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

[brettjrob]

From the 27/00z GFS. Just for posterity:

 

 

 

It goes without saying that temperatures, and therefore instability, are likely underdone. I agree with Tony regarding the "threshold" idea. Realistically, that threshold is IMO probably somewhere in the neighborhood of 750-1000 J/kg, at least if we're talking about long-track tornadoes from discrete supercells. If for whatever reason (most likely widespread early initiation) instability falls short of that range as the GFS is showing, then the ceiling for the event obviously will not be approached. But to focus on the literal CAPE values printed out by that model at this range is to ignore history completely.

 

Just as a rough comparison with Super Tuesday, I looked at the observed 00z KLZK sounding that day vs. the above KMEM forecast sounding. H5 temperatures are very similar, while the H3 temperature is a couple degrees warmer on the GFS. The surface dew points are about the same, but unsurprisingly, the actual temperature on Super Tuesday was ~3 C warmer. To me, the takeaway is that when accounting for the typical cool BL bias in the GFS, I'd expect a relatively similar thermodynamic profile to Super Tuesday should the GFS verify in a synoptic sense. CAPE could be somewhat lower due to poor lapse rates aloft, though. Verification at KLZK from Super Tuesday was 1850 J/kg.

 

I will say the NAM does not impress me much, if taken verbatim. Low-level winds are far weaker and more veered. A dProg/dT over the past 24 hrs reveals a rapid trend toward the GFS in terms of the trough evolution, so it may be a moot point soon.

[tornadotony]

From the 27/00z GFS. Just for posterity:

 

kmem_h72.png

 

khsv_h78.png

 

It goes without saying that temperatures, and therefore instability, are likely underdone. I agree with Tony regarding the "threshold" idea. Realistically, that threshold is IMO probably somewhere in the neighborhood of 750-1000 J/kg, at least if we're talking about long-track tornadoes from discrete supercells. If for whatever reason (most likely widespread early initiation) instability falls short of that range as the GFS is showing, then the ceiling for the event obviously will not be approached. But to focus on the literal CAPE values printed out by that model at this range is to ignore history completely.

 

Just as a rough comparison with Super Tuesday, I looked at the above KMEM forecast sounding vs. their 00z sounding that day. H5 temperatures are very similar, while the H3 temperature are a couple degrees warmer on the GFS. The surface dew point is about the same, but unsurprisingly, the actual temperature on Super Tuesday was ~3 C warmer. To me, the takeaway is that when accounting for the typical cool BL bias in the GFS, I'd expect a relatively similar thermodynamic profile to Super Tuesday should the GFS verify in a synoptic sense. CAPE could be somewhat lower due to poor lapse rates aloft, though.

 

I will say the NAM does not impress me much, if taken verbatim. Low-level winds are far weaker and more veered. A dProg/dT over the past 24 hrs reveals a rapid trend toward the GFS in terms of the trough evolution, so it may be a moot point soon.

We just had a seminar given by the SOO at WFO BMX on tornado forecasting and nowcasting in Alabama.  With the cases he had from his CWA, the "threshold" was usually about 500J/kg.

 

One other important item of note: if we see anything near Super Tuesday levels of instability, then the ceiling may actually end up being even a touch higher than Super Tuesday.  The GFS soundings show well over 500 m^2/s^2 of 0-1km SRH by 00z Wed and likely increasing even more after that.  For reference, here was the BNA sounding from 00z during the Super Tuesday outbreak.

 

EDITED: correct BNA sounding

[Stebo]

We just had a seminar given by the SOO at WFO BMX on tornado forecasting and nowcasting in Alabama.  With the cases he had from his CWA, the "threshold" was usually about 500J/kg.

 

One other important item of note: if we see anything near Super Tuesday levels of instability, then the ceiling may actually end up being even a touch higher than Super Tuesday.  The GFS soundings show well over 500 m^2/s^2 of 0-1km SRH by 00z Wed and likely increasing even more after that.  For reference, here was the BNA sounding from 00z during the Super Tuesday outbreak.

 

EDITED: correct BNA sounding

 

 

Yeah just comparing this sounding to the forecast winds, one would note that there is a slight backing to SSE with the winds at the surface this time around, just adding an extra punch in the 0-1km shear.

