The SPC Mesoanalysis is a set of hourly objective-analysis fields produced at the Storm Prediction Center that blends a Rapid Refresh model background with the latest surface and upper-air observations, giving forecasters a common gridded picture of the severe weather environment. The output covers surface variables, upper-air fields at 25 mb increments, and derived parameters such as CAPE, shear, storm-relative helicity, and composite indices.
How it is built
A short-term Rapid Refresh forecast is used as a first-guess field. That background is then adjusted using surface observations, mesonet data, upper-air soundings, aircraft reports, profiler and VAD winds, and satellite-derived products. The result is a roughly 40 kilometer grid updated hourly, typically posted about fifteen minutes after the top of the hour.
Because both the background model and the observations are updated each hour, the analysis reflects recent changes in the boundary layer, the low-level jet, and the placement of surface features better than a stale model run does.
How forecasters and chasers use it
Forecasters use the mesoanalysis to locate ingredient overlap, monitor trends, and support watch and mesoscale discussion decisions. Chasers use the same page to compare regions before deployment, to check whether a target area is still stacking ingredients, and to watch how instability and shear are evolving through the afternoon.
The value is standardization. When two people are looking at the same significant tornado parameter or effective bulk shear map, they are looking at the same analysis, which makes discussion and coordination faster.
Where the analysis misleads
Comparisons with field-project soundings have shown the SPC mesoanalysis captures the broad severe environment well but can smooth out sharp gradients and underrepresent very local features. Values near a boundary or in a narrow moist plume should be treated as an estimate, with real soundings preferred where available.
The grid also cannot see storms in progress. Once convection is ongoing, cold pools and outflow boundaries can reshape the environment in minutes, and the next hourly analysis has not caught up yet. Use the mesoanalysis alongside current radar, satellite, and observations rather than as a standalone answer.