On my way home after photographing monsoon thunderstorms northeast of Flagstaff, I noticed smoke rising over the hills along Townsend-Winona Road. I thought it might be another tree fire, but as I rounded a bend, it turned out to be a terrible house fire. Checking radar, it looks like there were 3 lightning strikes over that location from 2:45-3:00 PM. Several fire trucks were on the scene but the fire was overwhelming and it took quite a while before it seemed to be brought under control. I'm afraid the house may have been completely lost.

A couple of the lightning strikes along Townsend-Winona Rd.



The house fire at Townsend-Winona and Bullion Hill Rd.





Arizona Storm Chase - 9 August 2015

After noting a great supercell near Winslow, I opted to head toward Twin Arrows to see if some developing convection would take off there. It was good for a lot of heavy rain, but hardly any lightning and it didn't manage to organize.


While I was toying with that mess, another storm north of Flagstaff crossed the threshold to the Colorado River Valley, west of Wupatki and went supercellular.


As I pondered my situation and whether I could race to that storm in time before it drifted into the extremely hard to navigate spaces west of Hwy 89, it picked up a tornado warning. So I dropped the slop I was on—to at least give it a try. By the time I had visibility on Hwy 89, it had the merest remnants of an elevated base.


On the chance it might cycle up on some new convection to the south, I took a pretty decent forest service road along the cinder cones north of Sunset Crater. What did pop up didn't develop rotation but still managed to make for some nice storms and lightning.





Arizona Storm Chase - 8 August 2015

More storms showing up with couplets this day, but I didn't manage to intercept them during prime structure. The landscape made up for a lot of those issues. These shots are from Hwy 89 north of Flagstaff along the Mogollon Rim/Colorado River Valley margin.

A scud bomb merging into the updraft between Sunset Crater and Wupatki National Monuments.

More disorganized convection playing with sunbeams north of the San Francisco Peaks.

Benign convection percolating as the atmosphere begins to stabilize.

Sunset Crater is trying to peek between the trees on the right.

Convection has turned to mush almost everywhere, leaving a great sunset aftermath—just northwest of Sunset Crater National Monument, looking toward the San Francisco Peaks.



The Mogollon Rim Convergence Zone worked its magic the past 3 days with southwest flow leading to some especially favorable shear along the Colorado River Valley.

On my way north to meet the best shear parameters—which I thought would be best near Page and the Arizona Strip, I encountered some heavy convection and a nice roll cloud and gust front north of Cameron on Hwy 89.


I figured this one would probably stabilize the air mass pretty solidly, so after following it a bit, getting photos, looking for lightning and doing some roadside nowcasting, I started making my way towards Page. A couple hours later I found myself at The Gap to pick up a replacement 9-volt battery for the lightning trigger. Radar showed a couple strong storms lighting up to my south—where I thought things had already been played. So I raced back south and started catching sight of a very healthy looking anvil peeeking over the plateau to my west. Once I cleared the horizon-blocking hills, I got to meet a beautiful Arizona supercell drifting toward me from the west.

This is the first time I've caught Kelvin-Helmholtz waves along the elevated base of a supercell—and it was an hour from home. This view faces northwest as the cell moves over the edge of the Painted Desert.

Another view as the storm starts to pass to the north

I followed it through Tuba City and further east where it was trying to hand off to a new base before slowly withering.

I've finished evaluating road networks for Arkansas, Louisiana, Mississippi, Alabama, Tennessee, Kentucky, Indiana, Ohio, Michigan, and Wisconsin to wrap up the central US area. I also worked up California and Florida for road options at the tornado hors d'oeuvres they serve up. To help distinguish things better, I added a gray tone to states that haven't been evaluated yet.

US Storm Chase Map - with forested areas

US Chase Map 15 May 2015 - with forest

US Storm Chase Map - without forested areas

US Chase Map 15 May 2015 - without forest

US Storm Chase Map Project

I’ve had a goal of creating a detailed US Chaseability map for a couple years now. I wanted to factor in road grid, tree density and terrain. I’ve made progress on the first two items, and it’s at a point now where it should help inform my chase planning this year. I wanted to share in case anyone else finds it helpful. (For chasers that dwell and chase frequently in the central US, this might be superfluous :) )

My intention for it is to frame what I might expect and be ready for during a chase, or possibly inform my targeting decisions (all other thing being equal).

