January 28-30 Severe threat. S Plains to TN valley to SE

[tornadotony]

It did at 96hr, then 120hr came out and it was pretty much wtf.

?  It has a secondary sfc low.  To me, this is even scarier than the 00z GFS, and that's scary enough.  You're putting a 1000mb sfc low right next to a 60-75kt LLJ and probably 65 degree dewpoints.

[Stebo]

?  It has a secondary sfc low.  To me, this is even scarier than the 00z GFS, and that's scary enough.  You're putting a 1000mb sfc low right next to a 60-75kt LLJ and probably 65 degree dewpoints.

 

Well I would agree there, though I think the low is too far South and East personally. I don't like the look of the trough lagging behind that much.

[tornadotony]

Well I would agree there, though I think the low is too far South and East personally. I don't like the look of the trough lagging behind that much.

No, it's not.  Plenty of SE US outbreaks have occurred with positive-tilt troughs such as the one on the 00z Euro.  I still think we're more likely to see a GFS-style solution, but the Euro is certainly onboard now for significant severe weather.

[Hoosier]

Probably doesn't pay to dissect the 00z Euro too much. Given the moves it has made over the past few runs and where the majority of the other guidance is right now, I wouldn't be surprised to see it take another step on the next run.

[Stebo]

No, it's not.  Plenty of SE US outbreaks have occurred with positive-tilt troughs such as the one on the 00z Euro.  I still think we're more likely to see a GFS-style solution, but the Euro is certainly onboard now for significant severe weather.

 

Yeah I am not discounting it as being a bad run, and I do like that it has jumped significantly toward the GFS.

[Stebo]

Probably doesn't pay to dissect the 00z Euro too much. Given the moves it has made over the past few runs and where the majority of the other guidance is right now, I wouldn't be surprised to see it take another step on the next run.

 

Correct, you can only micro analyze this run so much, the fact it has moved toward other guidance is significant.

[CUmet]

Given that quality moisture is guaranteed to be in place for the warm sector (set up by days of low-level trajectories from the Caribbean), and also the strong jet dynamics in play, this event has a very high ceiling IMO.  The latest 00z ECMWF trending towards the GFS/UKMET solution of ejecting the vort max around the base of the large-scale trough, instead of cutting it off in the SW US, is concerning.  I would wait another few model cycles to see whether this is legit, but the odds of some sort of significant severe event Tuesday-Wednesday appear to be increasing.

[andyhb]

Good to have you aboard.

 

I have strong suspicion the new D4-8 will reintroduce the D4 for Tuesday and possibly even add a D5 for Wednesday considering tonight's model runs.

[Stebo]

Good to have you aboard.

 

I have strong suspicion the new D4-8 will reintroduce the D4 for Tuesday and possibly even add a D5 for Wednesday considering tonight's model runs.

 

Correct

 

 

