05/11/05 FCST: Central/Southern Plains

Oh boy, another forecast from Ben Prusia!

For Wednesday, May 11: A very potent upper level storm system will have its second day in the Plains States during the day on Wednesday. By the 0Z GFS on Friday, May 6, the center of this system is in south central Nebraska with a measure of 997mb at 0Z Thursday. The model depicts a very well defined dryline heading to the south-southwest from the system, into the eastern Texas Panhandle. The model also shows an area of precipitation breaking out in an area along the dryline in OK/TX and also in an area to the east of the upper level storm system in Nebraska. Of course, this is 144 hours out from the time of this forecast and is very subject to change, but it appears to be a very good severe weather setup on our hands this coming week. I am just hoping that moisture isn't hosed for this setup from this weekend's setup.

Graphic for this forecast available on the "My Chase Forecasts" link below.
 
I like the mid week setup better than I do this weekend's. The weekend one looks rather boring and I dont see too much to get excited over. However, I like the models for the middle of next week. It looks more favorable for a classic May severe weather event. I hope everything pans out and next week holds a couple good chase days for the Central Plains region. The weekend system looks very promising for the Southern Plains folks though.
 
Since nobody else wants to comment on Wednesday, I guess I will. At 00Z an elongated surface low is forecast to be located in NW/SW Kansas. The NAM is showing the gradient tightening along the dryline which will run N/S near the Kansas/Colorado border. Dewpoints should be >60 with CAPE at 2500-3000J/kg near the triple point and along the dryline. Right now deep layer shear doesn't look that great along the dryline at about 35kts. Shear is forecast to be better along a front that will run from the corner of NW Kansas to Omaha and into Scentral Iowa. I don't want to call it a warm front since it is forecast to drop South throughout the week. Helicity is also forecast to rapidly increase along and North of the front. The NAM has precipitation North of the front throughout the day, with new precipitation breaking out along the front by 00Z. Right now there are upsides and downsides to the three target areas I see. The first target area would be Scentral Iowa along the front. Low level shear is excellent and dewpoints are forecast to reach the 70's, but 300mb winds are nonexistent. Target area two would be in SE Scentral Nebraska along the front. CAPE is forecast to be highest here and with NE storm motions it is possible that storms could track along the front and move into the area of backed surface winds. And target area three would be the dryline in Kansas. Deep layer shear is going to be about 35-40kts and CAPE should be around 3000J/kg. I am sure a lot will change and I don't know that this is going to be the tornado outbreak we all are hoping for, but it is the best thing we got and I think there will definetely be some tornadoes on Wednesay. It's May, it has to happen. Doesn't it :roll: ? I would expect a moderate risk if the NAM were to verify.
 
Originally posted by Michael Gribble
Since nobody else wants to comment on Wednesday, I guess I will. At 00Z an elongated surface low is forecast to be located in NW/SW Kansas. The NAM is showing the gradient tightening along the dryline which will run N/S near the Kansas/Colorado border. Dewpoints should be >60 with CAPE at 2500-3000J/kg near the triple point and along the dryline. Right now deep layer shear doesn't look that great along the dryline at about 35kts. Shear is forecast to be better along a front that will run from the corner of NW Kansas to Omaha and into Scentral Iowa. I don't want to call it a warm front since it is forecast to drop South throughout the week. Helicity is also forecast to rapidly increase along and North of the front. The NAM has precipitation North of the front throughout the day, with new precipitation breaking out along the front by 00Z. Right now there are upsides and downsides to the three target areas I see. The first target area would be Scentral Iowa along the front. Low level shear is excellent, but 300mb winds are nonexistent. Target area two would be in SE Scentral Nebraska along the front. CAPE is forecast to be highest here and with NE storm motions it is possible that storms could track along the front and move into the area of backed surface winds. And target area three would be the dryline in Kansas. Deep layer shear is going to be about 35-40kts and CAPE should be around 3000J/kg. I am sure a lot will change and I don't know that this is going to be the tornado outbreak we all are hoping for, but it is the best thing we got and I think there will definetely be some tornadoes on Wednesay. It's May, it has to happen. Doesn't it :roll: ? I would expect a moderate risk if the NAM were to verify.