Please also note that I have not completed road network analysis on Wisconsin, Indiana, Michigan, Ohio, Florida, and Mississippi River Valley (see future plans at bottom of this post).

US Storm Chase Map - with forested areas

US Chase Map 5 May 2015 - with forest

US Storm Chase Map - without forested areas

US Chase Map 5 May 2015 - without forest

I want to make this available as a resource to the storm chasing community. If you are interested in editing or adding content to the layered PSD file, please let me know and I can provide a download link. It is too big—150MB—to provide an ongoing public link (my web host would probably threaten to terminate my account if I did that). If anyone wants to do their own work on it, I’d just ask that any copies or derivatives of this content be re-distributed non-commercially. I can be reached at the email address in the header of this blog.


Road grid quality

  • Green = Typically 1 mile grid with some 2-3 mile gaps
  • Yellow = Typically 2-4 mile network with some 8 mile gaps / 1-2 mile network with discontinuous junctions
  • Orange = Typically 5-10 mile network/uncertain network with gaps up to 16 miles
  • Empty = Questionable or non-existant. Mainly highway chasing.

Tree Density

Contour of areas with highest tree density.

Urban Areas

Highlighted in dark red.


  • This is not intended as a tactical navigation resource. It is meant to provide a strategic overview of chase navigability/storm visibility.
  • Road grid quality does not speak to actual road conditions—mud bogs, sand traps, plowed-over roads, and map mirages.

Map choice

To avoid copyright issues, I took my first dip into working with shapefiles from the US Census Bureau using QGIS on the Mac to convert to DXF and then import into Illustrator. This provided vector data I could use to add county and state boundaries, interstate paths, and urban areas.

I chose a map projection for the data that was compatible with Google Maps mercator projection (EPSG:900913). This aligned with the road network resource I used and the default projection at Data Basin.

Road Network Method

The US Census Bureau provide shapefiles for all roads in the US, but the number of shapefiles is enormous (3200+) and without scripting would be an extremely tedious process. However, reddit user, WestCoastBestCoast94, did go through this process and used the data to generate a high-res PNG image of all roads in the US. I referenced this image to make estimates of road networks and to draw in boundaries. I gave preference to networks with primarily straight roads and perpendicular intersections. There may be decent networks with lots of diagonal roads and angled intersections (I’m looking at you, Texas), but without a more detailed & lengthy examination, I can’t tell which of these are halfway-decent and which are terrible, so I tended to leave them in the lower quality buckets.

I did not have an eternity to do this, so there is going to be some slop in places—taken as a whole, it should provide a reasonable estimate of road network. However, DeLorme, Garmin, Google, Yahoo, Microsoft, whatever map software of your choice, would still need to be the prime resource for current/reasonably-accurate info.

I am not including the actual road-network map in the image above or in the layered PSD file, because I don’t know if ‘WestCoastBestCoast94’ wanted it to be re-distributed in a Creative Commons non-commercial sense. However, you can find his US map and more detailed individual state maps in the directory he created here: http://foid.me/roads/. It is scaled such that you could paste it into the layered PSD document to compare to contours I’ve drawn.

Tree Density Method

I used the ‘Mask Of Forested Lands Contiguous US’ data from Data Basin to draw contour lines around the areas of highest tree density. There are less dense tree signals that I did not include in the boundaries. I am also not sure how well the data correlates to the real world and whether it includes other annoying, visibility-killing plant life.

