Severe threat april 14, Tornado outbreak possible

[JoMo]

The 12z NAM continues to show a favorable setup in Eastern KS and Oklahoma on Thursday.

yeah the NAM is really keeping the winds backed. Looks to be a bit slower as well.

[SEMIweather]

yeah the NAM is really keeping the winds backed. Looks to be a bit slower as well.

Yes it's definitely a bit slower. Also keeps LCLs lower than 1500m (in some cases lower than 1000m) which certainly helps the threat even more. Looks to break the cap between 21z and 00z which would allow for plenty of destabilization before stuff fires.

[brettjrob]

NAM is showing classic full self development cyclogenesis with some Shapiro-Keyser type development and a potential sting jet. NAM verbatim is mixing down 70+ knots in parts of western Colorado. I mentioned it in the winter thread too--storms like this with a potentially deep tropofold and an overall slow moving but rapidly deepening cyclone owing to the intense moist latent heat effects/self development are the NAM's bread and butter with its non-hydro package mesoscale model traits. I disagree with Brett-jrob-I don't see this potentially speeding up significantly but stalling owing to the type of cyclogenesis. Not booking anything though--and I am cautious like Brettjrob--but for different reasons. If anything the weak scenarios would potentially be more GFS like--but still ominous. NAM would be a potential significant event. These bombing lows can't be overlooked for severe threats--they almost always are more impressive than the severe parameters may suggest.

Good discussion. I was just referencing some of the model biases I've observed in this area so far this year, without regard to the specifics of this system, and making a general complaint about the poor chase offerings so far. My rants are rarely to be taken too seriously, lol. In fact, I see the 12z NAM is slightly slower yet, so it's beginning to look like even a faster-than-verbatim solution would be somewhat ominous.

I dare say the H5 map on the NAM now looks more similar to May 10, 2010, than to May 10, 2008. With low-level moisture in a whole different league and low-level flow unlikely to exceed half the intensity of that event, I don't expect comparable results, but it does seem possible a similar area could ultimately be affected. Really interested in NE OK into SE KS close to the deepening surface low.

[Jim Martin]

The GFS is now showing a 996 mb low over northeast Kansas at 7 pm cdt Thursday evening.

[baroclinic_instability]

The 12Z GFS is some sort of freak show. Positive feedback self development shows the massive changes possible run by run.

[baroclinic_instability]

Good discussion. I was just referencing some of the model biases I've observed in this area so far this year, without regard to the specifics of this system, and making a general complaint about the poor chase offerings so far. My rants are rarely to be taken too seriously, lol. In fact, I see the 12z NAM is slightly slower yet, so it's beginning to look like even a faster-than-verbatim solution would be somewhat ominous.

I dare say the H5 map on the NAM now looks more similar to May 10, 2010, than to May 10, 2008. With low-level moisture in a whole different league and low-level flow unlikely to exceed half the intensity of that event, I don't expect comparable results, but it does seem possible a similar area could ultimately be affected. Really interested in NE OK into SE KS close to the deepening surface low.

Ah no worries--I wasn't being critical just difference of opinion. Nobody honestly knows at this juncture--but wow at the 12Z GFS bomb. I will have to glance at the May 10 2010 maps when I get home. What are your thoughts for severe potential?

[JoMo]

May 10th 2010

May 10th 2008

[JoMo]

I'm not sure how quickly the Gulf can recharge though. Looking at some readings, Houston has a dewpoint in the 30's at this time. Even a couple 40 degree readings in the Gulf itself.

[CUmet]

I absolutely love this type of trough, as this has been associated with major outbreaks in the past as others have alluded to (5/10/10 and 5/10/08). This flat type of trough usually is associated with great directional shear in the warm sector, shear vectors oriented perpendicular to the initiating boundary, and colder mid-level temps. Given that the instability is substantially less than those events, I wouldn't expect a major tornado outbreak quite on that level, but the moisture is still decent given the cool mid-level temperatures. I think this will probably be MDT risk worthy on day 1, and is somewhat of a sleeper setup.

[Thundersnow12]

[Ed Lizard]

I'm not sure how quickly the Gulf can recharge though. Looking at some readings, Houston has a dewpoint in the 30's at this time. Even a couple 40 degree readings in the Gulf itself.

53ºF DP at the databuoy just East of GLS, and that is still with a Northeast wind. Upper 50s to as high as 61ºF around BRO and SPI.

[JoMo]

Looks like the Euro is back in line with the other guidance regarding track. It was farther south on the 00z run.

