CBM Numerical Weather Prediction and Forecast Models 3

Question 1

Which NWP model product provides probabilistic information about the likelihood of a specific weather event exceeding a threshold, such as winds over 35 mph?

Accepted Answer

Ensemble probability forecasts

Answer

Ensemble probability forecasts calculate the fraction of ensemble members exceeding a given threshold, providing direct probabilistic guidance that is more useful than deterministic model output alone.

Question 2

The 'butterfly effect' in atmospheric predictability, attributed to Edward Lorenz, implies that:

Accepted Answer

Small errors in initial conditions can grow exponentially, limiting deterministic forecast skill

Answer

Lorenz demonstrated that because the atmosphere is a chaotic system, tiny errors in initial conditions amplify over time, fundamentally limiting deterministic NWP skill — the theoretical basis for ensemble forecasting.

Question 3

When a broadcast meteorologist evaluates 500 mb geopotential height anomalies from model output, they are primarily assessing:

Accepted Answer

Large-scale atmospheric flow patterns and ridges or troughs affecting the weather forecast

Answer

The 500 mb level represents mid-tropospheric flow; positive height anomalies indicate ridges (generally fair weather) and negative anomalies indicate troughs (stormy weather), making it fundamental to synoptic-scale pattern recognition.

Question 4

Which statement best describes the concept of 'model spin-up' and why it matters?

Accepted Answer

The time required for a model's physical processes to adjust from initial conditions to a dynamically consistent state, which can degrade very short-range forecasts

Answer

Model spin-up refers to the adjustment period (often 0–6 hours) when precipitation and other fields may be unrealistic as the model's dynamics and physics balance from the initial analysis — making the 0–3 hour model output less reliable.

Question 5

The North American Ensemble Forecast System (NAEFS) combines members from which two modeling centers?

Accepted Answer

NCEP (USA) and CMC (Canada)

Answer

NAEFS is a joint effort between NOAA/NCEP's GEFS and Environment and Climate Change Canada's (CMC) ensemble system, producing a larger combined ensemble for improved probabilistic guidance.

CBM - Certified Broadcast Meteorologist Practice Test

CBM - Certified Broadcast Meteorologist Practice Test

CBM Numerical Weather Prediction and Forecast Models 3