05/06 2009
Monster hail reported from N TX yesterday
Activity yesterday has been slightly more isolated than it was expected from the model runs before, strong cap did hold most of the airmass well capped below EML. SPC had downgraded the outlook to SLGT risk at 20z yesterday, as widespread initiation was not expected anymore. But environment still showed a classic loaded gun sounding as can be seen on the DFW sounding below and it was just about a matter of stronger SFC convergence to initiate storms:
During the late afternoon into the evening hours, warm front stoped moving north as evident OFB was coming from the MCS on going in ECNTRL OK mentioned in the forecast yesterday, and became Q-stationary in N TX near I-20. Dryline was mixing from west TX as SFC low was deepening over NM/W TX state border as well as increasing LLJ jet was ahead of it, nosing LL thermal ridge towards north TX. As can be seen on the 00z SFC analysis below, triple point was located just west of Abilene in that time, while warm front was extending Ewards just north of I-20 into northern LA.
At around 23z, on VIS satellite imagery rapidly growing cumulus clouds were evident along the warm frontal boundary just NE of Abilene, in the line Albany-Breckenridge-Weatherford and initiation was just about to start as cap weakened. First storm fired up just east of Albany, but quickly dissapeared as it appears cap was still too strong and did not allow it to organize.
However, it did not last long before another cell exploded practically over the same area, likely slightly improved SFC convergence played a role fo its initiation, probably also from the previous cell. This one then extremely rapidly became organized and took supercell caracteristics. Given the above DFW loaded gun sounding and having in mind upper 60s to low 70s SFC dewpoints in place with overlaping 60kts+ of 0-6km bulk shear, such rapid development was expected. Storm quickly became severe and soon made a right moving mode which turned to start hailing with large monster hail.
Zoom-in into this cell, a strong hailcore well visible, as well asclassic hook feature:
Several chasers and spotter in the area of it were reporting extremely large hail up to baseballs and softballs (4-5″ = 10-13cm in diameter!) and many of them got caught in the main hailcore, damage their vehicles and windshields. On this supercells, large wall clouds were observed, but no tornadoes spotted. This radar image is pretty ineteresting, showing many chasers/spotters extending along road US180 just east of Breckenridge.
Below are several hail reports on SPC website of giant hail from this supercell, as well as a video of a storm chaser Connor McCrorey who got caught by this monster hail:
0100 200 3 NW STRAWN PALO PINTO TX 3258 9853 SPOTTER NETWORK REPORT OF 2 INCH HAIL 3 MILES NW OF STRAWN (FWD)
0101 400 5 W STRAWN STEPHENS TX 3255 9858 STORM CHASER HAD CAR DAMAGED BY 4 TO 5 INCH HAIL ON HWY 207 WEST OF STRAWN. (FWD)
0128 275 6 N HUCKABAY ERATH TX 3243 9830 SPOTTER NETWORK REPORT OF BASEBALL HAIL 2 MIELS ENE OF THURBER (FWD)
Giant hail – courtesy of Connor McCrorey.
Later on, when LLJ increased, an elevated storms began to fire on its nose over ECNTRL OK into NE TX and an overnight MCS was racing Ewards towards S AR/N LA with hail and damaging winds as the main threat.
05/05 2009
Giant hail and tornadoes possible today over northern TX
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.
No comments05/04 2009
10th anniversary of May 3rd 1999 tornado outbreak in central OK
On May 3rd, 1999 a major historical tornado outbreak hit central OK, parts of TX and KS. Numerous large and violent tornadoes causes extensive damage with 40 deaths and more than 600 injured in OK where the most memorable event was F5 tornado which hit Moore and southern Oklahoma City metro area. Additionally, few deaths and injured people were also reported from Wichita, KS metro area.
Below is likely the most known radar image of a classic hook echo feature which is usually a sign of a tornado-producing supercell thounderstorm. In addition, there is also another radar image where tornado was passing I35 from Oklahoma City – Moore. On the right side, SR velocity image is attached.
This image shows approximate locations and paths of the most damaging tornadoes occured in central Oklahoma state:
Please, refer to these additional links to read some more interesting information about this historic event:
05/01 2009
Supercells with monster hail likely today across NW TX
Very dangerous situation appears likely today across SW OK into NW TX as extreme instabillity and favorable wind shear will be in place for monster supercells development. A wide upper-level trough over northern America/Canada slightly extends while several short-wave troughs are moving across southern States. At low levels, cold front is racing SSEwards across cental Plains while there is also massive outflow boundary well visible on the latest satellites, ejected from the large mesoscale convective complex over central Plains which was on going in the last 12hrs. This OFB is however also aligned with the SFC cold front.
