US Chase Map Project

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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).

The two images below are 1920 pixels wide. The original is 13,500 pixels wide, so I can export larger if ST is able to host images larger than 2MB.
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 Storm Chase Map - without forested areas

For any who are interested, I’d like to make this available as a community resource. If you’d like to edit, proof, or add 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.


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: 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


Apr 24, 2012
Bourbonnais, Illinois
I'm wondering if the Indiana whiteout is due to lack of knowledge of the state? I know that for the most part central, northern and western Indiana, at least in the northern 1/2 or so, has paved road grids for the most part.

Sorry, I see now that you have plans to update Indiana in the future
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william whittom

i spot and chase in central kentucky and here you only hill top. trees, unpaved roads and if it is raining a lot of back roads flood. best advice have a local guide or dont.
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Oct 20, 2004
Huntsville, AL
Visit site
Hey now... that's neat! I wanted to do something very similar to this nearly 10 years ago, but never found the time to put it together. Most of that looks quite good....... I can attest that it looks very accurate for my home state (Missouri) and my current state (Alabama).
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Thanks for the feedback, Matthew! So far I've only marked up Alabama for tree cover. A quick peek, at that little whisper of lightly-treed terrain on the north edge of the state looks like it has about 3-4 counties' worth of gridded roads, but interspersed between Huntsville and surrounding urban centers.

After a bit more searching, I came across some interesting content from the USGS with better resolution/detail for tree canopy/coverage, and another pretty nice one for landforms that would help with the terrain aspect. Now it's down to seeing if I can get their data to cooperate without an epic technical battle.

Jeff Duda

Resident meteorological expert
Staff member
Oct 7, 2008
Broomfield, CO
This is something I have wanted to do since I took a GIS class back in 2010. This looks really good. I'm glad someone finally got around to doing it.

I had started an ST thread in 2010 about an idea I had, but I never got around to doing it (lack of ability + other stuff getting in the way). It looks like the threaddidn't survive the failures over the years. I have a picture of it, though.


Anyway, I figured you could take some elements from my proposed methodology to incorporate terrain, land use, and perhaps improve the roads method. Great job!
@Marc R. O'Leary — thanks for the input—I hope it turns out to be of some use.

@Jeff Duda — thanks for sharing the reminder about that post! I think I remember reading that. (Although ST search function didn’t locate it, it is still here —> )

I think your proposed strategy for evaluating chase suitability is the ideal way to go—a lot more objective. I especially like the possibility it would bring out those ‘sleeper areas’. I wonder if any of the road shapefile resources contain data on paved vs unpaved? That would go a long way toward refining the road network—even if it was 10% out of date, it would still be very telling. I’d probably have to quit my day job to figure out how to make all of this work though…same problem most everyone has, I guess. The tactics I’m using on this one are pretty subjective, but maybe it can serve as a stop-gap or inspiration for a future version with much more precise evaluations.

For the better USGS canopy and landform maps I thought I found earlier this week, I’m now having trouble locating shapefile data for those that QGIS doesn’t get stumped on. I may have to use image warping in Photoshop to morph the high-res map images to the right projection and process from there.

Thanks @Brandon Centeno . Yeah that one probably works best on an ATV. A lot of the reservation areas do seem to confirm as slim pickings for decent road networks.
Oct 25, 2004
Tucson, Arizona
This is marvelous! Now a statistics freak can easily see why Nebraska has always had a pronounced "tornado drought" in the Sandhills portion of the state.....there are few trustworthy chasing roads there. This is in spite of radar verifications showing tornadoes frequenting this area year after year. It's not uncommon for these to occasionally be large, long-track tornadoes, as well. I don't know how many times I've personally had to terminate my chases of tornadic storms and sometimes actual tornadoes on the ground due to the propensity of poor roads in there. To be fair, there are remote ranch-access roads usually miles apart from each other in the Sandhills, but experience has repeatedly proven her point to me to stay off those no-maintenance/sand+clay roads, especially during wet episodes. Knowing Nebraska as well as I do as a native who LOVES chasing the entire state, I do see some areas on this map that I believe I could update. I'll be in Nebr. the last week of May to begin my month-long chase vacation, and will seek to verify this as I chase here and throughout the remainder of the alley as well.
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@JamesCaruso Thanks for the feedback, James.

