04/23/10 FCST: TX/AR/OK/LA/KS/NE/MO/IL

[David Wolfson]

The same synoptics that look promising for south TX on 4/22 appear to translate to the Arklatex for this day. Shear, moisture, potential instability and a negative-tilt axis all point to the possibility of widespread serious storms starting in the northeast TX/Texarkana area and extending toward the MO bootheel in the overnight. While a ways away (fer shurr!), the potential for severe somewhere in the area seems a pretty good bet, and to my eyes the best spring setup so far this year. FWIW.

 

[Darren Addy]

Not sure why this day isn't being talked about more... maybe people are waiting to take a look at it once the NAM comes into play.

Is anybody else seeing a possible triplepoint play for northern chasers in NE KS and SE Nebr.? It looks to me that the show is going to start earlier than we normally like to see, but it looks like parameters supporting supercells and low LCLs to me. Surface winds are backed but predicted marginal at 15kts in NE KS. DPs will only be in the 60-65 range, but temps should be under 70.

What am I missing here?

 

[matt patterson]

Not sure why this day isn't being talked about more... maybe people are waiting to take a look at it once the NAM comes into play.

Is anybody else seeing a possible triplepoint play for northern chasers in NE KS and SE Nebr.? It looks to me that the show is going to start earlier than we normally like to see, but it looks like parameters supporting supercells and low LCLs to me. Surface winds are backed but predicted marginal at 15kts in NE KS. DPs will only be in the 60-65 range, but temps should be under 70.

What am I missing here?

I think that one thing that is keeping me from looking a whole lot at this day (as of right now) is the uncertainty of where the convection from Thursday will be as of Friday Morning.. Friday in my mind will be very tough to forecast until Friday morning as clearing starts to occur.. Plus the last "go round" looked pretty good at 100+ hours and started sucking thereafter, IMO!

 

[Brian Stertz]

Not missing anything Darren...trends are slower which would be right on the money given how massive the upper system is. It's those small waves ejecting ahead of the main ball of energy that will probably factor in enhanced severe wx and supercells on Friday. Need things to get a little closer in before biting on a precise target. I think the order of Friday's chase (in my first thoughts) will be to hang with the deeper moisture targets KS/OK dryline zone. I am going to be updating my Vortex Times forecasts once the 00z data updates the next few nights.

 

[Skip Talbot]

Not sure why this day isn't being talked about more... maybe people are waiting to take a look at it once the NAM comes into play.

I think Friday is still a little more questionable depending on what happens Thursday. Having the NAM in range will definitely help as well. If the GFS is right, I think we'll see the highest probabilities from SPC in eastern TX, LA and AR. The instability is forecast to be highest here along with very strong speed shear. This area could see lots of hail and damaging winds. Tornadoes would be possible too given the strong LLJ, low LCL's.

The area I'm watching more closely is the triple point which you mentioned over SE NB. Winds back strongly here and instability is forecast to approach 2000 J/Kg. This is also a much more manageable terrain to chase than targets to the south. The dryline looks like it will be positioned over eastern KS, but the 850 mb winds are much more veered here with might result in more of a linear mode.

The GFS has been too fast with the system, showing areas further north and east more favorably than what the NAM is depicting. The triple point might very well end up in Kansas, and if the trough advances more slowly the dryline might look more appealing with better directional shear than what is being shown now. Good targets might be anywhere from SE NE down through central KS depending on where the surface features wind up. There might also be warm front play across southern IA or northern MO as well.

 

[Chris C Sanner]

Just for anyone planning on chasing this day right now, I would consider shifting your targets 100 miles west or more given this year's model trends of the ECMWF's slower solutions more closely verifying compared to the GFS' solutions. In Oklahoma, the GFS has already moved the dryline from the OK/AR back to I-35 and I wouldn't doubt if it continues to slow things down even further since the GFS is still noticeably faster than the EC. Friday won't be a chase in the hills (thankfully) given current trends. From a very wishcast/no other evidence except trends and recent history point of view, I won't be surprised to see the dryline set up as far west as Graham - Lawton - Watonga - Medicine Lodge.

My main worry about Friday is the degree of forcing may be a little 'too' much, as sometimes happens with strong systems and you end up with a line. Thursday looks to be the best balance of forcing/cap/parameters still. As always, I'll keep the blog updated at the link in my sig.

 

[Scott Olson]

This is the first setup this year that I've genuinely liked. Ample upper support in a large upper low, several days of moisture return resulting in moderate instability. A front which should largely intiate from Nebraska all the way down into Oklahoma. Vector orientation is about 20 degrees in Nebraska and 45 degrees into OK/TX. With low ML LCL's and bulk shear from 40kts north to 60kts south, it's a very prime setup. I see two perspective targets. One near the WF in Nebraska where helicity will be maximized. However, with the vector and not such a strong cap we can count on quite a bit of storms, likely a QLCS line.

To the south though, say Oklahoma. We are looking at 60kts bulk shear over moderate instability, low LCL's and a favorable angle to the storm vector. That's pretty sweet all in all. Not that there isn't some caveats. Exactly how far south intiation will occur. Up farther north, I think it's pretty clear Nebraska will see significant activity on a day like this.

