diff --git a/about.html b/about.html
index 746b0c1..bd87b34 100644
--- a/about.html
+++ b/about.html
@@ -27,7 +27,7 @@
   <link rel="preconnect" href="https://fonts.bunny.net" />
   <link href="https://fonts.bunny.net/css2?family=Fraunces:ital,wght@0,900;1,300&family=Manrope:wght@400;600&family=JetBrains+Mono:wght@400;600&display=swap" rel="stylesheet" />
 
-  <link rel="stylesheet" href="./assets/about.css">
+  <link rel="stylesheet" href="./assets/about.min.css">
 
   <!-- Structured data for AEO / AI search -->
   <script type="application/ld+json">
diff --git a/assets/css/header.css b/assets/css/header.css
index 0ed407e..ab28d57 100644
--- a/assets/css/header.css
+++ b/assets/css/header.css
@@ -53,10 +53,11 @@
   margin-top: 14px;
 }
 
-/* "↳ Pangbourne, Berkshire" */
+/* "↳ Location, Somewhere" */
 .utci-current-loc {
   font-family: Fraunces, serif;
   font-style: italic;
+  font-weight: 800;
   font-size: 18px;
   margin-top: 12px;
   color: #1e1208;
@@ -70,7 +71,7 @@
   color: #b09870;
   display: block;
   margin-top: 4px;
-  margin-left: 18px;
+  margin-left: 15px;
   letter-spacing: 0.08em;
 }
 
diff --git a/assets/js/compute.js b/assets/js/compute.js
index 67a66ee..20e8438 100644
--- a/assets/js/compute.js
+++ b/assets/js/compute.js
@@ -12,7 +12,7 @@
 
 import {
   vaporPressureHpa, solarElevationDeg, calcTmrt, utciApprox,
-  calcConcreteTemp, calcVehicleInteriorTemp,
+  calcConcreteTempPass, calcVehicleInteriorTemp,
   calcIndoorTempPass, calcManagedIndoorTempPass,
 } from './physics.js';
 import { windCompass8, uvSplit, cloudCategory, precipPenalty } from './utils.js';
@@ -55,20 +55,23 @@ export function buildHourlyRows({ forecast, airQuality, location, vehicleType, v
     const soilT0 = h.soil_temperature_0cm    ? h.soil_temperature_0cm[i]    : null;
     const soilT6 = h.soil_temperature_6cm    ? h.soil_temperature_6cm[i]    : null;
     const soilM  = h.soil_moisture_0_to_1cm  ? h.soil_moisture_0_to_1cm[i]  : null;
+    // iso is a local wall-clock string e.g. "2026-05-13T14:00" (no Z).
+    // For display we slice the string directly - no Date object needed.
+    // For solarElevationDeg (which uses .getUTC* internally) we need the
+    // true UTC instant: treat the local time as UTC then subtract the offset.
+    // e.g. Brisbane UTC+10: local 14:00 - parse as UTC 14:00 - subtract 10h - UTC 04:00 -
+    // iso is a local wall-clock string e.g. "2026-05-13T14:00" (no Z).
+    // For solarElevationDeg (which uses .getUTC* internally) we need the
+    // true UTC instant: treat the local time as UTC then subtract the offset.
+    const dt   = new Date(Date.parse(iso + 'Z') - utcOffsetMs);
+    const elev = solarElevationDeg(location.lat, location.lon, dt);
     // Use direct_radiation (beam sunlight) + a fraction of diffuse for concrete.
     // direct_radiation is zero on fully overcast days - far more accurate than
     // shortwave_radiation which can be unreliably high even at 100% cloud cover.
     // Diffuse (scattered light through cloud) contributes ~20% as much heat to
     // a surface as direct beam, so we weight it accordingly.
     const effectiveRad = dir + dif * 0.2;
-    const concreteT = calcConcreteTemp(Ta, effectiveRad, va);
-    // iso is a local wall-clock string e.g. "2026-05-13T14:00" (no Z).
-    // For display we slice the string directly - no Date object needed.
-    // For solarElevationDeg (which uses .getUTC* internally) we need the
-    // true UTC instant: treat the local time as UTC then subtract the offset.
-    // e.g. Brisbane UTC+10: local 14:00 - parse as UTC 14:00 - subtract 10h - UTC 04:00 -
-    const dt   = new Date(Date.parse(iso + 'Z') - utcOffsetMs);
-    const elev = solarElevationDeg(location.lat, location.lon, dt);
+    // concreteT is now stamped in the two-pass section below (thermal lag).
     const vehicleT = calcVehicleInteriorTemp(Ta, glob, elev, vehicleType, vehicleVent);
     const eh       = vaporPressureHpa(Ta, RH);
     const Tmrt     = calcTmrt(Ta, dir, dif, glob, elev);
@@ -132,20 +135,37 @@ export function buildHourlyRows({ forecast, airQuality, location, vehicleType, v
       cc, ccLow, ccMid, ccHigh, cloudCat,
       uv, uvA, uvB,
       precip, snow,
-      soilT0, soilT6, soilM, concreteT, vehicleT,
+      soilT0, soilT6, soilM, vehicleT,
+      effectiveRad,
       elev, Tmrt, utci, utciAdj, eh, compass,
       visKm, aqi,
       grassPollen, birchPollen, alderPollen, mugwortPollen, olivePollen, ragweedPollen,
     };
   }) : [];
 
