are likely to continue, with drought expansion depicted across nearly all of Oklahoma and Texas. This is supported by the 30-day and 90-day outlooks from CPC, NDJ climatology, and La Niña composites.
Dryness and drought are also expected to continue across the Midwest Region, though there is greater uncertainty regarding the outlook in Indiana and Ohio. Typically during a cold season La Niña, the Ohio Valley is favored to receive above normal precipitation which would help to alleviate any drought. However, this tilt in the odds towards above normal precipitation usually comes later in the cold season, and is less likely in NDJ.
In the Southeast Region, only a few areas of abnormal dryness remain, after a very active Atlantic hurricane season (which officially ends on November 30th) and several landfalling systems along the Gulf Coast. The challenge is to determine how much drought might develop late in the NDJ season, and where.
Climatology and 90-day precipitation deficits indicate one area that is more predisposed towards future drought development includes southern Georgia and northern Florida.
The seasonal drought outlook for the Northeast Region is especially problematic at this time, because of the unexpectedly prolonged duration of dryness and drought in this region.
La Niña composites, recent widespread ample rains (1-3”), forecast short-term heavy precipitation, and a non-dry climatology, are thought to be enough to warrant some improvement/removal of drought for most of the Northeast, with the exception of the vicinity of Pennsylvania, which has less support for any drought mitigation.
CPC’s NDJ seasonal precipitation outlook favors above normal precipitation in Hawaii, as do La Niña composites and the onset of the climatological rainy season. Therefore, drought improvement and removal is predicted across the Islands.
The small area of moderate drought (D1 in the U.S. Drought Monitor) in northwest Alaska is also slated for removal, consistent with the 90-day precipitation outlook.
Puerto Rico currently has no drought, thanks largely to the close passage of Tropical Storm Isaias in late July, and no development is anticipated during the early portion of its dry season (Dec-Apr).
Forecast confidence for the Southeast Region is low to moderate.
- Though there are several lingering pockets of abnormal dryness (D0) in the Southeast Region, there is no drought. This is largely attributed to a very active Atlantic hurricane season, and the impacts from three tropical cyclones in September and early October: Hurricane Sally, Tropical Storm Beta, and most recently Hurricane Delta.
- Stationary fronts draped across the Southeast aided in the drought’s removal.
- However, climatology favors dryness across the Southern Atlantic Coast during NDJ, though any dryness that develops will likely occur later in the season.
- Precipitation departures for the past 90-days depict 1-3 inch deficits in southern Georgia and northern Florida, with some localized spots of 4-6 inch deficits. Therefore, if dryness/drought does develop, it will most likely develop in parts of Georgia and Florida late in the NDJ season.
Forecast confidence for the Southern Region is moderate to high.
- Drought and abnormal dryness have been confined primarily to western and central portions of Oklahoma and Texas in the Southern Region, which is consistent with NDJ climatology.
- Precipitation deficits range from 2-4 inches over much of Oklahoma, Texas, and northwestern Arkansas during the last 30-days.
- In contrast, the San Angelo/Edwards Plateau area in southwestern Texas received significant rainfall in the past month, resulting in 1-, 2-, and even 3-class improvements in the drought monitor depiction.
- Though eastern sections of Oklahoma and Texas may experience short-term rainfall, CPC’s monthly and seasonal precipitation outlooks favor enhanced chances of below normal precipitation, which is the most likely historical outcome of a significant La Niña event. Accordingly, drought development is favored over most of the remainder of Oklahoma and Texas.
Forecast confidence is moderate for western sections of the Midwest Region, and low to moderate for eastern sections.
- There are large variations in drought conditions across the Midwest Region, ranging from no drought to pockets of extreme drought (D3).
- Precipitation deficits during the past month generally range from 1-3 inches, with some areas reporting 3-4 inch shortfalls.
- Dryness and drought are forecast to persist during the late autumn and early winter.
- Climatology favors drier conditions across western portions of the Midwest Region, which is where some drought development is indicated.
- The outlook becomes less clear over the eastern portions of the Region. With significant La Niña-related precipitation typically occurring later in the winter, it is thought that persistence of the drought areas in Indiana and Ohio may be a better bet for NDJ.
Forecast confidence for the High Plains Region is moderate.
