4/06/06 FCST: KS/NE/IA/MO/OK/AR/TX

[Matthew Havin]

<div align="left"> --General forecast target will be updated when necessary over the next few days--
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A strong low pressure system will be moving into the central/northern Plains on Thursday.
Several days of strong return flow between now and Thursday will allow for a potent severe weather episode Thursday afternoon and evening.

Looking at various models up to the 6Z run, thoughts are a surface low between 983-990mb will move into eastern Nebraska by Thursday afternoon..... NAM is a tick fast and pushes the low into IA by this time.... while on the other end the 00Z Canadian goes for a 983mb bomb lagging back in NW KS.

Rich moisture looks to move ahead of the progressing 500mb trough by Wednesday. The NAM catches onto this quite well.....pumping 65+ dewpoints into eastern Kansas and cooking west OK with low 90s temps.
This will continue into Thursday, where 65+ dewpoints and 3000+ CAPE are a possible by afternoon ahead of the dryline in E KS/NE.

This far out.....this is as much as I will detail. A possible sub-990mb low ejecting into the Plains with moderate instability of 3000+ CAPE in early April sounds good to me!

 

[Jeff Snyder]

I find it rather interesting how similar the Thursday chase looks compared to last Thursday's setup (3/30/06), or at least the models' forecasts of last Thursday in the days leading up to the event. This morning's 12z NAM run has the surface features in almost identical locations, with similar shear profiles. As with 3/30, and 3/12 for that matter, I wouldn't be surprised to see everything shift west a tad, since the NAM seems to be having a tendency to be too far east with surface features in the 60-84hr time-frame. At least the 12z run seems to indicate the we will see >65F tds up to I40 in eastern OK. Of course, yet again, the models have overforecast Tds along the dryline this year so far, so I'm hesitant to believe it attm.

Whatever the case, 500mb winds are progged to be ~70-80kts, so any chasers will need to attach their chasemobile rocket boosters that were used in previous chases this year. It seems as though 3/12 and 3/30 were strongly affected by Tds and CAPE that were just a little too low (on the 3/12, CAPE and Tds were pretty low for 3-5 counties east of the dryline, though that become less of an issue as the storms moved into central MO)... So, I'm certainly playing the waiting game. My head tells me I need to learn when to say "no" to a chase setup, especially given how this upcoming one looks to the 3/30 setup, but I greatly expect not to be able to deny the temptation. LOL I certainly would not have guessed that my best chase so far this year would have occurred in an environment characterized by temperatures and dewpoints in the 40s (I'm referring to the 3/20 cold-core chase in nw OK), particularly given the apparently-favorable synoptic setups that we've seen this year.

 

[Jeff Snyder]

The similarities with 3/30 continue on this evening's 0z NAM run. I'm rather intrigued by how similar the setup looks... Strong deep-layer shear in the warm sector and atop the dryline, decent flow at all levels (strong at 500mb and above, so time for the rocket boosters), etc. This also means that we may face similar issues as last time -- a rather narrow instability axis, at least on the southern end of the target, and issues with cloudcover (reflected in the sfc temp field). AT tihs time, the NAM is indicating >2000 CAPE across portions of the KS/OK/TX target, but that's dependent upon sufficient moisture return. With the history of overforecasting Tds, I'll have to wait and see if this will actually materialize. Given the pattern recognition with 3/30, my gut is telling me to hedge northward in KS, but we're a little too far out for that specific of a fcst from me.

 

[Matthew Havin]

Looking at the Tuesday morning models up to the 6Z..... significant severe weather outbreak looks increasingly likely across the Plains Thursday. 6Z NAM and GFS...along with the sluggish 0Z Canadian.....insist on slowing down the progression of the low east Thursday. Consensus points to 985-990mb low moving into east NE by Thursday afternoon. I wouldn't be suprised to see the initial SPC Day 2 risk be scaled west.... at least in a line from Beatrice NE to Manhattan KS to Ponca City OK. SPC Day 3 does have hatched significant severe over about 150,000 square miles of real estate..... already mentioning long-tracked supercells and tornadoes...and mention planned upgrade to Mod. Good luck picking a target!

Agree with Jeff on the Td issue.....NAM has been shouting on the last few setups and wouldn't be suprised to see Tds 2-4 degrees below what is printing out. 6Z NAM has dews hitting 62-64F ahead of the dryline by afternoon....with CAPE hitting 2900 near Beatrice NE and 64Td with 4.5EHI. So even if the models are shouting, 2000+ CAPE will still be quite possible across most of E NE/KS/OK ahead of the dryline Thursday. The NAM is getting a more favorable look at low level winds.....with strong SSE-SE winds at 21Z ahead of the entire dryline from E NE/KS and NE OK.