Target 4...central Illinois. Very high instability progged across central Illinois, around 3500. MCS is forecasted to track across the northern part of the state early in the period, leaving an outflow boundary across the central part of the state. Intense convection should develop along this boundary during the afternoon, after substantial heating occurs. Enhanced helicity and baroclynicity along this outflow boundary could lead to some rotating storms.
 
Currently all we can hope for is that the ETA's moisture forecast is underdone by some degree. Although I see no precip/MCS signals through 0Z Thursday, it continues to forecast horrid moisture holes across the forecast area through the target time.

Right now we're left with a skinny little finger of 60oF dewpoints to play on the dryline......but I think it may be time to go and investigate real surface obs and see if the LLJ really is going to cut it this time over the next 72hrs or so.

I woud throw one other bone out there - in that this system stinks of anafront. It is hard not to notice the crashing cold front (southerlies meeting northerlies) progged each day throughout the Pains until the front finally ends our joy come Friday. This sort of setup is NEVER truly favorable for chasing and I think that there may be some inherent difficulties with a system of this nature.

I can chase Tuesday and Wednesday - but I think that Nebraska will be plain too far to go on Tuesday for me considering the marginal nature of the event. Wednesday is still shaping up like the big day - which may be a dryline chase from west Texas to western Kansas if the progged strong southeasterlies verify and we can keep the cirrus-monster from attacking us again.

KR
 
I think that you could can call that boundary across Iowa a warm front on Wednesday. The boundary appears to move north slowly, or a bit more quickly in the case of the GFS. It appears to become a cold front on Friday when it finally moves out of the plains.
Given that the front will likely be a warm front, that there will be high areas of Theta-E and Helicity along the front, I can see some convection forming in southern or central Iowa. Warm frontal situations are not always the best for severe weather, but they have been known to cause some tornadic events.

This sort of setup is NEVER truly favorable for chasing
I beg to differ. I remember a day last year when a cold front moved through Iowa causing a few tornadoes, and then the front moved back north as a warm front the next day. We had 21 tornadoes in Iowa that day. I remember thinking the same things on the days leading up to May 22nd that I am thinking now.

I am not necessarily forecasting a large outbreak, but I am forecasting the possibility of at least some isolated tornadoes along the warm front and possibly along the dryline. The warm front will likely have many favorable conditions in place. If we can get some nice convergence and sunshine in that area, then I think we the chance will increase.
 
I have been looking at some forecast soundings at DDC to AMA and I am not real excited about Wednesday as of the latest NAM run. I think Tx panhandle would be the place for a slim chance of discrete supercells given the latest data. CAPE looks good in the range of 2500 to 3000 J/kg from DDC down to AMA but the shear in both areas are forecast to be so weak (with this run) and that leads me to believe it will be a multicell setup at this point even along the dryline. I mean not much is going to come form 30kt at 500mb and 700mb both.

At this point I am out of the race but still leaving the door open for possible chase pending better shear. I can deal with 60 Td temps, but with the high CAPE and low shear combo I will choose not to super size it.

EDIT: My CAPE values above are a little high. 1500 to 2500 J/kg. Pardon me.


Mick
 
I'm not sure I feel confident enough with my forecasting skills yet to chime in on this kind of setup, but here goes anyway...

Wednesday is a complicated mess that has a wide range of potential.. right now, I'm thinking of hugging the KS/OK border just north of the Panhandle; Liberal, Kansas to name a town. My thoughts are that areas too far south don't show the greatest dynamics although the CAPE is there. I think the best shots for good storms will be from the Oklahoma Panhandle northward to the front; which could be anywhere between the Gulf Coast and Nova Scotia by Wednesday with the way things have been handled. A narrow band of 2500+ CAPES arch from the TX Panhandle all the way into Southwestern Kansas before turning east towards extreme NE Kansas; this seemingly where the ETA feels the front will be.