[tornadotony]

Euro says good night and good luck.

 

http://www.instantweathermaps.com/ECMWF/2013012700/USA_HGT_500mb_072.gif

[Stebo]

Euro says good night and good luck.

 

http://www.instantweathermaps.com/ECMWF/2013012700/USA_HGT_500mb_072.gif

 

 

The hotlink doesn't work.

[tornadotony]

The hotlink doesn't work.

Huh.  Well, just go to www.instantweathermaps.com and follow the toolbar to the Euro.

[Stebo]

Huh.  Well, just go to www.instantweathermaps.com and follow the toolbar to the Euro.

 

I know Just saying for the sake of you wanting to post the image lol

[brettjrob]

The core of the LLJ is even more backed on the Euro than the GFS, albeit slightly less extreme in magnitude at 00z (50-60 kts). Here is the H5-H85 crossover:

 

 

I have to mention that the Euro is indicating relatively cool temperatures at the surface and SBCAPE < 1000 J/kg, as it has for several runs now. This is largely the result of widespread initiation in the morning that plows across the warm sector all afternoon. For example, for the 21z-00z period, the 0.5" QPF isopleth encompasses almost half of AR. It will be interesting to see how much of that is due to convective parameterization run amok.

 

In any case, we have to keep in mind the GFS is not off on its own crazy island with the meager CAPE values. If the NAM comes around to the consensus solution tomorrow, perhaps its thermodynamics will give us a better picture.

 

Also, we shouldn't count out central to northeast TX per the slower Euro, as shear profiles are plenty impressive there with fewer questions of instability.

[Stebo]

The core of the LLJ is even more backed on the Euro than the GFS, albeit slightly less extreme in magnitude at 00z (50-60 kts). Here is the H5-H85 crossover:

 

130127061739.gif

 

I have to mention that the Euro is indicating relatively cool temperatures at the surface and SBCAPE < 1000 J/kg, as it has for several runs now. This is largely the result of widespread initiation in the morning that plows across the warm sector all afternoon. For example, for the 21z-00z period, the 0.5" QPF isopleth encompasses almost half of AR. It will be interesting to see how much of that is due to convective parameterization run amok.

 

In any case, we have to keep in mind the GFS is not off on its own crazy island with the meager CAPE values. If the NAM comes around to the consensus solution tomorrow, perhaps its thermodynamics will give us a better picture.

 

Also, we shouldn't count out central to northeast TX per the slower Euro, as shear profiles are plenty impressive there with fewer questions of instability.

 

The bold part is due to the storms themselves, there is nothing in that part of AR until later in the day, you'd expect there to be QPF by that point due to the convection from the event.

[brettjrob]

The bold part is due to the storms themselves, there is nothing in that part of AR until later in the day, you'd expect there to be QPF by that point due to the convection from the event.

 

Yes, but the extent and nature of the QPF signature looks a lot more like an MCS or squall line than discrete supercells. The Euro runs at high enough resolution that it's often possible to differentiate, and I've seen plenty of cases where one can clearly tell it's predicting discrete mode.

 

I probably could've used better phrasing, but my point is that should a more discrete mode dominate into the afternoon and evening, I would expect higher CAPE values than indicated on even the Euro.

[thewxmann]

With many of these neutral-positive tilt, not-so-well-phased systems, there tend to be weak lead impulses drawn up by the subtropical jet. Any one of these can prematurely spark off storms in the warm sector, and I believe this is what the GFS and Euro see that puts a damper on instability early on.

[Stebo]

Yes, but the extent and nature of the QPF signature looks a lot more like an MCS or squall line than discrete supercells. The Euro runs at high enough resolution that it's often possible to differentiate, and I've seen plenty of cases where one can clearly tell it's predicting discrete mode.

 

I probably could've used better phrasing, but my point is that should a more discrete mode dominate into the afternoon and evening, I would expect higher CAPE values than indicated on even the Euro.

 

Yeah I would agree with this, I was just making sure for clarification.

[OKpowdah]

With many of these neutral-positive tilt, not-so-well-phased systems, there tend to be weak lead impulses drawn up by the subtropical jet. Any one of these can prematurely spark off storms in the warm sector, and I believe this is what the GFS and Euro see that puts a damper on instability early on.

