Copernicus Day for August has come and gone.

It marks a day when long-range forecast data for the months ahead gets released.

Here's what it shows! 🧵 A La Niña-like pattern will be in place as winter approaches.

Cool water in the Pacific affects climate patterns worldwide.

Marine heat waves in the mid-latitudes may lead to warm fall weather in parts of the United States, Europe and Asia.

There have been varying meteorological forces behind recent extreme rainfall events, but they are all connected by very unusual amounts of moisture pulsing above the United States.

Precipitable water, a measure of the total amount of water in the atmosphere, has been above the 90th percentile on half of all days so far this summer — the largest number of days to-date since records began in 1940. It's been above-average on all but five days.

Forecasters use precipitable water to gauge how much fuel is available for storms and how much rain can possibly fall. While it's not a one-to-one relationship, higher precipitable water brings a higher the chance for extreme rainfall — as long as there's a mechanism to squeeze the moisture out of the sky.

Globally, precipitable water reached record levels in 2024. So far, 2025 is a few notches below last year's record pace, but corridors of unusually high atmospheric moisture have developed near areas of much warmer than average oceans. This includes the central and eastern United States, Europe and eastern Asia.

Part of a meteorologist's job is to be an atmospheric detective — to understand and help others understand why certain things are happening.

Yes, it rains hard and sometimes floods during summer, but to understand what's driving this season's excessive rainfall is critically important. To dismiss it as 'just weather' is selling it short.

I think there's plenty of evidence to suggest that the trend toward a moister atmosphere is leaving an imprint on weather patterns in the United States this summer. Corridors of unusually high atmospheric moisture have developed near areas of much warmer than average oceans — which happen to be located near densely populated parts of the Northern Hemisphere.

Copernicus Day for July 2025 has arrived — a day when weather fans around the planet can learn about possible patterns in the months ahead.

Here's what the world can expect 🧵 A big global story is how warm the oceans are, especially in the Northern Hemisphere.

This may cause summer-like heat to last into fall and enhance downpours in many places.

Neither La Niña nor El Niño is currently active in the Pacific, but La Niña may return later this year.

June was more humid than average for a whopping 290 million people across 40 states.

Did it feel particularly sticky where you live?

New Mexico, Kentucky, Maryland, North Carolina and Ohio were the most unusually humid states.

🧵 on June Nights during June were very unusually warm.

Around 270 million people experienced above-average minimum temperatures. It was below-average for just 8 million people.

Overnight temperatures were most unusually high in Utah, Pennsylvania, New York, Vermont and Ohio.

Record-breaking humidity levels hit the Northeast and southern Canada on Monday, with dew points surging into the low-to-mid-80s.

Heat index values neared 115 degrees.

This illustrates that the current weather pattern exceeds typical summer weather.

Why it's so humid 🧵 Behind the extreme humidity is an air mass that took a winding, week-long, 4,000-mile journey northward from the Caribbean islands to the Northeast, bringing tropical weather to people that live far from the tropics.

Eyes will be on East Coast cities this week where temperatures will reach 100 degrees for several consecutive days, potentially breaking June records.

Around 40 million people may face triple digit heat 🧵 It could reach or exceed 100 degrees for up to five days in a row in some eastern areas this week.

For many places in the Northeast and Mid-Atlantic, the June record is at most two 100 degree days in a row.

Extreme humidity — not just extreme temperatures — will make headlines over the next week as a heat dome develops.

Humidity levels will surge across 40 states and southern Canada, bringing tropical rainforest-like conditions, especially next week 🧵 What feels humid to one person may not to another, so it’s important to recognize that the stickiness of the air is subjective.

This table describes the humidity level associated with dew point thresholds — and how each feels.

Copernicus Day for May 2025 has arrived, a day for long-range weather fans around the world!

Let's take take a look at what the data is showing for the upcoming summer 🧵 Neutral conditions in the equatorial Pacific could adjust toward a La Niña-like direction later in 2025, in concert with a potential negative Indian Ocean Dipole.

Warmer than average seas are predicted in much of the Northern Hemisphere, bolstering summer heat.

Is May becoming more like a summer month?

This map shows how May temperatures have changed since the 1980s. It's trended warmer for 90 percent of U.S. counties.

States that have warmed the most: Washington, Pennsylvania, Tennessee, West Virginia, Ohio, Vermont & Massachusetts. April featured impressive levels of warmth:

• 11 days above 90˚F in Tampa (record)

• Nine days above 80˚F in Washington D.C.

• 12 days above 70˚F in New York City

• 79˚F in Ireland (record)

• 120˚F in Pakistan

Will it continue into May?

Copernicus Day for March 2025 has arrived!

It's a day when long-range climate model data comes out, giving us clues as to what the next few months may hold.

Here's what it shows 🧵 The picture in the tropical Pacific, home to the oscillation that includes El Niño & La Niña, is complicated.

An El Niño Costero (coastal El Niño) is occurring near western South America as La Niña wanes in the central Pacific.

This tug-of-war will influence patterns worldwide.

Tropical Cyclone Alfred will lash southern Queensland & northern New South Wales, Australia, making landfall later this week.

Significant damage is possible in this densely populated region where tropical cyclone impacts are not uncommon, but landfalls are.

