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.

Post storm wrap up

Wild day. 37 reported tornados. maximum hail size of 4.25". Max reported wind gust to 100 mph.
Looks like a number of fatalities have occurred as well.

Well forecast event by SPC. The uncertainty was well forecast at 1200 and 1300 Day 1 outlooks:
1. Initial storms would take time to organize thus Initiation area would be removed from maximum tornado risk.
2. moisture return would not be an issue.

BUT, the 1630 UTC update suggested that 21 UTC would be the new initiation time. Doubt crept in. Even to go as far as to say that central and southern OK would be capped and that models were over-aggressive. The 2000 UTC update re-instated the aggressive coverage southward based on the satellite data: cumulus cloud field developed in advance of and in proximity to the dryline.

What was not well forecast was the timing of CI. SPC was calling for a 18-19 UTC CI in SW KS, with another bout further south into OK by 21-22 UTC then further south into central and southern OK. The focus was on the cap and favorable moisture return.

Indeed the actual event sequence began like SPC said: SW KS near DDC for 2nd and 3rd storms in a bunch at 18 UTC. The storms appeared further SE into OK to the northwest of WWR by 1850 UTC and another east southeast of Gage and a few weak storms further south. These storms never really got going though they were players later when they merged with the northern storm ... that storm became tornadic after those mergers though it isnt clear they were the cause.

Now heres where the forecast goes awry. The dryline has not been dogged by storms. It was still going strong. At 2000 UTC a weak storm complex was near JWG. It almost dies, then out of nowhere re-intensifies into a nasty linear looking supercell. Much like the Nov 2005 Ames tornadic supercell or really much like high shear supercells.

By 2100 UTC a new batch of weak storms in advance of the dryline form and these quickly become supercellular in a cluster. The dryline is far removed from these storms. Much further south more storms get going, more likely previously involved storms with the dryline down there. Between these 2 areas another loan supercell formed and merged with the OUN cluster. This rogue supercell seemingly merged into the southern side of the northern supercells and that was in Norman or close by. differential storm motion for some reason on that storm.

New storms form off the dryline by JWG and move northeast to form a more linear looking cluster. By 2142 more storms form on the dryline to the west of OUN. This cluster appeared to form a line before devolving or maybe evolving into nasty hook echo supercells. Quite spectacular.

The supercells came in waves, seperated by time and/or space in clusters. They were at times poorly spaced but productive, and well spaced and spectacular. We saw the whole range of high shear supercells. More importantly we saw that the model forecast paradigm broke down. The soundings launched by vortex2 will be invaluable to assessing the environment on this day. This will be one of the most studied days in VORTEX2.

Big cities under the gun

Wichita and Oklahoma city are under tornado warnings and basically in between. A number of large tornado reports have come out, amidst the very brief 30s to 3 minute variety. The supercells have shown all kinds of high shear characteristics today.

The most crazy is a left mover split that eventually produced tornado warnings in kansas off the woodward storm. It crept in behind another storm, and then that one went tornadic as well. The woodward or likely a variant of it, because it merged with at least two other storms (of linear shape and very weak reflectivity speaking).

and the reports are coming out fast. You actually have to wonder what the impact of having a great weather dept. at OU has done for safety in Oklahoma. If there are storms you can bet like 30-60 chasers will be out combing the plains for tornados, and some of them will be relaying information back to the NWS. This doesnt prevent damage, but it should make people more aware of tornados and there warnings.

and the tornado warnings come out

Couple of reported tornados in what looks like a set of massive circular blobs which was the most continuous feature associated with the shortwave trough.

DDC initial storm just got its act together. Possible hook and strong rotation noted on radar. It appeared the evolution of such storms were very typical of high shear environments ... stretched out along the mean wind until repeated bouts of deep convection upshear culminated in protecting the storm.

This is also the case for the woodward storm though it got going later and split with the left mover not moving very far off yet. The main tornadic portion of the cell appeared to be linear! it now has a kidney bean shape with reflectivity over 65.

Situation is still somewhat chaotic between these two nice storms. no warnings and there appears to be no organization with them which is strange.

Dew points up to 68-70 in OK just west and south of OKC. Despite that the storms south of the woddward storm just cant get going. They are struggling. would love to see the sounding from OUN, as there might be a stronger cap in place which would protect OUN till later tonight.

FWD sounding was strongly capped. so was DDC though I will have to review the radar data at 1715 to see which air mass was being sampled, environment of low level storm.

Nice outflow in CO.