SRH is much higher in Kansas as opposed to the TX Panhandle, so I'd think the best combination of the two will be close to the front and the low in Southwestern Kansas where things seem to want to converge on at the surface.

In any case, I'd be aiming for east of the low and along the front which hopefully hangs back a bit and not sweep through too quickly as to kick all the goodies out.
 
Wednesday; 5/11 appears like a marginal chase day at this point, yet does wet my interest. Highly dependent on if any MCS activity during the TUE timeframe pushes the annoying cold front southbound, thus killing the ideal setup (in this case; photogenic isolated sups along the dryline). Meso ETA depicts grim setup; while the GFS backs off slightly w/ the polar express. Good CAPE (2-3000 J/kg) and 0-6km shear for sups; better upper level support farther NW however. Somewhat concerned about T/Td spreads resulting in higher based convection... however

Currently: http://stormeyes.org/maps/txmesonet.gif

Upper 60/Low 70 Tds lurk just S of the Red River; and have been progressing N/NW all day. Not believing/nor do I understand the dry Td patch over NW TX) as per the NAM/ETA. Somewhat confident moisture (upper 60/around 70 Td) will be in place across SW KS/OK PAN and points S WED). Will wait for tonight’s runs before committing a final decision to marathon for what potentially could become mediocre miscalculation of mesoscale meteorological mischief.

That said, will remain optimistic for WED; regardless of all the negatives.


..Blake..
 
Hmm... It looks like the upper-level low will remain over the intermountain west, yielding weak mid-upper level flow over most of the western plains warm-sector. The better mid-upper level winds ("better" being >40kts) does begin to spill into the plains, but much of it lies north of the cold front in the cold sector. This results in rather poor deep-layer shear over the western plains (30-35kts), and the southeasterly winds between the sfc and 850mb yields pretty weak low-level shear (0-3km SRH currently indicated to be 100-200). I was REALLY hoping the system would kick out into the plains a little faster, but that doesn't appear to be the case (bias would show it to be the other trend). Additionally, models indicate 55-65 tds, resulting in 1500-2500 CAPE (which isn't too bad), but with mid-80s, that's yet again 20-30 T-Td deficits and very high LCLs. Overall, I'm REAAAAALLY hoping this will change, since I'd like to chase the dryline Weds in western KS or the panhandles, but I'm not confident to say the least. Additionally, it looks as good as anything else in the next week or 10 days south of Nebraska, given that the models drive the cold front well into the southern plains (or down through the Gulf of Mexico.... AGAIN!), with any sort of stronger mid-upper flow well into the cold sector. Given the evolving pattern in the models, it certainly seems feasible that this may be the lowest May tornado count in OK tornado history. Yay. The year of the cut-off, non-progressive system continues...
 
Not a whole lot has changed with the 00Z run of the NAM. The NAM has moved everything South from the 00Z run yesterday. The front in SE Nebraska and southern Iowa will probably both have some tornado potential, but I am thinking the dryine is where I am going. SW Kansas looks like my target as of now. The surface low is centered over the Oklahoma panhandle and the intersection of the Kansas/Colorado border. Dewpoints should be >60. CAPE is forecast at 2500-3500J/KG with 35-40kts of deep layer shear. 500mb winds out of the SW at 40-45kts is OK. Upper level winds could be better. If we can get good insolation ahead of the dryline and dewpoints are respectable, this might be pretty good. I find it hard to complain about this setup considering what we have had so far this year.
 
Originally posted by Jeff Snyder
This results in rather poor deep-layer shear over the western plains (30-35kts), and the southeasterly winds between the sfc and 850mb yields pretty weak low-level shear (0-3km SRH currently indicated to be 100-200). I was REALLY hoping the system would kick out into the plains a little faster, but that doesn't appear to be the case (bias would show it to be the other trend).

Whew... The 0z NAM DOES actually show 500mb winds a good 10kts stronger than previous runs! Now, the 500mb flow across the dryline ranges from 40-45 kts for the most part! That's definately more doable. As of this latest run, I'll probably be going out... Then again, I suppose the next run could revert back to the old solution of 30kts at 500mb, which is particularly possible with the understanding that the 0z NAM run reverses the previous trend of slowing down the eastward progression of the low/trough. Right now, I'm not sure where along the dryline would be my prelim target... Probably between Shamrock, TX, and Liberal, KS...
 
