VORTEX2 science workshop recap

It’s been nearly three years since the field phase of VORTEX2 ended. Two weeks ago, a group of about 30 PIs and scientists reunited at a retreat near Austin, Texas. I was asked to send a few tweets from the workshop since the V2 media liason wasn’t in attendance.

VORTEX2 science workshop group photo

VORTEX2 science workshop group photo


At the end of the field phase, the PIs divided up case studies and initiated collaborations. Over the three-and-a-half days of the workshop, participants updated the group on their most recent findings, including low-reflectivity ribbons (a feature whose significance is still not completely clear), an apparent case of bottom-up tornadogenesis, an uber-composite supercell environment generated from over 700 rawinsonde launches, and UAV transects across multiple gust fronts. There were also discussions about lessons learned (particularly from the UAV group), new tools (EnKF analyses have proven to be a popular tool for filling in the spatiotemporal gaps between observations), and directions for the future.

In the past three years, life has changed for many of the participants. Some have changed jobs or institutions, graduated (waves), or had families. In spite of all this mobility, electronic collaborations and conferences have enabled quick dissemination of results. (It took 10 years for some results from the original VORTEX to see print.) Josh Wurman aggregated a list of all the peer-reviewed VORTEX2-related manuscripts published so far: the paper count currently stands at 14, with 9 more either accepted or in press. It was decided that the group will shift focus in the next few years towards synthesis studies rather than individual case studies.

It wasn’t all work, of course. There was time for some fun, including a zip line ride across Lake Ted!

2013-04-17: Wall clouds in SW OK

KFDR reflectivity image of the Faxton storm

Cutting south across the forward flank of the first Faxton, OK storm on April 17.

It was my first day back at work after a long week of travel that spanned nearly 15 degrees of longitude. (More on that later.) I went into work extra early, and managed to scramble a chase partner (Gerry C.). We departed the NWC just after 2 p.m., and headed southwest on I-44. We initially targeted a storm west of Anadarko, OK, only to abandon it quickly when its high cloud base made frontal undercut evident.

Next, we cut across the forward flank of a tornado-warned supercell passing over KFDR, intercepting it near Cache, OK. Sitting on top of a hill on Cache Road just north of Faxton, OK, we observed a wall cloud to our distant southwest that extended a few enticing purple scud fingers. However, it quickly filled from behind with emerald green and gusted out toward us.

Faxton, OK Wall Cloud

Faxton, OK wall cloud about 5 p.m. CDT, as seen from Cache, OK

We escaped east toward Lawton with numerous other chasers, but were overtaken by the advancing core. A few nickel-sized hailstones thumped against my roof. I dropped a few miles south on SW 82nd Street and allowed the Faxton storm’s hook to pass by us to the north.

By this point, it was evident that a second supercell – following an almost identical track over KFDR and Manitou, OK – was now the tail end Charlie and the preferred target. Proceeding west along Baseline Rd., we stopped near the intersection with Indiahoma Rd. where we had a good view toward the west and a new wall cloud. Unfortunately, that wall cloud met the same fate as the last one – after rotating lazily, it grew increasingly Z-shaped as an advancing gust front pushed it out from behind.

It was growing darker, and we both needed to return home for logistical reasons. As we merged back onto I-44 at Lawton, we heard a spotter report of a tornado near Ft. Sill, a few miles to our northwest. Our view was blocked by trees, but we could see a dark lowering beneath the cloud base in that direction. We pulled off I-44 for a few minutes to observe, but never saw a tornado or the reported power flashes. We missed the Grandfield tornado, which happened even farther to our southwest, after dark.

By then, the southwest-to-northeast oriented line of supercells was now situated over I-44, signifying a slow and messy return drive. Lou W., who had been nowcasting for us via text message from back in Norman, suggested that we drive straight east through Duncan to I-35, and return to Norman that way. It added about 30 miles to our drive length, but was precipitation-free for all but the last 10 miles. We took the Lindsey Street exit just as our old target storms congealed into a mini-bow. The next morning, my home rain gauge had 2.1 inches of refreshing rain in it.

