Forecasting and Operational Meteorology Flashcards

A meteorologist preparing an expert report for litigation examines historical data and finds that a Doppler radar observed a reflectivity core exceeding 65 dBZ at 25,000 ft MSL at the time of a hail-producing storm. This value primarily indicates:

Answer: Very large hail was likely present in the storm, given that high reflectivity at altitude suggests large or dense hydrometeors aloft

Reflectivity values exceeding 65 dBZ at high altitudes are a strong indicator of large hail, since only large, dense hydrometeors produce such intense radar returns aloft.

Which concept describes the forecasting challenge when the atmosphere transitions from a state where numerical models perform well to one characterized by intrinsic unpredictability at the synoptic scale?

Answer: Predictability limits, where small errors in initial conditions grow exponentially due to chaotic dynamics

The inherent chaotic nature of the atmosphere causes small initial-condition errors to grow exponentially, imposing a fundamental predictability limit of roughly 2 weeks for synoptic-scale forecasting.

A CCM is asked to evaluate whether a derecho caused structural damage. Which characteristic best distinguishes a derecho from a typical thunderstorm wind event?

Answer: A derecho is a widespread, long-lived convective windstorm producing a concentrated swath of straight-line wind damage exceeding 240 miles with gusts ≥58 mph

By definition, a derecho must produce a continuous damage swath of at least 240 miles with wind gusts reaching or exceeding 58 mph along most of its length.

When applying Model Output Statistics (MOS), the guidance corrects for which common problem in raw NWP model output?

Answer: Systematic biases in model forecasts by using statistical relationships between past model output and observed weather elements

MOS uses regression equations derived from historical model and observation pairs to remove systematic model biases and produce calibrated station-specific guidance.

A consulting meteorologist is asked about snow water equivalent (SWE) for a snowpack assessment. If a 24-inch snowpack has a snow density of 15%, what is the approximate SWE?

Answer: 3.6 inches of liquid water

SWE equals snow depth multiplied by snow density: 24 inches × 0.15 = 3.6 inches of liquid water equivalent.

Which synoptic pattern is most favorable for significant lake-effect snow downwind of the Great Lakes?

Answer: Cold, northwesterly flow with a long fetch over open lake water after cold air outbreaks, with lake-to-air temperature differences exceeding 13°C

Lake-effect snow thrives when cold arctic air streams over relatively warm, open lake water, with temperature differences exceeding 13°C generating vigorous convection and heavy snow downwind.

In an operational setting, which product best communicates forecast confidence and explicitly shows the range of possible outcomes for a developing high-impact weather event?

Answer: Ensemble spaghetti plots or probability plumes showing the spread among ensemble members

Ensemble spaghetti plots and probability plumes display the range of outcomes across all ensemble members, explicitly communicating forecast uncertainty to decision-makers.