-  // Two-pass indoor temperature: needs the full hourly arrays so thermal
-  // lag can look back at previous hours. Run after hourlyRows is built,
-  // then stamp each row with its indoorT value.
+  // Two-pass calculations: concrete thermal lag + indoor temperature.
+  // Both need the full hourly arrays so they can look back at previous
+  // hours. Run after hourlyRows is built, then stamp each row.
   if (hourlyRows.length > 0) {
-    const TaArr   = hourlyRows.map(r => r.Ta);
-    const globArr = hourlyRows.map(r => r.glob);
-    const elevArr = hourlyRows.map(r => r.elev);
+    const TaArr       = hourlyRows.map(r => r.Ta);
+    const globArr     = hourlyRows.map(r => r.glob);
+    const elevArr     = hourlyRows.map(r => r.elev);
+    const radArr      = hourlyRows.map(r => r.effectiveRad);
+    const vaArr       = hourlyRows.map(r => r.va);
+    const uvArr       = hourlyRows.map(r => r.uv);
+    const cloudCatArr = hourlyRows.map(r => r.cloudCat);
+    const soilMArr    = hourlyRows.map(r => r.soilM);
+    const precipArr   = hourlyRows.map(r => r.precip);
+    const snowArr     = hourlyRows.map(r => r.snow);
+
+    // Concrete surface temperature with thermal lag (1.5 h time constant).
+    // A slab baking in the sun retains heat when cloud rolls in, and takes
+    // a couple of hours of sunshine to fully heat up from a cold start.
+    const concreteTemps = calcConcreteTempPass(
+      TaArr, radArr, vaArr, elevArr, uvArr, cloudCatArr, soilMArr, precipArr, snowArr
+    );
+    hourlyRows.forEach((r, i) => { r.concreteT = concreteTemps[i]; });
+
     const indoorTemps = calcIndoorTempPass(TaArr, globArr, elevArr, buildingType);
     const managedTemps = calcManagedIndoorTempPass(TaArr, globArr, elevArr, buildingType);
     hourlyRows.forEach((r, i) => { r.indoorT = indoorTemps[i]; r.managedT = managedTemps[i]; });
diff --git a/assets/js/physics.js b/assets/js/physics.js
index 341621c..8a01f69 100644
--- a/assets/js/physics.js
+++ b/assets/js/physics.js
@@ -6,7 +6,9 @@
 //
 //  Exports (in order of appearance):
 //    SIGMA, EPSILON_P, A_K, ALBEDO_GRASS, ALBEDO_CONCRETE  (radiation constants)
-//    calcConcreteTemp(Ta, globalRad, windSpeed)             urban surface temp
+//    LAG_HOURS_CONCRETE                                     slab thermal time constant
+//    calcConcreteTemp(Ta, globalRad, windSpeed, ...)        urban surface temp (instantaneous target)
+//    calcConcreteTempPass(arrays...)                        thermal-lag pass over full hourly arrays
 //    calcIndoorTempPass(TaArr, globArr, elevArr, buildingType)  passive indoor temp
 //    calcManagedIndoorTempPass(TaArr, globArr, elevArr, buildingType) managed indoor temp
 //    calcVehicleInteriorTemp(Ta, globalRad, solElev, vehicleType, ventilated)
@@ -42,26 +44,189 @@ export const ALBEDO_CONCRETE = 0.30;
 // CONCRETE SURFACE TEMPERATURE (Urban profile)
 // -------------------------------------------------------------------
 // Estimates the surface temperature of exposed concrete using a
-// simplified energy-balance approach:
-//   - Absorbed solar = globalRad - (1 - albedo)
-//   - No latent heat (no evaporation - concrete is dry)
-//   - Convective loss to air proportional to wind speed
-//   - Result is clamped to a physically plausible range
+// multi-factor energy-balance approach. Six physical effects are
+// modelled beyond the basic solar-gain / convective-loss pair:
 //
-// This is what matters for contact heat stress in cities - the UTCI
-// standard uses grass, which runs ~5-15 -C cooler than urban concrete
-// on a sunny day because grass sweats (transpires).
+//  1. SUN ANGLE CORRECTION
+//     At low solar elevation the sun hits the surface obliquely,
+//     spreading energy over a larger area. A sin(elev) factor
+//     reduces absorbed solar proportionally. Clamped at a 5-deg
+//     minimum so the result stays finite near the horizon.
+//
+//  2. CLOUD TYPE TRANSMITTANCE
+//     Cloud cover category drives a transmittance multiplier.
+//     Low cloud (stratus) is far more opaque than high cirrus:
+//       clear    1.00 - full beam reaches the surface
+//       wispy    0.92 - cirrus barely attenuates
+//       scattered 0.72 - broken cumulus, significant blocking
