Click on a thumbnail graphic to view a gallery of drought data from the US Drought Monitor.

US Drought Monitor October 13, 2020.

West Drought Monitor October 13, 2020.

Colorado Drought Monitor October 13, 2020.

Click here to go to the US Drought Monitor website. Here’s an excerpt:

This Week’s Drought Summary

A dry pattern continued this past week over large portions of the continental United States, with a few exceptions being areas impacted by Hurricane Delta or its remnants, parts of the Upper Midwest and middle Missouri River Valley, and parts of the Northeast. In areas of the Northeast that received an inch or two of rain, some improvements were made in the ongoing drought areas there. As a storm system and associated cold front brought showers and thunderstorms to parts of the Middle and Upper Missouri River Valley and to the Upper Midwest, some improvements were made to ongoing drought there. Abnormal dryness abated in a few areas of Louisiana and Mississippi, which received copious rainfall from Hurricane Delta. Degradations or persistence of ongoing drought was common in parts of the Midwest, Great Plains, and West that received little or no precipitation this week. Temperatures this week were warmer than normal across most of the Lower 48. The central Great Plains and middle Missouri River Valley were the warmest compared to normal, with temperatures from 9 to 12 degrees above normal common. New England experienced milder conditions this week, with a few below-normal readings taking place in northern Vermont, New Hampshire, and Maine…

West

The West generally experienced warmer than normal temperatures again this week, with most areas coming in between 3 and 9 degrees above normal for the week. Generally, the southern half of the region stayed dry, while some precipitation occurred over the north, particularly in far northwest California, western Washington and Oregon, western Wyoming, and western portions of Montana and Idaho. Due to recent precipitation, extreme drought in western Oregon reduced in coverage. In southwest Oregon, where short- and long-term precipitation deficits were worsening, severe and extreme drought increased in coverage. Extreme drought also increased its foothold in west-central Nevada, where soil moisture profiles continued to worsen along with short- and long-term precipitation deficits…

High Plains

Drier than normal conditions continued across much of the High Plains region, where temperatures were also generally 6 to 12 degrees warmer than normal. Consequently, as short- and long-term precipitation deficits grew amid warmer than normal weather, and near surface moisture and agricultural impacts worsened, widespread degradation in drought conditions occurred. Moderate, severe, and extreme drought coverage increased across most of the region, with the exception of northeast Nebraska and adjacent portions of Iowa and South Dakota, where a storm system brought locally high amounts of rain. In the areas with highest rainfall, short-term precipitation deficits improved enough such that extreme and severe drought decreased in coverage…

South

Category two Hurricane Delta and its remnants delivered above-normal rainfall from far east Texas through most of Mississippi, southeast Arkansas, and southern Tennessee, leading to the reduction of abnormally dry areas in Louisiana and Mississippi. Elsewhere, dry conditions occurred, and existing areas of drought expanded. Short-term drought continued to plague the southern high plains regions of Oklahoma and Texas, where moderate, severe, and extreme drought continued to spread amid worsening short-term precipitation deficits, decreasing soil moisture, and drying vegetation. Temperatures in the region were also mostly warmer than normal, with the warmest areas (compared to normal) being found in the Oklahoma and Texas panhandles, where temperatures were 9 to 12 degrees warmer than normal…

Looking Ahead

A series of cold fronts over the next week are forecast to bring a higher chance of cooler than normal temperatures to the north-central continental United States. With the exception of the northern tier of states, much of the West is forecast to be dry through the evening of October 19. Farther east, higher rainfall amounts of a half an inch or more are possible from the Mid-Atlantic coast north, while lighter precipitation is forecast in the Midwest. Glancing ahead to the October 20-24 period, cooler than normal conditions are more likely to be widespread from the Pacific Northwest to the western Great Lakes, while in the eastern United States, warmer than normal temperatures are favored in this period. Widespread increased chances for above-normal precipitation are forecast in the northern Rockies and much of the Great Plains, Midwest, and East, while below-normal or near-normal precipitation is favored elsewhere in the Lower 48.

From NOAA (John Bateman):

With 3 months left, 2020 could rank among three-warmest years on record for globe

Unprecedented heat around the world vaulted September 2020 to the hottest September since 1880, according to scientists at NOAA’s National Centers for Environmental Information.

The month’s warmth also contributed to 2020’s trend as a remarkably hot year, with the year-to-date global temperatures running second highest in the 141-year climate record.

Below are more facts and stats from NOAA’s latest monthly global climate report:

Climate by the numbers
September 2020

The average global temperature in September was 1.75 degrees F — 0.97 of a degree C — above the 20th-century average of 59.0 degrees F (15.0 degrees C).

This surpasses the average global temperatures for both September 2015 and 2016 by 0.04 of a degree F (0.02 of a degree C), which previously tied for the hottest Septembers on record.

The 10-warmest Septembers have all occurred since 2005, with the seven-warmest Septembers occurring in the last seven years.

The year to date | January through September 2020
The year-to-date (YTD) average global temperature was the second hottest on record at 1.84 degrees F (1.02 degrees C) above the 20th-century average. This is only 0.07 of a degree F (0.04 of a degree C) shy of the record set for the same YTD in 2016.

