Jonathan Lee @lee-cyclone.bsky.social · 25/08/2026one could use emergent constraints but that might not be the intent here 010 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026Some thoughts (here I implicitly assume a fixed threshold definition) - bsky.app/profile/lee-... 011 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026(None of this is particularly new, but perhaps a useful and underappreciated insight - and a relevant one considering the increasing frequency of extreme weather in recent days and decades.) 000 0
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026This means that some compound extremes could be increasing at faster rates than the sum of individual hazards alone, explained by (a) simple probability (assuming each hazard’s own probability is rising), (b) changing physical relationships between two hazards (especially if strengthening). 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026… or there is a common driver behind two different hazards (e.g., a persistent jet stream/block enabling both heat and flooding in different places). 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026Oftentimes different physical hazards are linked in some way (via feedbacks or couplings, or one hazard often serves as a precursor to another (e.g., in some areas, extreme heat —> more instability and moisture —> added flooding risk) … 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026The independence assumption above is naive. Even in a past climate, the compound event probability could be greater (or less than) ab. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026Example: If A and B each become 20% more frequent, compound A-B events become 44% more frequent. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026Now suppose warming shifts each individual risk, so that the new probabilities are a+h and b+k. The (independent) joint probability of both occurring at the same time is (a+h)(b+k) = ab+ak+hb+hk. (This is more than linear/additive — relative changes multiply rather than add.) 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026Consider two hazard types A and B (e.g., heat and flooding) occurring with probability a and b, respectively — in a past climate, for a given region. Assuming independence for now between the events (which may or may not hold - more later), the combined probability of occurrence is ab. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 19/07/2026🧵Compound extremes are probably increasing faster than individual extremes in a warming world: a thread 140 4
Jonathan Lee @lee-cyclone.bsky.social · 07/07/2026(5/5) Also it is worth noting that, broadly, climate change is intensifying extreme precipitation events, and most so in the Northeastern US. (Ref. www.nrcc.cornell.edu/services/blo... and repository.library.noaa.gov/view/noaa/32...) 020 2
Jonathan Lee @lee-cyclone.bsky.social · 07/07/2026(4/5) Impressively, a nearly stationary cell persisted just south of Queens for hours. Here is a radar loop of the rainfall showing that. There is a secondary area of 2”+ rain well north of NYC, also due to a persistent, quasi-stationary band of showers. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 07/07/2026(3/5) A “moderate” risk (threat level 3 out of 4) of flash flooding was advertised for the NYC and LI area. The potential for flash flooding was there, but the exact location of heavy rain was (and often is) hard to pinpoint much in advance, though. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 07/07/2026(2/5) Fortunately the bullseye of the rain was offshore, though southern Queens and Brooklyn got quite a bit of rain. Many areas got 2”+ of rain, though Manhattan <1”, with isolated spots up to 4” in Long Island. 100 1
Jonathan Lee @lee-cyclone.bsky.social · 07/07/2026🧵(1/5) Just ~15 miles southeast of midtown Manhattan, it rained about 8” in the past 24 hours. It would have been a vastly different story had storms were just a few miles north … 100 1
Jonathan Lee @lee-cyclone.bsky.social · 03/07/2026yeah, I would guess that the actual value of c < 0.5 010 1
Jonathan Lee @lee-cyclone.bsky.social · 03/07/2026Using w ~ c*sqrt(2*CAPE) and CAPE ~ 3000 J/kg (from SPC mesoanalysis), and assuming c ~ 0.5 (a very rough estimate), w ~ 39 m/s, which seems quite high for a pulse storm 110 1
Reposted by Jonathan LeeAndrew Dessler @andrewdessler.com · 30/06/2026On The Climate Brink, I explain how we connect extreme weather to climate change. Yes, it's another draft chapter from my forthcoming climate risk textbook. www.theclimatebrink.com/p/how-climat...theclimatebrink.comHow climate change influences extreme weatherHow science shows us how warming makes heat waves, floods, hurricanes, and wildfires more likely or more severe — and why this science is becoming a major public-policy battleground. 23214 32
Reposted by Jonathan LeeKatharine Hayhoe @katharinehayhoe.com · 28/05/2026RCP and SSP scenarios are not emission scenarios. I repeat: they are not emission scenarios. They are radiative forcing scenarios. Forcing = human emissions + the response of the climate system to those emissions You can only back out emissions by making assumptions about climate sensitivity. 220656 206
Jonathan Lee @lee-cyclone.bsky.social · 03/04/2026and today’s temperatures - a remarkable warmup especially in upstate NY compared to yesterday, with a cooler coast (almost opposite Wednesday’s temperature pattern). 010 1
