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 …
Canadian, TX tornado – May 23 2019
May 23rd, 2019. Day 4 of our 2019 chasecation. Only a few days after the infamous and frustrating "high risk bust" in Oklahoma on May 19th (which remains the worst chase day I've had), we found ourselves in the Texas Panhandle under a Moderate risk - having driven all the way from Missouri the preceding …
Trump on climate change: what he should have said
If I followed up every time Donald Trump opened his mouth on climate change with a blog post pointing out where he was wrong, I'd have no time left to do anything else - but this one is a bit more special. This week, Trump visited the U.K., and part of that visit involved a …
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Final Stratospheric Warmings
The stratospheric polar vortex is currently at record-strong levels, based on the metrics of 10 hPa 60°N zonal-mean zonal-wind and 60-90°N average temperature. This is likely to be due to a combination of the timing and duration of the major Sudden Stratospheric Warming (SSW) in January: the duration of easterlies (most of January) shielded the …
A “winter heatwave” in a warming world
The final week of February 2019 has been characterised by anomalously warm, record-setting conditions over NW Europe. The United Kingdom broke its all-time maximum record temperature for February on several occasions and at several stations - the previous record of 19.7C from 1998 was obliterated, replaced with a new record of 21.2C (a huge difference …
The January 2009 SSW
This blog was originally published on 24 January 2019, and updated on 24 January 2020. January 24th, 2009. This was the 'central date' (defined as the day on which the 10 hPa 60N zonal-mean zonal wind reverses from westerly to easterly) of a remarkable, record-breaking major Sudden Stratospheric Warming event, and there are several reasons …
Not all SSWs were created equal
Non-downward propagating SSWs? Major stratospheric sudden warming events (SSWs) attract widespread attention because they are now known to have significant impacts on the tropospheric circulation (e.g. Baldwin and Dunkerton 2001, hereafter BD01). Anomalies in the stratospheric circulation (often expressed as the Northern Annual Mode (NAM) index, or polar cap geopotential height anomalies) propagate downwards through …
The Stratosphere – why do we care?
I study the stratosphere, the layer of atmosphere above the troposphere that extends from about 10-50 km above the surface. Some people might joke (I hope) that "nobody cares about the stratosphere", primarily because, unlike the troposphere, it contains no 'weather' in the traditional sense. Being very dry (...literally), it can't be seen on visible …
Simon H. Lee 