Applied forecasting
Chase day forecasting
On a real chase day, the forecast lives in your head from about 6 AM until you're standing next to your car at 3 PM watching a storm fire. Here is how experienced chasers actually walk through it.
The night before
- Read the SPC Day 2 outlook. Where is the risk area? Marginal, Slight, Enhanced, or higher?
- Look at the 00Z NAM 12km run. Where does it plot >2500 J/kg MLCAPE tomorrow afternoon?
- Check 06Z GFS if the run is available.
- Sketch a rough target region on a mental map.
- Book a hotel in a fallback location — you can always cancel.
Morning update (7 AM local)
- SPC Day 1 outlook — has the risk area shifted? Widened? Narrowed?
- Latest morning HRRR — 12-24 hour high-resolution forecast. Where are storm modes discrete vs linear?
- RAP model output — the fastest-updating model.
- Overnight soundings from the region. Is the atmosphere setting up the way models thought?
Refining the target (10 AM - noon)
- SPC Mesoanalysis (see our guide).
- Where is MLCAPE building? Where is SBCIN weakening?
- Where is the surface boundary? Dryline, warm front, outflow?
- What does the composite reflectivity forecast look like at 18Z, 21Z, 00Z?
- Where does the current visible satellite show cumulus growth?
- Choose your first target area — usually a specific highway intersection or town.
Positioning (1 PM - 4 PM)
Position for what comes next, not for what is happening now:
- Drive to a spot 30-40 miles ahead of the target region.
- Watch the visible satellite. Where are cumulus towers going up?
- When storms initiate, choose the cell with the best environment — usually the southernmost.
- Watch radar velocity for the first hint of rotation.
- Reposition to be south/southeast of the strongest cell.
The chase itself
- Approach from the south. Never from the north — you'll be in the rain.
- Watch the storm base for lowering. That is the mesocyclone descending.
- Track the RFD — a dry slot punching in on the back side of the wall cloud signals imminent tornadogenesis.
- Have your escape route east or south. Never let the storm cut off your only road out.
- Make sure you're on paved roads.
Post-chase
- Report the tornado to the local NWS via Twitter, phone, or Skywarn radio.
- Note the exact time and location of touchdown, path direction, and time it dissipated.
- Photo/video is welcome but a written report is what forecasters actually use.
- Log the chase in your chase log.