Archive for May, 2009

Massive squall line with embedded strong tornadic supercells blasted through the Plains

As expected, a cold front was racing SE-wards across the Plains during the afternoon/evening hours and overnight bringing all types of severe weather all the way from western OK NE-wards into western IL. For now, here are only a couple of satellite/radar images and satelite animations as I am running out of time. More details about this impressive setup with be added in the next days.

It just had to be noted, that tornadic supercells with several late afternoon strong tornadoes caused extensive damage in NE-ern MO while some tornadoes also occured over SE KS and w-cntrl OK after dark. Unfortunatelly, also at least three people were killed and several people were injured by the strong tornado that swept through city of Kirksville, MO. Numerous chasers documented large wedge tornadoes in that area, some of them were pretty close calls.

Anyways, here is a SFC analysis at 21z when the cold front was extending from central IA SW-wards through NW-ern MO and SE-ern KS into NW-ern OK and further SW into TX Panhandle where dryline was extending SSW-wards into W TX.

SFC analysis 21z

Weakening capping inversion and strong SFC wind convergence along the frontal boundary soon initiated storms. Frontal boundary was clearly visible on satellites and radar images as can be seen on the next images, extending from Kansas City to just south of Wichita and towards Gage, OK.

VIS satellite 2133z

KS radar

Due to extreme instability and strong shear overlapping ahead of this boundary across warm sector, storms very rapidly organized into supercells, some of them soon became tornadic. Especially over northern MO as wind shear and helicity were very high. Numerous storms fired up along the front from IL towards W OK.

VIS satellite 2315z

OK radar

On this radar for whole MO state, a strong tornadic supercell with strong tornadoes that caused fatalities in Kirksville can be easily recognized.

MO radar

Given the strong forcing, very strong LL flow which tend to be parallel to the frontal boundary and weaker ML flow, supercell storms quickly went linear and several Q-linear mesoscale system started to form. As for around 00z, storms were already pretty linear which was clearly seen both on radar and satellites.

IR satellite 0015z

cntrl Plains radar 00z

Later on, a massive squall-line formed all the way from IL across MO into SE KS and W-CNTRL OK and blasting SE-wards across the Plains overnight, causing strong winds and hail damage. This WV satellite shows this impressive linear MCS on going at 0245z.

US WV satellite

A squall-line tend to be broken on its SW-ern flank and therefore a few discrete tornadic supercells were still ongoing near OKC and SW-wards towards Anadarko, which was damaged by a tornado and strong downbursts at late evening. Radar image shows this monster supercell in that area.

radar OK

Here are also few animations of IR, VIS and WV satellite images, showing the evolution of severe storms along thr cold front and clustering into a massive MCS later on.

  • VIS satellite: http://www.youtube.com/watch?v=VtK3dV7yT80
  • IR satellite: http://www.youtube.com/watch?v=FXTwgJDDwxA
  • WV satellite: http://www.youtube.com/watch?v=JT1l0WO-C50
  • Severe weather/tornado outbreak possible across E OK/MO/IL today

    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.

    500mb heights

    850mb winds

    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.

    SRH3

    MLCAPE

    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

    MDT risk

    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.

    MCS

    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.

    Insane CAPE with strong cap over OK and severe weather possible over E KS/W MO

    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.

    zonal flow

    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.

    SBCAPE

    KSPS skew-t

    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.

    Harrisonville, MO skew-t

    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.

    LL jet

    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.