diff --git a/gallery/painting/gismeteo/api.py b/gallery/painting/gismeteo/api.py
index 5e6c549..bd5c829 100644
--- a/gallery/painting/gismeteo/api.py
+++ b/gallery/painting/gismeteo/api.py
@@ -41,7 +41,9 @@ class GismeteoApi(WeatherApi):
         # group values by 3 hours
         if len(values) > 8:
             n = 3
-            values = [merge_weather_values(values[i].date, values[i : i + n]) for i in range(0, len(values), n)]
+            values = [
+                merge_weather_values(values[i].date, values[i : i + n], "average") for i in range(0, len(values), n)
+            ]
         return WeatherResponse(
             location=location or "n/a",
             date=date,
diff --git a/gallery/sketch/weather/util.py b/gallery/sketch/weather/util.py
index 9c5f374..71a7749 100644
--- a/gallery/sketch/weather/util.py
+++ b/gallery/sketch/weather/util.py
@@ -1,8 +1,11 @@
 import datetime
 import statistics
+from typing import Literal
 
 from .model import Cloudness, Precipitation, Sky, WeatherValue, WindDirectionDeg
 
+MergeMode = Literal["interval", "average"]
+
 
 def build_weather_value(date: datetime.datetime) -> WeatherValue:
     return WeatherValue(
@@ -23,7 +26,15 @@ def build_weather_value(date: datetime.datetime) -> WeatherValue:
     )
 
 
-def merge_weather_values(date: datetime.datetime, values: list[WeatherValue]) -> WeatherValue:
+def _merge_values(values: list[int], mode: MergeMode) -> list[int]:
+    return [max(values), min(values)] if mode == "interval" else [round(sum(values) / len(values))]
+
+
+def merge_weather_values(
+    date: datetime.datetime,
+    values: list[WeatherValue],
+    mode: MergeMode = "interval",
+) -> WeatherValue:
     result = build_weather_value(date)
     temperatures = []
     pressures = []
@@ -44,8 +55,8 @@ def merge_weather_values(date: datetime.datetime, values: list[WeatherValue]) ->
         cloudnesses.append(value.sky.cloudness)
         precipitations.append(value.sky.precipitation)
         precipitation += value.precipitation
-    result.temperature = [max(temperatures), min(temperatures)]
-    result.pressure = [max(pressures), min(pressures)]
+    result.temperature = _merge_values(temperatures, mode)
+    result.pressure = _merge_values(pressures, mode)
     result.humidity = round(statistics.mean(humidities))
     result.wind_speed = round(statistics.mean(wind_speeds))
     result.wind_gust = round(statistics.mean(wind_gusts))