 

It's a little helpful in this case though, because for instance this first s/w moving through the central Plains tomorrow ahead of the main trough is the mechanism to initiate moisture return. The s/w preferably de-amplifies off to the northeast on Monday, such that there isn't a strong push back on the theta-e ridge, and then we're primed for the main trough

[Stebo]

Several of the GFS ensembles are popping a low at 72hrs over AR or Southern MO. This would most certainly lead to a localized backing of the winds in the warm sector.

[andyhb]

...TX TO IL SOUTHEAST ACROSS THE LOWER MS VALLEY...   PREFER THE SOMEWHAT SLOWER AND NOT SO PHASED DEPICTION OF THE UPPER   TROUGH AS SHOWN BY LATEST ECMWF AND NAM THROUGH EARLY TUESDAY. THESE   SCENARIOS INDICATE A MOIST BUT GENERALLY WEAK TO MODERATELY UNSTABLE   AIRMASS WILL BE SITUATED FROM TX NEWD ACROSS MO AND INTO IL BY   TUESDAY AFTERNOON. LACK OF STRONGER INSTABILITY WILL LIKELY BE   COMPENSATED FOR BY RELATIVELY RAPID ONSET OF INTENSE ASCENT   ASSOCIATED WITH THE APPROACH OF MID/UPPER TROUGH AND 100KT MID LEVEL   SPEED MAX SPREADING OUT ACROSS THE WARM SECTOR TO NEAR ARLATEX BY   AROUND 00Z. DEEP CONVECTION WILL ERUPT ALONG THE ENTIRE LENGTH OF   THE SHARPENING COLD FRONT THROUGH THE LATE AFTERNOON WITH STORMS   COMING UNDER THE INFLUENCE OF EVER INCREASING DEEP-LAYER SHEAR/FLOW.   EXTENSIVE QLCS APPEARS LIKELY TO SPREAD EAST ACROSS THE MID/LOWER MS   VALLEY INTO TUESDAY NIGHT WITH CELL MOTIONS FORECAST IN EXCESS OF   50KT LEADING DAMAGING WINDS. LACK OF STRONGER CYCLONIC DEVELOPMENT   ALONG THE COLD FRONT SUGGESTS LINEAR MODE SHOULD DOMINATE BUT   SUPERCELLS AND LEWPS EMBEDDED IN THE LINE AND NEAR TRANSIENT FRONTAL   WAVE STRUCTURES WOULD POSE SOME TORNADO THREAT WITH TIME.   UNCERTAINTIES REGARDING OVERALL TIMING AND DEGREE OF SURFACE-BASED   DESTABILIZATION PRECLUDE HIGHER OR SIGNIFICANT PROBABILITIES AT THIS   FORECAST RANGE. HOWEVER...FUTURE UPGRADE TO MDT RISK SEEMS POSSIBLE   IF THESE DETAILS BECOME CLEARER.

 

Was a bit intrigued by this with the new SPC D3....since I've noticed that essentially all of the runs of the NAM/Euro have trended towards the GFS recently.

[chase_stormz]

Was a bit intrigued by this with the new SPC D3....since I've noticed that essentially all of the runs of the NAM/Euro have trended towards the GFS recently.

 

The NAM and EURO have been trending towards GFS, wtf I'm so confused what SPC is seeing...

[Stebo]

Color me a bit surprised that they are relying so heavily on the NAM at this junction especially with it trending the way it has in successive runs.

[thewxmann]

It's a little helpful in this case though, because for instance this first s/w moving through the central Plains tomorrow ahead of the main trough is the mechanism to initiate moisture return. The s/w preferably de-amplifies off to the northeast on Monday, such that there isn't a strong push back on the theta-e ridge, and then we're primed for the main trough

Oh yeah, of course. But I was referring to even more subtle, weaker impulses riding in the stream ahead of the main trof axis the day of the event.

