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May 7th-9th Severe Weather Episodes

andyhb

By andyhb,
in Central/Western States

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JasonOH

JasonOH

Posted
Posted

Put forecasters with no access to models of any kind, just recent obs and satellite imagery, up against straight verbatim model output and the models will destroy them, long-term certainly, but short term as well. 

 

With tropical tracks (not intensity) we are basically at the point where verbatim consensus model output is consistently beating NHC tracks (of course the latter has been adjusting to using essentially verbatim output for forecast tracks).  This obviously is a very simplified, straightforward forecast problem compared to Midwest severe or east coast snow (and nobody does well at tropical intensity, human or computer) so the gap is narrower with these forecast problems. I'm not arguing that model output + a human forecaster isn't better than models or forecasters alone, of course. 

We aren't arguing that forecasters are better than models, even though a human can be better, especially at the mesoscale.  We are arguing that they still need interpreted and not blindly believed. 

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LocoAko

LocoAko

Posted
Posted

Another thing... Weiss gave a talk in one of my classes that models are sometimes initialized with incorrect inputs such that they perform better over a longer period.

Right. I think what you're saying essentially agrees with Brett -- that the obs are combined with the background field in a statistically optimal way for that model. In other words, the goal for the model is not to look exactly like the obs, but to form a dynamically balanced analysis to get the best forecast. I greatly enjoyed that class, too. :P

This is a really touchy subject, and there are a lot of complexities to consider. But there's definitely some degree of truth to that statement you mentioned from Twitter. It very much depends on the situation, the evidence used against the NWP output, and the timetable, though. For instance, there was a massive freakout yesterday morning about the 12z CRP and BRO soundings. From that lead time, looking at a couple point obs (which are, of course, themselves subject to some error) in a region far removed from Sunday's moisture source and concluding that the entire setup will be massively different than progged is unwise.

 

Our DA systems have improved markedly over the past decade, incorporating many types of obs (including some we never really look at) in a way that's statistically optimal. So when it comes to analyzing current vis sat over the Gulf, I can be swayed that we're probably looking at moisture tomorrow that will verify on "the low end" of current NWP guidance - which is exactly what I'm expecting, BTW. But from 24-30 h lead time, given our current NWP and DA, I really doubt dew points verifying 7-8 F lower than the consensus on a widespread basis. The only type of analysis that would convince me such a massive NWP failure is likely tomorrow is someone very intimately familiar with the operational DA systems and/or the PBL/LSM schemes pointing out precisely how that failure is already evident in the source region. We've all seen in the past few years how improperly modeled surface fluxes actually can wreak havoc on short-term moisture forecasts when drought exists on the Plains, but that shouldn't be a significant issue tomorrow. It's possible some comparable failure is occurring over the Gulf with regard to moisture flux, but that's not something I have great knowledge of. I do know it's been a long time since I've seen a broad NWP consensus completely fall on its face with regard to moisture return at this lead time, excepting the drought issue. If there's one instance off the top of my head that might qualify, it was 6 June 2007 in KS/NE - but that was a long time ago, and NWP in 2016 is not the same. On the other hand, I can recall several very last-minute moisture return situations around this time of year where doubt the day before a significant event was pervasive (including from me), e.g. 4 May 2007 and 1 May 2008.

 

All that babbling is basically to say that I agree upper 60s are unlikely, at least until early-mid evening along the I-35 corridor, perhaps. But the low-mid 60s consistently advertised by the ECMWF for almost a week now, and now representing something like the 30th-50th percentile of NWP guidance, are probably a decent bet. Even within that range, details matter, and we just won't know them until tomorrow morning or even lunchtime. A longitude-average 2 m dew point of 62 F a couple counties E of the dryline may put a real damper on any widespread/significant tornado threat, where an average of 64 F could be enough for multiple storms producing tornadoes on multiple cycles from 5pm onward. We shall see.

 

EDIT: I just noticed the 12z ECMWF really doesn't have much of a QPF signal in OK, even as late as 06z, so that is somewhat concerning. Could indicate that capping and CI are still questions that hinge on the precise quality of moisture return, especially S of I-40.

Fantastic post.

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jojo762

jojo762

Posted
Posted

I'm not even arguing for higher-end DPs, just 63-66, which is what the GFS/Euro show, not those upper 60s that the NAM is showing. Not sure why the guy mentioned the GFS, because over Oklahoma, it really only shows 62-66, which seems pretty probable given all the things in play, e.g, very moist soils due to recent heavy rains, an intense overnight LLJ, and a sufficient diurnal LLJ to advect the moist tongue in the far western gulf (heck look at the RAS/NQI/BEA 21Z SFC obs. They are all upper 60s and even 70.) 63-66DPs are going to be sufficient for a pretty solid tornado threat in my mind. Keep in mind the wind profiles we will be dealing with, and that LCLs won't be that high really.