Jonathan Lee @lee-cyclone.bsky.social · 02/04/2026Early April temperatures in New York State: yesterday vs today. Some remarkable temperature gradients! 110 1
Reposted by Jonathan LeeDaniel Swain @weatherwest.bsky.social · 24/03/2026Given recent discussion regarding indirect role of anomalous precip (& associated upstream diabatic heating) in amplifying record-breaking heatwaves, even thousands of miles away (inc. Mar 2026 event), I wanted to share this excellent paper from 2025:nature.comBlocking diversity causes distinct roles of diabatic heating in the Northern HemisphereNature Communications - Atmospheric blocking patterns are often categorized into several types and diabatic heating is thought to primarily contribute positively to blocks. Here, the authors show... 28718 87
Reposted by Jonathan LeePam Kan-Rice @ucanrpam.bsky.social · 19/03/2026Phone weather apps are inaccurate. Those apps are fully automated and use algorithms that aren’t “sufficiently dynamic,” @weatherwest.bsky.social @ucanr.edu said — and in a nutshell, they’re lacking human expertise and customization behind the scenes. 45825 58
Reposted by Jonathan LeeTomer Burg @burgwx.bsky.social · 12/03/2026One of the wildest 24-hour loops you'll see in the Mid Atlantic - from mid-upper 80s and tornado warnings to 33F and heavy snow 04920 49
Jonathan Lee @lee-cyclone.bsky.social · 26/02/2026AI/ML algorithms can sometimes generate unphysical forecasts: a case in point 000 0
Jonathan Lee @lee-cyclone.bsky.social · 02/02/2026Here is the (more reliable) seasonal temperature forecast from NOAA’s Climate Prediction Center. 000 0
Jonathan Lee @lee-cyclone.bsky.social · 02/02/2026Over the past decade, Phil has only been accurate 30% of the time in subseasonal forecasts of spring temperature anomalies in the US. More details in the attached abstract (and graphical abstract, courtesy of NOAA). 100 1
Reposted by Jonathan LeeSimon Lee @simonleewx.com · 23/01/2026The extreme cold across eastern N America is due to the Alaskan Ridge regime, which on average brings the coldest winter weather to this region. Is this happening more often? No. During the modern warming era, there has been no observed trend in the occurrence of this regime at this time of year. 38028 80
Jonathan Lee @lee-cyclone.bsky.social · 11/01/2026Given that SEAS5 seems to capture well the extreme frequency/duration of GH blocks, if the GH persistence trend happens to be caused by internal variability (or eventually stops), should one still worry about a systematic bias in the seasonal and/or climate models? 100 1
Reposted by Jonathan LeeJonathan Lee @lee-cyclone.bsky.social · 24/12/2025🧵How might snowfall change in a warming world? I set up a very simple “toy” statistical model to explore this question. Isn't it obvious that snowfall decreases as temperatures get warmer? Yes, but … 142 4
Jonathan Lee @lee-cyclone.bsky.social · 24/12/2025🧵How might snowfall change in a warming world? I set up a very simple “toy” statistical model to explore this question. Isn't it obvious that snowfall decreases as temperatures get warmer? Yes, but … 142 4
Jonathan Lee @lee-cyclone.bsky.social · 24/12/2025More details and plots found here: colab.research.google.com/drive/18sc0I.... The plots have interactive sliders, and you can change the temp and other parameters. (Works best on laptop or tablet).colab.research.google.comGoogle Colab 000 0
Jonathan Lee @lee-cyclone.bsky.social · 24/12/2025How does total snowfall depend on the mean and stdev of temp? As spread of T increases, the “optimal” temp for snowfall decreases (since more snow is lost to the warmer tail), from ~-2° to -8°C. At cold enough T, warming increases snowfall modestly (⬆️ moisture dominates). 110 1
Jonathan Lee @lee-cyclone.bsky.social · 24/12/2025With some simplifying assumptions, I use two equations to estimate the change in snowfall (more details in link later) Here I show how warming from -6±5°C by 1 degree changes snowfall (intensity-weighted frequency). κ = 1.07 (7% more intense per C), c = 1 (Clausius-Clapeyron scale factor) 100 1
Jonathan Lee @lee-cyclone.bsky.social · 24/12/2025… precipitation intensity does depend on the temperature. A warmer atmosphere can “hold” more moisture (roughly 7% per °C). ⬇️ frequency may be compensated by ⬆️ moisture. How important is each effect? When does warming actually *increase* snowfall? 100 1
Jonathan Lee @lee-cyclone.bsky.social · 18/12/2025The success of atmospheric science in recent decades was built on steady, gradual improvements - a silent revolution - as computer models (like WRF, developed at NCAR) advanced & forecast errors declined. NCAR has played an instrumental role in the development of the entire field. #SaveNCAR (3/3) 051 5
Jonathan Lee @lee-cyclone.bsky.social · 18/12/2025Here’s a video of an interactive tornado exhibit there! (2/3) 120 2
Jonathan Lee @lee-cyclone.bsky.social · 18/12/2025#NCAR is a beautiful place and a national treasure. I had the chance to visit the NCAR Mesa Lab last summer, and their exhibits (free and public) are the coolest and most informative ones I’ve seen on atmospheric and climate science. (1/3) 183 8
Jonathan Lee @lee-cyclone.bsky.social · 13/12/2025agreed, and this might inspire me to share some mediocre GFD jokes (yes, I presented a GFD-themed stand-up comedy at a student seminar) 010 1