Home · Articles · How to read the
Chase forecasting

How to read the SPC mesoanalysis

The SPC Mesoanalysis is the single most useful real-time forecasting tool a chaser or storm-watcher has. Here is how to actually use it.

The layout

Every hour, the Storm Prediction Center runs the Rapid Refresh model, extracts a few dozen atmospheric parameters, and overlays them on a US map. The page (spc.noaa.gov/exper/mesoanalysis) has ten tabs: Surface, Upper Levels, Composite, Winter, and more. Chasers care about about 8 of the panels.

The 8 panels chasers actually watch

SBCAPE
Surface-based Convective Available Potential Energy. Instability if the storm parcel starts at the surface. >2500 J/kg supports strong storms.
MLCAPE
Mixed-layer CAPE. Instability using averaged surface parcels. More representative than SBCAPE. Chasers watch MLCAPE + SBCIN together.
SBCIN
Cap strength. -50 J/kg is a breakable cap. -200 J/kg usually caps out.
0-6 km Shear
Deep-layer wind shear. >40 kt = supercell environment.
0-1 km SRH
Storm-relative helicity in the lowest kilometer. >150 = tornado supportive; >300 = strong tornado potential.
STP
Significant Tornado Parameter (fixed). 1+ = significant tornadoes possible. 3+ = PDS. 6+ = historic.
EHI
Energy-Helicity Index. Combines CAPE and helicity. 2+ = tornadic potential.
SCP
Supercell Composite Parameter. 4+ = supercell likely.

Building a chase forecast from mesoanalysis

  1. Start at MLCAPE. Is instability >1500 J/kg somewhere reachable?
  2. Check SBCIN over the same region. Is the cap breakable?
  3. Look at 0-6 km bulk shear. >40 kt somewhere in that region?
  4. Overlay 0-1 km SRH. Where does high SRH intersect high CAPE?
  5. Check STP. The bullseye of high STP is your target region.
  6. Cross-check with EHI and SCP.
  7. Watch the surface panel for boundaries — outflow, dryline, warm front.

The panel legend colors

SPC panels use a rough color code: greens = weak, yellows = notable, oranges = significant, reds = extreme. Trust the color; the exact number matters less than the trend and the overlap with other parameters.

Time evolution

The most important thing about a mesoanalysis is the trend. Is STP building or eroding? Is SBCIN weakening? Watch the 3-panel time series — 15z, 18z, 21z — to see whether the atmosphere is loading or unloading. A single snapshot lies; the sequence does not.

Learn more