With the 00z NAM run out, it appears we have the makings of a legitimate triple point on Wednesday. Surface low forecast around SW KS, with a definite airmass contrast (in terms of surface temps) along a SW to NE gradient from SW KS to S Central NE -- with temp difference from 80+ degrees near Hayes, KS down to 55 at NW tip of KS. As Jeff mentioned, 45 to 55 kt Swly flow at 500mb overhead this area to provide some venting.

In terms of instability, dewpoints ahead of the dryline forecast from 62 to 66td and 0-3km CAPE values are in the 2,000 j/kg range in the warm sector. 0-1.5km lapse rates approach the "absolutely unstable" condition of 9 to 10 from W Central and SW KS, southward along the dry line through the TX panhandle.

Along and behind the wind shift/cold front line draping across NW KS, 0-3km SRH exceeding 500m2s2, with SRH values ahead of the front at around 150m2s2.

Re wind crossover, southerly flow at 850mb of 25-35 kts is generally at ~ 45 angle to the aforementioned 500mb flow. At the surface, although 15-20kt winds ahead of the front are pretty much from due south in KS, appear to be slightly backed further down the panhandles.

Re chances and location of convective initiation, there is a well defined area of surface moisture convergence along and out ahead of the front. Further south along the dryline, this is much more problematic. Indeed, forecast accum. precip drops off the chart just south of the OK panhandle.

In beginning to think about targeting for Wed, at this time I would be partial to the area up closer to the anticipated triple point than too far south along the dryline. In addition to flirting with lower probabilities of initiation, I like the somewhat more workable LCL's closer to the front and, although not ideal, I like the closer proximity to better deep layer shear. Trying hard not to be a slave to microanalyzing these runs 48 hours out, but prospects still are encouraging for our chase vacationers on Wednesday!
 
Looks like we will be seeing a classic triple point setup during the day on Wednesday via the 12Z NAM. The NAM model shows an upper level system at 997mb centered right about on the Colorado/Kansas border. From the system, a dryline heads south into the eastern part of the Oklahoma and Texas panhandles. For most of the system, 850mb winds will be out of the south and howling at a pretty good clip with winds progged at 30-40 knots. Higher at the 500mb level, winds will be to the southwest at 45-50 knots for anywhere of a 30 degree crossover of winds in Kansas, to slightly higher down in the panhandles of Texas and Oklahoma. 500mb winds will be modest, with speeds of 40-50 knots (hopefully enough to sustain isolated supercells) along the northern portions of the dryline running into the triple point. 250mb winds will be strong, mainly in western Kansas, but weaken the further south you head on the dryline. Modest instability will exist along and east of the dryline with SBCAPE readings up to 2500 J/Kg, but can reach slightly higher. A lifted index of -6 will exist for most of west central Kansas ahead of the dryline and east of the triple point. The best moisture available will be 65+ degree dewpoints along a front that extends to the northeast of the triple point, and expect best moisture and instability to the east of the triple point. For a target choice right now, I am pinpointing anywhere from Wakeeney to the east, Colorado State Line to the west, and Garden City/Dodge City to the south.

Graphic for this forecast is up at "My Chase Forecasts" link below.
 
Don't have too much time to write here; for once again my indecisiveness has cost me travel time.

Agreed WED 5/11 looks more favorable than last night. Not many addition points to tack on here. Favoring the I-70 corridor and points S along DL (US 183 corridor). H5 at 40-45 across the general area of interest; (50kts in S. NE); H7 30-35kts; etc... ample moisture return not as big of a scare as last night; regardless of the ETA/NAM progged jackassery (IMO). Not confident about the SW/SC NE region due to the polar front; however not ruling it out. Memories of 22-May-04 return to haunt me (i.e. suckered N to the WF) but really haven't had time to re-analyze since around noon. Yes, the MDT got my blood pumping through the veins; and have re--re-arranged my work schedule to fit this marathon.