ZCZC SPCSWOD48 ALL   ACUS48 KWNS 260925   SPC AC 260925      DAY 4-8 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0325 AM CST SAT JAN 26 2013      VALID 291200Z - 031200Z      ...DISCUSSION...   LATEST SUITE OF MODEL GUIDANCE PRESENTS A BETTER GENERAL CONSENSUS   IN THE FORECAST EVOLUTION OF THE LARGE SCALE PATTERN ACROSS THE   CONUS INTO THE MIDDLE OF NEXT WEEK...ESPECIALLY WHEN COMPARED TO   THIS TIME YESTERDAY. WHILE THERE REMAIN DIFFERENCES IN THE   CONFIGURATIONS AND MAGNITUDES OF THE VARIOUS FLOW FIELDS AND   PARAMETERS...ANALYSIS OF THE GFS/ECMWF/UKMET/CMC/GFS ENSEMBLE AND   DPROG/DT LOOPS LEND SUFFICIENT SUPPORT FOR THE REINTRODUCTION OF A   SEVERE WEATHER FORECAST...NOW VALID FOR D4/TUESDAY...WITH A   CONTINUING THREAT INTO AT LEAST PART OF D5/WEDNESDAY.      AS INDICATED IN THE D3 OTLK...A WARM MOIST BOUNDARY LAYER IS   EXPECTED TO RESIDE ACROSS THE SCNTRL U.S. AHEAD OF A STRENGTHENING   LARGE SCALE TROUGH AND ASSOCIATED DEVELOPING COLD FRONT. WHILE ECMWF   CONTINUES TO FORECAST A SLIGHTLY SLOWER AND LESS FULLY-PHASED UPPER   TROUGH WHEN COMPARED WITH GFS/UKMET MODELS...EVEN IT COMES AROUND TO   FORECASTING AN AMPLIFIED AND SUBSTANTIALLY PHASED LARGE SCALE UPPER   TROUGH ACROSS THE SCNTRL AND ERN U.S. BEGINNING D4/TUESDAY AND   CONTINUING THROUGH D5/WEDNESDAY. THIS PROCESS WILL CONTRIBUTE TO A   RAPID ONSET OF DEEP-LAYER ASCENT AND SUBSEQUENT TSTM DEVELOPMENT   ALONG AND AHEAD OF A SHARPENING COLD FRONT THAT WILL SWEEP EWD/SEWD   ACROSS THE CNTRL/SRN PLAINS DURING THE DAY TUESDAY...AND THEN TO THE   TN VALLEY/NRN GULF COAST AND SOUTHEAST THROUGH WEDNESDAY. SHEAR AND   INSTABILITY AS CURRENTLY FORECAST WILL PROMOTE ORGANIZED STORMS IN   EITHER SUPERCELL OR LINEAR FORMS FROM NORTHEAST TX ACROSS THE   ARKLATEX TO SERN MO/WRN TN. SQUALL LINE OR LINE SEGMENT EVOLUTION   SHOULD BECOME MORE LIKELY WITH TIME AS COLD FRONT/CONVECTIVE COLD   POOLS FURTHER INTENSIFY AMIDST MODEST INSTABILITY. DAMAGING   WINDS...POSSIBLY WIDESPREAD...WILL BE THE GREATEST HAZARD WITH THIS   CONVECTION. HOWEVER...LOW LEVEL SHEAR WILL BE STRONG ENOUGH FOR   TORNADOES AS WELL.      EXPECT THE STRONG FORCING AND SHEAR TO MAINTAIN A QLSC WITH DAMAGING   WIND POTENTIAL AT LEAST INTO THE TN VALLEY THROUGH EARLY   WEDNESDAY/D5. BEYOND THIS TIME...GREATER MODEL SPREAD AND RESULTING   UNCERTAINTY BEGIN TO IMPACT FORECAST CONFIDENCE IN SEVERE WEATHER.   HAVE OPTED TO RELY ON GFS ENSEMBLE JOINT PROBABILITY FORECASTS FOR   INSTABILITY AND SHEAR THROUGH LATE WEDNESDAY. THESE PRODUCTS SUGGEST   THAT SEVERE WEATHER POTENTIAL WILL BE MUCH MORE UNCERTAIN WITH EWD   EXTENT DESPITE STRONG QPF AND UVV SIGNALS ALONG THE ADVANCING FRONT   TO THE EAST COAST. PORTIONS OF THE SOUTHEAST MAY BE ADDED IN LATER   OUTLOOKS IF MODEL CONSENSUS IMPROVES.

[andyhb]

Great discussion from Carbin there.