For your amusement, here’s a video clip from Chris Novy showing spotter network activity during the 17 April event. Despite the number of glowing green ants, we didn’t run into any horde-related issues. We found decent parking spaces and observed safe driving habits all around.

A storm observer’s pledge

Inspired some behavior I’ve witnessed on YouTube recently…

As a research meteorologist, storm chaser, and an admirer of the atmosphere, I hereby pledge that:

  • I will conduct myself professionally, regardless of whether or not I am observing a storm as a duty of my employment.
  • I will obey all federal, state, and local laws.
  • I will never misrepresent who I am or in what capacity I am observing a storm. I will never impersonate a law enforcement officer or emergency responder.
  • I will conduct myself safely and ethically, even if doing so costs me a “money shot.”
  • I will report promptly any hazardous conditions that I observe to the NWS, and share my insights with local authorities.
  • I will never willfully imperil myself or others, thereby diverting emergency resources from the local population.
  • I will not operate a handheld camera while driving. I will ask my chase partner(s) to take images and video for me.
  • I will never exploit tornado victims for personal gain.
  • I will not cheer on a tornado, since I can never know what’s beneath it.
  • I will admit promptly to my mistakes, and offer explanation and redress.

Minnesota Skywarn Workshop

Just a heads up that I will be giving a keynote talk at the 2013 Minnesota Skywarn Workshop on Saturday, 13 April 2013. As many of you know, I grew up in the Twin Cities, so this venue is a perfect fit for me. I’m looking forward to the chance to visit my old stomping grounds and reconnect with the spotter community up north. Minnesota weather weenies (and yes, I still count myself among them) are a very special breed!
2013 Minnesota Skywarn Workshop

New pub

This month’s issue of Monthly Weather Review contains my newest paper, EnKF assimilation of high-resolution, mobile Doppler radar data of the 4 May 2007 Greensburg, Kansas supercell into a numerical cloud model, describing the second half of my dissertation research. (Yes, I know I graduated over a year ago… Publication takes a long time, as well it should!) The take-home message of the paper is that low-level (< 1 km AGL) wind observations make more realistic analyses of supercells (and other rapily-changing atmospheric phenomena). Supercells have a lot going on under the hood – updraft and downdraft pulses, mesocyclone cycling, cold pool generation, etc. – not all of which are apparent to the naked eye or even to an advanced, 4D observing system like a radar. Computers can help fill in some of the gaps via process called data assimilation (DA).

For those not familiar with DA, it means combining atmospheric observations (such as those from a radar) with a computer-generated weather forecast in order to produce a mathematically optimal, 3D analysis of the atmospheric state. You then use the analysis to launch a new forecast. Rinse and repeat every few minutes. The end result is a series of 3D snapshots of the storm, which you can use to diagnose the storm’s inner processes. (There is a gargantuan body of theory required to combine these two very different types of input and assess the quality of the analyses. I shan’t bore you with the two semesters’ worth of details that I slogged through in grad school.)

For this study, I used an advanced DA technique called the ensemble Kalman filter (EnKF) to assimilate NEXRAD (from Dodge City, Kansas) and UMass X-Pol data collected in the Greensburg storm. In one set of experiments, I withheld the UMass X-Pol data (which were collected more frequently and closer to the surface). The mesocyclone of the simulated Greensburg storm was much stronger and more persistent in the experiments where I used the UMass X-Pol data, and the updrafts and downdrafts stronger and more compact. While we lacked independent data to use for verification, making our assessment necessarily qualitative in some regards, our results are consistent with previous DA studies using artificial, “perfect” radar observations.

Simulated Greensburg storm (reflectivity)

Here’s the simulated reflectivity in the Greensburg storm, after assimilating (left) WSR-88D data only and (right) also UMass X-Pol data. Both storms are in the same place and look similar overall…


Simulated Greensburg storm (vertical velocity, vorticity)

BUT… the velocity fields are very different! Updrafts (red) and downdrafts (blue) are more intense. Also, the vorticity bullseye corresponding to the Greensburg tornado (black contours) is much stronger.

