4/13/07 FCST: TX / OK / AR / MO / IL / TN

[Jonathan Racy]

Day 3 MDT risks

We have the ability to issue Day 3 moderate risks. It would consist of a 45% severe probability. We can also issue "hatched" areas for significant severe. The ability to issue Day 3 moderate risks was implemented last February and has never been done to this date. Issuing a Day 3 moderate risk would require a lot of certainty in a highly volatile situation.

http://www.spc.noaa.gov/misc/SPC_Prob_Conv_Otlk_Change_20060214.html


Jon

Well first off I just want to say that the SPC has issued a day three MODERATE risk before. It didnt really verify in the target area, it was June-12-05 I beleive. They had a moderate risk up for the eastern texas panhand and western oklahoma down into the texas south plains. However as we all know the south plains had a nice localized tornado outbreak that day, but anyways back on subject.
This system is really complicating things for me. I live in SC Oklahoma so Location isnt an issue here. But I really would like to see the moisture much deeper and the storm track further to the north and west. Even though I do think north texas and southern Oklahoma WILL see tornadoes I dont know how widespread or significant they will be, or how chaseable these storms will be. Cape values around 1200j/k and extremely powerfull wind feilds may not be a good combination, and yet if very well might given the extreme dynamics and lift with this system. But Honestly in an environment such as this one I have seen that not enough cape and to much in the way of wind shear causes the towers to be ripped apart. Also this system may generate to many storms all at once. However If Isolated storms form or even a cluster of storms can form and ride along the warm front and establish good inflow then We should be all set. This storm just represents to many quetions right now for me. I will make a choice on whether I will go or not sometime tomarrow.

 

[Adam Atkins]

Model trends continue to throw on the brakes and dig this trough further south....00UTC NAM shows the triple point between Wichita Falls and Gainsville, TX. Mid-level flow still screaming and low level jet is now becoming better juxtaposed with the instability axis near the warm front and dryline. I'm becoming a bit more optimistic about storm chase territory and the overall setup.

 

[Jim Tang]

There have been two MDT Day 3's. One prior to June 10, 2005 (that one was a complete bust) and one was prior to Jan 2, 2006.

Basically right now I'm worried about the juxtaposition of the low level jet axis and the instability. Another thing is just where the sfc low is? The models continue to trend stronger and stronger with a high to the north, and thus the sfc low continues to be progged weaker and further south. Keep in mind that the ground and the water temps in the GOM are still relatively cold, and the LLJ will bring a relatively warm air mass just above the cold sfc, so the closer to the Gulf the warm sector is, the greater the chances are that it will be a cloudy, dirty, drizzly warm sector.

Finally if the forcing's too strong, stratiform rain will overspread the warm sector, limiting instability and ruining the setup.

 

[Chris C Sanner]

I agree Jim. I'm really concerned about this turning into the setup we had earlier this month which was a moderate 15% hatched tornado setup. We ended up with a bunch of rain and a few "spinners" on the front of an embedded squall line. Right now, I'm thinking the system will still be a bit further W than the models are predicting (still). I'm not convinced it'll progress as far eastward as progged. Right now, I'm thinking being close to the low might be a good idea if we can get some clearing. But either way there are way too many details to sort out and I'm not entirely convinced we're going to see a decent severe weather event at all yet until the bigger questions are answered, and there's a lot of em...

 

[Jonathan Racy]

My apologies to Ray and Jim. I stand corrected. There were indeed MDT Day 3s issued June 8 and Dec 31 2005, valid for 3 days later of course. And, the probability has to be 45% hatched to be a MDT, now for Day3. Sorry for the confusion.

JPR

There have been two MDT Day 3's. One prior to June 10, 2005 (that one was a complete bust) and one was prior to Jan 2, 2006.

Basically right now I'm worried about the juxtaposition of the low level jet axis and the instability. Another thing is just where the sfc low is? The models continue to trend stronger and stronger with a high to the north, and thus the sfc low continues to be progged weaker and further south. Keep in mind that the ground and the water temps in the GOM are still relatively cold, and the LLJ will bring a relatively warm air mass just above the cold sfc, so the closer to the Gulf the warm sector is, the greater the chances are that it will be a cloudy, dirty, drizzly warm sector.

Finally if the forcing's too strong, stratiform rain will overspread the warm sector, limiting instability and ruining the setup.

 

[SteveCarter]

Looks like things are starting to come together rather nicely now. This could possibly be a major outbreak..POSSIBLY..in and around the Arklatex. DP's will GREAT, moisture..no problem, and lapse rates, instability, etc etc etc...looking pretty impressive. Thinking about leaving Friday 5AM for Shreveport, LA...10 hour drive, then staying on the MS/AL line late Friday, to be ready for Saturday! lol Then "home" for Sunday.

