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The op Canadian, op EURO, and GFS ensembles still give Saturday April 2nd a chance to go the more severe way.
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That's one time window I'm watching, and then I think the main time window that lines up with MJO propagation and such is roughly April 14th-16th, before subtropical ridging builds across the Southeast late April and going into May. MJO timing and teleconnections and such suggest that 4/6-4/8 + 4/14-4/16 scenario may be comparable to other active periods in the past where you have one significant threat at the start of an MJO velocity couplet and then the bigger threat at the end of the velocity couplet (3/17 -> 3/25 last year and 4/15 -> 4/27 of 2011 are two examples of just such a scenario in terms of timing progression, *not* of the magnitude of what may happen this April). There would also be the potential for other events peppered in of lesser magnitude.We need to keep a serious eye out for the April 6th-8th time frame.
That's one time window I'm watching, and then I think the main time window that lines up with MJO propagation and such is roughly April 14th-16th, before subtropical ridging builds across the Southeast late April and going into May. MJO timing and teleconnections and such suggest that 4/6-4/8 + 4/14-4/16 scenario may be comparable to other active periods in the past where you have one significant threat at the start of an MJO velocity couplet and then the bigger threat at the end of the velocity couplet (3/17 -> 3/25 last year and 4/15 -> 4/27 of 2011 are two examples of just such a scenario in terms of timing progression, *not* of the magnitude of what may happen this April). There would also be the potential for other events peppered in of lesser magnitude.
Has support from 12z GFSWe need to keep a serious eye out for the April 6th-8th time frame.
Has support from 12z GFS
I wouldn't rule out a threat (maybe even a significant one) around the 7th-8th or so right after the -NAO weakens. From there on out, all ensemble data is screamingly consistent (run to run and ensemble family to ensemble family) that the whole pattern lays down and goes low amplitude, the classic low amplitude pattern that you would expect during a strong -PDO, a firmly established La Nina and a high-end +TNI spike.
The 00Z/06Z EPS/GEFS are once again trending toward a higher-amplitude solution as we approach nearer in time to 6–8 April. So far I am still not seeing the kind of atmospheric response that I would expect in a background state dominated by the strong -PDO, -ENSO, and +TNI. The latest models are trending toward split flow and a pinched-off trough with mid-to-high-latitude blocking and a mostly meridional trough axis. Like clockwork this has been happening. Of course, we could still see plenty of tornadoes and severe wind with QLCSs and embedded vortices, but large-scale outbreaks based on discrete cells once again seem harder to come by than one might expect in this kind of environment.Has support from 12z GFSView attachment 12933
The 00Z/06Z EPS/GEFS are once again trending toward a higher-amplitude solution as we approach nearer in time to 6–8 April. So far I am still not seeing the kind of atmospheric response that I would expect in a background state dominated by the strong -PDO, -ENSO, and +TNI. The latest models are trending toward split flow and a pinched-off trough with mid-to-high-latitude blocking and a mostly meridional trough axis. Like clockwork this has been happening. Of course, we could still see plenty of tornadoes and severe wind with QLCSs and embedded vortices, but large-scale outbreaks based on discrete cells once again seem harder to come by than one might expect in this kind of environment.
Those are some, uh, not great analogs on that sounding. (The 1977 Birmingham F5 and three other events that all produced at least one violent tornado.)All that said, today's 12Z GFS painted a pretty ominous picture for Dixie Alley on 4/5. Looks like it could be similar to the last (and upcoming tomorrow) go-around, but with more instability. Forecast sounding from near Sawyerville, AL (of both 4/27/11 and 3/25/21 infamy):
Plenty of time for this to change one way or the other, but it's looking pretty likely a thread will eventually be needed for this day and possibly others early-mid next week. Gotta get through tomorrow's event first.
By “large-scale,” I am referring to an outbreak that produces discrete long-trackers and multiple long-lived families, not a top-tier, historic event like 3–4 Apr 1974, 27 Apr 2011, and so on. I am talking about events that feature ~10 or more intense (EF3+) tornadoes and roughly twice as many EF2s, including multiple violent (EF4+) events. Examples: 5–6 Feb 2008 (Super Tuesday), 27–28 Apr 2014, and so on. My point is that a robust -PDO, moderate -ENSO, and strong +TNI should produce at least one or more of these kinds of events during both meteorological winter and spring, involving a low-amplitude setup(s). So far only the major December outbreak has qualified, but one would expect one or more events of similar or greater scale come springtime. So far, however, the high-amplitude, meridional setups refuse to abate. The 48h H5 trend on the 12Z GFS shows a shift toward high-latitude blocking. Maybe the warm SSTs offshore of the Eastern Seaboard result in greater incidence of blocking and springtime split flow.All that said, today's 12Z GFS painted a pretty ominous picture for Dixie Alley on 4/5. Looks like it could be similar to the last (and upcoming tomorrow) go-around, but with more instability. Forecast sounding from near Sawyerville, AL (of both 4/27/11 and 3/25/21 infamy):
Yep… I have seen a few people say that April definitely needs to be watchedIf this pattern just becomes little less amped , lookout big trouble lays ahead .ensembles has system after system that has to be watched
So far I am not seeing any signs of a transition to lower amplitude.If this pattern just becomes little less amped , lookout big trouble lays ahead .ensembles has system after system that has to be watched
Fits with my and Fred's thinking that March was a warm-up... Not saying it will resemble 2011 obviously
12z euro looks quite ominous next week. , and even bigger stronger system setting up on day 10.