Must depart to Quincy, IL and pick up my chase partner -- hope to make Salina by early A.M.

Best of luck to all whom venture out WED.

..Blake..
 
After looking at the 00Z NAM I am not quite as excited as I was before, but it sill looks like a couple of tornadic supercells are likely. The surface low is located in NW Kansas. It might be a hair farther South than it was with the previous run. Dewpoints will be in the 60's with 65 a little further to the East. Near the triple point shear should be >45kts with 2500-3500J/KG CAPE and 500mb winds at 50kts. Weak shear will be a problem for any storms along the dryline South of central Kansas. Lapse rates are forecast to be very steep near the triple point and along the dryline. It looks like HP will be the primary mode tomorrow.
The target area for tomorrow is a no-brainer for me. First of all the NAM doesn't show any precipitation along the dryline except for near the triple point, not that I buy into that though. Second of all, storms that form on the northern portion of the dryline/triple point will be tracking NE into an area of increasingly lower LCL heights and higher helicity plus they will have stronger shear. I am expecting storms to come off of the triple point and right turn once they organize and encounter the better helicity. I will be heading towards Colby where I will fine tune my forecast. For those who are interested, there is a wifi spot on the West side of the road after you get off of 70 in Colby. I only glanced over things and I don't really know what I am talking about so don't put too much stock in my forecast. I will look more closely at things in the morning, but from the glance I took the only problems I see are LCL heights that are a little too high, CAPE that is a little too low, directional shear could be better, and stronger upper level winds would be nice. Bottom line though, what we got will be good enough to get the job done. I will see you all out there tomorrow and good luck.
 
Surprised no one is mentioning Illinois...even the SPC only has 15% prob. This is easily the best set up illinois has seen this year. CAPE progged around 3000-4000 by mid afternoon, with surface temps in the mid 80s...and td's around 65-70. Outflow boundary from overnite mcs and warm front over the central part of the state should serve for intense convective development early afternoon. They should quickly become severe, and likely supercellular with good shear, and helicty values around 300-400. Additionally, any storm that forms near the outflow boundary will be able to interact with it, tapping into enhanced helicity areas, enhancing the tornado threat. Be interesting to see if the SPC is watching this at all...or if we're sneaking in under the radar again with the attention on the plains. Things could change overnite...but attm, it appears Illinois and Indiana should be monitored.

The forecast sounding for Macomb, IL tomorrow afternoon has cape @ 4000, strong SE winds, EHI of 4.2, and supercell pot. of 77%. Now, yes, these are just forecasts, and indicies...but...surprises me to see no one talk about this situation.
 
I agree with Michael in the post above this one... For whatever reason, the >65 tds just can't get to the dryline.. .Now, remember that the models tend to lengthen/smooth the gradient, so we may see higher Tds near the DL. Regardless, CAPE should be in the 2000-2500 range, with 0-3km helicity good near the front in northern KS. This looks like the first, and little more like-to-produce, target. While flow in the mid-upper levels is sufficient, the lack of much speed shear results in 0-6km deeplayer shear (per the 0z NAM) that is on the low-end for supercells -- 25-30kts.

Farther south, same story as far as deep-layer shear is concerned. The >65 Tds appear to nudge up against the dryline a little better, and the NAM is picking up on a little stronger low-level shear (helicity) east of the dryline by afternoon and evening across eastern tx ph, far nw ok, and into sw/sc KS. Again, however, the NAM does not break out precip along the dryline until after 0z.

Overall, it still looks like the best bet is up with the sfc low, though I'm not quite as excited as I was before. Regardless, I think the dryline may be a good place for those who don't have time to make it farther north. I don't mind WF chases, but it seems that storms tend to congeal into lines/clusters more quickly than their dryline counterparts. We'll see.
 
NAM shows convection firing in the early afernoon along the warm front in southern/southeat Nebraska. I think the main show will hold off until later in the afternoon over northwest Kansas/southwest Nebraska on the triple point.

