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Classic tornadic setup tomorrow over the southern Plains. Conditions are coming together for severe storms with violent long-track tornadoes possible in late afternoon/evening hours over east-central KS, as well as SE KS.

Here is a skew-t diagram for point just about 15mi south of Norman, OK tomorrow at 00z.

Stay tuned for future updates on this incredible setup.

An outbreak of severe weather with very large hail and few strong tornadoes seems likely across eastern OK into MO and IL. A deep trough over northern Plains surrounded by strong polar jet on its southern side translates towards Great Lakes in the next 24hrs. At surface, a cold front extending from SFC low in south Canada SW-wards across upper Mississippi valley towards KS/OK and TX Panhandle is racing SE-wards across the Plains. Impressive 50-60kts SW-erly LLJ jet ahead of this front supports healthy moisture advection NEwards from central Plains into MO and W IL.

A well defined MCV was on going over E OK moving NE-wards into S MO, where at least one outflow boundary blown N-wards is evident on VIS satellite and radar images. This boundary could serve a focus for afternoon’s storm initiation along it, when airmass will destabilize. Very steep ML lapse rates will spread over the warm sector and in combination of rich BL moisture, surface dewpoints expected to be in upper 60s to low 70s from E OK into MO, extreme instability with MLCAPE values in excess of 3000 J/kg will result. Visible clearing skies behind the warm front over central MO allow strong surface heating during the day and weakening cap is expected later in the afternoon with an approaching forcing. Storms will likely form ahead of NE-wards moving residuals of MCV while additional initiation of storms will take places along numerous SFC boundaries/convergences from past storm systems on going over these areas. Expect rapid development of severe storms in this very unstable enviroment with strong shear. Stronger shear will be in place over MO/IL closer to the polar jet, while only weak to moderate shear will be in place more SW-wards over OK. Therefore, strong tornadoes are possible over MO/IL given the high 0-3km SR helicity values in range 400-600 m^2/s^2 and locally enhanced LL shear. More isolated severe storms are expected over OK where a few tornadoes are possible, but mainly threat for very large to giant hail exists.

Strong SW LLJ jet and quite linear hodographs suggest storms to rather quickly take linear mode, so threat for stronger tornadoes can be expected in the early stages of any supercell that forms in this favorable environment. Given the significant eroding of cap over larger area in the afternoon, widespread coverage of storms can be expected and for this reason, SPC has issued MDT risk with 10% area for tornadoes and 45% hatched area for very large hail from E OK towards W IL.

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1136 AM CDT WED MAY 13 2009

…SEVERE THUNDERSTORMS EXPECTED FROM THE CENTRAL/SOUTHERN PLAINS TO THE MID MISSISSIPPI VALLEY LATER TODAY AND TONIGHT…

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE DEVELOPMENT OF TORNADOES…LARGE HAIL AND DAMAGING WINDS FROM THE CENTRAL/SOUTHERN PLAINS TO THE MID MISSISSIPPI VALLEY LATER TODAY AND TONIGHT.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

NORTHWEST ARKANSAS
ILLINOIS
SOUTHEAST KANSAS
MISSOURI
OKLAHOMA

As mentioned above, storms will be more isolated across E-CNTRL OK given the stronger cap and less forcing in place. Weak to moderate shear does support supercells while SR helicity remains low, but enhanced values along SFC boundaries can support tornadoes as well, along the very large to giant hail given the extreme instability with MLCAPE over 4000 J/kg in place. A bit higher chances and veering wind profiles exist in southern OK, but this area still looks well capped and might not see storms initiation before front surges in during the evening.

Later towards the evening, as cold front continues to race SE-wards across the MDT area, storms will cluster into linear MCS or two with likely embedded strong squall-line. The system will continue as a large mesoscale complex overnight moving NE. Therefore threat for large hail and damaging winds seems likely where bowing segments might occur.

As for the place to be today, its quite a hard one. There could be three best places today… one over central MO just north of expected MCV location in the afternoon as OFB can serve as a trigger for initiation, storms there will quickly go tornadic given the strong shear and moderate instability. Secondary target is the one I like the most and could be a NNE-ern OK in triangle Enid-Coffeyville-Tulsa, as shear is still moderate and extreme instability is there, cap is not too strong and a tail-end charlie supercell would be the game. Latest RUC does have breaking precips there as cap erodes towards 22z. Third area could be SW OK ahead of E-wards mixing dryline from W TX, some backed LL flow in weak shear and extreme instability is in place, but also the strongest cap. If storms manage to initiate there, they will rapidly become severe with threat for giant hail and also a weak tornado or two.

