Validate precipitation probabilities and ice wording

internal/forecast/derive.go

@@ -192,6 +192,9 @@ func BuildDailySummary(bundle *weatherdata.Bundle, date time.Time, location *tim
 	if bundle.Hourly == nil || len(bundle.Hourly.Periods) == 0 {
 		return nil, fmt.Errorf("hourly forecast data is required")
 	}
+	if err := ValidatePrecipitationProbabilities(bundle.Hourly.Periods); err != nil {
+		return nil, err
+	}
 	day := timeutil.CivilDay(date, location)
 	windows, err := ResolveDayparts(date, location, dayparts)
 	if err != nil {
@@ -247,6 +250,15 @@ func SelectDiscussion(bundle *weatherdata.Bundle) *weatherdata.Discussion {
 	return bundle.Discussion
 }
 
+func ValidatePrecipitationProbabilities(periods []weatherdata.ForecastPeriod) error {
+	for i, period := range periods {
+		if !period.HasValidPrecipitationProbability() {
+			return fmt.Errorf("hourly forecast period %d has an invalid precipitation probability", i+1)
+		}
+	}
+	return nil
+}
+
 func SummarizeDaypart(name string, period timeutil.Period, periods []weatherdata.ForecastPeriod) DaypartSummary {
 	summary := DaypartSummary{
 		Name:          name,
@@ -357,12 +369,24 @@ func indicatorsForText(text string) Indicators {
 	lower := strings.ToLower(text)
 	return Indicators{
 		Snow: strings.Contains(lower, "snow"),
-		Ice:  strings.Contains(lower, "ice") || strings.Contains(lower, "freezing") || strings.Contains(lower, "sleet"),
+		Ice:  mentionsIce(lower),
 		Fog:  strings.Contains(lower, "fog"),
 		Wind: strings.Contains(lower, "wind") || strings.Contains(lower, "gust"),
 	}
 }
 
+func mentionsIce(text string) bool {
+	for _, token := range strings.FieldsFunc(text, func(r rune) bool {
+		return !('a' <= r && r <= 'z')
+	}) {
+		switch token {
+		case "ice", "icy", "freezing", "sleet":
+			return true
+		}
+	}
+	return false
+}
+
 func mentionsThunder(text string) bool {
 	return strings.Contains(strings.ToLower(text), "thunder")
 }

internal/forecast/derive_test.go

@@ -297,6 +297,41 @@ func TestBuildDailySummaryRequiresHourlyData(t *testing.T) {
 	}
 }
 
+func TestBuildDailySummaryRejectsInvalidPrecipitationProbability(t *testing.T) {
+	location := time.FixedZone("Test", -5*60*60)
+	for _, probability := range []float64{-1, 101, math.NaN()} {
+		bundle := &weatherdata.Bundle{Hourly: &weatherdata.ForecastRun{Periods: []weatherdata.ForecastPeriod{
+			hour(location, "2026-05-29T06:00:00-05:00", "2026-05-29T07:00:00-05:00", "Showers", 70, nil, ptr(probability), nil, nil),
+		}}}
+		_, err := BuildDailySummary(bundle, mustParse("2026-05-29T12:00:00-05:00"), location, []DaypartDefinition{{Name: "morning", Start: "06:00", End: "12:00"}})
+		if err == nil {
+			t.Fatalf("BuildDailySummary(%v) error = nil, want invalid precipitation probability", probability)
+		}
+	}
+}
+
+func TestIndicatorsForTextClassifyIceVocabulary(t *testing.T) {
+	for _, tt := range []struct {
+		name string
+		text string
+		want Indicators
+	}{
+		{name: "ice", text: "Ice likely", want: Indicators{Ice: true}},
+		{name: "icy mixed case", text: "ICY roads", want: Indicators{Ice: true}},
+		{name: "freezing punctuation", text: "Freezing-rain possible", want: Indicators{Ice: true}},
+		{name: "sleet punctuation", text: "Sleet, then rain", want: Indicators{Ice: true}},
+		{name: "unrelated nice", text: "Nice weather"},
+		{name: "unrelated spicy", text: "Spicy conditions"},
+		{name: "other conditions unchanged", text: "Snow and fog with gusts", want: Indicators{Snow: true, Fog: true, Wind: true}},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := indicatorsForText(tt.text); got != tt.want {
+				t.Fatalf("indicatorsForText(%q) = %#v, want %#v", tt.text, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestAlertOverlap(t *testing.T) {
 	location := time.FixedZone("Test", -5*60*60)
 	raw := json.RawMessage(`{"event":"Flood Watch","headline":"Flooding possible","severity":"Moderate","effective":"2026-05-29T07:00:00-05:00","expires":"2026-05-29T10:00:00-05:00"}`)