La Niña conditions are present during September, and are likely (~75% chance) to continue through the Northern Hemisphere winter. The forecaster consensus favors a borderline moderate event during the peak November-January season, then gradual weakening in early 2021 with the possibility of ENSO neutral conditions by the March-May period.
During September, drought coverage and intensity continued to expand across the CONUS, mainly in the West and New England. The near failure of the Southwest monsoon season, subnormal precipitation across most northern sections of the CONUS, and temperatures averaging 2 to 6 degF above normal west of the Rockies resulted in expansion and intensification of D1-D4 from 66.93% on August 25 to 73.37% on Sep. 22 in the Western region.
D3-D4 drought also ramped up in the West, going from 16.88% to 29.21% for the same 4-week period. The dryness and heat also sparked a near-record amount of large wild fires across the West, taking dozens of lives, charring millions of acres of forests, and destroying numerous homes and buildings – with October yet to come.
Unfortunately, October is usually one of the most active months for wildfire activity, especially in California, when the Santa Ana winds tend to kick up.
Subnormal precipitation also fell on the northern and central Plains, expanding D0-D2 there. Nearly all of the Northeast saw less than half of normal precipitation from Aug. 29-Sep. 28, with many areas recording <25% which led to a 1-2 category deterioration during the past 4 weeks.
However, a strong system slowly passed through the East Coast on Sep. 29-30, bringing badly-needed rains (1-4 inches) to much of the Northeast, but any improvements to the USDM won’t be depicted until next week (Oct. 6) as the rains fell after the 12UTC Tuesday USDM cutoff.
The southeastern quarter of the Nation remained nearly drought free due to several September tropical systems (Sally, Beta) and lingering short- and long-term wetness. Abnormal dryness and drought also intensified and spread across Hawaii, Alaska had a few pockets of D0 and D1 on Kodiak Island and in the northwest, and Puerto Rico was drought-free.
With the ongoing and expected to continue La Niña, the seasonal (OND and into winter) forecasts tilt toward subnormal precipitation and above-normal temperatures across the southern tier of States, with above-normal precipitation in the Northwest.
For October (climatologically one of the driest months of the year), the ongoing La Niña, many areas currently in drought, and the short-term (QPF), extended-range (ERFs), Weeks3-4, and updated 1-month long-lead forecasts (LLFs) – which are in agreement for large areas of subnormal precipitation and above normal temperatures – favor persistence, deterioration, or development of drought in much of the West, Plains, and Midwest.
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This also includes Hawaii (persistence) where the expected La Niña impacts for above-normal rainfall typically occurs later in the winter.
This is unfortunate for the farmland and pastures of the Plains and Midwest as autumn’s lower temperatures and little or no evapotranspiration allows for excellent soil moisture recharge – when decent rains occur – before the ground freezes.
In contrast, some areas have recently (e.g. Northeast) or are expecting to see above-normal precipitation during October, and as a result, some improvement is expected in the Pacific Northwest (as their wet season gets underway), the Northeast (Sep. 29-30 rains and more chances for rain in early October), and Alaska (recent rains and enhanced ERF chances).
The wet Southeast should remain drought-free through the end of October even though the forecasts expect subnormal precipitation (except in Florida).
Forecast confidence is high for the Southeast Region.
- Currently no drought is present in the Southeast Region, with only a few small D0 areas in northeastern Alabama and eastern Georgia.
- Heavy rains from Tropical Storm Beta fell on the Alabama D0 area, effectively erasing it, while lighter totals were reported in eastern Georgia. With several tropical systems inundating most of the Southeast during the past several months, surplus amounts have enveloped most of this region in both the short and long-terms.
- Although the QPF, ERFs, Weeks 3-4, and October LLF all indicate subnormal precipitation (except for Florida), October is normally a dry month in the Southeast, and with subnormal temperatures expected and the growing season just about over, no development is anticipated by the end of the month.
Forecast confidence is high for the South Region.
- The Southern Region is a tale of two contrasting moisture regimes; the central and eastern sections have either adequate or ample moisture and little or no D0 or drought, some of it obtained from tropical systems Beta, Laura, and Hanna, while the far western sections endured very dry conditions, including the failure of the Southwest monsoon that normally brings well over half of the annual rainfall of New Mexico and western Texas.
- The October precipitation climatology is somewhat wet in south-central Texas, but with all forecasts (QPF, ERFs, Weeks3-4, and the updated Oct LLFS) favoring subnormal precipitation in most areas and above normal temperatures in western portions, a gradual creep of abnormal dryness and drought (e.g. development) is expected during October from west to east.
- Fortunately, the current short-term surpluses in central and eastern sections should stall drought development until later in the year.
- In addition, tropical storm activity in the Gulf of Mexico is possible during October, creating a wild card for excess precipitation along the South’s Gulf Coast.
Forecast confidence for the Midwest is low in the east, moderate in the west.
- Since late August, the Midwest generally observed improvements during the past 4 weeks in much of Iowa, southeast Minnesota, southwest Wisconsin, northern Illinois, lower Michigan, eastern Indiana, and Ohio.
- Much of these improvements came from above-normal precipitation during the past 30-days that fell on those aforementioned areas, along with seasonal to slightly below-normal temperatures.
- Meanwhile, where subnormal precipitation fell, some deterioration was made where either D0 or D1 was added, and that included southern Illinois and Indiana and southwestern Missouri (D2).