[baroclinic_instability]

I just had a OMG moment when I saw the 12Z Euro. What an IPV bomb.

[JoMo]

I just had a OMG moment when I saw the 12Z Euro. What an IPV bomb.

Look really severe or does it wrap up really fast and squall line it all out?

[SEMIweather]

Look really severe or does it wrap up really fast and squall line it all out?

I'll admit I have no clue how to tell whether or not the ECMWF is supporting supercells or a squall line but surface winds are backed at 00z Friday and there's 2000-3000 J/kg of CAPE in Eastern OK and SE Kansas.

[baroclinic_instability]

Look really severe or does it wrap up really fast and squall line it all out?

I don't see a major threat for a squall line with this--at least not early on. The moderately curved hodographs near the front as well as strong low level helicity values would be indicative of potentially semi discrete and large supercells even in the presence of not so impressive CAPE values. The SW flow aloft and strongly backed low level wind fields owing to the rapid height falls as the storms turn NE would suggest potential for large dominant right movers as they move into a low level vorticity rich environment with somewhat low LCL's. I don't know if there has been studies or something--but I can't stress it enough--these tanking lows almost always support rather large and at least semi discrete dominant supercells and are often under-estimated events if one looks at severe parameters alone. These non-linear synoptic bombing events--just as they can create extreme winter weather--seem to support the development of extreme convection in the form of very well developed supercells. The jet pattern aloft and associated jet circulation are highly favorable. I would be interested in what Tony and the other severe guys think.

[Ed Lizard]

Euro at 0Z Friday (Thursday evening) has 55ºF dews to about St. Jo, 60ºF dews East of I-35 as far North as Wichita.

Forecast skew-T for 36.7ºN, 96ºW, just East of precip, LFC about 790mb, LCL about 900 mb, -60 J/Kg inhibition, 1800 J/Kg CAPE, TT of 57, near surface winds 15 knots from SSE, 850 mb winds SSW at 50 knots. Almost 460 m^2/s^2 helicity.

From the AccuWx PPV Euro. Picking a skew-T ahead of the precip, near the KS/OK line.

[baroclinic_instability]

The 18Z NAM continues the trend towards a synoptic bomb of which I have never seen. Truly impressive storm system--and I think this thing will be catching folks by surprise since it seemingly isn't making much noise anywhere. Whether we are talking the potential 60-80 mph wind gust potential, blizzard potential, or significant outbreak of severe weather--I am not fathoming what I am seeing in terms of potential with this storm. Even the weaker scenarios are absolutely ridiculous solutions.

[JoMo]

The 18Z NAM continues the trend towards a synoptic bomb of which I have never seen. Truly impressive storm system--and I think this thing will be catching folks by surprise since it seemingly isn't making much noise anywhere. Whether we are talking the potential 60-80 mph wind gust potential, blizzard potential, or significant outbreak of severe weather--I am not fathoming what I am seeing in terms of potential with this storm. Even the weaker scenarios are absolutely ridiculous solutions.

yeah from the TX/OK border up to the KS/NE border it pops storms after 21z Thurs. A couple points plotted right ahead of the storms show long looping hodographs.

Still a question of quality moisture return though.

[baroclinic_instability]

yeah from the TX/OK border up to the KS/NE border it pops storms after 21z Thurs. A couple points plotted right ahead of the storms show long looping hodographs.

Still a question of quality moisture return though.

I don't think moisture return will have any issues whatsoever. We are talking over 2.5 days of relatively strong cross barrier Rocky mtn flow and subsequent lee troughing. I have seen 1 day returns from the GOM to the northern plains with big winter storms. I don't see it being an issue here at all.

[huronicane]

That was a very interesting article, thanks for sharing.

http://www.weather.gov/os/assessments/pdfs/mothers_day09.pdf

The actual service assessment.

_______________________________

Hodographs look good across E. OK/E. KS for 00z 15 Apr. I like the divergence over the area Thursday afternoon, looks like it could be a pretty good day.

[Superstorm93]

18z NAM is looking quite volatile.

00z Friday:

[tornadotony]

This setup is actually reminiscent of one of the Virtual Chase Cases...and yes I know I have been derelict on those...

[JoMo]

http://www.weather.g...thers_day09.pdf

The actual service assessment.

_______________________________

Hodographs look good across E. OK/E. KS for 00z 15 Apr. I like the divergence over the area Thursday afternoon, looks like it could be a pretty good day.

Nice, I'll have to read the actual report while my BBQ chicken cooks on the grill. Thanks for finding that.

[huronicane]

Nice, I'll have to read the actual report while my BBQ chicken cooks on the grill. Thanks for finding that.