Any supercells that form near the triple point and can room themselves along the warm front will produce several tornadoes. Shoot, any supercells that form near the triple point at all have the potential to produce tornadoes, but they risk crossing the warm front with the 25-35knot northeast storm motion.
 
Target 1: Concordia, KS

Target 2: Hill City, KS

Deepening 999 mb sfc low will be in place over western KS by 00z with warm front draped between the I-70 corridor and NE border and attendant dryline extending southward into the OK panhandle and the far eastern extents of the TX panhandle. 50-60 kt 500 mb jet max enters northwestern KS during the forecast period, balancing the potent 30-35 kt flow at 850 mb. Helicity will be maximized along the warm front, similar to the storm initiation seen Tuesday. 0-6 km bulk shear of 45 kts will support sustained supercells in an area from areas northward of Sherdian Co. in the west and Ottawa Co. in the east. The dryline exhibits a nice bulge south of the warm front with 65+ Tds available further east from the sfc low.

My favorite target from the 00z run would be Concordia, KS which will be rooted along the warm front with some jaw-dropping NAM forecast sounding parameters: 335 m2/s2 0-3 km SRH, SBCAPE 4500 J/Kg, 3 km EHI 9.6, LCL ~750 m, storm motion 225 ~ 25 kts. Only concerns are CIN of -56 J/Kg...but forcing mechanisms should be in place to break this down late in the day and moisture is very shallow so long-lived tornadoes will be difficult..many small ones like Tuesday will be likely. Hill City and points closer to the sfc low north of I-70 are also enticing, but moisture does not appear to be as ample despite nice low-level shear. Adjustments will be likely after the 12z NAM and RUC come into play in the morning. Looks like we'll be departing OUN around 9:30am for the drive up north. Good luck to everyone heading out tomorrow!
 
Well, as usual, the RUC and NAM are at odds. The 0-3km SRH is crap on the RUC, while it's pretty awesome east of the entire dryline on the NAM. With 35-48kt SSE 850mb flow, we'll see awesome low-level shear east of the dryline dryline, more see across KS then OK/TX panhandles. With CAPEs progged to be in the 2500-3000 range, I could certainly see a 15% hatched tornado risk across western/northern KS, and maaaaybe down the dryline farther south. If we lower LCLs / higher moisture, and we had a little stronger upper-level flow, I could see a high risk... well, that's assuming the NAM will verify. RUC breaks precip down in eastern TX panhandle, and along the warm front, while NAM breaks out precip along the entire dryline. I'm planning on heading up to I70, then west. Stop for data... if it appears that NAM is verifying, won't worry about going too far north... If the RUC appears to be doing better, will have to move northward closer to KS/NE border.
 
I agree to an extend with what Jeff said. The NAM is forecasting the backed 850 winds to remain backed while the RUC shows them veering a bit back towards the south by 00Z. But that shouldn't matter to much for the best area which is still northwest Kansas/southwest Nebraska and east along the Nebraska/Kansas border along the warm front. That area looks amazing for tornadoes no matter which verifies.

I agree there is still good tornado potential further south along the dryline if the NAM verifies given great forecast hodographs. Personally I'd head further north and play that game (if I could chase), but I guess that's a distance preference. Of course there's concern with respect to storms crossing the warm front and becoming elevated/dissipating, but any that turn right and ride the warm front will be tornado machines!

Happy Chasing!
 
analysis

Mesoscale analysis as of 11:00 AM shows supercell composite parameters as high as 10 and significant tornado parameter at 1 across portions of northern Kansas. There is also evidence that the cap is weakening. CAPE as high as 3500 in vicinity of Salina.
 
Originally posted by Jeff Snyder
I could certainly see a 15% hatched tornado risk across western/northern KS, and maaaaybe down the dryline farther south.

Looks like SPC agreed with you in their latest day 1 tornado outlook. They upgraded to a 15% hatched area.


If the RUC appears to be doing better, will have to move northward closer to KS/NE border.

I think this is where I will play today. I'm looking to setup near the NE/KS border, just south of Beatrice. Although, there's still a lot of day left so it will probably change :)
 
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