diff --git a/homeassistant/components/smhi/weather.py b/homeassistant/components/smhi/weather.py
index 3d5642a2784..aac4c5d24be 100644
--- a/homeassistant/components/smhi/weather.py
+++ b/homeassistant/components/smhi/weather.py
@@ -218,7 +218,9 @@ class SmhiWeather(WeatherEntity):
 
             data.append(
                 {
-                    ATTR_FORECAST_TIME: forecast.valid_time.isoformat(),
+                    ATTR_FORECAST_TIME: forecast.valid_time.replace(
+                        tzinfo=dt_util.UTC
+                    ).isoformat(),
                     ATTR_FORECAST_NATIVE_TEMP: forecast.temperature_max,
                     ATTR_FORECAST_NATIVE_TEMP_LOW: forecast.temperature_min,
                     ATTR_FORECAST_NATIVE_PRECIPITATION: forecast.total_precipitation,
diff --git a/tests/components/smhi/snapshots/test_weather.ambr b/tests/components/smhi/snapshots/test_weather.ambr
index 0d2f6b3b3bf..d825e22d470 100644
--- a/tests/components/smhi/snapshots/test_weather.ambr
+++ b/tests/components/smhi/snapshots/test_weather.ambr
@@ -6,7 +6,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'clear-night',
-          'datetime': '2023-08-08T00:00:00',
+          'datetime': '2023-08-08T00:00:00+00:00',
           'humidity': 100,
           'precipitation': 0.0,
           'pressure': 992.0,
@@ -19,7 +19,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'clear-night',
-          'datetime': '2023-08-08T01:00:00',
+          'datetime': '2023-08-08T01:00:00+00:00',
           'humidity': 100,
           'precipitation': 0.0,
           'pressure': 992.0,
@@ -32,7 +32,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'clear-night',
-          'datetime': '2023-08-08T02:00:00',
+          'datetime': '2023-08-08T02:00:00+00:00',
           'humidity': 97,
           'precipitation': 0.0,
           'pressure': 992.0,
@@ -45,7 +45,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'sunny',
-          'datetime': '2023-08-08T03:00:00',
+          'datetime': '2023-08-08T03:00:00+00:00',
           'humidity': 96,
           'precipitation': 0.0,
           'pressure': 991.0,
@@ -223,7 +223,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'cloudy',
-          'datetime': '2023-08-07T12:00:00',
+          'datetime': '2023-08-07T12:00:00+00:00',
           'humidity': 96,
           'precipitation': 0.0,
           'pressure': 991.0,
@@ -236,7 +236,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'rainy',
-          'datetime': '2023-08-08T12:00:00',
+          'datetime': '2023-08-08T12:00:00+00:00',
           'humidity': 97,
           'precipitation': 10.6,
           'pressure': 984.0,
@@ -249,7 +249,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'rainy',
-          'datetime': '2023-08-09T12:00:00',
+          'datetime': '2023-08-09T12:00:00+00:00',
           'humidity': 95,
           'precipitation': 6.3,
           'pressure': 1001.0,
@@ -262,7 +262,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'cloudy',
-          'datetime': '2023-08-10T12:00:00',
+          'datetime': '2023-08-10T12:00:00+00:00',
           'humidity': 75,
           'precipitation': 4.8,
           'pressure': 1011.0,
@@ -275,7 +275,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'cloudy',
-          'datetime': '2023-08-11T12:00:00',
+          'datetime': '2023-08-11T12:00:00+00:00',
           'humidity': 69,
           'precipitation': 0.6,
           'pressure': 1015.0,
@@ -288,7 +288,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'cloudy',
-          'datetime': '2023-08-12T12:00:00',
+          'datetime': '2023-08-12T12:00:00+00:00',
           'humidity': 82,
           'precipitation': 0.0,
           'pressure': 1014.0,
@@ -301,7 +301,7 @@
         dict({
           'cloud_coverage': 75,
           'condition': 'partlycloudy',
-          'datetime': '2023-08-13T12:00:00',
+          'datetime': '2023-08-13T12:00:00+00:00',
           'humidity': 59,
           'precipitation': 0.0,
           'pressure': 1013.0,
@@ -314,7 +314,7 @@
         dict({
           'cloud_coverage': 100,
           'condition': 'partlycloudy',
-          'datetime': '2023-08-14T12:00:00',
+          'datetime': '2023-08-14T12:00:00+00:00',
           'humidity': 56,
           'precipitation': 0.0,
           'pressure': 1015.0,
@@ -327,7 +327,7 @@
         dict({
           'cloud_coverage': 88,
           'condition': 'partlycloudy',
-          'datetime': '2023-08-15T12:00:00',
+          'datetime': '2023-08-15T12:00:00+00:00',
           'humidity': 64,
           'precipitation': 3.6,
           'pressure': 1014.0,
@@ -340,7 +340,7 @@
         dict({
           'cloud_coverage': 75,
           'condition': 'partlycloudy',
-          'datetime': '2023-08-16T12:00:00',
+          'datetime': '2023-08-16T12:00:00+00:00',
           'humidity': 61,
           'precipitation': 2.4,
           'pressure': 1014.0,
@@ -358,7 +358,7 @@
   dict({
     'cloud_coverage': 100,
     'condition': 'cloudy',
-    'datetime': '2023-08-07T12:00:00',
+    'datetime': '2023-08-07T12:00:00+00:00',
     'humidity': 96,
     'precipitation': 0.0,
     'pressure': 991.0,
@@ -373,7 +373,7 @@
   dict({
     'cloud_coverage': 75,
     'condition': 'partlycloudy',
-    'datetime': '2023-08-13T12:00:00',
+    'datetime': '2023-08-13T12:00:00+00:00',
     'humidity': 59,
     'precipitation': 0.0,
     'pressure': 1013.0,
@@ -388,7 +388,7 @@
   dict({
     'cloud_coverage': 100,
     'condition': 'fog',
-    'datetime': '2023-08-07T09:00:00',
+    'datetime': '2023-08-07T09:00:00+00:00',
     'humidity': 100,
     'precipitation': 0.0,
     'pressure': 992.0,
@@ -403,7 +403,7 @@
   dict({
     'cloud_coverage': 100,
     'condition': 'cloudy',
-    'datetime': '2023-08-07T15:00:00',
+    'datetime': '2023-08-07T15:00:00+00:00',
     'humidity': 89,
     'precipitation': 0.0,
     'pressure': 991.0,