Simon Lee
@simonleewx.com
Lecturer in Atmospheric Science, University of St Andrews. Large-scale weather & climate variability, prediction & change. simonleewx.com
Brief note regarding potential major SSW in the forecast: the formal definition requires the *daily-mean* 10 hPa 60°N U wind to turn negative. A sub-daily reversal wouldn’t qualify as a major event using the most widely established criteria.
November 25, 2025 at 2:13 PM
Brief note regarding potential major SSW in the forecast: the formal definition requires the *daily-mean* 10 hPa 60°N U wind to turn negative. A sub-daily reversal wouldn’t qualify as a major event using the most widely established criteria.
North American weather regime forecasts have shifted from Greenland High toward Alaskan Ridge. This is consistent with forecasts of the forthcoming SSW shifting toward an event dominated by wave reflection and a quick reintensification of the vortex.
simonleewx.com/ecmwf_north_...
simonleewx.com/ecmwf_north_...
November 24, 2025 at 5:18 PM
North American weather regime forecasts have shifted from Greenland High toward Alaskan Ridge. This is consistent with forecasts of the forthcoming SSW shifting toward an event dominated by wave reflection and a quick reintensification of the vortex.
simonleewx.com/ecmwf_north_...
simonleewx.com/ecmwf_north_...
The importance of weather and climate science in the insurance industry
"Insight" article in @rmets.org Weather from @mattpriestley.bsky.social & @hcbloomfield19.bsky.social
doi.org/10.1002/wea....
"Insight" article in @rmets.org Weather from @mattpriestley.bsky.social & @hcbloomfield19.bsky.social
doi.org/10.1002/wea....
The importance of weather and climate science in the insurance industry
Click on the article title to read more.
doi.org
November 24, 2025 at 4:23 PM
The importance of weather and climate science in the insurance industry
"Insight" article in @rmets.org Weather from @mattpriestley.bsky.social & @hcbloomfield19.bsky.social
doi.org/10.1002/wea....
"Insight" article in @rmets.org Weather from @mattpriestley.bsky.social & @hcbloomfield19.bsky.social
doi.org/10.1002/wea....
Reposted by Simon Lee
Just added "chiclet plots" to my website, showing the North American weather regime of the ensemble mean for the past 90 runs of the subseasonal NCEP GEFS & ECMWF IFS
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
November 21, 2025 at 4:14 PM
Just added "chiclet plots" to my website, showing the North American weather regime of the ensemble mean for the past 90 runs of the subseasonal NCEP GEFS & ECMWF IFS
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
Reposted by Simon Lee
This is really striking (to me). Temperatures over global land areas so far this year are still the 2nd warmest on record (after last year)... 🫥
Data from www.ncei.noaa.gov/products/lan...
Data from www.ncei.noaa.gov/products/lan...
November 21, 2025 at 6:47 PM
This is really striking (to me). Temperatures over global land areas so far this year are still the 2nd warmest on record (after last year)... 🫥
Data from www.ncei.noaa.gov/products/lan...
Data from www.ncei.noaa.gov/products/lan...
Just added "chiclet plots" to my website, showing the North American weather regime of the ensemble mean for the past 90 runs of the subseasonal NCEP GEFS & ECMWF IFS
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
November 21, 2025 at 4:14 PM
Just added "chiclet plots" to my website, showing the North American weather regime of the ensemble mean for the past 90 runs of the subseasonal NCEP GEFS & ECMWF IFS
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
GEFS: simonleewx.com/gefs_north_a...
IFS: simonleewx.com/ecmwf_north_...
A stunning Cumulonimbus
snow shower cloud out over the North Sea in the northerly flow this afternoon. Dry and sunny in St Andrews as we’re sheltered by the Cairngorms to the north!
snow shower cloud out over the North Sea in the northerly flow this afternoon. Dry and sunny in St Andrews as we’re sheltered by the Cairngorms to the north!
November 20, 2025 at 4:10 PM
A stunning Cumulonimbus
snow shower cloud out over the North Sea in the northerly flow this afternoon. Dry and sunny in St Andrews as we’re sheltered by the Cairngorms to the north!
snow shower cloud out over the North Sea in the northerly flow this afternoon. Dry and sunny in St Andrews as we’re sheltered by the Cairngorms to the north!
A polar vortex of confusion simonleewx.com/2025/11/20/a...
A polar vortex of confusion
Meteorologists have a historical penchant for giving names to atmospheric phenomena which, in today’s world, sound rather like phrases made up to fit a dramatic headline than real scientific …
simonleewx.com
November 20, 2025 at 11:52 AM
A polar vortex of confusion simonleewx.com/2025/11/20/a...
