Thread by @BeccaLizE

After the extreme #heatwave in the PNW & Canada last year, a few of us at @ECMWF & @UniRdg_Research set about evaluating how well we predicted it🔥
Q: Were we able to successfully predict the unprecedented?
Short answer: Yes
Longer answer: A 🧵

This research was published today and is free to read online 🔗: rmets.onlinelibrary.wiley.com/doi/epdf/10.10…

The first signal last year for unusually warm temps in June in the Pacific Northwest (PNW) was seen in the @ECMWF seasonal forecasts produced in April and May. 50-70% probability of temperatures in the top 20% of past temperatures in the region. No specifics, but a first hint.🔆

3 weeks before the heatwave, forecasts starting to predict above-normal temperatures & heat stress. 2 weeks ahead, our daily forecasts consistently indicated the possibility of exceeding the maximum in our model climatology (historical record).📈

By the time we reached 2 days before the start of the heatwave, and 5 days before the peak, every single one of the 50 ensemble members (50 diff possible forecast scenarios) predicted temperatures & heat stress exceeding the historical record. 100% of the forecast scenarios 💯

Were the forecasts perfect? No. Do forecasts need to be perfect to be useful? Also no. We show that forecasts were able to, and did, predict an unprecedented extreme event, with a magnitude beyond anything the model had seen before, and with very high confidence.

We also talk a lot about UTCI & Humidex, which are indices that give a "feels-like" temp based on many environmental factors (solar & thermal radiation, wind speed, humidity...) and how the human body reacts. Super important to consider these for health impacts of heatwaves! 🥵

"In a time where our climate is rapidly changing, and it is well known that we will see more, and more extreme, extreme events, how can we increase trust and encourage anticipatory action when forecasts begin to tell us to expect the unprecedented?"

⬆️ the last sentence of our article. It's been playing on my mind a lot over the past couple of weeks, watching the evolution of the forecasts for the current #UKHeatwave from several models indicating record-breaking temperatures and significant health impacts.

Read more here: rmets.onlinelibrary.wiley.com/doi/epdf/10.10…

An update from @ECMWF on the ongoing #heatwave in UK & Europe: ecmwf.int/en/about/media…

Forecasts began to indicate the potential for this event 3 weeks ahead, with confidence increasing with time. Important to keep updated with your national / regional forecasts & warnings☀️🔥⚠️