Future Plans & Possibilities

  • Road Network: Add contours for California, Wisconsin, Indiana, Michigan, Ohio, Florida and Mississippi River Valley.
  • Evaluate color choices for accessibility and easy evaluation of features (it's probably pretty bad for deuteranopes at this point).
  • Terrain: flat / hilly (maybe 2 or 3 degrees of this?) / rugged / mountainous — with obstructions (rivers/escarpments)
  • River crossings
  • Hostile counties: I’m collecting a list (e.g., Barber Cty, KS)
  • Rest Stop/Boondocking locations

Storm Chase — 19 March 2015

This was a chase-of-opportunity with my kids while visiting family in western Oklahoma. Before heading out, I brewed up my traditional personal estimate for success for the day:

  • Thunderstorms 75%
  • Transient Structure 50%
  • Supercell 15%
  • Rotating Wall/Funnel 5%
  • Tornado 1%

I got a late start getting out of the fog and drizzle of Elk City and got to my target in Vernon by 20Z — about an hour later than I wanted to. It was nice to see clearing and bubbling cumulus to the south. After fueling up and messing around with the latest data for too long, we headed further south into the clear and near the junction of Hwy 183 and 277 by 21Z. There were two areas of initiation at this point: some early development to my northwest north of Seymour, and a more mature cell near Archer City. The Archer City tower looked great, but I opted for the Seymour target since it didn’t involve playing catch-up, and being closer to the triple point, I thought it might have a better fetch of backed surface winds. The problem with this is that the western target was also further north and so was first to greet the cold front. It also got to choke on stable inflow from the Archer City storm. (click images for larger versions)

My daughter checking out the Archer City tower — 2110Z

Until it got wiped out though, it was a nice early-season chase. After grabbing a few shots of that tower to the east, we drove back north to watch the inbound Seymour storms. At an overlook east of Lake Kemp I met Marcus Diaz, Jason Boggs, Bobby Hines, Mark Eslick, and Tyler Hudson. We shared the views for a while as the convection gained strength and developed some structure. As the forward flank gust front finally started spitting rain on us, we hopped in our cars and headed our separate ways. Road options were pretty scarce, and we had to get a ways south of the storm before getting back east on Hwy 277 to get ahead of it.

Some structure on the developing cell near Lake Kemp — 2150Z

Marcus Diaz, Mark Eslick, Tyler Hudson and Jason Boggs check out radar and the storm base east of Lake Kemp — 2151Z

Encroaching outflow — 2204Z

A north option on SR 25 put us in a spot to look into a beautifully sculpted vault with a lengthy arcus/inflow tail spanning the sky and racing into the storm base. As the forward flank started gusting toward us, we cruised back south to get out of the way.

Storm base and pump jack from SR 25 — 2242Z

Terraced vault with arcus/inflow tail racing westward from SR 25 — 2247Z

Arcus and shelf gusting southward along SR 25 — 2247Z

Heading south, I wondered why truck traffic was backed up. Turns out a chaser had a yellow vehicle parked partway into the southbound lane and placing his body even further into the lane. So the trucks were waiting their turn to safely pull into the opposing lane to get around him as he waved people around. There were plenty of great pull-offs on this road—I used a couple of them. And the grass shoulder was huge and in good shape too, so there was no reason for treating the shoulder and pull out areas like hot lava. It was really really frustrating and embarrassing. I needed to get ahead of the gust front and didn’t have time stop and attempt a chaser-101 session, or get a good read of the decals on the vehicle.

Chaser obstruction — 2249Z

The storm was pretty strung out at this point but still dishing out some interesting sights. We got further east to Holliday and noticed a bell shaped lowering. It appeared to be a new updraft trying to forming well to the east of the base I had been watching, and it had what appeared to be a bit of RFD curling in and lowering a wall cloud/RFD shelf around itself before gusting out and merging with the forward flank.

Transient updraft/lowering seen west of Holliday — 2305Z

After that, we bailed out on the storm and headed south for some views of the other storm as it approached Bowie. We got a look at the back of the storm and its upswept flanking line before calling that one off too in some beautiful country.

Backside view of the other storm approaching Bowie — 2349Z

I’ve been watching the GFS signals for this Thursday (19 March 2015) flicker on & off for the past week. It’s nice to see a thin glimmer of hope for tomorrow. Moisture is forecast to move up to the Red River with dew points around 60 degrees. Lapse rates aren’t so great, and NAM and GFS vary on the degree of instability from 250-500 j/kg for GFS and up to 1000 j/kg from NAM. A cold front will sag southward and into this area of instability with storms firing as it forces its way into the warm sector. A shortwave trough over the southwest will feed 40-50 knot H5 winds over the area. So this leads to the possibility for some severe storms with a lot of caveats—especially marginal instability and an undercutting cold front.