[Ground Scouring]

Well, the outlook has certainly changed since I last posted, but I still see issues with the set-up. First, the 700-mb vector by 12Z on 01/30 does not favor a very strong dry punch preceding the arrival of the trough over the warm sector. Given the very high PWAT return that is to be expected, I have a feeling that the GFS is underestimating morning convection over E TX / W AR / W LA preceding the arrival of the cold front later in the afternoon. This would slow the northward retreat of the warm front but more importantly cut instability before afternoon. While deep-layer shear will certainly be strong, the positive tilt of the trough should keep the highest 0-2 km SRH northwest of the juiciest areas in the warm sector. Given the possibility of less-than-adequate instability and possibly lower dew points north of S AR / NE LA / W MS, the likelihood is that the advent of afternoon supercell activity will be delayed until much stronger, more linear forcing arrives in the late afternoon, essentially resulting in a bowing QLCS / squall line with very damaging winds rather than tornadoes. Some of the CIPS analogs like 02/20/2002 and 03/10/1992 strongly suggest more of a wind than a tornado threat. Given the elongation of the surface low plus the limited instability, the tornado threat that might be expected to materialize with higher instability would not likely occur this time. Still, the damaging-wind threat bears strong watching, plus the potential for very heavy rainfall across much of the MS Valley and even the southern Appalachians.

[andyhb]

Well...

I) There is plenty in terms of low level shear in the warm sector, both speed and directional, on the GFS. I really don't think that is an issue.

II) WRT CIPS, there are also several events over the past few runs that have suggested a significant tornado threat as well, both with discrete cells ahead of the line, and in the QLCS.

III) Adjusting thermos for more realistic environmental temps, even with cloud cover, yields more instability than the, say, GFS, is outputting.

IV) There have been several events, particularly in the Ozarks/Mid South region, that have featured more elongated sfc lows like this. Obviously not saying an event of this caliber will happen, but 2/5/08 was one of them IIRC.

[brettjrob]

The 12z GFS is strikingly similar to Super Tuesday in some ways, andy. For some reason I recalled that event having a more robust sfc low, but I double-checked the Mesoanalysis archive and there was only a closed 1000 mb contour for a couple hours during the afternoon. Sfc winds were not particularly backed over most of the warm sector. Instability was in the ballpark of what one could expect after removing the GFS low/cool bias.

 

The 12z Euro doesn't look all that different, now, with a sizable threat centered over the Ozarks.

[andyhb]

The 12z GFS is strikingly similar to Super Tuesday in some ways, andy. For some reason I recalled that event having a more robust sfc low, but I double-checked the Mesoanalysis archive and there was only a closed 1000 mb contour for a couple hours during the afternoon.

 

Yeah, the sfc pressure envelope was actually smaller with the 2/5/08 event by the time the event was really getting going than what is being progged on the 12z GFS.

[tornadotony]

The 12z GFS is strikingly similar to Super Tuesday in some ways, andy. For some reason I recalled that event having a more robust sfc low, but I double-checked the Mesoanalysis archive and there was only a closed 1000 mb contour for a couple hours during the afternoon. Sfc winds were not particularly backed over most of the warm sector. Instability was in the ballpark of what one could expect after removing the GFS low/cool bias.

 

The 12z Euro doesn't look all that different, now, with a sizable threat centered over the Ozarks.

One of the things that strikes me about this upcoming threat, when comparing it to Super Tuesday, is that the moisture progged may actually be even better with this storm.

[OKpowdah]

So obviously one of the things that's changed since I started this thread 8 days ago is the "IMPORTANT" part (lol) regarding the persistence of confluence off to the northeast

[CUmet]

One of the things that strikes me about this upcoming threat, when comparing it to Super Tuesday, is that the moisture progged may actually be even better with this storm.

Granted, the mid-level temperature profiles were better on Super Tuesday, and I think there may be more potential issues with early convective initiation with this event.  Also, there's the possibility that the upper level winds might become too backed if the trough is too amplified...it looks fine the way it's progged now (comparable to Super Tuesday), but we still have another 3 days to go.  Super Tuesday is about where I would put the ceiling on this event, but I think it's pretty unlikely at the moment that the upcoming event will reach that ceiling.

[Minnesota Meso]

I'm surprised as how quite this sub forum is, the severe threat may be just east of this area, but still I would have expected some chatter here.