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1900hurricane

1900hurricane

Posted
Posted

Lots of talk about dewpoints today I see. I just got off of a full day of work so I haven't really gotten a chance to do much in any way of analysis, but the boundary layer moisture did mix out pretty substantially across most of Texas. There might be a little bit of a richer tongue near CRP, but sub 60*F dewpoints extend out into the Gulf in many places.

 

voOOoOJ.gif

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Stebo

Stebo

Posted
Posted

Lots of talk about dewpoints today I see. I just got off of a full day of work so I haven't really gotten a chance to do much in any way of analysis, but the boundary layer moisture did mix out pretty substantially across most of Texas. There might be a little bit of a richer tongue near CRP, but sub 60*F dewpoints extend out into the Gulf in many places.

 

voOOoOJ.gif

I wouldn't be looking at the mid gulf dewpoints, the deeper moisture is closer to the coast and that is where the models have it originating from.

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1900hurricane

1900hurricane

Posted
Posted

I wouldn't be looking at the mid gulf dewpoints, the deeper moisture is closer to the coast and that is where the models have it originating from.

 

Yeah, the stuff more towards the middle of the Gulf is definitely modified continental air. I was looking more along the Texas coast (although that really wasn't clear in my original post).

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brettjrob

brettjrob

Posted
Posted

I mean, I knew something would happen today, but... I effin hate CO. Pretty much no way we top this tomorrow now, from a chaser's standpoint.

 

Ch5HJI3VIAA8QEn.jpg

 

https://twitter.com/StasIsChasing/status/729098465146343424

 

EDIT: Already seen at least four experienced chasers call it the best intercept/video of their careers. Unreal.

 

EDIT 2: No doubt a top 5 tornado of the year when the season is done, likely top 3. https://twitter.com/SeanSchofer/status/729101575260536832

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brettjrob

brettjrob

Posted
Posted

Yeah, CO is on my list of destinations for sure when I head out there later in May. Hopefully we get one of these upsloping events then.

 

You have to live there, spend all spring trying each of the 15-25 days that look similarly mediocre/flawed, or hit the lottery. Head out there the next day that looks qualitatively similar to today, perhaps with a few ingredients stacking up a bit better, and you'll be treated to the most outflow-dominant garbage this side of the Mississippi. It's the most frustrating thing.

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weatherextreme

weatherextreme

Posted
Posted

I mean, I knew something would happen today, but... I effin hate CO. Pretty much no way we top this tomorrow now, from a chaser's standpoint.

 

Ch5HJI3VIAA8QEn.jpg

 

https://twitter.com/StasIsChasing/status/729098465146343424

 

EDIT: Already seen at least four experienced chasers call it the best intercept/video of their careers. Unreal.

 

EDIT 2: No doubt a top 5 tornado of the year when the season is done, likely top 3. https://twitter.com/SeanSchofer/status/729101575260536832

 

 

 

 

Looks like the first telephone pole on the right side is leaning to its right while the others in front of it look fine.  Wonder if that's the way its suppose to be or did the tornado cause it?

 

 

Unless I'm looking at it all wrong

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David Reimer

David Reimer

Posted
Posted

I'm looking at the colorado pictures and smacking my head against my desk. Unbelievable photos and video coming out of what could be the tornado of the year. Even if we do have tornadoes tomorrow they'll probably find a way to be HP garbage or after sunset. I hate Colorado...

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Chicago Storm

Chicago Storm

Posted
Posted

I mean, I knew something would happen today, but... I effin hate CO. Pretty much no way we top this tomorrow now, from a chaser's standpoint.

Ch5HJI3VIAA8QEn.jpg

https://twitter.com/StasIsChasing/status/729098465146343424

EDIT: Already seen at least four experienced chasers call it the best intercept/video of their careers. Unreal.

EDIT 2: No doubt a top 5 tornado of the year when the season is done, likely top 3. https://twitter.com/SeanSchofer/status/729101575260536832

Sean Schofer's video is top notch.
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Chinook

Chinook

Posted
Posted

Those are some pretty amazing pictures and video I have seen around Wray. If I would have chased, I would have probably gone to the wrong place around Greeley because I don't have radar on my phone, or a whole lot of chasing experience.

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