- Although the rains eased drought in Iowa, there was still some lingering D1-D2 in western sections, along with some spotty small areas of D1 in Illinois, Indiana, Ohio, northern Minnesota.
- With the October precipitation climatology somewhat dry except around the Great Lakes region, and most forecasts (QPF, ERFs, Weeks3-4, Updated Oct LLFs) favoring subnormal precipitation with temperatures initially cool then becoming warmer, the tendency is toward deterioration.
- However, with the recent rains and improvements across most of the Midwest, lower temperatures, and the end of the growing season, there was not of a strong signal to add development in most existing D0 areas – except in southwest Missouri and far western sections where it has been drier recently. Thus, persistence was left for the remaining D1 areas.
Forecast confidence is moderate to high for the High Plains Region.
- Well below normal precipitation and subnormal temperatures were measured across the High Plains Region during the past 30 days.
- Although some small 1-category improvements were made in parts of South Dakota, Kansas, and Colorado, the latter from an unseasonably heavy and early snow storm, an overall deterioration during the past 4-weeks occurred in Montana, Wyoming, North Dakota, and Nebraska.
- With the October climatology rather dry, little or no precipitation in the QPF, and good odds for subnormal precipitation and above-normal temperatures in the extended-range forecasts (ERFs, Weeks3-4, Oct LLFs), persistence, intensification, and development is likely by the end of October.
Forecast confidence is high for the Western Region.
- The West Region endured another dry and warm 30-days since late August. Although the summer months are typically dry in the Far West, especially California, other Western States rely on the southwest monsoon moisture for a large portion of their annual precipitation.
- Unfortunately, this year’s southwest monsoon basically failed, and when combined with above normal temperatures, the drought rapidly spread and intensified across much of the West. As of Sep. 22, 73.37% of the West was in drought (D1-D4), with 29.21% in D3-D4, both statistics up from 4 weeks earlier.
- Not surprisingly, numerous large wildfires burned across many portions of the West, especially California, Oregon, and Washington, taking dozens of lives, blackening millions of acres, and destroying numerous homes and buildings. October is also climatologically dry for California, and notorious for the Santa Ana winds that are deadly for spreading wildfires.
- Since California is normally dry during October, no development was added for this month. For the rest of the West where drought existed, persistence or intensification is most likely.
- In contrast, the wet season is underway in the Northwest, and with various forecasts hinting at above-normal precipitation, some improvements were made to the Pacific Northwest (Washington, northwestern Oregon, northern Idaho, northwestern Montana), with development not added where there was some uncertainty of the October precipitation forecasts (e.g. Idaho, western Montana).
Forecast confidence is moderate for the Northeast Region.
- During the past 30 days, the Northeast Region mainly saw deteriorating conditions as minimal rains (<50% of normal) fell across most of New England, including some parts with less than a quarter of normal precipitation (western New York, western Maine, northern New Hampshire and Vermont, eastern Connecticut, and Rhode Island).
- Fortunately, temperatures averaged slightly below normal during this 30-day period – unlike early this summer when heat accompanied the dryness and produced flash drought. Still, widespread areas of short-term D2 and pockets of D3 were present on the Sep. 22 USDM, with USGS 7-, 14-, and 28-day average streamflows at or near-record low values.
- In contrast, beneficial rains fell on southwestern secrtions of the Northeast during September, easing drought in northern West Virginia, western Pennsylvania, and into Ohio. Then late in the month (Sep. 29-30), a slow-moving cold front dropped moderate to heavy (1-4″) rains on much of the Northeast, but the precipitation fell after the 12UTC Tuesday cutoff for the Sep. 29 USDM.
- With some improvements expected from the late month rainfall in the Oct. 6 USDM, additional rains expected in the next 7 days (QPF), above-normal precipitation favored in the 6-10 day ERF, EC for 8-14 day ERF, Weeks 3-4, and Oct’20 LLF, along with a wetter October precipitation climatology as compared to the rest of the country, lower temperatures, and a favorable time for soil moisture recharge, an overall reduction in the severity and extent of the drought is expected by October 31.
- This may not remove or improve all current drought areas, but more improvement than persistence should occur.
Forecast confidence is high for Alaska.
- In Alaska, abnormal dryness lingered over portions of the northwestern and southern mainland Alaska, with D1 drought on Kodiak Island and near Kotzebue on the northwest coast during September. However, recent heavy rains (4-6″) on Kodiak Island, and lighter amounts in the northwest should be enough for removal of D1 in those two areas.
- With winter fast-approaching and ERF and Oct LLF forecasts of above-normal precipitation, removal of the two small D1 area is likely, with no development elsewhere.
Forecast confidence is moderate for Hawaii.
- In Hawaii, a La Niña event usually brings enhanced rainfall to the islands during their normally wet winter season, but this typically occurs later in the winter and not during October.
- Therefore, with the current trend of drier weather and 1-2 categories of drought deterioration since late August, persistence is the best bet for the islands, with enhanced rainfall (and improvement?) occurring later in the year.
Forecast confidence is high for Puerto Rico.
- A small area of abnormal dryness in south-central Puerto Rico remained after encounters from several tropical systems during the summer that erased the island’s drought.
- Although the likelihood for another tropical system to impact Puerto Rico during October decreases, this hurricane season has been very active, and cannot be ruled out.
- With no strong evidence for a very dry October, no development is expected for Puerto Rico by the end of this month.