webberweather.bsky.social
Gov't meteorologist. UNCC & NCSU Alum. Specializes in Climate Dynamics & S2S variability. Opinions are my own & not a reflection of my employer.
webberweather.com
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We certainly won’t have the cleanest MJO passage thru the Eastern Hemisphere next go around thanks to the standing wave over the Tropical Western Pacific.
However, even if the MJO “dies”, the low frequency pattern w/ active west pac convection, is also trying to force a -PNA in late April
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Another reason to believe this -PNA/-NAO pattern is being triggered by low frequency forcing:
We’ve actually seen a -PNA/-NAO in every April since 2020.
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Closest thing I've seen to the forecast S2S base state in late April/early May (near peak climo) is 1961.
Rather prolonged outbreak sequence that year at the end of April (& lots of tors are missing too as usual for this era).
en.wikipedia.org/wiki/Tornado...
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If this lower frequency dominance continues later in the month closer to peak tornado climatology, we’re going to have big problems.
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The winds being too southwesterly here actually probably caused the very strong low-level flow to get blocked by the Organ Mtns. Had to go the long way over the terrain.
We had quite a few obs with sustained winds < 10 kt and gusts of 35-40+ knot. These SSW-SW wind regimes love to do that here!
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Thanks 😀
Got super lucky here last night. Wind direction was too southwesterly for post (K2C2) but it enhanced the winds in the basin along a low-level barrier jet next to the Organ mtns.
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The overall pattern the day before this historic wind storm even looks similar…
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The extended GEFS, ECMWF Weeklies, CMC Weeklies, & JMA weeklies all also agree on the idea of a -PNA making a return by the middle of March or so
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I did notice positive precip anomalies on the east coast in mid-late summer of these years. I can see it being an east coast type of season for the conus (if any) given the active W Africa Monsoon & currently forecast quieter Gulf + Caribbean compared to the last few yrs.
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Nice! Hoping we spend some time up in Iowa this year.
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Looks pretty familiar! This is my May forecast (made earlier this week). Same idea as your plot. Categorical 1+ or -1 STD from the climo mean for the month.
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Also, here's how those analogs compare to the latest Apr-May-Jun Copernicus Climate Change Service (C3S) 500mb & precipitation forecasts over the CONUS + N America.
Again, that's probably about as close as you can get it.
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Here's how those analog years initialize the current global SSTa pattern.
That's about as close as you can get.
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Fwiw, here's what the 15-day total tornado count looks like in this subset of years vs climo.
Note the peculiar "double" peak in activity near the peak of the season.
This "double" peak in tornado activity actually also shows up in the 30-year mean climo data too as far back as the 1960s & 70s.
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What really catches my eye w/ this anomaly composite is how closely it resembles the long-term trends in favorable tornado environments (left figure from Gensini & Brooks (2018)).
This suggests that this year may reinforce some of the long-term observed trends in tornado activity over the CONUS.
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By Apr-May, notice aside from the central N Pacific, this (anomalous) poleward shift in the zonal wind anomalies comes to a halt over the W Hem
Perhaps more importantly however in Apr-May of these years, take note of the westerly jet stream-level anomaly (warm colors) over the CONUS. Not good 🙃
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Here's what these years look like rolled forward into March. Notice the poleward shift in zonal wind anomalies, as you'd expect from climatology, the GSDM/GWO, & MJO variability
Also note how close this generally is to the extended GEFS forecast by mid-late March.
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This winter has beaten it into our heads that when you see a big block trap a cold trough underneath, it’s not a good recipe for a sudden north shift
Outside of Nino winters when your southern stream is much more amped, you usually need the block to back off for places north of DC-BAL to jackpot
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Yep I agree. @antmasiello.bsky.social and I have been talking about the next mjo orbit after this one into the eastern hemisphere later this spring, which will favor -PNA. Guessing it happens in/around late April. Lines up with climo too
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What I inherently fear this year is we see a truly big tornado outbreak and all the cuts to important federal entities, including NOAA potentially, leave us woefully unprepared to respond to it afterwards 🙁
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Interesting you bring up 1971. I thought about the Delta Outbreak (ironically also in mid-Feb) when I saw this outlook
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Thanks 😃
That list sounds about right to me.
I came up w/ a similar list & plotted the 2-week total tor counts & saw this intriguing double peak w/ one in late April/early May & another in late May.
This "double" peak actually appeared in the long-term climo too. Not sure what's happening here 🤔
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Here comes the big -NAO on the EPS
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The planetary scale wave pattern there is just a classic looking +NAO to -NAO transition precursor, w/ the big Scandinavian block and the SE ridge/-PNA
journals.ametsoc.org/view/journal...
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Not talking about summer
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I’m really not sure on whether this winter will follow script of most years and end up being warm in Feb, or do we try to spice things up a little this time?
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Does make sense too from a climo standpoint for early Jan to turn better in a Nina (ish) winter. The biggest positive differences in the snow department for La Niña historically have tended to be in/around early January or so. Usually, the script flips badly away for many in early Feb…
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Some have also argued that cold surges E Asia are important in determining whether or not the MJO will cross the Maritime Continent
Although other things (Eq Rossby Waves & La Nina) are playing roles too, what we're seeing atm is consistent w/ this idea
rmets.onlinelibrary.wiley.com/doi/full/10....
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This is a -EAMT w/ much of the cold air getting dammed up against the western slopes of the Himalayas & lower SLP over Siberia & E Asia. Would need to see the bulk of this colder air/higher SLP spill out into China to kickoff a +EAMT.
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Normally, poleward shifts in the Pacific jet favor +EPO/milder weather over N America (as @antmasiello.bsky.social correctly predicted a few weeks ago).
Given the base state, uncertain if we'll get big +EPO like this composite, but -EPO that's dominated early Dec will be muted for a while at least
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There's a persistent, elongated/broad upper-level ULAC anomaly over the Indian Ocean & SE Asia. It's also NW of the convective heating anomaly over the MC & WP. Classic Matsuno-Gill type response.
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-EAMTs remove +U & also flux +U poleward downstream.
What’s really driving the increase in +U in the Pacific Jet here is WP MJO & a poleward shift.
In order for the jet to remain stronger despite the -EAMT, it moves poleward to conserve angular momentum (getting closer to earth’s axis of rotation)
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I think the difference here comes down to whether the Hudson Bay vortex can couple w/ the stratosphere
The subset of yrs w/ a colder Jan-Feb have a cooler/stronger stratosphere PV
This allows the troposphere Hudson Bay vortex to get "rooted" into the stratosphere, becoming stronger/more persistent
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This excerpt from Liang et al I think does a decent job at touching on some potential causes and I share generally similar sentiments
journals.ametsoc.org/view/journal...