The Northern Hemisphere’s YTD temperature tied with 2016 as the hottest on record, while the Southern Hemisphere saw its fourth hottest YTD.

According to a statistical analysis done by NCEI scientists, 2020 will very likely rank among the three-warmest years on record.

More notable climate facts and stats

Arctic sea ice was at near-record lows: Average Arctic sea ice coverage (extent) for September ranked second smallest on record. On September 15, sea ice covered just 1.44 million square miles of the Arctic, the second-smallest minimum extent on record behind September 17, 2012. The 14 smallest minimum annual extents have occurred in the last 14 years.

A record-hot YTD so far for some: Europe, Asia and the Gulf of Mexico had their warmest January-through-September period on record; South America and the Caribbean region had their second highest. No land or ocean areas had record-cold YTD temperatures.

From NOAA (Emily Becker):

La Niña’s reign continues in the tropical Pacific, with an approximately 85% chance of lasting through the winter. Forecasters currently think this La Niña will be on the stronger side.

Let’s check in with the tropical Pacific
The temperature of the ocean surface in the Niño3.4 region was about 0.8°C cooler than the 1986–2015 average, according to the ERSSTv5 dataset. We monitor the Niño3.4 index with a few different temperature datasets—more on that here—but they are all comfortably below the La Niña threshold of -0.5°C. The three-month-average Niño3.4 index, called the Oceanic Niño Index (remember this for later!) was -0.6°C. The Oceanic Niño Index is our primary metric for the El Niño/Southern Oscillation, aka ENSO, the whole El Niño/La Niña ocean/atmosphere system.

The atmosphere is responding to La Niña’s cooler-than-average ocean surface. A strengthened Walker circulation is what we expect with La Niña conditions, and it’s what we have: air rising vigorously over the very warm western Pacific, traveling eastward high up in the atmosphere, sinking over the cooler central-eastern Pacific, and traveling back westward near the surface.

Near-surface winds along the tropical Pacific (the trade winds) were stronger than average through the month of September and into early October, as were upper-level winds over the east-central Pacific. The two indexes we use to measure the change in sea-level pressure between the western and eastern Pacific, the Southern Oscillation Index and the Equatorial Southern Oscillation Index were positive, indicating the presence of more rising air (lower surface pressure) over the west and more sinking air (higher surface pressure) over the east—more evidence of an enhanced Walker circulation.

What’s on deck
Most of the dynamical computer model forecasts predict that La Niña will last through the winter and diminish in the spring. Also, there remains a substantial amount of cooler-than-average water under the surface of the central-eastern Pacific. This will provide a source of cooler water for the surface, giving confidence to the forecast that La Niña will continue.

Several computer models are predicting the Oceanic Niño Index will be, at its peak in November–January, more than 1.0°C cooler than the long-term average. We don’t have specific strength definitions for ENSO, but generally, a deviation of more than 1.0°C (1.8°F) from the long-term mean is considered a moderate-to-strong event. Stronger ENSO events don’t necessarily increase the strength of global weather and climate impacts, but they do increase the likelihood that those impacts will occur.

Speaking of impacts…
The altered atmospheric circulation of ENSO affects global weather (here’s how that works in general and La Niña in specific). Since ENSO can be predicted months ahead of time, a lot of research has gone into understanding the patterns of ENSO’s global weather impacts. The idea is that if we can predict ENSO, we can get an early picture of what global weather could look like months into the future.

A recent study by some of our colleagues at the International Research Institute for Climate and Society (IRI), led by Nathan Lenssen, carefully re-assessed global precipitation (rain, snow, etc.) patterns during ENSO events. They looked at La Niña and El Niño impacts separately, because the impacts are not always opposite. Meaning, although El Niño may be related to a wet winter in one location, La Niña doesn’t necessarily mean a dry winter in that location.

Their study included every ENSO event from 1951–2016 where the peak strength, represented by the Oceanic Niño Index, was at least 1.0°C (for El Niño) or -1.0°C (for La Niña). This excludes weak or borderline ENSO events, when the atmospheric changes are not as consistent.

Nathan’s team assembled this map, which may look familiar to ENSO Blog readers. While maps like these are very important for an overview of La Niña’s impacts, some people may need more information about how often the impacts occurred during past La Niña events. Fortunately, the IRI team has made this information available. You can select the three-month period, El Niño or La Niña, and above/below average precipitation, and the map will show you how often this impact has occurred. For example, 70% of past La Niña winters in Florida were drier than average. Warning—that maproom can be quite a time sink!

Turning impacts maps—either the one shown above, or probabilistic ones like on the IRI site—into an actual forecast can be a complicated process. (The second half of the IRI study assessed the accuracy of a few different forecasts based on ENSO impacts maps.) Official climate outlooks, like those from the Climate Prediction Center, take into consideration ENSO impacts, computer model forecasts, and knowledge of other climate patterns.

One thing you can be sure about is that we’ll be right here, keeping you posted on La Niña 2020/21 as it evolves! Well, I might be in the IRI maproom.