With the imminent weak polar vortex/potential SSW, one similar recent(ish) year is 1996/97, which saw a very weak early season vortex (date-record weak U10-60 in Nov). 96/97 also had an established easterly QBO & cool ENSO Neutral/borderline La Niña. Extremely strong late-season vortex ensued.
November 19, 2025 at 6:40 PM
With the imminent weak polar vortex/potential SSW, one similar recent(ish) year is 1996/97, which saw a very weak early season vortex (date-record weak U10-60 in Nov). 96/97 also had an established easterly QBO & cool ENSO Neutral/borderline La Niña. Extremely strong late-season vortex ensued.
I decided to code entirely with AI today. I got ~95% of the way there far faster (and better) than I could do myself, but the remaining 5% took so long — due to needing to learn the code — that in the end it probably took as long as if I’d done it myself. But I learned new functions in the process.
November 19, 2025 at 6:19 PM
I decided to code entirely with AI today. I got ~95% of the way there far faster (and better) than I could do myself, but the remaining 5% took so long — due to needing to learn the code — that in the end it probably took as long as if I’d done it myself. But I learned new functions in the process.
Reposted by Simon Lee
From damaging gusts to devastating floods, storms are no joke. But did you know storms can also ruin your cup of tea....
Hear more from Kirsty McCabe: www.rmets.org/metmatters/s...
Hear more from Kirsty McCabe: www.rmets.org/metmatters/s...
Storm in a teacup
From damaging gusts to devastating floods, storms are no joke. But did you know storms can also ruin your cup of tea?
www.rmets.org
November 14, 2025 at 9:38 AM
From damaging gusts to devastating floods, storms are no joke. But did you know storms can also ruin your cup of tea....
Hear more from Kirsty McCabe: www.rmets.org/metmatters/s...
Hear more from Kirsty McCabe: www.rmets.org/metmatters/s...
Reposted by Simon Lee
🚨New paper on heatwaves in a net zero world 🚨
In our study, led by @sarahinscience.bsky.social, we find that the intensity, length and frequency of heatwaves do not return to pre-industrial levels under net zero - and in many regions barely improve at all.
iopscience.iop.org/article/10.1...
In our study, led by @sarahinscience.bsky.social, we find that the intensity, length and frequency of heatwaves do not return to pre-industrial levels under net zero - and in many regions barely improve at all.
iopscience.iop.org/article/10.1...
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November 18, 2025 at 4:10 PM
🚨New paper on heatwaves in a net zero world 🚨
In our study, led by @sarahinscience.bsky.social, we find that the intensity, length and frequency of heatwaves do not return to pre-industrial levels under net zero - and in many regions barely improve at all.
iopscience.iop.org/article/10.1...
In our study, led by @sarahinscience.bsky.social, we find that the intensity, length and frequency of heatwaves do not return to pre-industrial levels under net zero - and in many regions barely improve at all.
iopscience.iop.org/article/10.1...
What a spectacular Pembrokeshire Dangler (technical term, of course). Or a Cornish Tickler?
November 19, 2025 at 1:00 PM
What a spectacular Pembrokeshire Dangler (technical term, of course). Or a Cornish Tickler?
The ensemble mean of today's IFS subseasonal forecast now predicts the earliest major sudden stratospheric warming in reliable records, beating 28 November 1968.
Will this verify? 👀
charts.ecmwf.int/products/ext...
Will this verify? 👀
charts.ecmwf.int/products/ext...
November 13, 2025 at 8:17 PM
The ensemble mean of today's IFS subseasonal forecast now predicts the earliest major sudden stratospheric warming in reliable records, beating 28 November 1968.
Will this verify? 👀
charts.ecmwf.int/products/ext...
Will this verify? 👀
charts.ecmwf.int/products/ext...
The ensemble mean from today's IFS subseasonal run almost predicts the earliest major sudden stratospheric warming on record 😮
Will be interesting to see if this signal progresses as it is just on the cusp of typical SSW prediction lead-times – daily runs of 101 members can still vary a fair bit
Will be interesting to see if this signal progresses as it is just on the cusp of typical SSW prediction lead-times – daily runs of 101 members can still vary a fair bit
November 12, 2025 at 8:32 PM
The ensemble mean from today's IFS subseasonal run almost predicts the earliest major sudden stratospheric warming on record 😮
Will be interesting to see if this signal progresses as it is just on the cusp of typical SSW prediction lead-times – daily runs of 101 members can still vary a fair bit
Will be interesting to see if this signal progresses as it is just on the cusp of typical SSW prediction lead-times – daily runs of 101 members can still vary a fair bit
Not the favoured outcome by any means, and I’m mostly posting this for fun (and my own interest in “unseen” model extremes), but the GFS 18Z has an historic major SSW on 26 November.
This would be the earliest in reliable records, beating 28 Nov 1968.
Not a forecast — just for interest!
This would be the earliest in reliable records, beating 28 Nov 1968.