As seen on the image above, this OFB/cold front feature is somehow horizontally oriented from WSW to ENE and is racing southwards into SW OK. A sharp dryline is also evident on the SFC observations and is expected to mix Ewards during the afternoon as surface low slowly deepens in west TX. A dryline bulge is expected to form in south TX Panh towards NW TX, while slowly increasing LLJ jet maintain incredibly rich boundary layer moisture between these boundaries, models are confidently simulating very high SFC dewpoints up to high 60s into low 70s in south-central OK and southwards into TX. Further south, stout cap is expected to be in place, while steepening lapse rates ahead of approaching weak mid-level disturbance into southern Plains and strong surface heating in relatively clear skies in warm sector SE of triple point outflow boundary/dryline/cold front, support extreme instability and rapid destabilization of the boundary layer is expected towards late afternoon as cap weakens.
Given the very high SFC dewpoints and steep lapse rates aloft, models are simulating extreme amounts of CAPE where especially RUC is going too high again due to its overestimated SFC dewpoints, this time even up to mid 70s, GFS and WRF are again more realistic predicting dewpoint as high as low 70s. But according to the latest SFC observations at OK mesonet, SFC dewpoints are already from 68-70 degrees F across south OK while similar environment is present also over northern and NWern TX. Models then suggesting a SBCAPE release as high as 4500-5000 J/kg (however, RUC has it even up to 6500 J/kg) and around 4000 J/kg of MLCAPE. Certainly an extreme instability in place for explosive convective development of any storm that will initiate in this environment.
Wind profiles are today slightly better than were yesterday, especially in the lowest 3km with 20-30kts of LL shear while DL shear remains around 40-50kts. LL shear will be slightly improving towards the evening as LLJ increases ahead of deepening low over W TX. This will create favorable wind shear for development of tornadoes. SR helicity is not expected to be very high this time, however enhanced values are expected along the surface boundaries and around the triple point.
Storm Prediction Center has gone with MDT risk over the NW TX into extreme SW OK for this reason, while the more confident reason for issuing higher risk over this area is due to extreme instability overlaping good with wind shear to support very large to giant hail. Extremely large hail as baseballs or even larger, up to softball size hail, are reasonable given such amount of SBCAPE in place.
Again, as it happened yesterday, marginal to moderate mid/upper level flow from the west is favorable for slow moving storms which tend to produce very structured and photogenic supercells and their striations due to such veering winds in the lowest few kilometers. In my opinion the best place to be today is a triangle between Wichita Falls-Childress-Abilene. Actually I would be a target in the middle of this area, so Seymour, TX sound like a great target today. There will be an extreme MLCAPE near or above 4000 J/kg in place and favorable wind shear and insane LL hodographs as can be seen below on the skew-t map, as an increasing LLJ kicks in over this area later towards the evening and increasing chances for some tornadoes as well, along with massive supercells with monster giant hail with any discrete cell that develops. Storms are expected to be isolated in the first place, however a large cluster of storms/MCS and elevated convection is expected overnight across most of OK when LLJ increases.
04/30 2009
Favorable setup for well structured supercells across OK today
Another marginal setup is expected over OK today, as somewhat weak NWern flow is present in upper levels while at low levels moderate SSWesterlies are in place across central Plains, overlaping good with extreme instability. At surface, cold front is slowly racing SEwards across central Plains during th day, while dryline is slowly mixing Ewards from Eern TX Panh into SW OK and over W TX. Several complex systems have been on going in the last 12 hours across central and southern Plains leaving several outflow boundaries behind. In addition, those convergence zones will likely be focus points today as well as Ewards mixing dryline interacting will a weak outflow boundary in SE TX Panh/SW OK later in the afternoon. Storms are also expected along SEwards racing cold front further north.
Shortly said, veering wind profiles, even the speed shear is only low to moderate, will create very favorable directional shear for supercells development all across warm sector between dryline on the western edge and cold front to the north. Given the pretty high surface dewpoints, which are currenty in upper 60s to low 70s in parts on N TX and in mid to upper 60s in much of OK, along with strong heating expected as clearing skies are evident on the latest satellites behind the early activity and steep lapse rates in low levels, high CAPE release and rapid destabilization of the boundary layer is expected to accur as cap weakens later in the afternoon.
Storms will likely initiate along mixing dryline and racing cold front first, while some isolated supercells can be expected in between across south-central OK as well, depends on local convergences along the outflow boundaries. Very high CAPE values along with directional but weak speed shear, will still become favorable for rotating updrafts while a classic setup for structured supercells could take place as such wind profiles, with NW flow aloft and SW flow beneath it, usually supports well structured supercells. Actually, similar happened yesterday over western KS with the monster classic supercell that has produced impressive stucture as well as numerous gustndoes, very large hail and also a couple of tornadoes near Garden City. So today the main threat can be supercells with very large hail and damaging winds, though weak tornadoes are also possible, especially along the boundary interactions which will lead into increased effective SR helicity.
I like the area ahead of the mixing dryline in the belt of very high instability near Lawton, OK. That would actually be my target for today. As can be seen from the skew-T diagram above, very favorable directional shear is present as well as several thousands of SBCAPE. However, as earlier said, only marginal to moderate speed shear will be present, but given the mid/upper-level WNWern flow, storms will not have much problems with rapid organization with severe weather threat and photogenic look.
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