+//       overcast  0.28 - thick stratus, mostly diffuse remains
+//     The raw effectiveRad already dims with cloud cover from the
+//     API, but this adds the qualitative distinction between cloud
+//     types that the single radiation number does not capture.
+//
+//  3. UV CLARITY FACTOR
+//     UV index is a proxy for atmospheric clarity beyond cloud cover -
+//     aerosols, haze, and humidity all reduce it. A UV of 8+ indicates
+//     a very clean, dry atmosphere with maximum direct-beam intensity.
+//     Normalised to a 0.85-1.00 range so it modulates rather than
+//     dominates. No UV data defaults to neutral (1.0).
+//
+//  4. EVAPORATIVE COOLING FROM SOIL MOISTURE
+//     Wet concrete loses heat via evaporation. Soil moisture at 0-1cm
+//     is used as a proxy for surface wetness (0 = bone dry, 1 = fully
+//     saturated). A saturated surface loses up to ~8-C relative to
+//     the dry case - consistent with published wet-pavement studies.
+//
+//  5. RAIN-WET SURFACE
+//     Active precipitation forces surface wetness regardless of soil
+//     moisture data. Above 0.5 mm/h the surface is considered fully
+//     wet and the maximum evaporative penalty applies.
+//
+//  6. SNOW COVER
+//     Snow on concrete insulates the slab from solar gain AND strongly
+//     reflects incoming radiation (albedo ~0.80 for fresh snow vs 0.30
+//     for bare concrete). When snowfall is active or lying snow is
+//     implied (snow > 0), absorbed radiation is cut by 85% and a small
+//     insulating offset is applied instead.
+//
+// Colour thresholds (same as before - surface contact risk):
+//   < Ta        - should not occur (clamped)
+//   Ta - 45 -C  - warm but bearable contact
+//   45 - 60 -C  - pain threshold for bare skin contact
+//   > 60 -C     - burns on contact (relevant for paws / bare feet)
 // -------------------------------------------------------------------
-export function calcConcreteTemp(Ta, globalRad, windSpeed) {
+export function calcConcreteTemp(Ta, globalRad, windSpeed, solElev, uv, cloudCat, soilM, precip, snow) {
   if (globalRad == null || Ta == null) return null;
-  const absorbed = globalRad * (1 - ALBEDO_CONCRETE); // W/m-
-  // Convective heat transfer coefficient: ~10 W/m-K still air, rises with wind
-  // (10 reflects realistic natural convection; 5 was too low and ran too hot)
+
+  // -- 6. Snow short-circuit --------------------------------------------
+  // Snow-covered concrete behaves like a white reflective insulator.
+  // Absorbed solar collapses; slab temp stays close to air temp.
+  if (snow != null && snow > 0) {
+    const snowAbsorbed = globalRad * (1 - 0.80); // fresh snow albedo ~0.80
+    const hcSnow = 10 + 4.5 * Math.sqrt(Math.max(windSpeed || 0, 0));
+    const Ts = Ta + snowAbsorbed / hcSnow;
+    return Math.max(Ta - 1, Math.min(Ts, 40)); // snow-covered slab rarely exceeds 40-C
+  }
+
+  // -- 1. Sun angle correction ------------------------------------------
+  // Low-angle sun spreads energy across a larger surface area.
+  // sin(elev) = 1.0 at 90-deg (overhead), ~0.17 at 10-deg (grazing).
+  // Default to sin(45-deg) ~0.71 when elevation is unknown.
+  const elevDeg = (solElev != null) ? Math.max(5, solElev) : 45;
+  const angleCorrection = Math.sin(elevDeg * Math.PI / 180);
+
+  // -- 2. Cloud type transmittance --------------------------------------
+  // Modulates beam quality beyond what raw radiation already captures.
+  const cloudTransmit = cloudCat === 'clear'     ? 1.00
+                      : cloudCat === 'wispy'     ? 0.92
+                      : cloudCat === 'scattered' ? 0.72
+                      : /* overcast */             0.28;
+
+  // -- 3. UV clarity factor --------------------------------------------
+  // UV index as atmospheric-clarity proxy. Scaled to 0.85-1.00 range.
+  // uv=0 (night or heavy cloud) - neutral 1.0 (no adjustment needed,
+  // radiation already near-zero). uv=8+ - max clarity bonus of 1.0.
+  const uvClarity = (uv && uv > 0)
+    ? 0.85 + 0.15 * Math.min(1, uv / 8)
+    : 1.0;
+
+  // -- Absorbed solar with all modifiers --------------------------------
+  const absorbed = globalRad * (1 - ALBEDO_CONCRETE)
+                 * angleCorrection
+                 * cloudTransmit
+                 * uvClarity;