Not a forecast — just for interest!
November 10, 2025 at 11:56 PM
Not the favoured outcome by any means, and I’m mostly posting this for fun (and my own interest in “unseen” model extremes), but the GFS 18Z has an historic major SSW on 26 November.
This would be the earliest in reliable records, beating 28 Nov 1968.
Not a forecast — just for interest!
This would be the earliest in reliable records, beating 28 Nov 1968.
Not a forecast — just for interest!
Reposted by Simon Lee
🌍 Postdoc research opportunity: Predictability and Climate Dynamics - University of Oxford, UK
📚 The position sits within the Predictability of Weather and Climate and Climate Dynamics research groups in Oxford’s Department of Physics.
@timwoollings.bsky.social
@oxfordphysics.bsky.social
🧵
📚 The position sits within the Predictability of Weather and Climate and Climate Dynamics research groups in Oxford’s Department of Physics.
@timwoollings.bsky.social
@oxfordphysics.bsky.social
🧵
November 8, 2025 at 9:30 PM
🌍 Postdoc research opportunity: Predictability and Climate Dynamics - University of Oxford, UK
📚 The position sits within the Predictability of Weather and Climate and Climate Dynamics research groups in Oxford’s Department of Physics.
@timwoollings.bsky.social
@oxfordphysics.bsky.social
🧵
📚 The position sits within the Predictability of Weather and Climate and Climate Dynamics research groups in Oxford’s Department of Physics.
@timwoollings.bsky.social
@oxfordphysics.bsky.social
🧵
06Z GFS has remarkably persistent Greenland blocking for the full run, and a very weak stratospheric vortex by the end of it too. Posting this just for fun, but falls within what seems to be the range of possible outcomes based on recent modelling.
November 8, 2025 at 2:45 PM
06Z GFS has remarkably persistent Greenland blocking for the full run, and a very weak stratospheric vortex by the end of it too. Posting this just for fun, but falls within what seems to be the range of possible outcomes based on recent modelling.
What is it that possesses someone to hold a phone call **on speakerphone** on an otherwise silent bus?
November 3, 2025 at 7:13 PM
What is it that possesses someone to hold a phone call **on speakerphone** on an otherwise silent bus?
Reposted by Simon Lee
A damaging hurricane in a warmer world
How would a major hurricane that hit Jamaica in 1903 be different today, in a warmer world?
It would drop more rain. (At least)
climatelabbook.substack.com/p/a-damaging...
How would a major hurricane that hit Jamaica in 1903 be different today, in a warmer world?
It would drop more rain. (At least)
climatelabbook.substack.com/p/a-damaging...
November 2, 2025 at 9:21 AM
A damaging hurricane in a warmer world
How would a major hurricane that hit Jamaica in 1903 be different today, in a warmer world?
It would drop more rain. (At least)
climatelabbook.substack.com/p/a-damaging...
How would a major hurricane that hit Jamaica in 1903 be different today, in a warmer world?
It would drop more rain. (At least)
climatelabbook.substack.com/p/a-damaging...
Reposted by Simon Lee
Alrighty, ready to see something really cool? (and maybe a little nauseating)
The evolution of Hurricane Melissa's mesovortices at peak strength.
The evolution of Hurricane Melissa's mesovortices at peak strength.
October 29, 2025 at 8:10 PM
Alrighty, ready to see something really cool? (and maybe a little nauseating)
The evolution of Hurricane Melissa's mesovortices at peak strength.
The evolution of Hurricane Melissa's mesovortices at peak strength.
Reposted by Simon Lee
1-minute #GOES19/#GOESEast Visible images showed that soon after making landfall, the eye of Hurricane #Melissa became cloud-filled as the storm interacted with higher terrain on the western edge of Jamaica.
October 28, 2025 at 8:58 PM
1-minute #GOES19/#GOESEast Visible images showed that soon after making landfall, the eye of Hurricane #Melissa became cloud-filled as the storm interacted with higher terrain on the western edge of Jamaica.
Reposted by Simon Lee
One factor that supported Melissa reaching this record: an Argo float southeast of Jamaica shows a dramatic decrease in upper-level ocean temperature before (18 Oct) and after (28 Oct) the storm.
My heart goes out to the folks in Jamaica facing this powerful hurricane's numerous hazards today. 💔
My heart goes out to the folks in Jamaica facing this powerful hurricane's numerous hazards today. 💔
October 28, 2025 at 5:27 PM
One factor that supported Melissa reaching this record: an Argo float southeast of Jamaica shows a dramatic decrease in upper-level ocean temperature before (18 Oct) and after (28 Oct) the storm.
My heart goes out to the folks in Jamaica facing this powerful hurricane's numerous hazards today. 💔
My heart goes out to the folks in Jamaica facing this powerful hurricane's numerous hazards today. 💔