When I wrote the first SSW blog on the evening of Tuesday 22 February, I did not expect to be writing the next one so soon after with such increased uncertainty. But there are many aspects to the way the world evolved over the last week which I would not have expected! Thanks to everyone …
Simon’s Stratosphere Watch #1
Welcome to a new blog series! Yes, the title was indeed chosen to fit the SSW acronym. In these posts, I intend to give a brief summary of the state of the Arctic stratospheric polar vortex and the latest forecasts. I have yet to decide how regular these will be. Tuesday 22 February 2022 Summary: …
Some thoughts on summer 2021
Predicting mid-latitude weather in summer can be more of a challenge than in winter. This is generally because components of the atmosphere-ocean system which provide predictability during winter aren't present in summer: we don't have fully developed El Niño-Southern Oscillation episodes; there's no stratospheric polar vortex; the Madden-Julian Oscillation tends to be less active; and …
The many faces of the NAO
To describe the large-scale atmospheric circulation on a given day, we often use patterns. An example pattern is the North Atlantic Oscillation (NAO), which I'm going to focus on here. In general, the NAO is a measure of the pressure difference between the Azores high and Iceland low, and is thus intrinsically related to the …
CFSv2 ain’t that bad: tips on using long-range forecasts
I've recently added some additional products from the NCEP Climate Forecast System version 2 (CFSv2) to my site -- namely, forecasts of the weekly-average 500 hPa geopotential height anomalies for the next 4 weeks, and forecasts of the monthly-mean 700 hPa geopotential height anomalies over the next 6 months. These sit alongside the 44 day …
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Weather and climate records are not mutually exclusive
The atmosphere is a chaotic system with an infinite number of configurations - the weather pattern on any specific day has never before been exactly the same everywhere. Thus, it is extremely difficult to link a specific weather event to climate change. And yet, when significant weather occurs, discussion immediately jumps toward climate change - …
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The link between climate change and Britain’s winter storms
This article originally appeared in the February 16th 2020 edition of The Sunday Times, and was co-written with Shingi Mararike. Every winter Britain gets hit by a series of storms. Ciara and Dennis are just the latest — but with two key differences. The first is their strength. Our storms get their energy from temperature …
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January 2020: Memories of January 2007
In the UK, it's currently mild - very mild. Provisional data through the 9th shows the mean Central England Temperature (CET) is running at 7.5°C, which is 3.9°C above the 1961-1990 average. The large-scale pattern during the month so far (Fig. 1) has been characterised by a ridge extending from the Azores to Europe, and …
There’s more to the UK winter than the stratosphere
The title might seem rather obvious - or a surprising statement coming from me! But what I seek to achieve in this short blog post is provide a simple reminder that historically cold weather has indeed happened without a sudden stratospheric warming (or significant stratospheric polar vortex disruption). The role of the stratosphere can sometimes …
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10 FAQs on “Increased shear in the North Atlantic upper-level jet stream over the past four decades”
Lee, S. H., P. D. Williams, and T. H. A. Frame, 2019: Increased shear in the North Atlantic upper-level jet stream over the past four decades. Nature, https://doi.org/10.1038/s41586-019-1465-z. What is the key result of the study? Our study shows that the annual-mean vertical west-to-east (zonal) wind shear over the North Atlantic at aircraft cruising altitudes (within the …