April 2023 #ENSO update: #ElNiño Watch — NOAA

Click the link to read the article on the NOAA website (Emily Becker):

Well, that was quick! Just two months ago I was writing about La Niña for what seemed like the 97th month in a row, and then by March La Niña had departed. Today we’re hoisting an El Niño Watch, meaning that conditions are favorable for the development of El Niño conditions within the next 6 months. In fact, there’s a 62% chance of El Niño conditions for the May–July period. Read on for the reasoning behind the outlook, thoughts about the potential strength of El Niño, and implications for global weather and climate.

Let’s run some numbers

The March average sea surface temperature in the Niño-3.4 region, our primary monitoring region for ENSO (El Niño/Southern Oscillation, the whole El Niño-La Niña system), was 0.2° Celsius (~0.4˚Fahrenheit) below the long-term average, according to ERSSTv5. This is solidly in the ENSO-neutral range, that is, between -0.5 and 0.5 °C difference from average.

Three-year history of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for the 8 existing multi-year La Niña events (gray lines) and the current event (purple line). Of all the previous 7 events, 2 went on to La Niña in their third year (below the blue dashed line), 2 went on to be at or near El Niño levels (above the red dashed line) and three were neutral. Graph by Emily Becker based on monthly Niño-3.4 index data from CPC using ERSSTv5.

The atmosphere is also looking quite neutral, overall. In March, both the Southern Oscillation Index and the Equatorial Southern Oscillation Index were close to zero. Both of these indexes measure the strength of the atmospheric component of ENSO, via the relative surface pressures in the western and central-eastern Pacific. Negative index values indicate the Walker circulation is weaker than average, an El Niño response, while positive values tells us the west-east pressure difference is greater than average, indicating a strengthened Walker circulation—a La Niña response. Near-zero, like the current values, tells us that the atmospheric patterns are near average over the tropical Pacific Ocean.


That’s where we are… but where are we going?? There’s a 62% chance that El Niño will develop during the May–July period, and more than 80% chance of El Niño by the fall.

NOAA Climate Prediction Center forecast for each of the three possible ENSO categories for the next 8 overlapping 3-month seasons. Blue bars show the chances of La Niña, gray bars the chances for neutral, and red bars the chances for El Niño. Graph by Michelle L’Heureux.

We spend a lot of time and effort monitoring and predicting ENSO because it can give us an idea about upcoming potential weather and climate conditions (and because it is a fascinating natural system!). When El Niño or La Niña are holding court in the tropical Pacific, they can affect global temperature and rain/snow patterns in specific ways, with the strongest impacts during the winter. Since ENSO can be predicted months in advance, we can start playing the odds on what sort of climate patterns can be expected. There is a lot of variety, and no prediction is ever perfect! But it’s currently the best tool we have to anticipate upcoming seasonal conditions.

I’ll get back to the potential impacts of El Niño in a minute—first, let’s discuss this confident forecast. Forecasts made during the spring are often less accurate than those made other times of the year. ENSO tends to change phase during the spring, and the tropical Pacific ocean-atmosphere system can be more susceptible to smaller pushes like short-term weather variations, contributing to the “spring predictability barrier.” So it seems the forecasters are really feeling their oats this month, to be giving El Niño such relatively high odds. What’s behind this?

First, the latest runs from our computer climate models are providing very high probabilities that El Niño will develop this year. When there is a lot of agreement among the models, we tend to give more credence to their predictions. For some examples, here’re Niño-3.4 forecasts from the European multi-model ensembleAustralia’s ACCESS-S2, and the North American Multi-Model Ensemble.

But it’s not just model advice supporting the forecast. We always keep an eye on the temperature of the water under the surface of the tropical Pacific. After many months cooler than average, the amount of warmer subsurface water has increased over the past month as a downwelling Kelvin wave—an area of warmer water that sloshes from the west to the east beneath the surface—traverses the tropical Pacific.

Water temperatures in the top 300 meters (1,000 feet) of the tropical Pacific Ocean compared to the 1991–2020 average in February–April 2023. NOAA Climate.gov animation, based on data from NOAA’s Climate Prediction Center.