I described in a previous post our serendipitous UMass X-Pol data collection in the Greensburg, Kansas storm of 2007, and how that evolved into a detailed case study published last year. My husband lead-authored a companion study earlier last year where he assessed whether modifications to the initial model environment changed the forecasts. (Answer: Yes. Quite a bit, in fact.) This pub completes the trifecta. As we were about to submit this paper for peer review, we made a last-minute decision to switch the DA software to a system that was more extensively tested for severe storms. Even though that added a month to the prep time, I am glad that we did, because the resulting analyses, generated from the same observations, looked markedly better.

I wrote this paper during my CAPS postdoc with the able assistance of my co-authors, representing a fruitful collaboration between SoM, NSSL, and CAPS. I manually edited and dealiased all the radar data (a task that took nearly two months). I had the benefit of two astute reviewers (including my brother-in-EnKF, Dr. James Marquis) who asked some mighty tough questions. And I got to share this MWR issue with some other super scientists – Tom Galarneau, Jeff Beck, and Chris Weiss.

2001-06-11: My first tornado, Benson, Minnesota

The “my first tornado” meme circulating on Facebook prompted me to dust off my first chase log book and relive the Benson, Minnesota tornado – my first ever. I kept an astonishing amount of detail, and it helped me reconstruct the chase. On subsequent chases, I’ve usually been in the driver’s seat and not kept such detailed logs. But when you’re packed in the back of a van with a dozen other students, there’s not much else to do besides observe and record.

AOS 455 students work to free Van #2 from Kansas mud.

Dr. Tripoli and his AOS 455 students work to free UW Van #2 from Kansas mud. A copy of this photo is still up on the wall of the AOS department at 1225 W Dayton Street.

In spring 2001, I had a freshly-printed B.S. diploma from the University of Wisconsin – Madison’s Atmospheric and Oceanic Science department in hand, and taken a job as a research intern at the Space Science & Engineering Center on Dayton St. I decided to enroll (as a “super senior”) in the biennial summer course AOS 455: Severe Storms Forecasting, taught by Dr. Greg Tripoli. After a couple of weeks in the classroom reviewing mesoscale meteorology, we piled into two white university vans and spent 10 days cruising the Great Plains, chasing turkey towers with Josh Wurman & Co. (who were then rolling in DOW2 and DOW3), sampling the local cuisine (ahem, Taco Tico), pushing the vans out of the greasy red mud, and taking in local sights (e.g., “No trespassing” signs riddled with bullet holes, and a storage facility eloquently named U-STUF-IT). This newly-minted meteorologist from the Midwest found plenty of warmth and charm in the rolling Plains. I distinctly remember watching majestic bubbling cumulus from a parking lot in Harper, Kansas one afternoon, surrounded by fields of waving wheat. I took a deep breath of balmy Gulf air, felt the wind tickle my short hair, and thought to myself, “You know, I could get used to this.”

Near the end of our trip, we migrated back north along I-35 in preparation for our return to Madison. It being early June, the jet stream had begun to migrate north as well. We started off the morning of 11 June in Rochester, Minnesota, and headed north toward St. Cloud. A surface low tracked across northern MN, dragging a cold front behind it, we anticipated the latter would touch off a round of storms in western MN. Wind profiles were marginal, but the air was sticky (72+ F dewpoints, thanks to the exhalations of the corn crop). We banked on the storms generating their own environment.

Radar composite of the upper Midwest on 11 June 2001

This HP supercell in western MN (yellow arrow) produced my first-ever tornado. Radar composite courtesy of UCAR.

We stopped for a couple of hours near Olivia, MN, watching backbuilding pulse storms fire off and scoot by to our north. One by one, they marched away to the east like lemmings and collapsed, much to the consternation of our green group of storm chasers, who were straining at the leash to chase something.