[Ground Scouring]

I am actually growing increasingly confident that a major outbreak will indeed evolve and am ready to throw in my lot. Compared to the 12Z runs yesterday, several of the 00Z GFS ensembles--along with the 00Z operational GFS--have trended toward a slower, less-amplified shortwave impulse that moves across the Dakotas as early as 00Z tonight and then weakens as it rotates over the N Great Lakes, with the main trough slowly deepening over the Four Corners region. This would likely mitigate early convective initiation somewhat, especially as the operational GFS, for the first time, actually shows a real dry punch in the warm sector tomorrow morning, with low 700-mb RH extending much farther north than on preceding runs. This, combined with much stronger model support for a robust, persistent secondary low developing over N MO Tuesday night, would keep the solid reservoir of moisture intact without sacrificing too much initial instability. The secondary surface low would actually bring 60°F+ dew points even farther north to the KMDH-KHUF-KEVV area. As nothing else seems likely to change, and given disconcerting model trends, I am now inclined to say that this event will produce at least a moderate tornado outbreak in addition to very damaging QLCS bowing segments (I say segments because new wind profiles now more strongly substantiate embedded tornadoes within the QLCS). If the models continue to trend toward a stronger dry punch, thus ricocheting instability upward, then my calling for a significant tornado outbreak potentially rivaling Super Tuesday 2008 will be very likely, given that this event will in my view have even better moisture return and synoptics at least as good, if not better, than those of 02/05/2008.

[Ground Scouring]

By the way, did Super Tuesday not also start with a Day-3 SLGT risk?

 

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.

This is just for historical purposes, but the ESRL reanalysis indicates that the Enigma outbreak (02/19-02/20/1884), one of the all-time winter outbreaks, coincided with a strongly positively-tilted shortwave trough.

[tornadotony]

The 00z GFS CIPS top-15 is really interesting.  Contains 1/7/08 (#3), 2/5/08 (#5), and 3/1/07 (#15), along with several other signficant and deadly events.

 

http://www.eas.slu.edu/CIPS/ANALOG/stats.php?reg=SE&model=GFS212&fhr=F072&flg=

[Ground Scouring]

The 12Z NAM has already shifted a bit closer to the GFS in that it shows somewhat greater phasing with the trough a day before the (likely) outbreak. There are already hints by 00Z on 01/30 that the NAM attempts to develop the secondary surface low which is well-established on the GFS ensembles and even the recent ECMWF. This trend was not apparent so early on previous NAM runs, so most likely it is depicting a somewhat deeper evolution of the low with greater backing of the low-level wind field this run. Of course, I expect the trend in the NAM to be gradual so that it will not have a complete grasp of the synoptics and thermodynamics until about a day before the actual event. At that range, the NAM should be much more useful with which to make an informed judgment re: convective mode, but at this point all the trends are moving toward more discrete and semi-discrete activity with a significant outbreak very likely.

Edit: The 12Z NAM now strongly backs the low-level winds by 00Z 01/30 relative to the 00Z run...which showed veering winds over the MS Valley in the same time frame--a rather significant and certainly drastic shift. Most amazingly, it brings near-60°F dew points a bit farther north than on the 00Z run...this time extending a bit north of KIKK and closer to KFWA. This means that a substantial severe threat would shift a good 40-60 mi farther north than on the 00Z run and even start to bring the Chicago outskirts into play with backed winds now near the lakefront. It also brings 60°F+ dew points as far north as beyond PAH early on 01/30 and actually suggests a nocturnal outbreak overnight 01/29-01/30 over E AR, N MS, NW AL, a fair chunk of W TN, and SW KY. This would put the Memphis area almost in the center, much as on 02/05/2008. Moreover, the NAM keeps backed winds from 00Z 01/30 throughout almost the entire day with very little mixing of the dew points due to the 850-mb vector relative to the front. For this time of year, this is as impressive as I have ever seen in all except a few, top-end winter outbreaks like Super Tuesday or 01/21/1999. The NAM suggests the significant TOR threat would extend as far east as NE AL, NW GA, E-C TN, and S-C KY early morning 01/30 (with 80+ kt 850-mb SSW jet!) and then into the Carolinas by afternoon-overnight with 60°F+ dew points as far north as DCA. The run is absolutely scary with eye-popping soundings across such a wide area and much higher instability and 0-2-km SRH than on previous runs. If this were to verify, a potentially record-breaking winter outbreak on a par with Super Tuesday or even the Enigma outbreak would be a very real possibility, which I am now beginning to contemplate.

[blackjack123]

  By the way, did Super Tuesday not also start with a Day-3 SLGT risk?