🧵 What to know Slow-moving Alfred will generate big waves.

The highest one-third of the waves will average 20-30 feet with individual waves as high as 50 feet.

Dangerous seas will pound the coast for days, with erosion, inundation, and damage possible.

The United States has been home to the most unusually cold air on the planet so far this year.

A desolate part of central South Dakota has been 11 degrees below average, making it Earth’s most unusually cold place in 2025 so far.

Here's why 🧵 The tropospheric polar vortex has been displaced to the south.

Strong high pressure near Alaska and Greenland contributed to above-average temperatures across the Arctic, displacing the region’s frigid air much farther south — over southern Canada and the United States.

Can you guess the snowiest place on the planet?

The answer might surprise you.

It's the Southern Patagonian Ice Field, where over 166 feet of snow falls annually. That's 15 stories or 2,000 inches.

I found someone who's been there 🧵 Southern Patagonian Ice Field 🌨️

“I can definitely confirm that the Southern Patagonia Ice Field is a snowy and windy place, and I would not be surprised if it is the snowiest place on the planet,” said Margit Schwikowski, professor emeritus from the University of Bern in Switzerland.

Schwikowski and a team of six researchers, including three Chilean glaciologists, visited the ice field in August 2006 to take ice cores from the Pio XI Glacier, the largest in the Southern Patagonian Ice Field.

“Although our work was finished after four days, we spent two weeks in tents up there. We could not get out because of snowfall and strong winds,” Schwikowski said.

“We took especially rigid tents, a lot of food and skis to be able to get out on our own if the helicopter could not fly. We prepared the GPS track of the escape route to Argentina,” recalled Schwikowski.

In other words, don’t try this at home. Getting to the snowiest place on the planet requires intricate planning, strong mountaineering skills, an escape route and much more.

It’s not about to become the next Instagram hot spot.

Photos: Theo Jenk and Beat Rufibach

A major weather disaster unfolded over the weekend in the island nation of Mayotte in the western Indian Ocean.

It took a direct hit from category four-equivalent Tropical Cyclone Chido - the strongest storm to strike the island on record.

Hundreds of people are feared dead 🧵 Tropical Cyclone Chido nearly reached category five strength north of Madagascar.

A southward jog and strengthening trend saw the storm slam into Mayotte, with a landfall in Grande-Terre and Petite-Terre, the two main islands, followed by another landfall in Mozambique.

Yesterday was Copernicus Day for December 2024!

It's a day for celebrating the arrival of seasonal climate data.

This data provides clues about weather patterns over the next several months 🕵️ A La Niña-like pattern in the equatorial Pacific will help to shape global weather patterns in the months ahead.

Marine heatwaves will also affect local conditions. These blobs of excessive ocean heat are becoming more common in a warming world.

Yesterday was Copernicus Day for November 2024! It's a day celebrated by weather nerds around the world.

Here are the climate trends to know about the season ahead 🧵 Despite a La Niña-like pattern of cool seas in the equatorial Pacific, mild winter temperatures are forecast across large swaths of the Northern Hemisphere - and the planet 🌡️

Yesterday was Copernicus Day for October 2024!

🔮 It's a day for long-range weather & data nerds across the planet!

Here's what you should know about the global climate from late 2024 into early 2025 ⤵️ A La Niña-like pattern in the tropical Pacific is forecast to be a key climate driver for Northern Hemisphere winter.

Elsewhere, excessive ocean warmth, which has built over recent years, is forecast to continue.

A North Pacific marine heatwave is particularly notable.

🔮 Yesterday was Copernicus Day for September 2024 - a holiday for weather nerds around the world!

It marks the day when new long-range forecast data becomes available, providing a glimpse at general climate patterns in the months ahead...

Thread 🧵 The main global climate driver in the months ahead is a developing La Niña.

Cool seas in the tropical Pacific will lead to changing rainfall and thunderstorm patterns there.

This has flow-on effects to weather patterns in distant places, otherwise known as a teleconnection.

Yesterday was "Copernicus Day" for August 2024 ~ a day on which weather nerds get their hands on lots of new long-range forecast data 🤓 💾

Here are five key takeaways 🧵 ⬇️ The height of Atlantic hurricane season is expected to be busier than normal 🌀

Islands in the Caribbean, Mexico, the southern/eastern U.S. + Canada, and even western Europe should be prepared for potential weather extremes.

Yesterday was "Copernicus Day" for July 2024, a monthly holiday for weather nerds around the world 🤓

A bunch of new seasonal climate data just dropped, providing a glimpse at forecast patterns in the months ahead.

🧵 Here's a quick thread about what it's showing... A La Niña-like pattern of cool water in the equatorial Pacific will be a key climate driver in the second half of 2024.

Most elsewhere, global sea surface temperatures are forecast to be above average, with marine heatwaves possible in the North & South Pacific.

Yesterday was "Copernicus Day", a monthly holiday for weather nerds around the world 🤓

A whole bunch of new seasonal climate data just dropped, providing a glimpse at patterns in the months ahead.

🧵 Here's a quick thread about what it's showing... A developing La Niña (cool equatorial Pacific) is expected to become the main climate driver in the second half of 2024.

Most elsewhere, global sea surface temperatures are forecast to be above or well above average, contributing to marine heatwaves and warmer air temperatures.