 

[Ray Walker]

Ya I knew there was at least one Moderate day three. I couldnt remember the exact date tho. This system, (in my opinion) is going to suprise alot of use at the last moment. I think it will look good and like it will produce an outbreak and then bust or look like a bust and then produce an outbreak. However I think the front will end up further north than proged. But that is just a hunch, a gut feeling, but all the models keep shoving it further south. We shall see.

 

[Jonathan Racy]

Fri the 13th

I'll still have to side with the ECMWF and GFS for Friday. I
don't trust the NAM, unless the event is within 12-18 hrs.
With that in mind, I'm thinking two primary areas of interest
for Friday afternoon.

Huge upper low over the Grtlks region now will be slow to
give up the ghost, so I'm not certain that the warm front
will be any farther north than the Red River during this
entire event. The LLJ axis appears to translate well ahead
of the dryline, impinging upon the e-w oriented front over
northeast TX during the afternoon. Thus, I reckon that "streamer"
type showers (HCRs)/storms will gradually intensify during the
late morning/afternoon into supercells. As they approach the warm
front, they could produce tornadoes. This area may end up being
the primary show. SPC SREF sigtor numbers are quite high
bounded by a TX I-20/30 corridor mid-late aftn Sat. That classic
"kissing jet/butterfly" orientation to the H25 flow looks great
for a good number of storms, probably backbuilding into ecntrl
TX during the evening. This would be a challenging chase for
sure!

Farther w, dryline/front will likely ignite later as the
primary height falls aloft spread ewd. Suspect that the
region along the Red River where the moisture "bends-back"
toward the sfc low may be an interesting spot, particularily
in light of colder temps aloft. Otherwise, backing low-midlevel
flow regime may spell rather quick transitions into a mixed mode
mess. But, it will be interesting given the Nascar festivities in
Fort Worth Fri-Sat!

Jon

 

[Billy Griffin]

While I have no meteorlogical explanation at all to this, I'm starting to have second thoughts on whether the more southern track will actually verify. Also, I wonder if this system just might slow down, if ever so slightly?

No, not wishful thinking, as I am medically unable to chase. But I'll be cheering you guys/gals on! So let's just call it a "gut feeling," - - I'm just wondering if the storm track and associated triple point will set up somewhere over SW / SC or even up into central Oklahoma with the associated WF making it as far north as I-40? I know that would likely spell trouble for chase terrain, (as cells would track into the jungle of SE OK as they continued east) but perhaps some initiation could occur along the I-44 / Highway 81 / I-35 corridor in southern Oklahoma? Again, not consistent with everyone's forecast, but just my .02 worth. Just for kicks though, I'll be eyeing southern Oklahoma!

 

[Brian Stertz]

12z ETA shows that there is definitely one hard target between Palestine and Texarkana (possibly as far north as the Paris-Clarksville TX areas on the Red River as well) tomorrow for the good combo of shear and decent moisture SB & 0-3km CAPE is maximized in this area. This looks to me to be the most threatened area for tornadic supercells tomorrow. Hate to discount the dryline further northwest and west (which should have some very strong ascent by evening)..but as far as reasonably clear targets, this would be the zone. This Day 2 MDT risk seems very well supported. Just not the most chaser friendly part of Texas where things may get wild and wooly.

 

[matt patterson]

I wont rehash what has already been said but the area from Gainsville to Paris is really intriuging.... I do worry about how much destabilization will actually occur in the warm sector...This may keep me a little closer to the Western half of the TA.... I read the AFD from Fort Worth and i think they sum it up very well

FACTORS
LEADING TO THIS EVENT ARE: A 50+ KNOT MOIST LLJ...VERY STRONG
DIVERGENCE AHEAD OF THE UPPER LOW...100+ KNOT 300MB JET...7 TO 8
DEGREE MID-LEVEL LAPSE RATES...35-50 KNOTS 0-3KM SHEAR AND 200+
HELICITY. EXPECT THE WORST FRIDAY AFTERNOON AND EVENING...
ESPECIALLY OVER THE EASTERN COUNTIES.

Cant wait to see what SPC says at 1730

 

[Jim Bishop]

It would appear there are two distinct regions to chase for this setup. The first is along the dryline near the Waco area east/northeastward late in the afternoon (easier target for me, personally). The second is right along the warm front much earlier in the afternoon along the I-20 corridor east of Dallas, maybe in the vicinity of Paris/Northeastern Texas.