There is the question of ongoing precip to the north, with the possibility of an overnight MCS moving across the area during the day. That would make the northern target considerably less attractive. But, it will depend on the timing and how big of an area of precip.

If I had to pick now, I'd pick the southern areas. This is our first good chance to get the tornado count to start going north!!!

 

[Andrew Pritchard]

I haven't looked much at the southern plains setup, but as previously mentioned there could be some really good warm front play somewhere near the Iowa/Missouri border and even potentially into western and southern Illinois though speed shear drops off the further east from the low that you get. It's 84 hours out, so this is probably stupid but I'm fairly intrigued by the Kirksville, MO to Quincy, IL area. Looks like a classic midwest warm front day with a large area of stratiform precip ahead of the northward moving warm front. Should see this begin to decay during the late morning hours as the warm front begins to creep north. Clearing skies south of the warm front should allow for rapid destabilization during the early afternoon with MLcape values reaching the 1500-1750 range by 21Z when low topped supercells could erupt in the warm sector. It's the anniversary of 4/20/2004, but I could see a scenario similar to that in a different location occurring. The main attraction will be the dryline and triple point in the plains, but I'd watch the warm front in areas east in NE Missouri and WC Illinois.

It depends on which model you choose to fall in love with if you're looking at playing the dryline in Oklahoma and surrounding areas. Based on the NAM, I'm not overly excited about that area. The GFS is slightly better. If you side with the NAM you're in between shortwaves with veered 850 flow. Only a narrow band of instability being shown as well, possibly owing to overnight convection.

If you're playing the dryline I'd be hugging the surface low, which will be further north in Nebraska. The best play right there at 84 hours out appears to be between Grand Island and Lincoln, NE. You're a little bit displaced from the best speed shear here, but there could be just enough coupled with great turning for some supercell thunderstorms, possibly trickling down the dryline as well with further development into NE Kansas during the evening towards Manhattan, KS where MLcape values could exceed 2000 j/kg.

So, at 84 hours my two targets would be along a Lincoln, NE to Manhattan, KS line and then further east along a Kirksville, MO to Quincy, IL line.

 

[Darren Addy]

Interesting how right now the GFS shows essentially a stacked low system, while the NAM has the surface low out in front. The NAM shows the 500mb low shrinking to a near-singularity-size by 0z. The Bulk Shear that the GFS draws looks a lot saner to me than the wonky NAM Bulk Shear for 0z. Will be educational to watch the models on this one as we get closer to Day 1. I've still got a lot to learn.

 

[Mike Hollingshead]

http://weather.cod.edu/forecast/GFS/gfsUS_500_spd_84.gif

http://weather.cod.edu/forecast/WRF/wrfUS_500_spd_84.gif

http://weather.cod.edu/forecast/ECMWF/ecmwf_500_spd_96.gif

NAM really stretches out the 500mb trough. ECMWF last night was closer to the same idea. While GFS brings out a nicer big singular chunk. Not sure how much of a change it will bring really. Low levels are sorta similar.

Has the feel of one of those setups where anything to the north half will be having to happen behind a big precip shield, maybe close to the precip shield. Hopefully not, but for some reason I keep thinking that. Probably that tendency for the 850mb flow to be veering off to the east, not as bad lately or on the NAM.

Pretty sure whichever is right, I'll be on the north side of that dryline arc, which would be north central NE into southern SD on the GFS, half a state or so further south on the NAM. Get weaker mid-level flow there and very strongly backed winds.

Interesting to note just how cold the 700mb temps are(0c on portion of DL arc I was looking at). Probably better be there damn early and have a jacket along.

http://weather.cod.edu/forecast/GFS/gfsUS_0_cinh_78.gif

I don't know what to think about the day as a whole. In one sense it feels like a big rainfest mess thanks to weak cap and possible early morning convection issues. But seeing how flat that mid-level flow is on the NAM and how off the dryline it is(even north on the arc), and over that big of an area, seems the day could be big. Somewhere on the dl arc to the nw of where it goes more n-s feels like a fine place(often right where it begins to arc nw). Getting back to Nebraska THAT early after Thursday in TX panhandle just ain't going to happen....maybe if it ended up northern KS I guess...and not northern NE. Decisions decisions.

 

[Aaron Dooley]

Friday, moving west again...

Friday:

System has slowed down even further according to the NAM/WRF. Dryline west of 35 by 00Z.

Models are having problems breaking out precipitation but I am not concerned and think it will happen.

I see 3-4 main areas that hold potential for this day. The first is north and south of the Red River along and west of I-35. The second is in central Kansas along the dryline again roughly aligned with I-35. The third and possibly most promising is in NE KS, SE NE, and into NW MO along the lifting warm front. Fourth and conditionally with enough dryline movement I think the area just north of Del Rio from 00Z to 06Z could produce big storms with more than enough tornadic potential.

I have included two graphics showing the SKEW-T and Hodograph for that area below. I see a stout capping inversion BUT the models are showing precip breaking out. Indeed, this is something I will be watching in future runs.