+
+  // -- Convective loss --------------------------------------------------
   const hc = 10 + 4.5 * Math.sqrt(Math.max(windSpeed || 0, 0));
-  // Surface temp: Ta + solar gain / convective loss
+
+  // -- Dry surface temperature ------------------------------------------
   const Ts = Ta + absorbed / hc;
-  // Clamp: can't be cooler than air, cap at 85 -C (melting asphalt territory)
-  return Math.max(Ta, Math.min(Ts, 85));
+
+  // -- 4 + 5. Evaporative cooling ---------------------------------------
+  // Rain-wet surface overrides soil moisture - surface is fully saturated.
+  const surfaceWet = (precip != null && precip >= 0.5)
+    ? 1.0
+    : Math.max(0, Math.min(1, soilM ?? 0));
+  // Max evaporative delta ~8-C at full saturation (published wet-pavement data).
+  const evapCooling = surfaceWet * 8;
+
+  const TsCooled = Ts - evapCooling;
+
+  // -- Final clamp: no cooler than air, no hotter than 85-C -------------
+  return Math.max(Ta, Math.min(TsCooled, 85));
+}
+
+// -------------------------------------------------------------------
+// CONCRETE THERMAL LAG TIME CONSTANT
+// -------------------------------------------------------------------
+// A standard urban pavement slab (~100 mm thick, exposed top surface,
+// air below via sub-base) has moderate thermal mass. Real-world
+// measurement studies put the e-folding time constant at 1.5-2 h for
+// this geometry - we use 1.5 h as representative of the thin end of
+// typical footway construction (block paving, tarmac-over-hardcore).
+//
+// If this ever needs to vary by surface type, pull it into a
+// SURFACE_TYPES preset object mirroring BUILDING_TYPES in utils.js.
+// For now a single named constant keeps the intent obvious.
+// -------------------------------------------------------------------
+export const LAG_HOURS_CONCRETE = 1.5;
+
+// -------------------------------------------------------------------
+// CONCRETE SURFACE TEMPERATURE - THERMAL LAG PASS
+// -------------------------------------------------------------------
+// Wraps calcConcreteTemp in the same exponential-blending pattern used
+// by calcIndoorTempPass. Instead of snapping to the instantaneous
+// target each hour, the slab temperature blends toward it at a rate
+// controlled by LAG_HOURS_CONCRETE.
+//
+// Effect in practice:
+//   - A slab baking at 55-C when cloud rolls in will still read ~48-C
+//     an hour later and ~44-C two hours later - not instantly 22-C.
+//   - A cold slab at dawn takes 2-3 hours of strong sun to fully heat.
+//   - Post-rain cool-down persists into the next hour even if it stops.
+//
+// Call AFTER building hourlyRows (same pattern as calcIndoorTempPass).
+// Returns a Float64-like plain Array of concrete temps, one per hour.
+//
+// Arguments are parallel arrays (one value per forecast hour):
+//   TaArr       - air temperature (-C)
+//   radArr      - effectiveRad (dir + dif*0.2) (W/m-)
+//   vaArr       - wind speed (m/s)
+//   elevArr     - solar elevation (degrees)
+//   uvArr       - UV index
+//   cloudCatArr - cloud category string
+//   soilMArr    - soil moisture 0-1cm (0-1 fraction)
+//   precipArr   - precipitation (mm/h)
+//   snowArr     - snowfall (cm/h)
+// -------------------------------------------------------------------
+export function calcConcreteTempPass(TaArr, radArr, vaArr, elevArr, uvArr, cloudCatArr, soilMArr, precipArr, snowArr) {
+  const n = TaArr.length;
+  const result = new Array(n);
+  const alpha = 1 - Math.exp(-1 / LAG_HOURS_CONCRETE);
+
+  // Seed from the first hours instantaneous value so we start somewhere
+  // physically reasonable rather than zero.
+  let Tc = calcConcreteTemp(
+    TaArr[0], radArr[0], vaArr[0],
+    elevArr[0], uvArr[0], cloudCatArr[0],
+    soilMArr[0], precipArr[0], snowArr[0]
+  ) ?? TaArr[0];
+
+  for (let i = 0; i < n; i++) {
+    const target = calcConcreteTemp(
+      TaArr[i], radArr[i], vaArr[i],
+      elevArr[i], uvArr[i], cloudCatArr[i],
+      soilMArr[i], precipArr[i], snowArr[i]
+    ) ?? TaArr[i];
+
+    // Blend slab temp toward this hours target.
+    Tc = Tc + alpha * (target - Tc);
+
+    // Slab cannot be cooler than air (no active cooling mechanism).
+    result[i] = Math.max(TaArr[i], Tc);
+  }
+
+  return result;
 }
 