 

[Joerg Kachelmann]

MOS Forecasts for dewpoints were better off than DMO recently due to the helping statistical background which prevents from overestimating Td. Current run forecasts 63 ie for Ponca City

MOS for Ponca City

 

[bbarjenbruch]

It's true, this is strikingly similar to 3/30. However, I see a couple differences working both for and against a better severe weather outbreak.

1.) There is quite a bit more cap initially (especially toward the northern half of the system). On 3/30, the storms had a strong tendency toward quasi-linear 60 mph junk, and this was largely due to weak capping early in the day. Stronger cap early ~ stronger CAPE later with heating to about 80 ~ better storm structure.

2.) The depth of the moisture is not great. Even if the NAM is right and Td's are in the mid 60s, LCL and LFC heights are forecast to be quite high on the soundings. It might work to kill a bit more of the tor threat.

It still looks like a fun chase, and as indicated earlier, I went to Home Depot and picked up a set of rocket boosters for my car this morning. WHEEEEEEEEEEEE!!!

 

[SteveCarter]

It's Tuesday morning now, and the latest models are looking VERY promising from a chasing standpoint. Especially, (for me) in the lower Tennessee Valley on Thursday. This setup is a LOT like what just went through, except the entire system may be slowing down a little, which is good as well. The BAD side of things is that my heart goes out for the people who have really went through so much aready, because it may be the same areas again. Right now....planning on leaving SC for the (gulp) Dyersville, TN area for Thursday.

 

[nickgrillo]

THUR looks like an incredible day in terms of widespread severe weather once again, but definitely not for chasing. So far, this year alone I have chased about three setups which featured me trying to catch up and maintain position with supercells moving northeast at 55-65mph, which is a royal pain in the neck -- and have got screwed on both March 30th and April 2nd. The deep-layer wind field on THUR is quite incredible, with the surface low much deeper at the surface than last THUR (with stronger CAPE available as well). The NAM shows the shortwave oriented as a positive tilt as it pushes into the central plains by the evening... With a surface low deepening to a whopping 985mb in eastern NE -- with strongly backed boundary layer flow ahead of the cyclone. In the midst of the strong 0-6km shear, the NAM shows widespread 2500-3500j/kg of SBCAPE out along/ahead of the dryline by 18z, supported by insolation and moist advection -- accompanied by enough 0-1km SRH for a very good tornado threat by the early afternoon (increasing by the evening). If I was chasing, I would definitely be playing the sfc low in eastern NE where at least 3000j/kg of SBCAPE and 150m2/s2 0-1km SRH exists, and the potential for some slightly slower moving storms also exists.

Nonetheless, storms which develop should move at an average of 45-55mph, with storms further south in the warm sector (e.g. southern KS and OK) moving even faster [55-65mph] being influenced by the 80kt 500mb speed max. I'll be sitting this one out for sure (I probably won't chase again til I leave for the plains again in late April).

 

[Mike Hollingshead]

The NAM shows the shortwave oriented as a positive tilt as it pushes into the central plains by the evening... With a surface low deepening to a whopping 985mb in eastern NE -- with strongly backed boundary layer flow ahead of the cyclone.
[/b]

http://www.rap.ucar.edu/weather/model/eta60hr_500_wnd.gif

Negative tilt, not positive.

Nonetheless, storms which develop should move at an average of 45-55mph, with storms further south in the warm sector (e.g. southern KS and OK) moving even faster [55-65mph] being influenced by the 80kt 500mb speed max. [/b]

http://www.wxcaster2.com/CENTRAL_ETA_ATMOS...MOTION_60HR.gif

ETA shows 25-30 knots for the sfc low stuff. I'm liking how little it moves that sfc low. Keep her in NE! I can't chase worth a crap outside of NE for some reason.

One important difference between this and the April 2nd system is the orientation of the 500mb flow(for places more south anyway). Sunday it was more westerly to the south and Thrusday is more southwesterly. The other difference seems to be the sfc flow ahead of the sfc low. It is prog'd a bit more southerly to southeasterly, which I guess it should be for a deeper, slower moving low.

 

[Eric Graham]

Looking like same set up as this last weekend for central IN. Potentional is there for another severe weather outbrake here in IN. Won't be suprised to see more tornados come through cental Indiana on Thursday evening. Hopefully tomorrow stays nice liked forecast so Indianpolis, Johsnon County, Shelby County and Tippecanoe County can clean up from tornado damage received by the weekend storms. Maps are looking descent for Thursday and on into Friday for severe weather.

 

[Scott Lincoln]

Looks like the models really slowed this one down recently, storm motion as well as motion of the low. Looking out towards the end of the period on thursday, the system almost seems to stall out.

