May 29, 2012

This was quite a day. The forecast worked out great knowing that with the minnamla flow regime the higher CAPE was favoured. The area up near the warm front would have been favoured if CAPE values were to be higher but the way the setup was, the big CAPE was needed to be able to tap the minimal shear available. This strategy worked out extrememly well and the show we got was spectacualr. But with the instability came the large hail, some of which was reported to be grapefroot sized. We were able to stay out it and had one close call as the back side of the meso begane to spit out some softballs near us. A quick u-turn had us out of it in a few seconds as storm motions were slow today. The storm was able to get its act together and form one brief tornado before the storm was undercut by its outflow.This picture was taken south of Piedmont, OK just before it produced the tornado.

May 30

Today looks like it will be yet another active day for severe storms. This time in the southwest portion of Oklahoma along the warm front which is currently sitting at or just south of the I-40. The primary triggers of interest here will be the outflow boudary (currently sitting in the Watonga, OK region), where it intersects the warm front, and the short wave trough deeping as it crests the Rockies into the TX panhandle. This setup is very similar to ysturday's with the one exception being that the large CAPE is not as crucial to get things spinning and there should be suffucient shear in the low levels along all the boudaries. At the moment the current high resolution models are having a tough time resolving this but monitoring the sfc observations satellite imagery should reveal what the day has in store. Image here shows the currently sufc low in TX area but with little curvature in hodographs splitting cells will dominate there and with slightly better curved hodogrpahs in the southwest OK region, this will be the play as the outflow boundary from overngiht convection and warm front interact. This area is also under the upper livel divergence from the 250 mb jet streaming in from the west.

Exhaustion is starting to set in somewhat after only having one down, which was used to drive from Wichita, KS to Clovis, NM to capture the solar eclipse. But I'm not complaining since the start of the trio didn't really looks like it would amount to very much but it has proven to be the opposite. Today's chase was a challenge as storm motions were fast and things got messy in a hurry. Further north ingredients looked to have come together much better and I'll have to look into as to why in a post analysis when time permits. I figured the southern play had a better shot ear the triple point and southward with shear vectors more perpendicular to the dry line. I guess the moisture mixed out a little more than expected not really allowing for much to get going in the southern targets. The day was not a total loss as were able to observe some structure and lightning.

For today it looks as though we will be in the southwest portion of Oklahoma into the Childress Texas region. Things do looks subtle the main features here are the dual jets aloft and the 500 mb flow. Where the 250 and 500 mb jets lign up should make for great divergence in the upper levels with sufficient diffluence at the 250 mb level.

What is slightly disappointing are the lack of 850 mb low level winds, which should kick up near sunset but I have my concerns that it may not be enough. At the surface things do not looks to bad with some ok backed winds along the surface cold front/stationary boundary which should setup through NE OK down through the central portion of the state and in through to the Childress TX region. With CAPE looking to push into the 1500-2000 J/kg range and 700 mb temps between 5-10 degrees Celsius, energetic and capping looks to not be an issue tomorrow. What I am worried for is the lack of much stronger forcing and again the chance for the low level moisture to mix out which would leave us with elevated storms once again. Shear looks to be ok as well and I suspect the low level shear should be enhanced along the front. Thus looks like it’s down to the southern plains for the next few day and looks like Wichita Falls, TX may not be to bad of a starting point for today.

I’ll have to apologize since I have not been able to post so much lately due to poor internet connections and trying to limit data usage while chasing and about 9 straight days of chasing will tire you out. To summarize the past few days; May 22 and 23 proved to be a little disappointing with some good setups. Unfortunately warmer 700 mb temps and a lack luster flow up from the Gulf really had these setups go to waste. May 24th proved to be less disappointing with a great structured supercell that spun up in a line of storms. It was brief but still produced a nice meso near Ottawa, KS. See image below.

May 25 was an incredible chase with the forecast working out perfectly. Our target area of Great Bend to Rush Centre had us right in the middle of all the action where the triple point had setup. Capping along with the ridge axis aloft had me a little concerned that nothing was going to be able to get going. But the low level shear and CAPE were able to break the cap and overcome the weaker flow aloft to produce. The cell in Lacross, KS was almost stationary at one point, which was a result of it being able to plant itself firmly in the boundary layer and latch on the warm front. This is why, in my opinion, the cell was able to produce as it did since it was able to feed off the added low level vorticity from the warm front. It resulted in a prolific EF-2 tornado which was lit up by lightning (video coming soon to http://www.severeweatherdiaries.com/video/) and a secondary EF-1 which hit Lacross. This first photo here shows the rope out stage of the EF-2 tornado and the second shows what I believe to be a dual meso signature. The circled area indicates our position on the northwest side of the circulation. Looks like we were in tight but the funnel was to our east passing in front of us then moving away. May 27 turned out to be a bust, even though we were on some cells near the 5:00 pm CDT hour which did give some very light rain and a few rumbles, the storms were not able to root themselves fast enough and were carried over the warm front by the flow aloft thus killing off the updrafts.

Today looks to be a little more promising with a strong trough working its way into the upper plains. Still not ideal with the upper low centered near the Canadian border in Montana, the vorticity maxima forecast to eject around the base of it should be the focal point for today's chase as shown in the 500 mb vorticity chart below.