Finally, a new storm west of Willmar began to look better organized. A pay phone call from Dr. Tripoli to nowcasters back in Madison confirmed that was our target. We headed west on U.S. Hwy. 12. As we approached Benson, MN from the east, at around 2015 UTC, we observed a rain-wrapped wall cloud. From our vantage point about 20 miles from Benson, the rain cleared, and in the peach back light of the late afternoon sun, we saw a cloud appendage with a persistent dust whirl beneath it. I had my VHF HT hooked to my belt, and could hear local spotters confirming a tornado in the direction we were looking. I snapped a few pictures before we got back in the van to follow the storm.

Benson, MN tornado of 11 June 2001

My first tornado. We are about 20 mi east of Benson, MN, looking W at 2015 UTC.

We observed a few more wall cloud cycles and dust clouds as we followed the storm back towards Willmar. Tornado warnings followed the storm too, but we never spotted another funnel or tornado. The Benson storm eventually outran us, and we abandoned the chase near Glencoe. I remember making a collect call from a gas station pay phone to my parents in St. Paul, warning them about the approaching hailer. (It did eventually evolve into a mini-bow as it passed over the Twin Cities, and left a fat swath of wind reports across western Wisconsin.) I can’t remember if we drove all the way back to Madison that night or not, but my log book doesn’t have another entry until 14 June.

My top three SLS talks

Proceedings of the recent 36th AMS Severe Local Storms conference in Nashville are now online. My new boss, Dr. Pam Heinselman, was one of the co-chairs. She never even broke a sweat!

It was a terrific conference. Highlights included:

  • Dave Lewellen’s ultra-high resolution simulations of tornadoes interacting with other-than-flat topography. Some of his simulations looked remarkably like my video of the 7 November 2011 tornado interacting with the Wichita Mountains!
  • Harold Brooks gave a “mythbusters”-style keynote talk about the 2011 and 2012 tornado seasons, and how the media hype (or lack thereof) squares with statistics. If you have 30 minutes, I highly recommend watching his recorded presentation. It’s an informative hoot!
  • Tim Marhsall, fresh back from surveying the dangling NYC crane from Hurricane Sandy, gave back-to-back presentations about his damage surveys of the 27 April 2011 Alabama tornadoes and the 22 May 2011 Joplin, Missouri tornado. He always makes me want to rip out the walls of my house to make sure they’re toe-nailed.

There were, of course, lots of other great presentations and posters, including a couple by yours truly, but these were my three favorite.

In addition to my professional contributions, I organized the traditional, less-than-formal “photo and video night” at the conference (with some help from Dan, Lou Wicker, and Judith Z. of the AMS staff). There were contributions ranging from all over the U.S. to Australia, Japan, and Germany. We noted sadly the howling vacuum created by the absence of Dr. Bob Schlesinger – a former colleague at UW-Madison – who is famed for the uniquely-styled presentations that he usually delivers at video night. A response to my inquiry at UW indicated that Bob was unable to travel to the conference because of health issues. I organized a get-well card for him, which was soon so densely scrawled upon by dozens of people that we had to resort to using the back cover. I certainly hope Bob comes back in 2014. It just wasn’t the same without him!

2012-11-10: The season fizzles to a close

Turkey towers over Greensburg

Turkey towers over Greensburg

Gusty southerly winds threatened to shove our car out of its lane on I-40 just after noon Saturday. We barreled up the Northwest Passage, dodging unusually aggressive tumbleweeds. We arrived in Greensburg, Kansas as the cumuli piled up on the dryline just to our west. “Hurry up and wait” time passed in the parking lot at Dillon’s, where we watched blips bubble and boil in the dry air for over an hour.

This late in the year, sunset comes around 5:30 p.m. local time (versus 9:00 p.m. or even later during May and June). The shorter days not only restrict photography opportunities, but also limit daytime heating and destabilization needed for storms. Today, however, the chief issue was moisture: although deep, dewpoints barely exceeded 55 F east of the dryline. Towers were too skinny, too mushy, too disorganized to garner any serious interest.

