diff --git a/lib/microwaveprop/propagation.ex b/lib/microwaveprop/propagation.ex
index f259d22c..0fd021e3 100644
--- a/lib/microwaveprop/propagation.ex
+++ b/lib/microwaveprop/propagation.ex
@@ -121,11 +121,13 @@ defmodule Microwaveprop.Propagation do
     end
   end
 
-  @doc "Returns all distinct valid_times for a band, ordered ascending."
+  @doc "Returns distinct valid_times for a band from now onward, ordered ascending."
   def available_valid_times(band_mhz) do
+    now = DateTime.utc_now() |> DateTime.add(-1800, :second)
+
     Repo.all(
       from(gs in GridScore,
-        where: gs.band_mhz == ^band_mhz,
+        where: gs.band_mhz == ^band_mhz and gs.valid_time >= ^now,
         select: gs.valid_time,
         distinct: gs.valid_time,
         order_by: [asc: gs.valid_time]