Dr Simon Lee

@SimonLeeWx

Atmospheric scientist. Postdoc . Stratosphere, climate dynamics, S2S. Co-Editor-in-Chief Weather. PhD & MMet from . My own views.

Manhattan, NY
simonleewx.com
Joined August 2012
4,532 Photos and videos Photos and videos

Tweets

You blocked @SimonLeeWx

Are you sure you want to view these Tweets? Viewing Tweets won't unblock @SimonLeeWx

  1. 19 hours ago

    I think this is a case of "the tweeter's curse"

    2 replies 9 likes
    Show this thread
    Show this thread
    Undo
  2. Retweeted
    21 hours ago

    Seeing that there’s been a lot of temperature extremes in North America recently, and a lot of accompanying anomaly maps, I thought I’d do a quick review of different methods to assess temperature anomalies: Thread 🧵 (1/n)

    2 replies 41 retweets 190 likes
    Show this thread
    Show this thread
    Undo
  3. Dec 27

    The forecast Z500 anomalies destructively interfere with mean tropospheric stationary waves (reduced vertical wave activity). In fact, they resemble the pattern we showed in to be linked to stronger SPV forecasts in C3S seasonal forecasts of JFM 2020.

    3 replies 2 retweets 17 likes
    Show this thread
    Show this thread
    Undo
  4. Retweeted
    Dec 27

    Four Flag Alert! Tonight's Green Bay radiosonde measured an incredible 207 knot (238 mph) jet at 250 hPa! 🚩🚩🚩🚩

    8 replies 51 retweets 306 likes
    Show this thread
    Show this thread
    Undo
  5. Dec 27

    Another remarkably strong 10 hPa stratospheric vortex forecast from today's ECMWF extended-range. Ensemble mean is far above model climate mean, effectively a "strong vortex" for the whole forecast (> ~40 m/s) & exceeds 90th percentile of model climate in late Jan/early Feb ‼️

    9 replies 6 retweets 49 likes
    Show this thread
    Show this thread
    Undo
  6. Dec 27

    Some people don't seem to realise that (a) what they like on Twitter is public via the 'Likes' tab, & (b) Twitter sometimes pushes the content that one person likes into another person's home feed - which can be a bit startling when it's something very much NSFW.

    11 replies 36 likes
    Undo
  7. Dec 27

    And you can read all about it in our GRL paper with & which celebrates its two year anniversary today 🥳 & is now free-to-access ✅:

    1 reply 1 retweet 7 likes
    Show this thread
    Show this thread
    Undo
  8. Dec 27

    GEFS has begun suggesting a transition to the Alaskan Ridge regime may occur in the middle third of January. Of the 4 North American regimes, days assigned to the Alaskan Ridge have the highest risk of severe cold for most of N America. One to watch!

    9 replies 12 retweets 69 likes
    Show this thread
    Show this thread
    Undo
  9. Dec 26

    Here's some sounding evidence of that steep temperature gradient even in the mid-troposphere: extremely high 500 hPa temperatures at SGF on the southern side of the jet, against below normal temperatures up at INL.

    3 retweets 5 likes
    Show this thread
    Show this thread
    Undo
  10. Dec 26

    And that is indeed what we have today -- look at the strongly sloped isentropes (i.e., large dT/dy) all the way up to ~300 hPa. It's not only the surface gradient that matters for thermal wind/jet strength.

    1 reply 5 likes
    Show this thread
    Show this thread
    Undo
  11. Dec 26

    The thermal wind shear is a function of height (pressure), and the temperature gradient at that level -- and thus the overall 'thermal wind' (the height integral of this) is maximised when there is a steep temperature gradient through a deep layer of the atmosphere.

    2 replies 6 likes
    Show this thread
    Show this thread
    Undo
  12. Dec 26

    An extremely strong jet streak is screeching across the Midwest today -- several 12Z soundings showed near or record-high 250 hPa winds for any time of year (Davenport shown here). These extreme jet stream winds sit atop an enhanced meridional temperature gradient (thermal wind).

    2 replies 4 retweets 28 likes
    Show this thread
    Show this thread
    Undo
  13. Dec 26

    Still waiting to see anything more than a few flakes here in New York. Meanwhile, back home… (am I a snow shield?)

    0:16
    Just absolutely stunning at Thruscross Reservoir this morning with some nice big prawn cracker flakes. 😍❄️
    2 replies 1 retweet 26 likes
    Undo
  14. Dec 25

    The religious case for Christmas is well known. But there’s a scientific one too | Alice Roberts

    1 reply 2 likes
    Undo
  15. Dec 24

    This means that -- at least in the last four decades or so -- the stratosphere has generally not helped to bring festive weather to parts of the Northern Hemisphere (especially places like western Europe). But this statistical oddity can't last forever, right? One day...❄️

    1 reply 34 likes
    Show this thread
    Show this thread
    Undo
  16. Dec 24

    Although 4 SSWs have been recorded in December since 1979, none have persisted through Christmas Day. In fact, the stratospheric polar vortex is generally quite strong on December 25th, and the last week or so of December is peak average vortex strength.

    2 replies 6 retweets 35 likes
    Show this thread
    Show this thread
    Undo
  17. Dec 24

    American in busy supermarket trying to get to something: “Excuse me sir… thank you” British person in supermarket trying to get to something: “Sorry… can I just… sorry, thanks… sorry.”

    4 replies 19 likes
    Undo
  18. Retweeted
    Dec 23

    It's pretty cool how you can follow along the anomalous high SLP descent in eastern Asia, to the Pacific, and then eventually Alaska in a continuous path from now through ten days.

    4 replies 17 retweets 106 likes
    Undo
  19. Dec 23

    The “Sisyphus Stones” and a beautiful New York sunset. (Even if the sun actually goes down on the New Jersey side of the river.) – at Fort Washington Park

    1 reply 17 likes
    Undo
  20. Dec 23

    I want to emphasize the use of "on average" -- factors aside from the simple strength of the stratospheric zonal winds (such as wave reflection events or the MJO) can influence the NAM and/or regional weather patterns, leading to cold air outbreaks.

    1 reply 12 likes
    Show this thread
    Show this thread
    Undo

@SimonLeeWx hasn't Tweeted yet.

Loading seems to be taking a while.

Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.

    You may also like

    ·