This warm subsurface will provide a source of warmer water to the surface over the next couple of months and helps provide confidence in the forecast.

Further bolstering the chance for El Niño is a short-term forecast for the Madden-Julian Oscillation (MJO). The MJO is an area of storminess that travels west-to-east along the equator. It’s flanked by wind anomalies, as surface level winds rush toward the area of storminess. The MJO is predicted to be in a phase that will weaken the trade winds (the consistent east-to-west winds near the equator) over the next couple of weeks. Weaker trade winds allow the surface to warm and can contribute to the growth or propagation of downwelling Kelvin waves.

One more observation supporting the potential development of El Niño is the currently very warm far-eastern Pacific. The Niño-1+2 index, which measures the sea surface temperature off the coast of Peru, was near-record warm in March. A coastal El Niño like this can precede a larger El Niño event, although not always.

To summarize, there are several signs pointing to the development of El Niño, including model predictions and the current state of the ocean and atmosphere. It’s still possible that a developing El Niño will sputter out, and the forecast includes around a 1-in-8 chance of neutral conditions in the late fall. However, from our current vantage point, there is enough evidence to support a confident forecast for El Niño.

How strong of an El Niño are we talking?

That’s a lot of support for El Niño developing, but how strong it will get if it forms is a different question. Some of the models are predicting pretty extraordinary Niño-3.4 values, but we put a lot less trust in those predictions—models tend to overestimate, especially in the spring. The ENSO team has a method of predicting the strength of an El Niño or La Niña event that combines human forecasts and model predictions. This method has shown promise so far, although we’ve only been using it for a couple of years. (Lots more detail in Tom’s post on the topic.) By that method, the current chance for a strong El Niño (Niño-3.4 greater than 1.5 °C) is about 4 in 10; a clearer picture of the potential strength of El Niño will develop as we emerge from the spring barrier.

What would an El Niño mean for global climate?

Right, I promised to get back to impacts! El Niño influences the Atlantic and Pacific hurricane seasons, usually leading to fewer tropical storms and hurricanes in the Atlantic and more than average in the Pacific. In the case of the Atlantic, El Niño increases vertical wind shear—the change in wind direction and strength from the surface to higher in the atmosphere—which can impede a hurricane’s growth. NOAA’s hurricane outlook comes out next month, so keep your eyes peeled for that.

You can check out some of the El Niño-related expected temperature and precipitation patterns during June–August and December–February here. We’ll get into more detail about these potential patterns in coming months.

One last comment! ENSO has a strong relationship with the global average temperature: in general, the warmest year of any decade will be an El Niño year, and the coolest a La Niña one. Global warming means that we can’t just say “El Niño years are warmer than La Niña,” since recent La Niña years (we’re looking at you, past 3 years!) have featured much higher global averages than El Niño years from the 1990s and earlier. 2022 was the 6th warmest year since records began in 1880, and that was with a non-stop La Niña. If El Niño develops this year, it increases the odds of record-warm global temperature.

Map showing the March 2023 sea surface temperature difference from the long-term average. Figure by climate.gov from NOAA Coral Reef Watch data.

@Northern_Water increases #Colorado-Big Thompson quota to 70 percent #SouthPlatteRiver #ColoradoRiver #COriver

Water from the Colorado-Big Thompson Project is delivered to water users north of Horsetooth Reservoir in this photo from summer 2018. Photo credit: Northern Water

Here’s the release from Northern Water (Jeff Stahla):

The Northern Water Board of Directors voted Thursday to increase its 2023 quota allocation for the Colorado-Big Thompson Project to 70 percent. Members voted 8-4 to increase the allocation from the 40 percent initial quota set in October.

Board members discussed the combination of this year’s above-average snowpack and streamflow projections contrasted against the lowest East Slope non-C-BT reservoir levels since 2013 and below-average soil moisture readings throughout much of the district.

Luke Shawcross, manager of the Water Resources Department at Northern Water, outlined water modeling showing the predicted storage levels in the project through the end of 2023 and into 2024, and he also discussed the available water supplies in regional reservoirs. Water Resources Specialist Emily Carbone and Water Scheduling Department Assistant Manager Sarah Smith also provided Board members with current water supply and availability data.

