Well my gut telling me that south central OK would be the best play wasn't quite correct.
The second initiation of convection to the south near Lawton just took forever to congeal into a supercell after many many mergers of smaller storms. The hint is that the cap was too strong, or the shear was too strong for the minimal instability being released. This would suggest that the stronger dynamical forcing to the north was a key factor in the rapid transition from small cells into bigger supercells.
The shear though was also questionable at FWD , despite 200 SRH, only the lowest km had significant hodograph curvature. aloft the hodograph was a straight line. At OUN, within some sort of convection, the hodograph was much larger and curvature much more pronounced.
The observed 500 hPa frontal zone was pretty much in contact with the main supercell of the day and had a pretty good connection to the initiation in southern OK. V2 soundings might shed light on this .
Overall I am not sure what to think of an event like this. The soundings to the north in OK appeared to be uncapped and the shear great. Tornado production was similar to the day before ... apparently present but most short lived. Moisture was present, SRH was high, BRNSHR was in the 10-80 range, and the hodographs all had good curvature.
To the south, there was a cap, perhaps weaker forcing until much later, hodographs were curved by trended to be more straightline (window of opportunity was shorter to the south perhaps), but the instability was greater. I did notice that the southern supercells, had outflow attached to them. So perhaps the mid level dryness enhanced cold pool strength. This case has lots of interesting questions.
Wednesday, May 19, 2010
dynamical devil
The dryline bulge is in western Oklahoma somewhat removed from the 500 hPa frontal zone as seen in water vapor imagery. However the circulation about this front has resulted (or speculated to have resulted in a narrow moist tongue over the proximate location of the dryline in OK.
I expect CI to be imminent, and perusal of vis sat imagery confirms the presence of a cumulus field in western OK. Not sure if the remnant outflow boundary is really a front or if the nocturnal MCS simply cooled and clouded over the northern portion of the front. Thus, not sure if this front is very active....or if it will truly be a focus for CI.
Vis imagery wave clouds would indicate that it is still relatively stable in Central and southern OK.
First echos on the dryline at 18:56 strengthened by 19:14 UTC. Looks like convection is right on time.
I expect CI to be imminent, and perusal of vis sat imagery confirms the presence of a cumulus field in western OK. Not sure if the remnant outflow boundary is really a front or if the nocturnal MCS simply cooled and clouded over the northern portion of the front. Thus, not sure if this front is very active....or if it will truly be a focus for CI.
Vis imagery wave clouds would indicate that it is still relatively stable in Central and southern OK.
First echos on the dryline at 18:56 strengthened by 19:14 UTC. Looks like convection is right on time.
The devil is in the dynamics
A nice little potential outbreak today for OK and North TX. Complicated situation as the night time MCS moves away from OKC, with no outflow boundary clearly visible. The low level cloud field is eerily similar to previous days. The complications are that the elevated mixed layer is well into the area, and the 500 hPa frontal zone is already through AMA. Surface convergence will be there to the north but it may be the dynamics that sets this thing off.
The cap is the big player and the models favor this opinion. NCAR ARW run from last night says multiple periods of initiation to the north, remniscent of May 10, again occurring earlier in the 18-19 UTC time frame. Then later on initiation occurs along a dryline boundary (around 22 UTC) before growing upscale. NSSL ARW run is a lot different probably because of the poor precipitation forecast it produced to the west of the MCS. So too much precipitation to the west virtually ensures that a subsequent trigger for new convection occurs earlier.
Both models agree that initial development will be scattered but not isolated. Thus storm interactions and outflow development may hinder chances at discreet, cyclic tornadic supercells. Today may be a tail-end Charlie kind of day.
The models are not very different with the dryline, but it appears the 500 hPa front is much stronger in NCARs run...though i have no proof since the NSSL run does not make available fields aloft...however the CI that occurs in NCARs run appears associated with the 500 hPa frontal circulation. This is inconclusive however because the 850 RH field is near saturated as well. Breaking the cap is easier when the PBL top becomes saturated.
