May 7th-9th Severe Weather Episodes

[andyhb]

Tornado warning SE of Denver. Upper 40s/low 50s dews, yet the MLLCL heights are still below 1000 m. Gotta love CO.

[tacoman25]

I'm currently NE of Denver on I-76 about 10 mi east of Lochbuie. That tor-warned storm looks to be headed this way or maybe a bit east, hard to tell with this flow.

Impressive radar echoes currently.

[bjc3395]

Tornado warning SE of Denver. Upper 40s/low 50s dews, yet the MLLCL heights are still below 1000 m. Gotta love CO.

Haha. I remember someone, Shane maybe, calling it "fake" instability or fake thermo last year. Interesting setups there.

[tacoman25]

Haha. I remember someone, Shane maybe, calling it "fake" instability or fake thermo last year. Interesting setups there.

Ha, nothing fake about it, just easier to achieve.

[andyhb]

Should probably note that the 12z Euro was well underdone (by as much as 1000-1500 J/kg in several spots) in terms of CAPE at 18z over CO and further south along the dryline (despite the rather low surface dewpoints).

[andyhb]

Great post from Greg Blumberg regarding on why tomorrow might not see mid 60s dewpoints: http://stormtrack.org/community/threads/2016-05-08-event-ks-ok-tx-mo.29154/#post-344251

 

Certainly concerning regarding the tornado potential.

[jojo762]

Great post from Greg Blumberg regarding on why tomorrow might not see mid 60s dewpoints: http://stormtrack.org/community/threads/2016-05-08-event-ks-ok-tx-mo.29154/#post-344251

Certainly concerning regarding the tornado potential.

I disagree with that 2nd line of thinking he has.... The location in which the GFS/NAM both show the moist tongue has no obs over it, to the west where both models show dry air does...and the OBS just to the north of where that forecast moisture tongue is at certainly has low-mid 60s which will easily be affected northward overnight/through tomorrow.

[andyhb]

I disagree with that 2nd line of thinking he has.... The location in which the GFS/NAM both show the moist tongue has no obs over it, to the west where both models show dry air does...and the OBS just to the north of where that forecast moisture tongue is at certainly has low-mid 60s which will easily be affected northward overnight/through tomorrow.

 

The problem is how far south that cold frontal intrusion earlier in the week sank. It basically cleared the entire Gulf of moisture and now we're looking at a situation where the moisture may return too late for I) lower LCLs and II) a weaker cap. It seems almost every setup this year that has had half decent wind fields ended up having some sort of frontal intrusion in the Gulf a few days before to clean the moisture out.

 

I had more optimism in this department earlier, but now it's not looking very favorable at all.

[JasonOH]

Texas is probably still pretty moist, which should work in our favor with moisture advection. At this point, the dews are in a hole in Obs. I still share the concerns. Dews should max around 65 degrees and I'm modifying forecast soundings accordingly.

[weatherextreme]

The problem is how far south that cold frontal intrusion earlier in the week sank. It basically cleared the entire Gulf of moisture and now we're looking at a situation where the moisture may return too late for I) lower LCLs and II) a weaker cap. It seems almost every setup this year that has had half decent wind fields ended up having some sort of frontal intrusion in the Gulf a few days before to clean the moisture out.

 

I had more optimism in this department earlier, but now it's not looking very favorable at all.

 

 

 

I'm assuming this wouldn't be much of an issue if we were closer to mid/late May.

[andyhb]

I'm assuming this wouldn't be much of an issue if we were closer to mid/late May.

 

Frontal intrusions of this strength are problems at basically any time of year when there's only a couple of days to recover from them.

[jojo762]

The problem is how far south that cold frontal intrusion earlier in the week sank. It basically cleared the entire Gulf of moisture and now we're looking at a situation where the moisture may return too late for I) lower LCLs and II) a weaker cap. It seems almost every setup this year that has had half decent wind fields ended up having some sort of frontal intrusion in the Gulf a few days before to clean the moisture out.

I had more optimism in this department earlier, but now it's not looking very favorable at all.

at all..? Hmm. I'd wait until you can at least see the effects of WAA overnight to say that. Even if moisture does not turn out to be mid 60s, we still have a pretty favorable environment toward sundown at 00Z when SFC temps will lower. When I get home I'll have to modify some soundings to see what a less-moist environment will look like as it relates to LCLs and instability... Gotta remember that the WAA regime is not going to subside much during the day on Sunday too, further, it might just mean that the main threat shifts a little further south than where it current is progged--possibly resulting in a bit less favorable conditions.

This reminds me of something earlier I saw on Twitter about people needing to stop thinking they are smarter than NWP. Not saying that that is you, but just saying if basically all the models are showing impressive moisture advection overnight and over the day, I would not doubt it too much.

[andyhb]

This reminds me of something earlier I saw on Twitter about people needing to stop thinking they are smarter than NWP. Not saying that that is you, but just saying if basically all the models are showing impressive moisture advection overnight and over the day, I would not doubt it too much.

 

But if the NWP is not initializing properly, then that becomes a real issue.