I could see there being some chase potential in eastern Nebraska and eastern Kansas, but some of the BUFKIT soundings i have been looking at tonight arent looking all that great. Not very much moisture at the surface giving way to crappy LCLs, and the winds not backing soon enough in the day.
I hope that changes....

 

[Bill Tabor]

I just did an approximation of storm velocity using Bunkers and in northeastern OK near TUL at 0z I get anywhere from 60 to 85 knots under the strongest jets with orientation slightly east of northeast! That is without any adjustments for propagation due to boundaries, convergence, orographics. This is similar to the other day (I think Mar 30th) when one cell was moving at 89mph!

 

[Scott Lincoln]

I just did an approximation of storm velocity using Bunkers and in northeastern OK near TUL at 0z I get anywhere from 60 to 85 knots under the strongest jets with orientation slightly east of northeast! That is without any adjustments for propagation due to boundaries, convergence, orographics. This is similar to the other day (I think Mar 30th) when one cell was moving at 89mph!
[/b]

Wow thats pretty fast. That is a little different than what the forecast motions were on the wxcaster page, where it was something like 50kts for KS and OK, and 30-40kts for Nebraska area around the low. In some ways i want the storms to move fast so they'll head into Iowa before too late, but if they move really fast they will be hard to chase.
I hope we see some changes in the deep layer moisture on the runs later tonight....

 

[bbarjenbruch]

In advance, sorry for the long post simply for a day 2 analysis of the general Eastern Nebraska area. I posted this for my lab students and just figured I'd get some more use out of it.

Strangely enough... the 00Z NAM seems to be accurate according to the initialization discussion. What's strange about this? How about a 981 hPa Low pressure center in Central Nebraska. This coinciding with really strong 500 diffluence and vort max entering Eastern Nebraska at the approximate time of initiation. Ample shear for supercell development is also available.

After examining BUFKIT, 2500+ CAPE appears likely throughout Eastern Nebraska with the CINH eroding away near LNK and OFK at ~ 2 or 3 PM. Low level helicity is in question, but supercell inflow should be good with SE winds across much of the area. Warm frontal postion appears to be on a line from ODX to OLU to OAX with the low roughly tracking ESE along the front. NOTE: in past runs, the surface low has been tracking farther southwest... I wonder if this trend will continue?

The dryline appears to surge out ahead of the low, cutting off some of the best moisture from some of the best dynamics, but that may not be an issue at all because the dynamics are still fairly good out ahead of the low. One more good/great thing to come out of the OOZ NAM are the new 500 wind progs. With the increased diffluence, 500 winds are expected to remain in the 60 knot range... still strong, but only indicating storm motions on the order of 30 knots. Much more manageable than 50 knots of other days.

Problems... once again, the possible inadequacy of low level moisture. However, with the gulf opening up, and the LLJ hopefully roaring for the next 36 hours, this could change, and we all know the NAM isn't exactly known for its accurate Td depictions. A lack of dewpoints would also result in the higher LCL's. There is also a slight problem with shear in the 0-2 layer being fairly unidirectional, but with the horizontal vorticity along the warm front and any residual outflow boundaries from overnight convection in place, it may be adequate for tornadogenesis regardless.

I'd say any chaser is in for at least some good organized supercell action on Thursday... possibly even some short lived tornadoes. But, unless something changes, I think the long track tornadic action does not appear probable at the time, and as far as I'm concerned, that is good news. Once again, sorry for the long post.

 

[Benjamin Sipprell]

The timing on the location of the dryline for both the NAM and GFS are significantly different ... the GFS placing the dryline further east in the 00Z April 5th model run. NAM models point to northeast NE to have the most significant tornado threat as 0-3 km helicity values run up to 300 m2/s2 (see soundings at KSUX at 48 HR ... doesn't suck ... http://www.wxcaster.com/modelskewts.php3?f...&STATIONID=ksux ... good curvature, maybe not great length) with CAPE values reaching nearly 3000 J/kg ...

Still the 500 mb and 300 mb jet max's make a left hand turn and slow just like on April 2nd and as everyone looked at SE Iowa and surrounding eastern regions most of the tornadic activity took place further east, interestly southeast as well from the low. So I do not believe locations like western KS are out of the question for chasing ... as Nick said everywhere is looking convective, not great for chasers, there's no central location.

Just have to wait for future model runs. Interestingly enough there is a line of signifcant CAPE values and moderate helicity values extending northeastern TX on northward in the NAM (http://128.121.193.153/CENTRAL_ETA212_SVR_CAPESRHSWEAT_48HR.gif) ... northeastern TX showing a region of high theta-E values collocated with moderate helicities (a secondary low perhaps?)