If I were chasing today, I would try to be south of OKC, probably in Norman. Wait to see how the cap holds to the north and if early storms stay isolated and discreet go for them. Then haul ass south later in the day as the next wave of CI occurs along the 500 hPa front. Otherwise south and east of Norman. The show should start by 19-20 UTC either way...3 hours from now.
Not sure of the tornado potential. Yesterday appeared to be ripe for tornados, yet the pictures and reports indicate short lived but strong tornados. Nice supercells on radar, though. wonder if the shear profiles were not ideal enough. The shear profiles from NCARs model at OUN at 21-23 UTC appear good enough, so this may be a right time right place scenario...brief window is implied. To the north it is less certain since storms may be on the warm front. I am still hedging my bets southward of OKC ...
The cap is the big player and the models favor this opinion. NCAR ARW run from last night says multiple periods of initiation to the north, remniscent of May 10, again occurring earlier in the 18-19 UTC time frame. Then later on initiation occurs along a dryline boundary (around 22 UTC) before growing upscale. NSSL ARW run is a lot different probably because of the poor precipitation forecast it produced to the west of the MCS. So too much precipitation to the west virtually ensures that a subsequent trigger for new convection occurs earlier.
Both models agree that initial development will be scattered but not isolated. Thus storm interactions and outflow development may hinder chances at discreet, cyclic tornadic supercells. Today may be a tail-end Charlie kind of day.
The models are not very different with the dryline, but it appears the 500 hPa front is much stronger in NCARs run...though i have no proof since the NSSL run does not make available fields aloft...however the CI that occurs in NCARs run appears associated with the 500 hPa frontal circulation. This is inconclusive however because the 850 RH field is near saturated as well. Breaking the cap is easier when the PBL top becomes saturated.
If I were chasing today, I would try to be south of OKC, probably in Norman. Wait to see how the cap holds to the north and if early storms stay isolated and discreet go for them. Then haul ass south later in the day as the next wave of CI occurs along the 500 hPa front. Otherwise south and east of Norman. The show should start by 19-20 UTC either way...3 hours from now.
Not sure of the tornado potential. Yesterday appeared to be ripe for tornados, yet the pictures and reports indicate short lived but strong tornados. Nice supercells on radar, though. wonder if the shear profiles were not ideal enough. The shear profiles from NCARs model at OUN at 21-23 UTC appear good enough, so this may be a right time right place scenario...brief window is implied. To the north it is less certain since storms may be on the warm front. I am still hedging my bets southward of OKC ...
Wednesday, May 12, 2010
warm front MCS
So I fell asleep last night and missed out on real time watching of the Mesoscale Convective Systems that formed. May 11-12 2010 .
I am always fascinated by the different evolutionary modes of convective initiation. Yesterday's mode was scattered convection under a moderate shear-high instability day. But it was effectively capped, given that multiple elevated supercells formed and quickly dissipated much to the chagrin of VORTEX2 participants. It was a classic Iowa warm front event, with little to no forcing but shear and instability abound.
at 2200 UTC, the first supercell was in the process of initiating in SW OK and after 1 hour falls apart. It skirts an area to the north just south of woodward I believe, and another set of CI takes place between 2345 and 0015 UTC. Again short lived supercells. However, the anvil aloft is cold and the cloud does not dissipate. So it looks like a storm is there, but on radar it was a useless blob of 30 dbz echo.
By 0145 the warm front in SE KS gets hot and explodes into the primary MCS. This initial convection gets going and after perhaps 45 minutes to an hour backbuilds to the west along the front while that old cloud shield drifts in by 0402. Not much longer later the old cloud shield is rapidly dissipated around the MCS as it swells to maximum size virtually covering MO by 1100 UTC.
at 0345 UTC SW KS sees another MCS initiate and suddenly from KS into NE convection is firing up. This MCS looks asymmetric almost half circle like but looks very similar to an MCC. Once these two systems get close enough to each other the eastern MCS appears to dissipate, at least its western end. The radar reflectivity pattern was chaotic in nature. This is a different breed of cloud system most notably MCC like. It doesnt come with much severe weather oddly enough given its environment. But the cloud shields are huge.
