Thursday, May 19, 2011

2011-05-19 Forecast: Central KS

Currently in Lamar heading east.

12z data combined with 09z RUC shows concordance of Ts and Tds, so I'm hoping the RUC is on-call for the day. 500mb closed low over the Rockies will continue to provide an optimal envrionment over KS/OK/TX, and even back toward CO. SW winds will be maximized in a thick, elongated zone from SE CO to TX/OK PH to NE with speeds AOA 50-55kts. The midlevels have cooled a lot over the region, but look very solid over SC OK and into TX, though the PH region and all of KS will have very cool midlevels.

Potent, well delineated dry punch should form over the OK PH and spread NE around DDC to Quinter serving as a potent focusing mechanism. The 990mb sfc cyclone in SE CO should once again intensify allowing backing along the dry punch with easterly winds as it moves up close to the I-70 corridor in KS. CIN will hold things in check, but most of KS and some of C OK should become uncapped with CAPE >2000 J/kg. A potent southerly LLJ of nearly 40kt will nose into OK into the S KS region between 21z-00z.

At this point, I'm going for the triple point and probably will head over to DDC for reassessment as the day goes on suspecting I'll probably need to move slightly NE to be in range.

Wednesday, May 18, 2011

2011-05-18: SE Colorado Cyclic Supercell & Tornado

I pretty much had abandoned all hope of convective initiation in SE CO, but resolved to stay put until after the 5pm hour (superstition). While I was busy posting about how bummed I was about storms not forming while sitting in La Junta, CO, storms erupted directly to my west.

From the get-go, a single cell on the eastern fringe of Pueblo Cty took on very characteristic visual cues that it would rapidly become severe and likely would sustain itself. This particular cell had unimpeded 25kt easterly winds and was rapidly consuming cells forming to its west and one cell to its south. As it did so, despite 30+ deg dew point depressions, the cell developed impressive laminar-appearing inflow bands from the south (which I suspect were actually failed updrafts) and a classic midlevel feeder band from the east and the LCLs began dropping immediately. I even was treated to a few horseshoe vortices along the beaver tail.

What was impressive was how rapidly this all occurred. The cell went from CI to classic supercell within an hour. The storm entered a perfect steady state and pulsed only a few times before it began to show visual cues of splitting. An RFD cut could be seen splitting the updraft as I proceeded north on CO 109.

As the RFD cut tightened the circulation on the northern-appearing split, massive amounts of hail began falling from the southern circulation. I still had internet access, so reported the hail (which varied from dime-to-nickel size, but managed to cause immediate hail fog). On radar the cell looked single cellular, but visually there were two updraft bases with the northerly one persistently with the stronger midlevel feeders.

Getting through the hail at 2330z, I managed to get under the northern cell's rain free base and for a short time got to enjoy warm easterly winds. By 2350z, the southern cell pulsed visually and formed a pretty impressive high based wall cloud. At first I thought this was due to outflow from the RFD cut, but got a terrific vantage to see the storm develop a brisk easterly sfc-level inflow jet. This was unmistakable, as was the westerly winds coming from the back of the cell from the RFD (which itself set off a westerly inflow jet/outflow boundary).

For more scientific purity, here it is the same shot with most labels removed.

I was approximately 5 miles WSW of Arlington on US 96 when the southerly storm developed sfc-level rotation under the wall cloud. At 2355z I was confident I wasn't looking at a gustnado, and data on radar suggested significant rotation at all levels, so I felt confident that this was a true mesocyclone storm tornado.

Note: above photo hasn't yet been fully processed. However, above the dust whirl, note the faint tube extending to near cloud base. Similar findings in the images below:

The tornado stayed over open land only 1 mile south of me, and it remained stationary under the southern updraft, but then obtained a brief dual vortex (both appeared slowly rotating and nonviolent), and the two vortices briefly "danced" around each other before the tornado dissipated at 0000z exactly. This was the only definite tornado I witnessed today, and it wasn't particularly pretty, but man did it feel nice to have a forecast verify when I had all but given up on the day.

By that time, the southern cell became undercut by very cold outflow from the RFD and remained undercut for the remainder of the subsequent hours. The northern cell rapidly became the dominant cell but was outflow dominant and only rarely re-ingested easterly wind. The cells both put out astounding dusty outflow and had beautiful gust fronts while periodically the northerly cell would redevelop impressive inflow bands at the midlevels and would take on classic supercell characteristics.