Shattuck left split's base

Shattuck left split’s base

A storm finally did materialize east of the dryline near Shattuck, OK, while the storms over Dodge City, KS, stubbornly refused to organize. We dropped back south to the KS/OK border, where the Shattuck storm had split into two moisture-starved miniature supercells. The base of the anticyclonic left split rotated lazily while a possible clear slot tried to cut across the cyclonic shear side (left). We finally stuck a fork in it at dusk.

Unless a miracle occurs, that is likely to be the end of my 2012 chase season!

2012-10-13: Veni, vidi, reliquit

We never even made it to Anadarko yesterday. I woke yesterday to cool temperatures and elevated showers passing through Norman. Not good. Temperatures struggled to get into the 70s all morning as persistent cloud cover and another round of showers kept us from reaching convective temperature.

Anticrepuscular rays converging east of Norman.

Anticrepuscular rays converging east of Norman.

Logistics for the day restricted us to within three hours of Norman, so we focused on looking for isolated convection within a 150-mile radius. Storms began to develop along the Pacific front in western Oklahoma around 1 p.m., and almost immediately lined out. KFDR was down for its dual-pol upgrade, so we had to base our decisions on coarser data from the more distant KTLX. We scoured the kinks and appendages in the line, looking for hints of discretization. Jana B. dropped by in anticipation of a short-fuse departure, and together, we watched the waning minutes of the OU-TX game. An isolated storm went up in the warm sector east of Frederick, OK, and we finally pulled out of the garage around 3:30 p.m.

We arrived in Chickasha, where we had to decide whether to head south on U.S. Hwy. 81 toward our original target, which by then had begun to deteriorate on radar, or west on OK-62 towards Anadarko and a quasi-isolated part of the line that exhibited a mesocyclone. We could see the lowered base of the latter, and we decided to go after it before it raced away to the northeast at 40+ kts.

Stable, stable, stable, north of Verden, OK.

Stable, stable, stable, north of Verden, OK.

As we approached Verden, OK, a solid wall cloud was visible against an emerald green wall of precipitation. We thought we briefly saw a tapered appendage on the north side of the wall cloud. It only lasted about 20 seconds; no one got a picture.

We headed north out of Verden on a paved county line road, watching as RFD precip swallowed the wall cloud. We turned east when the wind-driven precip crossed our road, and subsequently abandoned the storm as it left us behind in a gush of rain-cooled air. With no other viable storms in the area, and the line now fracturing into dozens of weaker cells, we decided to put a fork in it and headed back to Norman.

A multicell with a clear slot passes by Norman.

A multicell with a clear slot passes by Norman.

Later that evening, we observed another weakly-rotating, quasi-isolated cell pass north of Norman. A clear slot sliced across the foreground, but that was as good as it got. Sunset treated us to a stunning display of anticrepuscular rays set against mammatus clouds to our east.

In summary, the shear was good, but thanks to the two rounds of morning convection, the CAPE just wasn’t there. At least we didn’t drive very far (< 100 miles)!

Heads up, Madison!

I’ll be back in my undergrad stomping grounds to give a talk entitled “Unraveling tornadoes with mobile Doppler radar: Scientific storm chasing on the Great Plains” to the Madison, Wisconsin IEEE section on Friday, 16 November 2012. (The section is generously sponsoring my travel. Thanks, guys!) Here’s their announcement for the talk.

In other news: I’ve got a new job! As of today, I have transitioned to an NRC postdoctoral fellowship at the National Severe Storms Laboratory. I will be working with Dr. Pam Heinselman analyzing phased-array radar data. I’m excited to join her and the Radar Research and Development Division (R2D2)!

Last but not least, please enjoy this sunrise time-lapse I shot from the south rim of the Grand Canyon a few weeks ago on my vacation.

Originally, I uploaded sans audio, but YouTube suggested Carly Comando’s pleasant piano piece “Everyday,” and I decided it was a good fit.