After looping tonights water vapor imagery .... the eastern MCS traveled from IL through VA out over the Atlantic. I noticed a pretty compelling anticyclonic gyre aloft. very classic long lived system.
Also note that CI occurred on both sides of the water vapor dry slot ... to the east failed and to the west got going.
The surface data doesn't look that compelling .. where the warm front convergence was occuring in SE KS is where CI took place along the front. beyond that moisture was slowly working north (implied moisture convergence). Both systems were on the anticyclonic shear side of the upper level jet which was just by position only since the wind field aloft was pretty homogenous.
Soundings from LMN indicated the cap had weakened boasting CAPE of between 2-3000 J kg-1 at 2100 UTC. The wind sbacked at 0000 UTC and the low levels became saturated as the cap layer seemed to strengthen a bit. though perhaps the lapse rate steepened under slight cooling aloft. 6 hours later the layer below 850 had a nasty 50 kt LLJ and warmed and moistened appreciably. moisture depth to the east was high, as the low levels appeared to be saturated.
visible imagery indicated some sort of cloud boundaries, like elevated outflow boundaries that might be implicated here. But I dont have access to the OK mesonet data to see if anything showed up there. In my experience it doesnt show up on the sfc winds, but it might be in the pressure field.
Interesting day. Maybe V2 will have some photogrammetry of these supercell initiations.
I am always fascinated by the different evolutionary modes of convective initiation. Yesterday's mode was scattered convection under a moderate shear-high instability day. But it was effectively capped, given that multiple elevated supercells formed and quickly dissipated much to the chagrin of VORTEX2 participants. It was a classic Iowa warm front event, with little to no forcing but shear and instability abound.
at 2200 UTC, the first supercell was in the process of initiating in SW OK and after 1 hour falls apart. It skirts an area to the north just south of woodward I believe, and another set of CI takes place between 2345 and 0015 UTC. Again short lived supercells. However, the anvil aloft is cold and the cloud does not dissipate. So it looks like a storm is there, but on radar it was a useless blob of 30 dbz echo.
By 0145 the warm front in SE KS gets hot and explodes into the primary MCS. This initial convection gets going and after perhaps 45 minutes to an hour backbuilds to the west along the front while that old cloud shield drifts in by 0402. Not much longer later the old cloud shield is rapidly dissipated around the MCS as it swells to maximum size virtually covering MO by 1100 UTC.
at 0345 UTC SW KS sees another MCS initiate and suddenly from KS into NE convection is firing up. This MCS looks asymmetric almost half circle like but looks very similar to an MCC. Once these two systems get close enough to each other the eastern MCS appears to dissipate, at least its western end. The radar reflectivity pattern was chaotic in nature. This is a different breed of cloud system most notably MCC like. It doesnt come with much severe weather oddly enough given its environment. But the cloud shields are huge.
After looping tonights water vapor imagery .... the eastern MCS traveled from IL through VA out over the Atlantic. I noticed a pretty compelling anticyclonic gyre aloft. very classic long lived system.
Also note that CI occurred on both sides of the water vapor dry slot ... to the east failed and to the west got going.
The surface data doesn't look that compelling .. where the warm front convergence was occuring in SE KS is where CI took place along the front. beyond that moisture was slowly working north (implied moisture convergence). Both systems were on the anticyclonic shear side of the upper level jet which was just by position only since the wind field aloft was pretty homogenous.
Soundings from LMN indicated the cap had weakened boasting CAPE of between 2-3000 J kg-1 at 2100 UTC. The wind sbacked at 0000 UTC and the low levels became saturated as the cap layer seemed to strengthen a bit. though perhaps the lapse rate steepened under slight cooling aloft. 6 hours later the layer below 850 had a nasty 50 kt LLJ and warmed and moistened appreciably. moisture depth to the east was high, as the low levels appeared to be saturated.
visible imagery indicated some sort of cloud boundaries, like elevated outflow boundaries that might be implicated here. But I dont have access to the OK mesonet data to see if anything showed up there. In my experience it doesnt show up on the sfc winds, but it might be in the pressure field.
Interesting day. Maybe V2 will have some photogrammetry of these supercell initiations.
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