@joel ewing Thanks, Joel. The extent of that sandhills road gap was something I was interested in too. I had some nice, structure views of a tornado-warned supercell out there south of Arthur last year. But it was definitely a sandhills-style famine & feast scenario of being mostly too far out for consistent, clear views of the base, vs. timing an escape down the only road to dash out of the way. I hope Nebraska and everywhere else treat you well this year.
Map Update - 15 May 2015

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 Storm Chase Map - without forested areas
Apr 22, 2009
preferrably near a storm
Jeremy, thanks for all the hard work on developing this resource. I "discovered" the sandhills of NE last year and to say the least it's a challenge to chase. To plus it, it would be cool to combine these graphics with the Verizon 4G and NOAA NEXRAD radar coverage maps. Voila you have "prime" stormchasing/chaser convergence territory.
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Jeremy, thanks for all the hard work on developing this resource. I "discovered" the sandhills of NE last year and to say the least it's a challenge to chase. To plus it, it would be cool to combine these graphics with the Verizon 4G and NOAA NEXRAD radar coverage maps. Voila you have "prime" stormchasing/chaser convergence territory.
If you were going to overlay cell coverage, You'd almost have to include AT&T as well as many chasers use them. Some use both. One color for Verizon, one for AT&T, another where they both cover. The southern plains tends to be dominated by AT&T, although Verizon has made a lot of progress in recent years.
Apr 22, 2009
preferrably near a storm
@Jeff Hawkins — Thinking along the lines of that prime convergence territory...It's been pretty telling this afternoon, watching all the Spotter Network icons jamming up against Hwy 26 while the storms enjoy some breathing room on their way north : )

View attachment 8183
I got home late from work and missed the show online unfortunately, but have been watching the goings on since. That looks a bit crowded. I shifted my vacation back 2 weeks otherwise I'd probably be there too. Some things are worth missing : )
Aug 16, 2009
Amarillo, TX
I'm not sure if this has been mentioned because there's too much to read for my pea brain, but is there going to be any state zoomed maps depicting which county roads are paved and which aren't? I think on years like this year, it's important to know what roads are paved in the south plains due to all the rain we've received.


Feb 11, 2012
Athens, TX
I use a Garmin Nuvi 7" LMT and it is rarely misinformed about roads that are paved and roads that are dirt as per the road graphic depiction (lighter-dirt vs darker-paved). The biggest problem is many of the [dirt] roads it indicates are in actuality private ranch roads. I can not imagine chasing without my Garmin. It did a great job Saturday getting me from Magnum to Mountain Park in time to get in front of the Tipton cell (where down and over on 62 was not a possibility due to hail potential) so it routed me through the woods, as straight as possible, all paved roads

Plus, it is possible to add a topographic map when needed to look for higher terrain with road access.
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I'm not sure if this has been mentioned because there's too much to read for my pea brain, but is there going to be any state zoomed maps depicting which county roads are paved and which aren't? I think on years like this year, it's important to know what roads are paved in the south plains due to all the rain we've received.
Especially in the eastern Panhandle down through Childress as well as the far western OK counties. There were a lot of impassable mud pits down there on Saturday.
Jun 16, 2015
Oklahoma City, OK
Awesome map, definitely worth a bump. I recall finding the early version of this map online a while back, but now the update that includes more of the Mississippi Valley and Ohio Valley makes this just about complete for most chasing.

I chased in northwestern Ohio in August and I must say, it reminded me a lot of Iowa, visually. An excellent road network, great visibility and an array of wind farms. Perhaps one of the more underrated places to chase in the country...