Along with this are two other main features aloft that I like. The first is the strong curvature seen in the 250 mb jet stream as well in the 500 mb flow. Furthermore the main axis of stronger 500 mb flow lies within the warm sectors of the secondary low that spins up in west Kansas. This tells me that there will be added cyclonic vorticity and backed winds within the warm sector. The images below clearly indicate that the 500 mb jet lines up with the sfc warm sector but does not show winds as backed and I suspect the model may be underplaying this slightly.

Again moisture will be the limiting factor here again due to subtropical storm Beryl off the Atlantic coast not allowing for a full flow from the Gulf, but whatever flow there is should be more than enough the get upper 50's to even mid 60's dew points into the north central Kansas region by tomorrow afternoon. What also has me encouraged is that the CAP should not be as big of an issue as it has been over the past few days as 700 mb temperatures look to be in the 5 to 10 degrees Celsius time around initiation. With a strong 850 low level jet surging in around 00Z through north central Kansas and up into Nebraska low level shear should be more than enough to have rotating updrafts, even though the 850 flow is not ideally backed, but Ada, OK in 2011 had slightly veered 850's and look how that did, thus I'm not too concerned there. More encouraging is the NAM-WRF/GFS agree with the setup and the SREF H5 is also on board but is slightly north than the other two models. Thus the area between Phillipsburg and Smith Centre along hwy 36 looks to be the area of interest for me as I suspect anything north will be pretty sloppy. Then looks like for May 28 will be back down in southwest Oklahoma in the Lawton area. Currently I’m interested in the dual jet flow and the interactions they will have as seen on the 250 mb forecast below. Current sfc flow returns as a result from this feature are little weak but I believe the model will begin to pick up on this by tomorrow. I'll give more details on this tomorrow.

So yesterday turned out to be every eventful seeing 4 tornadoes near the Kingman, KS region, can see photos and videos here. I also proposed to Dayna as well and we are now engaged and could not be any happier. Today was a down day and decided not to chase the southwestern OK region and into TX since parameters were only showing pulsing cells with large hail threat. Thus it wasn’t worth the risk. We did drive to Clovis, New Mexico to photograph the eclipse. It was a long haul from Wichita, KS but we were able to make it in time. Now we need to decide whether or not we chase in southeast Colorado tomorrow or push on north to NE/SD to get into position for Tuesday.

May 21 (today)

The potential looks pretty marginal with broad upper ridge in place but the NAM/GFS looks to be doing something funky in through the CO area as winds begin to push back from the south. The combination of the upper wind maxima and the local vorticity that is produced in CO may potentially make for an interesting chase. The images here in order are 500 mb winds, 500 mb vorticity, 850 mb winds, sfc winds and Td/streamlines. The 500 mb wind maxima looks to be generating some subtle vorticity maxima aloft. At the sfc and 850 mb levels the strong SSW winds should enhance low level shear/vorticity in combination with the gradual upslope to possibly produce something interesting. Also note worthy is a very breakable cap is present with 1500-2000 j/kg of CAPE available through the afternoon. Parameters are still pretty iffy right now thus I'm not 100% committed to this yet since Tuesday holds more promise.

Tuesday May, 23

This day looks to hold more potential but is still a little questionable given that there is a slight disconnect with flow aloft and sfc. What is shocking to me is how similar this setup is to the setup on May 20 in KS. The following images show the 250 mb winds, 500 mb winds, sfc winds, and Td/streamlines. I'll just go over these for now to keep this brief. The similarity that I see is the scenario with the cold front darting south and gradually pinching off the dryline. I don't think this will occur as fast as it did on May 20 but right now my thinking is the same has I had on May 20. I'm favouring the intersect region of the dryline/cold front, even though aloft the flow would indicate to head more north I believe the amount of upper support along with the amount of CAPE present is more than enough to balance each other out. Furthermore, analysing the 850 mb winds the cold front at this level actually surges ahead slightly faster than the sfc front which would cut the good low level flow off to the more northern target as well thus rendering the dryline/coldfront area with more potential as the 850 flow will be free for any convection to utilize. The issues I do see are the possibility of a strong cap and the winds in the warm sector not backed as much as I would like. But I do suspect that the low level interaction with the dryline and cold front may produce some sort of mesoscale cyclonic feature which if materialises will help a great deal. The other concern is the larger CAPE into ND which may prove to be more beneficial. For now I'll stick with Murdo, SD and asses more tomorrow.

May 18 proved to be somewhat of a success. The forecast panned out and we were able to see a high based cell which had very broad and weak rotation a brief period of time. It had supercellular form but I'm a little reluctant to call it a supercell. We did call the chase off a little early since the cell did not show much promise and only went on to produce 1" hail, thus we were able get into position for today.

Although at the moment I am still a little uncertain as to where the final target will be. There appears to be two areas of interest right now and that would be the Beatrice, NE area and western Oklahoma or near the Alva, OK region. There are two reasons for this. The upper dynamics looks to be better for the SE NE/NE KS region with the upper trough taking on a little more of a negative tilt and lifting off more to the NNE along with upper support from the jet at 250 mb aloft. At the same time the upper flow shows descent curvature as well which may prove to help enhance the potential further to the south.

Moving down to the lower levels the 850 mb flow is pretty good out of the due south and is actually favourable for both locations, what is the issue is how fast the cold front will sink south and overtake the dryline. This along with the fact that the shear vectors looks to be more perpendicular to the dryline/cold front intersection and that there looks to be a greater chance for isolated cells along the dryline (see image below showing sfc-500 mb bulk shear) in western Oklahoma, I think we may head to that region but will have to look over more data in the morning since I'm not ruling out southeastern NE yet.