 // -------------------------------------------------------------------
diff --git a/build.js b/build.js
index 7085fb4..7ae5df4 100644
--- a/build.js
+++ b/build.js
@@ -38,6 +38,7 @@ function cleanDist() {
     path.join(DIST,   'index.html'),
     path.join(DIST,   'about.html'),
     path.join(ASSETS, '_tmp_flat.css'),
+    path.join(ASSETS, 'about.min.css'),
   ];
   for (const f of targets) {
     try { fs.unlinkSync(f); } catch (_) { /* ok if missing */ }
@@ -145,12 +146,22 @@ async function build() {
     console.log('    -> ' + htmlFile);
   }
 
-  // 5. Copy standalone CSS files that are not part of the main bundle
-  for (const f of ['about.css']) {
-    const src = path.join(ROOT, 'assets', f);
+  // 5. Minify standalone CSS files that are not part of the main bundle
+  // src name -> output name
+  const standaloneCSS = [['about.css', 'about.min.css']];
+  for (const [srcName, outName] of standaloneCSS) {
+    const src = path.join(ROOT, 'assets', srcName);
     if (fs.existsSync(src)) {
-      copyFile(src, path.join(ASSETS, f));
-      console.log('    -> assets/' + f);
+      fs.mkdirSync(ASSETS, { recursive: true });
+      await esbuild.build({
+        entryPoints: [src],
+        bundle:      false,
+        minify:      true,
+        outfile:     path.join(ASSETS, outName),
+        logLevel:    'warning',
+      });
+      const sz = fs.statSync(path.join(ASSETS, outName)).size;
+      console.log('    -> assets/' + outName + ' (' + (sz / 1024).toFixed(1) + ' KB minified)');
     }
   }
 
diff --git a/package-lock.json b/package-lock.json
index 2623e04..6cd18f9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,7 +8,7 @@
       "name": "sunscope",
       "version": "1.0.0",
       "devDependencies": {
-        "esbuild": "^0.21.0"
+        "esbuild": "^0.21.5"
       }
     },
     "node_modules/@esbuild/aix-ppc64": {
diff --git a/package.json b/package.json
index 74c4a50..a72f1f0 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,6 @@
     "build:watch": "node --watch build.js"
   },
   "devDependencies": {
-    "esbuild": "^0.21.0"
+    "esbuild": "^0.21.5"
   }
 }