[David Reimer]

I'm surprised as how quite this sub forum is, the severe threat may be just east of this area, but still I would have expected some chatter here.

Model uncertainty plus the first event in a while makes it quieter. Assuming a higher end threat does develop, I'd expect activity to increase.

[Ground Scouring]

Granted, the mid-level temperature profiles were better on Super Tuesday, and I think there may be more potential issues with early convective initiation with this event. Also, there's the possibility that the upper level winds might become too backed if the trough is too amplified...it looks fine the way it's progged now (comparable to Super Tuesday), but we still have another 3 days to go. Super Tuesday is about where I would put the ceiling on this event, but I think it's pretty unlikely at the moment that the upcoming event will reach that ceiling.

In light of the comparisons to 02/05/2008, the 18Z GFS, interestingly--like its 12Z predecessor--indicates that the best chance for a few significant tornadoes would be almost entirely centered over central and E AR around early afternoon 01/29. However, thermodynamics are less favorable to the east and linear forcing quickly takes over after 18Z that day. I think this event is to be much more limited in extent and duration than 02/05/2008 and might feature a few tornadoes--possibly strong, I will concede--but then quickly transform into a bowing QLCS. I know some people have mentioned strong tornadoes within the QLCS, but the projected wind fields on soundings after 18Z 01/29 do not seem to overtly suggest this, at least compared to other past QLCS events with embedded significant tornadoes. Plus, the trough is not as broad-based as I would like to see before making any comparison to 02/05/2008 in terms of the "ceiling"/potential, so the likely moisture return would not substantially affect the ultimate evolution of convection.

[Stebo]

In light of the comparisons to 02/05/2008, the 18Z GFS, interestingly--like its 12Z predecessor--indicates that the best chance for a few significant tornadoes would be almost entirely centered over central and E AR around early afternoon 01/29. However, thermodynamics are less favorable to the east and linear forcing quickly takes over after 18Z that day. I think this event is to be much more limited in extent and duration than 02/05/2008 and might feature a few tornadoes--possibly strong, I will concede--but then quickly transform into a bowing QLCS. I know some people have mentioned strong tornadoes within the QLCS, but the projected wind fields on soundings after 18Z 01/29 do not seem to overtly suggest this, at least compared to other past QLCS events with embedded significant tornadoes. Plus, the trough is not as broad-based as I would like to see before making any comparison to 02/05/2008 in terms of the "ceiling"/potential, so the likely moisture return would not substantially affect the ultimate evolution of convection.

Are you basing the thermodynamics purely upon what the GFS currently shows? Because I would say that the GFS is still underdoing the temps across the region by as much as 7 degrees, that would have a substantial impact on the instability going forward. If you modify closer to the high temperatures that the local NWS offices are putting out for Tuesday across the region you'll find the instability will double or even triple in magnitude.

[tornadotony]

In light of the comparisons to 02/05/2008, the 18Z GFS, interestingly--like its 12Z predecessor--indicates that the best chance for a few significant tornadoes would be almost entirely centered over central and E AR around early afternoon 01/29. However, thermodynamics are less favorable to the east and linear forcing quickly takes over after 18Z that day. I think this event is to be much more limited in extent and duration than 02/05/2008 and might feature a few tornadoes--possibly strong, I will concede--but then quickly transform into a bowing QLCS. I know some people have mentioned strong tornadoes within the QLCS, but the projected wind fields on soundings after 18Z 01/29 do not seem to overtly suggest this, at least compared to other past QLCS events with embedded significant tornadoes. Plus, the trough is not as broad-based as I would like to see before making any comparison to 02/05/2008 in terms of the "ceiling"/potential, so the likely moisture return would not substantially affect the ultimate evolution of convection.