This is just for historical purposes, but the ESRL reanalysis indicates that the Enigma outbreak (02/19-02/20/1884), one of the all-time winter outbreaks, coincided with a strongly positively-tilted shortwave trough.

  Day 3: http://www.spc.noaa.gov/products/outlook/archive/2008/day3otlk_20080203_1100.html

[Ground Scouring]

Check out this jaw-dropping 12Z NAM radiosonde--courtesy TwisterData--near Memphis 03Z 01/30, which in my view likely overdoes the inversion. At any rate, this is a classic winter profile strongly favoring discrete activity and strong tornadoes. This is one reason why I believe that the NAM reflectivity showing a solid squall line with almost no discrete activity is convective feedback:



By comparison, LKZ sounding from Super Tuesday, 00Z 02/06/2008:



Meanwhile, here is a good read for anyone who may prematurely write off the event 36 hours before it begins:

http://www.spc.noaa.gov/publications/evans/sup-tues.pdf

 

These “synoptically evident” (Doswell et al. 1993) events are quite rare with only a few such occurrences as clearly apparent in medium range model guidance each year. More typically, differing model solutions lead to inherently higher forecast uncertainty several days in advance of a severe weather event. Even if model guidance is in general agreement, the coarser resolution of these data sets limit the assessment of any sub-synoptic scale process...

 

 

 

In addition, some of the simulated radar reflectivity products available with the higher resolution WRF data sets (Weiss et al. 2006), tended to suggest rather weak and disorganized convection over the lower Mississippi valley through the afternoon (Fig. 6). SPC forecasters are aware of the limitations with these explicit, convection-allowing models, particularly in low instability environments, due in part to the ~4 km grid length that is relatively coarse to resolve convective-scale updrafts. However, operational use of high-resolution WRF output has proven useful in similar situations by providing unique convective details (e.g. mode and evolution). 

 

 

 

The weak, southern stream short wave trough increased deep moist convection in the form of elevated thunderstorms over north central Texas, which spread quickly into eastern Oklahoma and western Arkansas through the early morning hours of the 5th. However, by daybreak it became apparent the primary effects from this low latitude short wave trough would overspread the Ozark region, and likely not impact most of the warm sector during the day. Modified forecast soundings, using slightly warmer surface temperatures as predicted by local NWS forecast offices, indicated capping would therefore likely be broken across most of the warm sector by the mid afternoon.

 

 

[Stebo]

Check out this jaw-dropping 12Z NAM radiosonde--courtesy TwisterData--near Memphis 03Z 01/30, which in my view likely overdoes the inversion. At any rate, this is a classic winter profile strongly favoring discrete activity and strong tornadoes. This is one reason why I believe that the NAM reflectivity showing a solid squall line with almost no discrete activity is convective feedback:

 

 

Drier mid levels would imply potential of some sunshine, could really jack up the surface temperatures.

[SeminoleSullivan]

Just taking this at it's very basic: The speed in which it glides in, and the ambient amount of sunshine before the liquid sunshine, there does appear to be some of the basic building blocks for instability.

 

I was also intrigued to see the heavy reliance on the NAM, until I looked at at how it's been handling the mid-level when 12/24 hours out.  The NAM also appears to be the middle ground: being both Mean and the Mode, though it is steadily making its way toward the GFS. 

 

Though I have no dog in this fight, I wouldn't even be paying attention to surface reflection.

 

Should be interesting to see how it develops

[Ground Scouring]

Drier mid levels would imply potential of some sunshine, could really jack up the surface temperatures.

The same pattern was also present on Super Tuesday--which featured 80°F+ surface temperatures in the lower MS Valley--which bears an alarming resemblance to the radiosonde that I posted. The NAM has a tendency to underestimate surface temperatures in these cases, so it is certainly underestimating the instability. I believe it had the same problem three days prior to Super Tuesday but quickly latched on to reality, as it is steadily doing so now.

[SquatchinNY]

I am not that weather-wise in svrwx terminology, backing means the winds are moving at closer to a 90° angle to each other, right?

[JoMo]

I am not that weather-wise in svrwx terminology, backing means the winds are moving at closer to a 90° angle to each other, right?

 

Usually means S to SE winds at the surface. 

[SquatchinNY]

Usually means S to SE winds at the surface. 

Oh, ok. Thanks.