diff --git a/src/main/scala/db/PostgresService.scala b/src/main/scala/db/PostgresService.scala
index 418323c..4ea66f9 100644
--- a/src/main/scala/db/PostgresService.scala
+++ b/src/main/scala/db/PostgresService.scala
@@ -29,10 +29,17 @@ object PostgresService {
 
 class PostgresService(transactor: Transactor[IO], log: Logger[IO]) {
   def queryLatestTemperatures(cities: NonEmptyList[String]): IO[List[(String, LocalDateTime, Option[Double])]] = {
+    // The open-data source publishes fields on different schedules within
+    // the same hour (e.g. snow arrives well before the hourly temperature
+    // aggregate), so the single newest row for a city can have a real
+    // dateTime but a still-null tempAvg. Skip straight to DISTINCT ON's
+    // "most recent" pick by requiring tempAvg itself to be present, so a
+    // fresh partial row never hides an older row that actually has data.
     val query =
       fr"SELECT DISTINCT ON (city) city, dateTime, tempAvg" ++
         fr" FROM weather" ++
         fr" WHERE " ++ Fragments.in(fr"city", cities) ++
+        fr" AND tempAvg IS NOT NULL" ++
         fr" ORDER BY city, dateTime DESC"
 
     query.query[(String, LocalDateTime, Option[Double])]