- The U.S. Drought Monitor depicts conditions ranging from abnormal dryness (D0) to exceptional drought (D4) across the High Plains Region, with the worst conditions (in terms of spatial coverage and intensity of drought) being experienced in Wyoming and Colorado.
- Much of this region has 30-day Percent of Normal Precipitation (PNP) values within the lowest quartile of the historical distribution, and a significant portion of this latter area has values at or below the 10th percentile.
- Climatology favors dryness across most of the High Plains Region. The official 90-day precipitation outlook for NDJ favors below normal precipitation in Kansas, most of Colorado, and far southern Nebraska, above normal precipitation for most of the Dakotas, and EC in-between these two areas, which is consistent with La Niña composites.
- However, despite the favored above normal precipitation over the Dakotas, the benefits of that precipitation are expected to be delayed until after the NDJ season, due to frozen ground preventing the soil from adequately recharging.
- Therefore, drought persistence and some drought development is forecast.
Forecast confidence for the Western Region is moderate to high.
- Most of the Western Region has 30-day PNP values at or below the 25th percentile, and in most of those cases, values are at or below the 10th percentile. Exceptions include portions of the Northern Rockies where PNP’s span the 25th and 75th percentiles, and the Pacific Northwest, where precipitation surpluses exist (PNP’s between 110-200 percent of normal).
- At this time, only a few areas remain drought-free, such as coastal Southern California, western Washington state, and scattered areas primarily in Idaho and Montana.
- NDJ climatology favors wetter conditions for much of this Region west of the Continental Divide, while drier conditions are favored in central and eastern Montana, and New Mexico.
- Not surprisingly, CPC’s official 90-day precipitation outlook is similar to historical La Niña composites, which support increased odds of above normal precipitation across the Pacific Northwest, Northern Intermountain Region, and western Montana, and primarily support increased odds of below normal precipitation for most areas to the south.
- Accordingly, drought improvement/removal is favored for these northern areas, and drought persistence and development is favored for most of the remainder of the Western Region.
Forecast confidence for the Northeast Region is low.
- The Northeast Region continued to experience declining drought conditions during the last 30-days, with widespread precipitation deficits of 2-4 inches, with drought persisting longer into the autumn than anticipated earlier.
- Typically during this time of year, temperatures, evapotranspiration, and water demand decrease, and large-scale storm activity tends to increase.
- These factors help to recharge soil moisture and stream flows, and usually preclude drought from persisting into and through the winter months. Eventually, the decision was made to go with improvement and/or removal of drought.
- It is predicated upon the idea that 3-4 inches of precipitation forecast within the next 7-days (much of which fell after the 8am Tuesday morning data cutoff) will reduce coverage and intensity of the New England drought; making it easier for the remaining areas of drought to be removed by large-scale storm systems (such as nor’easters) in the NDJ period.
- La Niña composites for New England during this season favor improvement, especially when trend is considered. Despite this, confidence remains low for this Region.
Forecast confidence for Alaska is moderate to high.
- In Alaska, there is abnormal dryness in south-central and northwestern portions of the state, with a localized D1 (moderate drought) area around Kotzebue in the northwest.
- Climatology favors drier conditions from about the Alaska Range northward to the Arctic Coast, near normal conditions for the South Coast, and relatively wet conditions for much of the Panhandle.
- CPC’s 30-day and 90-day precipitation outlooks favor above normal precipitation in northwest Alaska, increasing prospects for drought removal.
Forecast confidence for Hawaii is high.
- During the past month, most dryness/drought areas in Hawaii have either remained static, or worsened by one category. The exception includes central and eastern portions of the Big Island, where a one-class improvement in conditions has occurred.
- The state is now entering its climatological rainy season, and the odds for above-normal precipitation also increase during a La Niña/cold event.
- These factors, combined with CPC’s forecast of above normal precipitation for Hawaii in NDJ, support the removal/improvement of drought.
Forecast confidence for Puerto Rico is moderate.
- In Puerto Rico, a fairly small area of abnormal dryness is indicated near/on the south-central coast. Puerto Rico saw drought removal during August, largely due to the close passage of Tropical Storm Isaias in late July, and has remained drought-free ever since.
- During Puerto Rico’s climatological dry season (Dec-Apr), La Niña typically brings subnormal rainfall, but no drought development is expected during the NDJ period.