Simulated Reflectivity

Simulated Reflectivity (also called synthetic radar reflectivity or model-derived reflectivity) represents numerical weather model calculations of equivalent radar return intensity expressed in dBZ (decibels of Z, where Z is radar reflectivity factor), providing photographers with forecast precipitation intensity and storm structure information before storms develop. Unlike actual radar which observes existing precipitation by measuring returned microwave energy from hydrometeors, simulated reflectivity is computed from model-predicted hydrometeor mixing ratios (rain, snow, graupel, hail) using empirical relationships between particle size distributions and radar backscatter cross-sections. The GFS model generates simulated reflectivity forecasts by converting predicted precipitation microphysics into equivalent radar reflectivity values, enabling advance visualization of where and when intense precipitation cores will develop. The dBZ scale is logarithmic: each 10 dBZ increase represents roughly a 10-fold increase in precipitation rate.

Interpretation for photography: simulated reflectivity below 20 dBZ indicates light precipitation (drizzle, light snow) with minimal storm structure—not visually dramatic. Reflectivity of 20-30 dBZ represents light-to-moderate precipitation with developing convection, producing visible rain shafts and modest cloud development. Reflectivity of 30-40 dBZ indicates moderate-to-heavy precipitation with organized storm cells, creating photogenic rain curtains, visible updraft-downdraft boundaries, and substantial cloud structure. Reflectivity of 40-50 dBZ represents heavy precipitation and robust thunderstorms with intense cores, dramatic precipitation columns, and strong visual contrast between precipitation and clear air—excellent for storm photography. Reflectivity of 50-60 dBZ indicates very heavy precipitation typical of severe thunderstorms, often containing large hail and producing spectacular visual intensity including towering cumulonimbus, anvil formations, and explosive updrafts. Reflectivity exceeding 60 dBZ suggests extreme precipitation rates and potential severe weather including giant hail or intense convection, creating the most visually dramatic but dangerous storm photography opportunities.

For photographers, simulated reflectivity forecasts serve multiple purposes: identifying timing and location of peak storm intensity (target periods when modeled reflectivity exceeds 40 dBZ), anticipating storm mode (linear high reflectivity suggests squall lines, discrete cells suggest supercells), and planning safety by avoiding areas forecast for extreme reflectivity values. Unlike real-time radar which shows current conditions, simulated reflectivity provides 0-120 hour forecasts enabling multi-day storm chase planning. PhotoWeather integrates GFS simulated reflectivity at 3-hour intervals, allowing photographers to track forecast evolution and refine targeting as model runs update. Practical applications: when planning storm photography, overlay simulated reflectivity forecasts on maps to identify where storms will be most intense, then cross-reference with road networks and topography to plan approach routes and shooting locations providing clear views of forecasted high-reflectivity cores.