diff --git a/static/score.js b/static/score.js
index e1a9f5a..3b7a3a7 100644
--- a/static/score.js
+++ b/static/score.js
@@ -111,15 +111,16 @@ function render(data) {
         <span class="score-num">${ov.score}</span>
         <div class="score-hero-label">
           <span class="score-grade">${esc(ov.grade)}</span>
-          <span class="score-sub">${recentYrs} vs ${baseYrs} · ${s.n_recent.toLocaleString()} recent days scored</span>
+          <span class="score-sub">Net change · ${recentYrs} vs ${baseYrs} · ${s.n_recent.toLocaleString()} recent days scored</span>
         </div>
       </div>
-      <p class="score-note">0 = no change from the long-term normal · 100 = an extreme shift.
-        Temperature, feels-like and humidity are weighted most.</p>
+      <p class="score-note">A net-change total across all metrics: 0 = no change from the long-term
+        normal · 100 = an extreme shift. Temperature, feels-like and humidity are weighted most.</p>
     </div>`;
 
   // ---- per-metric cards (annual) ----
   const cards = METRIC_ORDER.map((k) => metricCard(annual.metrics[k])).join("");
+  const wbNote = wetbulbNote(annual.metrics.wetbulb, baseYrs);
 
   // ---- by-season rows ----
   const seasonRows = SEASON_ORDER.map((sk) => {
@@ -138,6 +139,7 @@ function render(data) {
 
   scoreBody.innerHTML = `
     <section class="normals">${cards}</section>
+    ${wbNote}
     <section class="score-section">
       <p class="section-title">By season</p>
       <p class="score-legend">${METRIC_ORDER.map((k) => shortLabel(k)).join(" · ")}</p>
@@ -150,6 +152,22 @@ function render(data) {
   wireSummaryToggle();
 }
 
+// Explains what wet bulb is and reports the share of heat-stress ("wet-bulb")
+// days vs normal days, recent vs baseline. Re-rendered on unit change.
+function wetbulbNote(m, baseYrs) {
+  const def = `<strong>Wet bulb</strong> is how cool evaporation — like sweat — can make you in the
+    current air. When it climbs, sweat stops shedding heat and high temperatures turn dangerous.`;
+  if (!m || m.score == null || !m.freq) {
+    return `<p class="score-callout">${def}</p>`;
+  }
+  const thr = fmtTemp(m.freq.threshold_f);
+  const { f6, f45, d } = m.freq;
+  const delta = d ? ` <span class="pq-d ${d >= 0 ? "pq-up" : "pq-down"}">(${d >= 0 ? "+" : ""}${d} pts)</span>` : "";
+  return `<p class="score-callout">${def}
+    Heat-stress days (peak wet bulb ≥ ${esc(String(thr))}): <strong>${f6}%</strong> of recent days
+    vs <strong>${f45}%</strong> across ${baseYrs}${delta} — the rest are normal.</p>`;
+}
+
 // One metric score card (reuses .normal-card). Null metrics show a muted reason.
 function metricCard(m) {
   if (!m) return "";
diff --git a/static/style.css b/static/style.css
index 938933a..4700ffe 100644
--- a/static/style.css
+++ b/static/style.css
@@ -1732,6 +1732,12 @@ td.rec-date { color: var(--muted); font-size: 13px; }
 .score-section { margin: 20px 0; }
 .score-legend { font-size: 12px; color: var(--muted); margin: -6px 0 10px; }
 
+/* Wet-bulb explainer + heat-stress-day share. */
+.score-callout {
+  background: var(--surface-2); border: 1px solid var(--border); border-radius: 12px;
+  padding: 12px 14px; margin: 14px 0 4px; font-size: 13px; line-height: 1.5; color: var(--text);
+}
+
 /* One row per season: name · overall · a chip per metric. */
 .season-scores {
   display: grid; grid-template-columns: 64px 40px 1fr; align-items: center;