La Niña conditions are present, and are likely to continue through the Northern Hemisphere winter (75% chance). The forecaster consensus favors a borderline moderate event during the peak November-January season. La Niña conditions typically indicate a warmer and drier pattern across much of the southern tier of the CONUS, cooler and wetter conditions in the Pacific Northwest, and increased chances for precipitation in Hawaii.
A wild card for this outlook is the potential for a continuation of the active 2020 Atlantic hurricane season. Therefore, several synoptic-scale forcing mechanisms are considered in this forecast, in addition to the short-, medium-, and long-range model guidance and seasonal normals.
Drought continued to expand in the past 30 days over much of the western CONUS and in New England. The D3 category experienced a rapid increase, with extreme drought (D3) coverage rising from 3.83% to 11.55% on Sep. 8 as compared to Aug. 11. Overall drought (D1-D4) increased from 34.4% to 38.7% during the same time period, while D4 made a return on the Aug. 18 map and stood at 0.16% on Sep. 8.
In the Northeast, drought improvements are not expected to occur until later in the period (Nov-Dec), and may in fact worsen in the short-term (for the rest of September into early October) as the QPF, ERFs and Week 3-4 all favor below-normal precipitation.
Although the 1- and 3-month precipitation outlooks have EC for the Northeast, autumn is a favorable time for soil moisture recharge as several factors lend themselves toward positive water balances, and in general, droughts rarely linger in New England due to these factors.
In the Southeast, there was no drought, and with a few small areas of D0 in AL, GA, and SC which should be erased by Hurricane Sally rains, no development is expected through the end of the year.
In the Midwest, drought existed in parts of the Corn Belt (IA, IL, IN, OH), in southwestern Missouri, and northeastern Minnesota. With short-term precipitation forecasts mostly trending drier than normal, October and OND climatologies somewhat dry, and the October and OND 2020 outlooks at EC, no clear signal emerged, thus persistence was left. A exception for improvement was made in southwestern lower Michigan where winter lake-effect snows should ease the very small area of D1.
In the South, La Niña is expected to bring subnormal precipitation and above-normal temperatures during October and OND, thus development is expected into the south and south-central Great Plains and parts of the lower Mississippi Valley where D0 already exists. Areas along the Gulf Coast, parts of the lower Mississippi Valley, and central Texas were left blank due to previous tropical downpours (Hurricanes Hanna and Laura), heavy 30-day rainfall, or from future tropical systems as this has been a very active Atlantic hurricane season.
The late fall and winter are climatologically dry for the High Plains, and with no indication of any real above-normal precipitation events out to 3-months, status-quo (persistence) was left. However, southern sections (KS) and northwestern areas (WY) were forecast for development and improvement, respectively, based upon the expected La Niña impacts in the 1- and 3-month LLFs.
In the West, with anticipated above-normal precipitation odds across the Northwest and below-normal precipitation and warmth favored across the Southwest due to the La Niña, gradual improvement is likely across the Northwest (WA, OR, northern CA, ID, MT, WY) while persistence/intensification/developement is forecast for the southwestern quarter of the Nation.
In Alaska, even though subnormal October precipitation is favored in south-central sections (e.g. Kodiak Island), above-normal OND precipitation is expected along the western and southwestern coasts, and this should remove the two small D1 areas (Kodiak Island and near Kotzebue).
In Hawaii, although drought conditions have somewhat worsened and expanded in coverage during the past month, drought removal and improvement are favored during OND as La Niña usually brings above-normal winter precipitation – just as Hawaii is transitioning into a wetter time of the year.
Puerto Rico saw drought removal during August, largely aided by the close passage of Isaias in late July, and has remained drought-free ever since. With an active Atlantic tropical season continuing, no drought development is favored for Puerto Rico.
Forecast confidence is moderate for the Southeast Region.