18Z NAM shows 0-3 km Helicity maximized up to 250-350 m2/s2 narrowly along the cold front near the triple point at 00Z in the vicinity of Childress. 0-1km SRH is localized and probably barely worth noting near the triple point in the 50-100 m2/s2 range. 18Z GFS is much more conservative and also points further east—south of Wichita Falls. Obviously wouldn’t mind NAM’s optimism working out moreso than GFS at this point and I’m planning to give it a shot just in case. I’m planning to head out of Elk City with an initial target of Vernon, TX by early afternoon.

19 May 2013 Oxford Supercell Diagram

In my previous post, I diagrammed the Oxford, Kansas supercell from 19 May 2013. About 90 seconds after that shot was taken, a new area of low level rotation developed just ahead of the occlusion. This is a diagram of that moment as the inflow was forced into the updraft at that point and rapidly exposing circulation at the cloud base.

Oxford, Kansas Supercell Part 2 - 19 May 2013
Oxford, Kansas Supercell Part 2 - 19 May 2013 - Diagrammed

On the Continuum of Walls and Shelves

In 2010 after my first Great Plains chase, I spent a lot of time going through my photos and working to improve my understanding of storm structure. For one of those exercises, I diagrammed the Bowdle supercell. There was a lot of excellent feedback and discussion on all the structure in that beautiful, terrible, amazing storm.

Each new supercell I chase broadens my appreciation for all the ingredients and dynamics that make each one unique and awesome. I enjoy recapping each one and visualizing what was happening, so I've been keen to diagram some more recent storms.

What I especially wanted to work on were transition points in space or time where a shelf cloud is merging or morphing into a wall cloud/tail cloud and vice-versa. A lot of times it's pretty clear what's what. But because the storm and its environment don't care about taxonomy, there are plenty of cases where things ride along a diffuse spectrum. To me, it's educational to watch these things unfold and look for transitions where one thing becomes another, and what that means for the fluid movement and interaction of near-storm air masses.

So, here is a batch of a few more.

Denver Supercell - May 21, 2014

While this storm was still strengthening over Denver Metro and headed toward the airport, it had a very compact RFD shelf that I wanted to call a wall cloud at first glance. But the RFD appears to be responsible for lifting this prominent feature out ahead of the base while the true wall clouds spins away behind. Mike Olbinski's time lapse nicely demonstrates the dynamics (See the 6:24 segment of the video).

Denver Supercell - May 21, 2014
Denver Supercell - May 21, 2014 - Diagrammed

Goshen County Supercell - May 20, 2014

This was a view that to me, beautifully demonstrates the source of a weak wall cloud’s formation as the forward flank's rain foot intrudes into the updraft, drastically lowering the condensation level in that area. How much of the foreground lowering would technically be considered a wall cloud vs. RFD shelf was questionable to me.

Goshen County Supercell - May 20, 2014
Goshen County Supercell - May 20, 2014 - Diagrammed

Newkirk, Oklahoma Supercell - May 19, 2013

This is an example of a transition point where the RFD is smearing a weak wall cloud into a shelf cloud. At least that's how it seems to me. You can see that the foreground lowering is "pointing" toward the forward flank, and benefiting from lowered condensation as it rises into the base. But now it's being hurried and lifted on its way by the RFD gust front (which it "points" away from). It seems to be in a place between both 'definitions' and both dynamic conditions.

Newkirk, Oklahoma Supercell - May 19, 2013
Newkirk, Oklahoma Supercell - May 19, 2013 - Diagrammed

Oxford, Kansas Supercell - May 19, 2013

This storm had a shelf feature on the forward flank leading straight into the the RFD core that made me think of video of the Long Point, Illinois storm on November 17, 2013. Skip Talbot had commented that the forward flank shelf on that storm seemed to behave like a hybrid shelf cloud and inflow band.

Oxford, Kansas Supercell - May 19, 2013
Oxford, Kansas Supercell - May 19, 2013 - Diagrammed

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