As it has been shortly said yesterday, an interesting setup is shaping up for today over central Plains towards Misouri valley as upper level zonal flow continues to cross central US, where several embedded short-wave troughs are moving within this flow and will be a focus for storms development. At surface, quasi-stationary old OFB/weak frontal boundary is evident over S IA into SE NE near the weak SFC low located in SE NE, and extending SWwards into central Plains. Further south, a low pressure area over southern High Plains support rapid moisture advection northwards into central Plains, where SFC dewpoints are confidently expected by all models into the mid 70s as north as central OK. The focus for today’s storms development will likely be a convergence over NE/IA earlier and destabilization further south over E KS/W MO towards the late afternoon.

Impressively rich moisture advection with mid 70s over central TX into central OK and low 70s over northern OK during the afternoon pushed models to yield extremely high CAPE values, showing SBCAPE around 5000 J/kg or more where of course RUC model again is going out of control, having SFC dewpoints in upper 70s over S OK/NNW KS yielding AOA 8000 J/kg of SBCAPE. Besides this rapidly improving moisture at low-levels, warming of EML ahead of low pressure area over W TX with rising mid-level temperatures well above 20°C at H85, which resulted in strong cap over south-central Plains, will likely surpress any SFC based convection during the day. A dryline will be slowly mixing eastwards over W TX and Panhandles, but only weak SFC wind convergence, limited SFC heating due to LL cloud cover and no forcing aloft to support ascent, has no chance to overcome such a stout cap. Attached below is also a sounding for Wichita Falls, TX showing extremely high amounts of CAPE, but too strong cap and warm mid levels.

But anyway, further NE over E KS, W MO and northwards into SE NE and S IA right entrance of strong zonal flow allow enough ascent. Strong surface heating should result in sufficent weakening of the cap and destabilization will take place, storms should fire along the SFC boundary and likely continue to organize/maintain later as they move into better environment further SSE into E KS and MO. 60kt+ of 0-6km bulk shear, 20-30kts LL shear, improving LL moisture with 2000+ MLCAPE will be supportive for supercells development with the main threat as very large hail and damaging winds. Hodographs are impressive given the LL veering wind profiles. Still quite low dewpoints in this area, likely mid 50s over IA/NE and mid 60s further south, lower the tornado chances and limit them mostly to MO later on, as LCLs are higher than 1200m up there. However, main wind flow today is again pretty favorable for some photogenic structure of supercells, as veering profiles are impressive and also LCL are high enough.

So today’s target for some nice severe storms would likely be around state border KS/MO, I am virtually targeting a town Harrisonville, MO. Its just SE of Kansas City where parameters seems to overlap the best. However, given the strong mid/upper-level WNW flow, spliting supercells are very likely given such linear hodographs. Later in the evening, when LLJ increases over the Plains, elevated storms will likely take place along the nose of this LLJ over OK/KS with a MCS racing northeast overnight.

As regarding tomorrow’s setup, its still looking pretty good despite the limited forcing/ascent as flow is somewhat weaker than it was simulated yesterday, so cap will ikely be holding airmass capped well into the late afternoon. But at surface, positions did not change that much, dryline bulge evident over S OK into NW TX, strong shear and extreme instability in place support tornadoes along with very large to giant hail and damaging winds. More detailed outlook will be posted tomorrow.

I am running out of time attm to give a detailed outlook over the upcoming two days, but it does look interesting for both days. Thursday look an interesting setup over E OK into SE KS and MO, increasing LL jet ahead of developing SFC low in southern high Plains with returning moisture into the central Plains should create favorable environment for supercell development. My first guess would be Independence, KS as further south, even wind profiles are slightly better, strong cap could surpress storm initiation with a lack of SFC convergence and especially very warm mid-levels (high H85 temps) and lack of ascent.

On Friday, right entrance of strong upper-level zonal flow across US should pose enough ascent/upper-level divergence for storm initiation near triple point and southwards along the dryline in south OK, as SFC low deepens in SW OK during the afternoon. Rather strong cap will definatelly be holding storm initiation well into the late afternoon, but today 12z WRF run has it eroded easily after 21z timeframe, as a result of strong ascent under upper-level divergence and steepening lapse rates. Deepening SFC low over SW OK should create strong enough SFC convergence along the dryline as well as strong SFC heating is expected as it will likely be clear over warm sector. Low-level veering wind profiles again look very impressive with WNW flow aloft and extreme CAPE…overlaping together. Again massive gigantic baseballs and couple of tornadoes ca be expected with any isolated supercells that will form. Storm motion will be ESE and my best bet for initial target, at least from 12z NAM/WRF, would be Waurika, OK. GFS has triple point more south towards Throckmorton, but thats not confident enough and I’d put my bets on WRF simulations. Well still its 2 days out, so likely I’ll have a closer look and more details for Friday tomorrow afternoon.