You got it. I like reading the assessments, because they usually give me a thing or two that I can put into practice in my own dealings with severe weather.

[brettjrob]

Like baro, I'm fairly surprised by how little the severe aspect of this system is being discussed elsewhere. The 18z NAM continues the trend toward a slower solution, and the H5 pattern is quickly beginning to look like a classic SE KS/SW MO/NE OK outbreak scenario. The main limiting factor I see is the quality of low-level moisture. I feel like this could be on par with some of the bigger events in that region from the past decade if only it was early May and we had rich low-level moisture, but even as-is, a significant supercell event with a substantial tornado threat remains possible.

[OceanStWx]

I don't see a major threat for a squall line with this--at least not early on. The moderately curved hodographs near the front as well as strong low level helicity values would be indicative of potentially semi discrete and large supercells even in the presence of not so impressive CAPE values. The SW flow aloft and strongly backed low level wind fields owing to the rapid height falls as the storms turn NE would suggest potential for large dominant right movers as they move into a low level vorticity rich environment with somewhat low LCL's. I don't know if there has been studies or something--but I can't stress it enough--these tanking lows almost always support rather large and at least semi discrete dominant supercells and are often under-estimated events if one looks at severe parameters alone. These non-linear synoptic bombing events--just as they can create extreme winter weather--seem to support the development of extreme convection in the form of very well developed supercells. The jet pattern aloft and associated jet circulation are highly favorable. I would be interested in what Tony and the other severe guys think.

Shear vectors perpendicular to the initiating boundary would suggest discrete cells as well.

[tornadotony]

I'll believe this all when I see it. Model performance has been exceptionally abysmal this spring.

[baroclinic_instability]

Like baro, I'm fairly surprised by how little the severe aspect of this system is being discussed elsewhere. The 18z NAM continues the trend toward a slower solution, and the H5 pattern is quickly beginning to look like a classic SE KS/SW MO/NE OK outbreak scenario. The main limiting factor I see is the quality of low-level moisture. I feel like this could be on par with some of the bigger events in that region from the past decade if only it was early May and we had rich low-level moisture, but even as-is, a significant supercell event with a substantial tornado threat remains possible.

Yeah the low dew points are not impressive--but I guess you can't get both (a bombing PV Anomaly and high dew points together--at least it is highly unlikely).

[CUmet]

I don't see a major threat for a squall line with this--at least not early on. The moderately curved hodographs near the front as well as strong low level helicity values would be indicative of potentially semi discrete and large supercells even in the presence of not so impressive CAPE values. The SW flow aloft and strongly backed low level wind fields owing to the rapid height falls as the storms turn NE would suggest potential for large dominant right movers as they move into a low level vorticity rich environment with somewhat low LCL's. I don't know if there has been studies or something--but I can't stress it enough--these tanking lows almost always support rather large and at least semi discrete dominant supercells and are often under-estimated events if one looks at severe parameters alone. These non-linear synoptic bombing events--just as they can create extreme winter weather--seem to support the development of extreme convection in the form of very well developed supercells. The jet pattern aloft and associated jet circulation are highly favorable. I would be interested in what Tony and the other severe guys think.

This is an interesting topic to think about. To put it succinctly, from my experience, the intensification rate of the surface low is pretty irrelevant to the severity of the severe weather/tornado outbreak, and it's something that I rarely take into consideration. The main thing I look at (in forecast mode) is if there's superposition of parameters (CAPE, 0-6 km shear, helicity, etc.) over a large enough region. Obviously it's more complicated than that...there's the cap strength, mesoscale boundaries, storm mode, etc, but generally speaking you can get this superposition irrespective of whether the system is intensifying or not. I can name several examples of systems that were filling in at the time of the outbreak off the top of my head: 4/10/09, 3/15/08, even the Super Outbreak I believe featured a steady-state surface low. One could even make the argument that a rapidly deepening low is a bad sign because there's too much forcing, although this would have to be evaluated on a case-by-case basis.

Now, if you were to take all the major outbreaks and analyze the min SLP tendency of the low during the outbreak, I would guess that you'd find that on average, the low was intensifying at the time. However, this probably has more to do with the cyclogenesis maximum in the lee of the Rockies, and/or the fact that most major tornado outbreaks are associated with large synoptic scale troughs that generate significant surface cyclones (although most don't bomb out).

My philosophy is best illustrated in this particular case as: I'm pretty impressed with this setup overall, but it isn't because of the bombing of the low per se, however meteorologically-impressive it is.