GEFS

A GEFS spaghetti plot shows the same weather model run 31 different times, each with slightly different starting conditions. Every colored line is one "member" of the ensemble — one possible future for the atmosphere.

The yellow line is the control run (the model's best single guess). The faint colored lines are the 30 perturbed members. The white dashed line is the ensemble mean — the average of all members.

When you see tight, bundled lines, the atmosphere is predictable. When lines scatter in different directions, there's genuine uncertainty about what will happen.

For equestrians: Tight lines = confidence in your weekend plan. Scattered lines = have a backup plan for that outdoor show.

The 500mb level sits roughly in the middle of the atmosphere (~18,000 feet). The contour lines show geopotential height — essentially, where the pressure surface bulges up (ridges) and dips down (troughs).

Ridges (higher values, 5700m+) generally mean warm, dry, and stable weather below. A ridge parked over your region usually means clear skies and heat.

Troughs (lower values, below 5400m) mean the jet stream is diving south, bringing cooler air, clouds, and often precipitation.

What to watch for: - A deep trough approaching = storm system likely within 2-3 days - A strong ridge = extended fair weather, but watch heat index in summer - A trough that cuts off from the main flow = stalled rain event, potentially multi-day

The orange/red shading on the map shows ensemble spread — how much the members disagree in that region.

Low spread (no shading): Models agree. You can trust the forecast for that area out to the displayed time frame.

Moderate spread (light orange): Some uncertainty. The general pattern is agreed upon, but timing or exact position of weather features may shift.

High spread (dark red/orange): Significant disagreement. The models are offering genuinely different outcomes. This is where the forecast is least reliable.

Practical tip: If the spread is high right over your barn's location at the 72-hour mark, don't commit to outdoor plans. If spread is low, you're probably safe to plan that trail ride.

Each frame in the animation represents a forecast hour — F024 means 24 hours from when the model initialized, F072 means 3 days out, F168 means 7 days out.

As you animate forward in time: - Early frames (F024-F048) are usually tight and confident - Mid-range (F072-F120) starts showing some spread - Extended range (F168+) often shows significant scatter

The key insight: Watch how the pattern *evolves* through animation, not just single frames. A trough approaching from the west that all members agree on at F048 is basically guaranteed. The same trough at F168 with members splitting is still speculative.

For planning: Book the farrier at F048 confidence. Wait on the cross-country schooling if it depends on F120+ forecasts.

Mean Sea Level Pressure plots show the surface pressure pattern — the highs and lows that drive the weather you actually feel at barn level.

Low pressure centers (below 1000 hPa): Storms, rain, wind. The lower the value, the stronger the system. A 980 hPa low off the coast is a serious storm. A 1005 hPa low is a typical passing disturbance.

High pressure centers (above 1020 hPa): Fair weather, light winds, clear skies. Great riding weather.

Tightly packed contour lines = strong pressure gradient = wind. This matters for arena work, trailering, and temporary structures.

Widely spaced lines = weak gradient = calm winds.

For equestrians: When you see a strong low approaching with tightly packed isobars, secure your barn. That's wind, rain, and potentially lightning coming.