Upper level short-wave trough ejecting from the Rockies will cross south-central Plains during the afternoon and evening hours, where right entrance jet region with increase the potential for severe storms across southern Plains into lower Mississippi valley. At low levels, deepening surface low is expected to slowly move NEwards from SE NM over W TX. Currently a large MCS is still on going over south-central OK while further south a northwards moving surface warm front is extending from LA WNWwards over N TX into northern NM. Ahead/East of surface low a dryline is extending from NW TX southwards and is expected to mix eastwards during the afternoon.

MCS currently on going over south OK is a result of elevated instability/storms on the nose of a LLJ, where an outflow boundary is pushed SSWwards into Red River area behind this complex. Meanwhile relatively strong LLJ is resulting in rapid moisture return from the Gulf of Mexico as current surface dewpoints in mid to upper 60s are spreading northwards into N TX while additional increase is expected in the afternoon for a couple of more degrees, ranging from upper 60s to low 70s as north as Red River area. As steeper lapse rates are expected with the approaching trough aloft, high to extreme instability will take place, models are simulating MLCAPE in excess of 3500 J/kg while SBCAPE even above 4000 J/kg. Yet again, RUC model is overestimating SFC dewpoints to be in mid 70s and according to that, showing even more than 5000 J/kg of SBCAPE.

With an increase of LLJ and veering winds during the day, strong low-level wind shear will take place across warm sector, expected to be around 25-30kts or slightly more while deep-layer shear will be 50-70kts. Very favorable veering wind profile at low levels show a classic tornadic hodographs. But also an area of concern with this setup is relatively strong cap which will play a big role in today’s storm initiation outside/away from the main frontal boundary convergences, e.g. triple point at DL/WF or WF/OFB intersections. There, storm intiation is more likely along the warm front’s intersection with the southwards racing ouflow boundary. Models have a pretty stout cap south of I-20 which will likely surpress convection until the evening. However, models also suggest pretty strong dryline bulge to form in central N TX near Abilene, which could be a trigger for storm initiation.

What is interesting with this setup can be seen on the skew-t diagrams, where upper level flow is from WNW directions, that is also well visible on the satellite animations of cirrus cloud deck moving across the warm sector, however also thick low-level clouds are visible which might not allow strong surface heating to occur, dewpoint depression will remain quite low and should result in low LCL heights likely 500-800m AGL. This is then becoming favorable environment for tornado development along with increasing of SSW LL flow. Strong veering wind profiles in lowest 3 km suggest pretty high values of SR helicity where models, especially RUC and WRF simulating it well above 500 m^2/s^2 in 0-3km layer. When storms fire, they will rapidly organize and become severe given the favorable parameters in place. Therefore, stronger tornadoes are as well possible if storms manage to form in such environment.

Today, SPC has issued a MDT risk over N TX extending slightly into southern OK with 10% area for tornadoes and 45% hatched area for very largr hail over this area, given the very favorable wind shear and high instability that overlap over MDT area.

Given the all parameters in place today, strong wind shear, increasing LL shear and SR helicity along with extreme instability, strong tornadoes and giant hail are possible over northern TX towards Red River area. Limiting factors are strong cap southwards of I-20 behind the warm front and storms initiation there is questionable. Storms are more likely along warm front and along dryline bulge/triple point. These two areas are today focus for some extremely severe weather, where one should be looking at. First one would be lying right along warm front moving into Red River area, target for this area could be Graham towards Jacksboro. The more interesting target in my opinion would be along/ahead of dryline bulge just north of Abilene, probably Albany for an initial target. But this one is more questionable given the cap stenght. Both of these areas are in risk for tornadoes, giant hail and damaging severe wind gusts. However, if storms manage to form more southwards along I-20, therefore also western side of DFW metro area might be involved into higher tornado threat, but chances for now are pretty low.

Attached below is a skew-t diagram for Graham, TX showing impressive veering wind profiles at low levels, furthermore also SR helicity, and high instability which are supportive for tornadoes and very large hail. Therefore, a well visible convective inhibition as well should not be neglected and without strong convergence along existing boundaries initiation remains questionable before late afternoon/evening hours.

Later on towards the evening when an increasing LLJ kicks in, a large MCS will likely form over north TX/Red River area and track eastwards towards northern LA overnight, where large hail/damaging winds will be the main threat, DFW metro area might find itself in this complex. Flash flooding threat there could also lead to some damage.