I choose dryline convection because it should be both a more chaseable terrain and the storms should be more discrete & visible. The 12z WRF does break out convection in the Vicinity of Waco, or between I35 & I45 between 18z & 00z well south of the warm front along the dryline. The speed shear alone supports supercells, especially given the north-south orientation of the dryline. But the veered 850mb winds mediately east of the dryline concerns me a little. The storm motion will be northeast around 45 knots or more initially. So stormy should quickly move into a much better shear environment, and become tornadic supercells within a couple hours of initiation.

The other area is completely warm air advection storms - messy. The 0-1km helicity values will be incredible, so any discrete, surface based storms will probably produce tornadoes. These storms will be moving northerly rapidly socked in with low clouds. Given the less than ideal chase terrain, I really don't see a point in going up there for a chase. But, I would expect the highest probabilty of a tornado occuring in this target region.

 

[Glen Romine]

Huge upper low over the Grtlks region now will be slow to
give up the ghost, so I'm not certain that the warm front
will be any farther north than the Red River during this
entire event. The LLJ axis appears to translate well ahead
of the dryline, impinging upon the e-w oriented front over
northeast TX during the afternoon. Thus, I reckon that "streamer"
type showers (HCRs)/storms will gradually intensify during the
late morning/afternoon into supercells. As they approach the warm
front, they could produce tornadoes. This area may end up being
the primary show. SPC SREF sigtor numbers are quite high
bounded by a TX I-20/30 corridor mid-late aftn Sat. That classic
"kissing jet/butterfly" orientation to the H25 flow looks great
for a good number of storms, probably backbuilding into ecntrl
TX during the evening. This would be a challenging chase for
sure!

First off - thrilled to see SPC staff joining in on ST forecast discussions, I hope that you'll find time to offer insight on future events as well. As for tomorrow - there are several aspects that seem suspect to a big event coming together. That said, the lack of consensus in the primary forecast models - particularly with regard to surface evolution, plague a reliable forecast approach. The agreement among model is largely in place for a weak surface ridge setting up along the coast line, with a trend toward veering surface winds with time across much of the 'warm sector' (south of the warm front setting up from the Red River eastward) during the day. This seems to aid in persistent thick cloud deck forecast across much of east TX and LA during the day which could really slow the northward progression of surface moisture there as it will need to mix downward. Latest SREF trending toward focusing the instability axis to a narrower region along the western side, across east Texas during the late afternoon, with only a sliver of high confidence steep mid-level lapse rates by Friday evening. Surface winds are generally weak, and tending to veer during the afternoon particularly according to the GFS. Despite this, low-level shear is impressive with strong 850 mb flow, yet the flow is nearly unidirectional and shows little speed shear from that height up through mid-levels. I struggled to find forecast soundings near the warm front that showed any low-level instability despite very low LCLs. A sweet spot will probably come together somewhere in east Texas during the afternoon, but pinpointing where is appearing impossible at this stage.

It seems that the 00Z NOGAPS model run might be the exception (between 09Z SREF,12 Z NAM and 12Z GFS) for many of the noted low-level issues above - didn't look at the ECMWF. Other diffs between GFS and NAM is the latter has the lead shortwave extending much further south - potentially triggering convection early in the day across the warm sector which could markedly alter the evolution of the day. GFS tracks this feature north of the WF.

 

[Jeff Snyder]

My primary concern continues to be destabilization... Shear profiles will, no doubt, be very strong. The NAM continues, however, to indicate negligible CAPE until after 21Z, owing to widespread cloud-cover and precipitation keeping temperatures down near 60-65F, with an effective warm front south of I20 in the early-mid afternoon. Now, it does indicate rapid destabilization after 21Z across northern Texas, but I'm not terribly confident in that. The NAM also continues to indicate a narrow tongue of CAPE developing right along the dryline. However, with 45-50kt storm motion for storms except mature supercells, I fear that narrow axis will be outrun rather quickly by any storms that do develop on the dryline.

Of course, as has been known, a lot will depend upon the extent of overnight convection. If convection sticks around N Tx, we may not see any appreciable destabilization that may preclude the development of significant, tornadic (implied surface-based) supercells N of I20. Of course, if this convection fails to materialize overnight through tomorrow morning, there is the potential for ~2000 j/kg CAPE south of the Red River. I think there is a chance to see a high risk event tomorrow, but I think we'll see to see significant destabilization take place first. If not, I have large fears that we'll see something similar to what we saw on 3-30 -- a "waste" of a setup in which there was very impressive deep-layer and low-level shear in the 'warm' sector.

 

[Glen Romine]

Looking at the 1730 outlook - I'm surprised by the analogue case date given of March 28, 2000. Looking back at the event, it sure doesn't look too much like the forecast for tomorrow. About the best matching aspects are the 500 mb flow pattern east of the Rockies (horrble pattern match upstream). Thermodynamic aspects look quite different for tomorrow.
I have to look more into how those matches are made.