The gustfronts were intense and frequently developed very low LCLs, occasionally being only maybe 100ft AGL, and once had me terrified I'd misinterpreted the storm visually and it was about to put down a tornado right next to me. But the cold westerly winds and the fact the rotation lacked inflow to the east left me pretty convinced that it was part of the gust front, it just was so damned close to the ground.

I'll note that the supercell was staggeringly the big show with the tornado being merely icing on the cake. Data network availability throughout Kiowa Cty still remains pretty spotty in places, but I was reasonably impressed today with the strange places I suddenly had terrific cellular signal (try County Road E west of Galatea--huh?).

Today also marked my first chase with my new digital SLR (the Canon T2i). Since I had the original Canon Digital Rebel SLR (from my parents in 2003), the advance in technology coupled with a pretty snazzy new Canon EFS 18-200mm...the photos are already just lightyears better even preprocessing. Can't wait to share them very soon.

***Addendum to above: still have a lot to learn about the camera, sorry the quality is subpar. :)

***Addendum to addendum: I have some terrific artistic photos, but will due to me having been driving/chasing for the past 18 hours, I need some sleep. I'll also have had a chance to post-process quite a bit soon, which will enhance the photos a lot. Today's addenda were for documentation purposes, largely.

2011-05-18: Chase Forecast (Updated 0900 WDT)

Forecast time: 0100 WDT...From DEN

Looking at the 00z NAM, the 990mb sfc low continues to impress in SE CO by late day with some intense easterly progged winds AOA 20kts near Lamar to Campo. Cloud cover is going to play a big role in limiting sfc heating, and I think the NAM is right about forecast Ts in the 70s near the sfc low. Today in DEN it took a long time even to crest the 60 deg mark, and I'm worried cloud cover currently seen over the CO/NM border (presently 08z as I write this) may keep it cooler in SE CO. I'll have to verify after the morning soundings.

My target area remains firmly close to the sfc low (E CO, along 287) where hodographs favor broad 90 deg clockwise 0-3km shear profiles.

The dryline looks messy due to very poor sfc Tds, but should drape NW to SE, possibly with the hint of a NE bulge somewhere east of Pueblo by 00z. This still puts the best "pooled" moisture close to KS border, and in that respect, I'm hoping for some High Plains Hijinks to aid things. The backing winds should force both upslope flow and some upslope theta-e into the region, but T/Td spreads will still be pronounced.

Things get a bit trickier in the upper levels with the nose of the H5 jet just barely arriving before sunset, but still providing 30-45kt WSW winds over my tentative target area. The 850mb winds look great (ESE AOA 20kt at the CO/KS border). Steep lapse rates and only modest capping should allow convection.

FWIW, yesterday's 00z 4km WRF breaks out a nice, seemingly isolated precip blob in SE CO around 21z, likely reflecting arrival of the nose of the H5 jet with superimposed intensification of the LLJ at around that time. Things will become linear and multicellular after sunset, but sticking to the southerly cells should allow a pretty good opportunity for small tornadoes and some terrific lightning along the dryline into the night.

My chase target is now almost certainly going to be in an area between Lamar and Springfield along Hwy 287 pending am soundings and SAT.


Forecast update time: 0900 WDT...From DEN

SAT data shows a thick stratocirrus lid on things over almost all of CO, but this should move north and dissipate as the day goes on. W OK alread has cleared considerably, so I think the two targets will both find their daytime highs. I'm not optimistic about W OK hitting its Tc (AOA 95 deg) with H7 temps already in the 8-9 deg region and less forcing from the dryline. That said, my confidence in the CO target has diminished a bit too.

There are two sfc mesolows on obs this am. One is over Raton and should be the one that evolves in SE CO as the day goes on. But to my surprise, there appears to be a second mesolow in the region of the TX PH (mostly noted by wind shifts). If this were to move in a similar trajectory as the western low, it would really have a detrimental affect on both sfc winds and returning moisture to E CO by bringing more northerly winds into what I was hoping would be a strictly easterly upslope situation. That warrants hourly watching for now.

So my chase strategy for now is to get to Pueblo (which I'd be doing anyway), and then make the painful choice of either continuing S on I-25 to Raton to try to hit the Boise City area, or more likely hold up in Pueblo to begin a move eastward on US 50.

Normally most days with targets just a couple of hundred miles away from each other stress me out, but I think keeping my expectations on sculpted supercells today should more than help with indecision I'm feeling.

Packing up. En route to Pueblo.