- The Southeast has experienced long-term wetness (>6-months), but some short-term dryness (30- to 60-days) has appeared in portions of Alabama, Georgia, and South Carolina (small areas of D0). However, heavy rains from Hurricane Sally should fall on these D0 areas in the next day or so, effectively removing any chances for D1 to appear for a while.
- After Sally exits, the ERFs forecast much drier and cooler conditions, with the Week 3-4 predicting EC precipitation (except wet in Florida) and subnormal temperatures.
- The October and OND 2020 outlooks both favor warmth, with the October precipitation LLF having EC along the Gulf Coast, above-normal for the eastern Gulf and southern Atlantic Coasts, and below-normal in northern and western areas. The OND’20 precipitation LLF is more La Niña like, with subnormal odds in Georgia, and increasing toward the west.
- The balance between La Niña impacts (dry and warm along the southern tier of States) and the active Gulf and Atlantic tropical season makes the precipitation forecast more uncertain, but enough rain has fallen overall to fend off any large-scale development by the end of this year.
Forecast confidence is high in western areas, moderate elsewhere for the Southern Region.
- The Southern Region experienced a mixture of drought improvement (eastern Oklahoma, northern and eastern Texas, northeastern Arkansas, and eastern Louisiana) and intensification (western and southeastern Texas, southwestern Oklahoma, central Mississippi) during the past 30-days.
- With (soon to be moderate) La Niña ongoing, below-normal precipitation and above-normal temperatures are expected for much of the southern tier of states, extending into the lower Mississippi Valley.
- As such, drought persistence or intensification is favored for areas currently in D1 or drier throughout the Southern Region, with development favored across much of central and eastern Texas, eastern Oklahoma, and Mississippi.
- Development was not extended into southeastern Oklahoma, north-central Texas, western Louisiana, and most of Arkansas due to recent heavy rains, most of it associated with Hurricane Laura.
- In addition, the possibility of more tropical Gulf systems during the next 1-2 months halted the depiction of development along the Texas and Louisiana coasts while also lowering the overall forecast confidence for widespread development during a La Niña event.
Forecast confidence is moderate for the Midwest Region.
- Similar to the Northeast, the Midwest experienced a combination of drought improvement and deterioration in the last month. Some improvements were made in Minnesota, eastern lower Michigan, and Ohio during the last month, but drought intensified or developed in Iowa, Illinois, Indiana, and southwestern Missouri.
- Western Iowa was hardest hit, with 3-month deficits of 4-8 inches and 6-month shortages of 8-12 inches, resulting in D2 and D3.
- Short-range forecasts (QPF, ERFs, Week 3-4, and October LLF) are generally tilted toward below-normal precipitation, with above-normal temperatures in western portions and below-normal temperatures in eastern sections.
- Above-normal temperatures are likely in the OND’20 LLF, with EC for the seasonal precipitation outlook. Although this would be a good time for soil moisture recharge with the lowering temperatures and evapotranspiration, October and OND are normally drier months of the year, especially in western parts.
- With no definitive signal for above-normal precipitation out to the end of the year, no improvements were made. No development was added either due to a dry climatology, minimal evapotranspiration, and low temperatures.
- Later in the winter, however, La Niña usually has a wet signal for the Ohio Valley, so we will have to wait and see if this occurs.
Forecast confidence is high for southern sections, and moderate elsewhere for the High Plains Region.
- In the High Plains Region, drought expansion and intensification prevailed in Colorado, Wyoming, central Nebraska, central South Dakota, and western North Dakota during the past 30-days where subnormal precipitation fell. Some slight relief occurred in southern North Dakota, northeastern South Dakota, and western Kansas since mid-August.
- Fortunately, temperatures cooled in late August and into early September after a warm start to summer.
- In the short-term (QPF, ERFs, Week 3-4), no improvement is forecast for the Plains as subnormal precipitation and above-normal temperatures dominate.