With enormous SRH and 0-6km bulk shear vectors roughly 45 degrees (or a little more) from the likely QLCS orientation, the wind profiles would be highly supportive of numerous tornadoes, some potentially significant, with the QLCS.  Also, the amplitude and wavelength of this trough is very similar to Super Tuesday and I don't see how anyone can make a legitimate argument against that.  The orientation is slightly different, with the Super Tuesday trough deepening and becoming a bit more negatively tilted faster than is what is progged by the model output with this trough.  But at this stage of the game prior to Super Tuesday, the models were indicating the same thing.  It wasn't until 24-36h before the outbreak that the models swung around more to a slightly more negative tilt.  The thermodynamics of this setup are very unclear.  I have a feeling some of the thermodynamic shortcomings may be more linked to convection being depicted as too widespread on the GFS, largely due to its resolution.  We can't make too many judgements about thermos at this time, though I echo CUmet's sentiments that there may be a few issues with early convective initiation, although I don't know how much that caps the ceiling of events in the midsouth and southeast.  To me, it seems that it doesn't have the same effects that early initiation has on the Plains or in the Midwest.

 

The bottom line of all this is the following.  It would be foolish at this stage in the game to call for this to be something along the lines of Super Tuesday.  That outbreak, in terms of overall severity and breadth, is THE benchmark, IMO, for wintertime tornado outbreaks (an argument can be made in the breadth category for 1/21/99, but overall, Super Tuesday is #1 on record combining breadth and severity).  I personally don't find it very wise to forecast benchmark events at this range.  If things were to stay the same, I would guess that this event would likely fall short of Super Tuesday.  But many of the players have yet to reveal themselves clearly, and discounting the outside possibility of an event of that caliber is not quite the way to go either.  If I had to go out on a limb, I'd say a moderate tornado outbreak is likely, with a handful of strong tornadoes and at least some potential for it to be a major tornado outbreak depending on exactly how the thermodynamics and the mesoscale evolve.

[Ground Scouring]

With enormous SRH and 0-6km bulk shear vectors roughly 45 degrees (or a little more) from the likely QLCS orientation, the wind profiles would be highly supportive of numerous tornadoes, some potentially significant, with the QLCS. Also, the amplitude and wavelength of this trough is very similar to Super Tuesday and I don't see how anyone can make a legitimate argument against that. The orientation is slightly different, with the Super Tuesday trough deepening and becoming a bit more negatively tilted faster than is what is progged by the model output with this trough. But at this stage of the game prior to Super Tuesday, the models were indicating the same thing. It wasn't until 24-36h before the outbreak that the models swung around more to a slightly more negative tilt. The thermodynamics of this setup are very unclear. I have a feeling some of the thermodynamic shortcomings may be more linked to convection being depicted as too widespread on the GFS, largely due to its resolution. We can't make too many judgements about thermos at this time, though I echo CUmet's sentiments that there may be a few issues with early convective initiation, although I don't know how much that caps the ceiling of events in the midsouth and southeast. To me, it seems that it doesn't have the same effects that early initiation has on the Plains or in the Midwest.

The bottom line of all this is the following. It would be foolish at this stage in the game to call for this to be something along the lines of Super Tuesday. That outbreak, in terms of overall severity and breadth, is THE benchmark, IMO, for wintertime tornado outbreaks (an argument can be made in the breadth category for 1/21/99, but overall, Super Tuesday is #1 on record combining breadth and severity). I personally don't find it very wise to forecast benchmark events at this range. If things were to stay the same, I would guess that this event would likely fall short of Super Tuesday. But many of the players have yet to reveal themselves clearly, and discounting the outside possibility of an event of that caliber is not quite the way to go either. If I had to go out on a limb, I'd say a moderate tornado outbreak is likely, with a handful of strong tornadoes and at least some potential for it to be a major tornado outbreak depending on exactly how the thermodynamics and the mesoscale evolve.

Thanks for this discussion, Tony. Though my thoughts differ a bit from yours, mainly in the bolded, I cannot disagree with the reasoning underlying any of these points.