[bjc3395]

at all..? Hmm. I'd wait until you can at least see the effects of WAA overnight to say that. Even if moisture does not turn out to be mid 60s, we still have a pretty favorable environment toward sundown at 00Z when SFC temps will lower. When I get home I'll have to modify some soundings to see what a less-moist environment will look like as it relates to LCLs and instability... Gotta remember that the WAA regime is not going to subside much during the day on Sunday too, further, it might just mean that the main threat shifts a little further south than where it current is progged--possibly resulting in a bit less favorable conditions.

This reminds me of something earlier I saw on Twitter about people needing to stop thinking they are smarter than NWP. Not saying that that is you, but just saying if basically all the models are showing impressive moisture advection overnight and over the day, I would not doubt it too much.

forecasters certainly are smarter than models.

That said, people complaining about moisture right now need to proceed with caution. This time of yeAR and with the low level flow progged, these profiles can change rapidly.

[David Reimer]

17Z experimental HRRR shows impressive WAA tonight with low 60s dewpoints making their way to the Red River by 6 AM tomorrow. A very wet Texas will surely help with moisture transport tonight. The first spring in a while that we haven't had inherent drought issues to complicate moisture return. It'll be impressive to see how quickly moisture spreads north tonight. 

[Msalgado]

I'd agree that dewpoints that are far above 65 aren't likely and their likelihood of them decreases as you move north.  That being said, dewpoints along the red river are already int he mid 50s, and 60+ dewpoints are showing up along the South Texas coast.  This certainly isn't a dire situation regarding tomorrow's setup.  Its probably not ideal, and honestly I do question the placement of the moderate area a bit, but I still think this is the best tornado setup we've seen of the year.

[JasonOH]

This reminds me of something earlier I saw on Twitter about people needing to stop thinking they are smarter than NWP. Not saying that that is you, but just saying if basically all the models are showing impressive moisture advection overnight and over the day, I would not doubt it too much.

There's a reason forecasters exist, NWP isn't perfect. The nam moist bias is well known. The model doesn't know it, but forecasters do. NWP is a tool, not a forecast.

[jojo762]

But if the NWP is not initializing properly, then that becomes a real issue.

66 at RAS, 68 at NQI, 68 at SPL as of 19Z in S TX... The GFS initialized perfectly fine, really look at where those buoy obs are vs. what the GFS shows for those locations, it is the same... Then compare it over S TX where it shows the moist tongue, it is the same. DPs around ~65 are pretty plausible in OK, maybe not much above that, and likely decreasing with northward extent, but they'll be there (in C/W OK) by 00Z.

[jojo762]

There's a reason forecasters exist, NWP isn't perfect. The nam moist bias is well known. The model doesn't know it, but forecasters do. NWP is a tool, not a forecast.

The problem with this is essentially all the models show DPs in the 63-66 range at least. both NAMs overdo moisture-- but that's almost always a given...

Given the degree of WAA overnight and throughout the day tomorrow, it makes perfectly good sense that adequate moisture will be in place, probably not insane, abundant moisture, but that might be a good thing. I'm not trying to support the idea of upper 60s DPs, because those seem out of reach, but at least 63-66, which is adequate.

[andyhb]

Strong couplet SW of Wiggins right now.

The problem with this is essentially all the models show DPs in the 63-66 range at least. both NAMs overdo moisture-- but that's almost always a given...

He mentioned the GFS as well in his post.

[Chicago Storm]

Nice couplet near Wiggins, CO...

[brettjrob]

This reminds me of something earlier I saw on Twitter about people needing to stop thinking they are smarter than NWP. Not saying that that is you, but just saying if basically all the models are showing impressive moisture advection overnight and over the day, I would not doubt it too much.

 

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.

[bjc3395]

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.

[KSWx]

Beautiful inflow notch on that storm.

[jojo762]

Strong couplet SW of Wiggins right now.

He mentioned the GFS as well in his post.

yes he did. Just whatever... You'll see tomorrow at 00Z when there are DPs of 63-66 across OK like the GFS shows. Won't be amazing in the morning at 12Z, but a lot of the moist advection into the target area is going to occur during the day. Literally let one long post change your line of thinking. The obs that those buoys show are the exact same that the GFS shows. There are absolutely no bouys underneath the moist tongue in the far western gulf that all the models show... and on the northern periphery of the progged moisture tongue, where we actually have obs sites at, we are seeing upper sixties DPs.

[Derecho!]

forecasters certainly are smarter than models.

 

 

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. 

[andyhb]

yes he did. Just whatever... You'll see tomorrow at 00Z when there are DPs of 63-66 across OK like the GFS shows. Won't be amazing in the morning at 12Z, but a lot of the moist advection into the target area is going to occur during the day. Literally let one long post change your line of thinking. The obs that those buoys show are the exact same that the GFS shows. There are absolutely no bouys underneath the moist tongue in the far western gulf that all the models show... and on the northern periphery of the progged moisture tongue, where we actually have obs sites at, we are seeing upper sixties DPs.

 

What are you trying to prove here with this kind of rhetoric? You asked me before where you were making posts like this almost dumbfounded and yet here we are again. Relax.

[Disc]

[bjc3395]

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.

You have no idea what you're talking about then.

[bjc3395]

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.

You have no idea what you're talking about then.