- The October LLF precipitation favors EC in the northern parts and below-normal in the southern sections, with more EC in the OND’20 LLF precipitation, and some slight tilt toward above-normal precipitation in Montana and Wyoming (part of the Northwest wet signal).
- As such, drought is expected to persist for much of the High Plains, with development possible in Kansas where October and OND LLFs favor subnormal precipitation and above-normal temperatures.
- Some improvement may occur in northern Wyoming in conjunction with the La Niña wet signal in the Northwest.
Forecast confidence is moderate (Northwest) to high (Southwest) for the Western Region.
- Extreme to exceptional drought intensified in the West, with D3-D4 increasing from 8.34% on August 11 to 25.6% on Sep. 8. Much of the expansion in drought coverage (D1 and worse) took place in the Four Corners States (UT, AZ, NM, CO) due to the near failure of southwest monsoon season, and it was coupled with extreme heat.
- These conditions were ripe for widespread, numerous large wild fires that charred millions of acres across the West, especially in northern California, Oregon, and Washington, and took dozens of lives while destroying numerous homes and buildings.
- The outlook for the Southwest continues to looks bleak with the ongoing (moderate) La Niña, with the highest probabilities for above-normal temperatures and below-normal precipitation favored from southern California eastward into Texas. Not surprisingly, persistent, intensification, and development are likely across the southwestern quarter of the Nation.
- In contrast, La Niña tends to bring above-normal precipitation and more seasonable temperatures to the Northwest as depicted in the October and OND 2020 LLFs, thus improvement is depicted for the Northwest (WA, OR, extreme northern CA, ID, MT, and northern WY). In addition, the Northwest is entering into a wetter time of year which should provide additional help toward easing drought.
Forecast confidence is low for the Northeast Region.
- The Northeast region has seen conditions deteriorate in parts of New England, southwestern New York, and central Pennsylvania during the past 30 days, although southwestern Pennsylvania and upstate New York have improved with heavy rains.
- However, short-term forecasts (QPF, ERFs, Week 3-4) are not favorable for any additional improvement, and instead may portend worsening drought through September into early October.
- On a longer term, the 1- and 3-month LLFs favor EC for precipitation and above-normal temperatures. Fortunately, temperatures and evapotranspiration are decreasing with the fall and winter, frontal and storm activity (Nor’easters) usually increase during the cold season, climatology is evenly-distributed (no dry or wet months), and drought are typically short-lived in New England.
- There are no definitive signals from 1- to 3-months for either improvement or worsening drought, but the odds slightly favor some improvement in parts of the Northeast as compared to deterioration and development, although not every area should expect to see improvement (e.g. a mixed bag, with long-term deficits lingering into January 2021).
Forecast confidence is moderate to high for Alaska.
- Small areas of D1 existed on Kodiak Island and north of the Seward Peninsula (near Kotzebue) in the latest Drought Monitor, with some eastward expansion of D0 into northwestern and south-central sections of the state.
- With the transition to winter underway and storms frequenting the western and southern sections (and Oct and OND precipitation LLFs showing above-normal odds in the west), the small D1 areas are expected to improve before the state goes into deep freeze for the winter.
Forecast confidence is moderate to high for Hawaii.
- Forecast confidence is moderate to high for Hawaii.drier conditions led to an expansion of D0 and drought across Hawaii. Fortunately, the autumn months are when Hawaii begins its transition into a climatologically wetter time of the year (winter).
- In addition, with La Niña conditions now ongoing, the odds increase for above-normal precipitation, particularly in the latter half of the OND period. Therefore, a general improvement of drought conditions are favored in Hawaii.
Forecast confidence is high for Puerto Rico.
- Above-normal precipitation and the passing of Isaias eliminated drought conditions in Puerto Rico in late July and early August. A small abnormally dry (D0) area remained along the southeast coast, but with an active Atlantic hurricane season still occurring, the odds favor above-normal precipitation, at least for the next month or so. As such, no drought development is likely.