 

[Andrew Pritchard]

I'm becoming increasingly confident in a few tornadoes occurring in far NE Missouri, and possibly western Illinois into the evening hours. Target at 60 hours out would be in a region bounded by Quincy to Columbia to St. Louis. This is very chaseable terrain and road wise.

Vorticity maximum and associated 500 jet max will be screaming into central Missouri by noon. This, coupled with impressive 0-3km cape values and sbcape values around 1000-1500 j/kg should lead to the initiation of robust convection by mid-afternoon. Incredible looped hodographs in the vicinity of the warm front will be more than favorable for rotating storms, possibly minisupercells that should be more than capable of producing tornadoes. The cap should be pretty weak, so my main concern at this point is too much early convection associated with the speed max too early in the day. Obviously another question as always will be the amount of destabilization that occurs, which goes hand in hand with the potential issue of too much early convection.

It would be really hard for me to turn down a hodograph like this however, if it appears destabilization appears likely.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=060&STATIONID=kuin

At this point however, I think the NE quadrant of Missouri bears close watching, perhaps stretching into western Illinois during the late evening.

The other obvious target is in eastern Nebraska right now. The obvious issue with this area is the flow at H5. The stronger jet max is punching into Missouri during the evening leaving Nebraska under fairly weak and southerly flow. Strongly backed flow at 850 could compensate for this however and be sufficient for a few tornado reports. My main concern in this area is that the show ends up being more of a QLCS event quickly as convection becomes widespread. Severe weather is an almost sure thing in this area, but the flow at H5 is what is potentially keeping is from being a bigger tornado producer. Lincoln, NE would be a good starting point for this target. Maybe a hair north of that.

I've got a geographical bias against the southern plains target with the two closer targets up north, but just looking at the stacked flow down there it does not look like a big tornado day to me. Take that for what little it's worth though, as I said I have not looked at all the minor details. Just pulling up the 850 charts turned me away, however.

 

[jshields]

i'm really liking the northern target as far as the tornado threat. as long as there is some kind of clearing, i think there could be a pretty big day from eastern neb/ne kansas over to southern iowa and northern missouri, wherever the warm front sets up. the nam shows alot more available cape, at least for the northern target than the gfs does. i was also taking a look at the 0-3km cape and it looks amazing, parts of southeast nebraska/northeast ks are between 300-400 j/kg. so unless i'm missing something that is a ton of low level cape for all the naders?! combined with 40-60 kts of bulk shear and the day2 spc outlook just came out and there was talk of moderate risk and strong tornadoes! i will be out somewhere in the region on friday!

 

[Jeremy Den Hartog]

I'm a little surprised more people haven't commented on this day as it looks to be very active over a large section of the middle part of the country. The SPC has gone with a moderate risk for AR and LA areas. They have also hinted at doing the same for the northern target - which is where I will be chasing tomorrow. Initially I'm targeting southwest Iowa (maybe around Atlantic, IA) but that depends on how things clear out in the morning. There may be some strong tornadoes this day (as jshields said) so it should be fun. Good luck to those of you who decide to go out...

Check out this NAM sounding from just southeast of Omaha...

 

[Bill Schintler]

Chase Target for Friday, April 23

Chase target:
Seward, NE (15 miles northwest of Lincoln).

Timing and storm mode:
Storms will develop along an occluding warm front by 4 PM CDT. All modes of severe weather are likely, including tornadoes. Storm motion will be towards the northeast at 20 mph.

Discussion:
Tonight, storms will increase across the area as the LLJ increases and advects an increasing theta-e AMS over the H85 WF. A large area of elevated convection, associated with the WAA wing and increasingly diffluent flow aloft, will be ongoing during the morning hours Friday. This convection will exit the region to the N by noon, leaving a thick layer of SC blanketing the area.

A persistent upper low pressure, currently over AZ, will finally begin to track towards the E and NE, reaching NWRN KS by 00Z, 04/24/10. At the SFC, cyclogenesis will increase in extreme ERN CO, with an attendant WF extending E of this feature. This low will begin to occlude as a CF of Pacific origin pushes EWD. Further E, a diffuse DL will slowly mix EWD. Model runs continue to slow the progression of the system. Dewpoints will increase to 60-65F along a narrow axis between the WF and DL courtesy of SELY SFC flow and a 10-12C H85 LLJ.Insolation will be inhibited N of the WF by the aforementioned thick SC, reinforcing the baroclinic zone.

Storms should initiate by 21Z at the WF/DL triple point and quickly build to the NW in an arc along the occluded WF, and track towards the N at 20kts. The favored storm will be the “tail-end Charlieâ€￾ on the S end of this arc of storms. Instability will increase as cooler H5 temperatures advect over a 200mb-deep well-mixed moist layer, with MLCAPEs in excess of 2000J/kG. Meanwhile, SFC-6km deep-layer shear will increase throughout the period as an 80kt H5 streak ejects from the ULVL system and overspreads the area. LLVL helicity will be maximized along and N of the WF where SFC flow remains backed.-
Bill
9:18 PM CDT, 04/22/10