Public input was also considered in the Board’s decision.

While current soil moisture conditions on Northeastern Colorado farmland prompted several Board members to ask for consideration of a higher quota, others cited the uncertainty of future hydrology to support their approach this year.

The Board has been setting C-BT quota since 1957 and 70 percent is the most common quota declared. It was also the quota set for the 2021 water delivery season. In 2022, the final quota was 80 percent. Quotas are expressed as a percentage of 310,000 acre-feet, the amount of water the C-BT Project was initially envisioned to deliver to project allottees each year. A 70 percent quota means that the Board is making 0.70 acre-feet of water available for each C-BT Project unit, or collectively, 217,000 acre-feet.

The quota increases available C-BT Project water supplies by 93,000 acre-feet from the initial 40 percent quota made available in November 2022. Water from the C-BT Project supplements other sources for 33 cities and towns, 120 agricultural irrigation companies, various industries and other water users within Northern Water’s 1.6 million-acre service area. According to recent census figures, more than 1 million residents now live inside Northern Water’s boundary. To learn more about Northern Water and the C-BT quota, visit www.northernwater.org.

Screenshot of the Colorado-Big Thompson Project boundaries via Northern Water’s interactive mapping tool , June 5, 2019.

#Hayden sees worst flash flooding in many residents’ memory, and it likely isn’t over yet — Steamboat Pilot & Today #DryCreek #YampaRiver #GreenRiver #ColoradoRiver #COriver

Click the link to read the article on the Steamboat Pilot & Today website (Dylan Anderson, Tom Skulski and John F. Russell). Here’s an excerpt:

Hayden’s Dry Creek certainly didn’t live up to its name Thursday, as flash flooding from melting snow crested its banks around midnight. The floodwaters closed streets, Hayden Valley Schools, the town’s parks and a 38-mile stretch of U.S. Highway 40 to start the day…Many Hayden residents — whether they are new to town or have spent decades in the Yampa Valley — said they had never seen flooding like this before. While for part of the morning there was a true sense of panic in town, many residents were quick to pump water out of their houses, and their neighbors were ready to help…

While Thursday’s flooding was significant, officials expect flooding to continue as snow keeps melting. Water in Dry Creek was starting to rise again Thursday evening…Hayden officials closed several streets on Thursday as well, with Third, Fourth and Poplar streets all seeing significant flooding. The water submerged roads, flooded garages and made its way into some people’s homes…U.S. 40 was closed to through traffic between Steamboat and Craig until after 1 p.m. Thursday, though the road was largely free of the flooding. Rather, CDOT officials were concerned about a key bridge just west of Hayden, and waited for an engineer to inspect it before reopening the highway. The bridge may eventually close the highway again if floodwaters rise overnight after a day of melting, DeMorat wrote in his update.

Fast-melting snow in #Colorado mountains sends #water to downriver reservoirs — with flooding along the way — The #Denver Post #runoff #snowpack #MancosRiver #YampaRiver #GreenRiver #ColoradoRiver #COriver #aridification

Click the link to read the article on The Denver Post website (Bruce Finley). Here’s an excerpt:

Mountain snow-melting intensified this week with an unusually abrupt “flick of the switch” from cold to hot, leading to flooding that on Thursday cut off northwestern Colorado’s main transportation route and forced a shutdown of schools. The statewide heat that brought Denver temperatures to 85 degreesbreaking two records, combined with mountain snowpack more than a third above the norm, also has boosted the potential for early replenishment of water supply reservoirs, including those along the Colorado River

But rapid melting here and around the Southwest this week has brought higher-than-expected flows in rivers, such as the Mancos River in southwestern Colorado, along U.S. 160, and in the Yampa River in northwestern Colorado, along U.S. 40…Water in the Yampa and tributaries on Thursday gushed over banks and submerged a bridge near Hayden, forcing state transportation officials to close U.S. 40, the main transportation route in northwestern Colorado, between Steamboat Springs and Craig…

As the Mancos River swelled near Cortez, Montezuma County officials who had anticipated possible flooding in May or June suddenly faced those perils a month early.