One ominous thing that I will note is that the 18Z GFS--significantly, in comparison to its 18Z predecessor yesterday and in contrast to the 00Z and 12Z runs--now shows a rather deep (995-mb) secondary surface low forming just SE of the Quad Cities beginning around 20Z on 01/29. This low substantially backs the low-level wind profile on the run and concomitantly serves to extend the northward portion of the warm sector as far north as KGCI-PAH-KCKV. If this were to come to fruition in succeeding model cycles--though few of the 12Z GFS ensembles even hinted at this--then my expectations for this event would be revised upward.

[thewxmann]

I can't really be sure of any type of outcome for this event until the models converge on a solution. However if I had a pick an outcome right now I'd guess something similar to the Christmas event in terms of severity and scale -- or a little less.

[Hoosier]

Outside of this subforum but anyone see the barbaric 100 kt 850 mb winds on the GFS at 78 hours?

[andyhb]

Outside of this subforum but anyone see the barbaric 100 kt 850 mb winds on the GFS at 78 hours?

 

Just saw that, crazy stuff.

[tornadotony]

I can't really be sure of any type of outcome for this event until the models converge on a solution. However if I had a pick an outcome right now I'd guess something similar to the Christmas event in terms of severity and scale -- or a little less.

Based off of what?  This is such a radically different setup from Christmas that I can't envision a way that the scope/scale of almost any outcome from this system is as limited or more limited than Christmas.  We can argue back and forth on severity, but I think scale is in the bag for this system.

[Stebo]

Thanks for this discussion, Tony. Though my thoughts differ a bit from yours, mainly in the bolded, I cannot disagree with the reasoning underlying any of these points.

One ominous thing that I will note is that the 18Z GFS--significantly, in comparison to its 18Z predecessor yesterday and in contrast to the 00Z and 12Z runs--now shows a rather deep (995-mb) secondary surface low forming just SE of the Quad Cities beginning around 20Z on 01/29. This low substantially backs the low-level wind profile on the run and concomitantly serves to extend the northward portion of the warm sector as far north as KGCI-PAH-KCKV. If this were to come to fruition in succeeding model cycles--though few of the 12Z GFS ensembles even hinted at this--then my expectations for this event would be revised upward.

The 00z continued the theme of the surface winds backing slightly ahead of the front at 00z Wednesday.

[tornadotony]

The 00z continued the theme of the surface winds backing slightly ahead of the front at 00z Wednesday.

The 00z GFS has shear profiles that would make major tornado outbreaks of the past blush.

 

We're learning more and more that, especially in the south/southeast, CAPE/instability is more of a game of thresholds.  Once a certain threshold is reached (whatever is needed to form/sustain sfc or near-sfc-based convection for a given forcing and shear profile), the amount of instability doesn't matter much beyond that point.  Given that we're going to have plenty of forcing with this system and dewpoints sky-high for late January, it seems unlikely that we won't have sufficient instability to maintain updrafts.  At that point, the low-level shear takes over, and the 00z GFS becomes a very scary prospect.

[Stebo]

The 00z GFS has shear profiles that would make major tornado outbreaks of the past blush.

 

We're learning more and more that, especially in the south/southeast, CAPE/instability is more of a game of thresholds.  Once a certain threshold is reached (whatever is needed to form/sustain sfc or near-sfc-based convection for a given forcing and shear profile), the amount of instability doesn't matter much beyond that point.  Given that we're going to have plenty of forcing with this system and dewpoints sky-high for late January, it seems unlikely that we won't have sufficient instability to maintain updrafts.  At that point, the low-level shear takes over, and the 00z GFS becomes a very scary prospect.

 

Completely agree with all of this, honestly I think SBCAPE around 500-750 J/kg will get things going in a big way, and realistically if we were to modify soundings closer to the forecast highs for the region vs what the GFS is pumping out, we are probably looking at over 1000 J/kg SBCAPE.