850 mb T alone shows that warm air is present aloft but doesn't reveal
whether it's the textbook cap structure — a warm 700 mb above an EML
plume. The three new layers expose the canonical capping diagnostics
visually:
* T @ 700 mb — ≥10 °C is the southern Plains "moderate cap" threshold
* Td @ 700 mb — wide T-Td depression at 700 mb signals the EML plume
* Lapse 850→700 — steep mid-layer lapse rate (≥7 °C/km) over a moist
boundary layer is the cap mechanism itself
All three derive purely from the existing pressure-level profile (Rust
already fetches up through 700 mb), so no Rust pipeline changes needed.
