diff --git a/config/test.exs b/config/test.exs
index 7bcd4612..6243114e 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -65,6 +65,7 @@ config :microwaveprop, narr_req_options: [plug: {Req.Test, Microwaveprop.Weather
 
 # Route HTTP requests through Req.Test stubs
 config :microwaveprop, nexrad_req_options: [plug: {Req.Test, Microwaveprop.Weather.NexradClient}, retry: false]
+config :microwaveprop, rtma_req_options: [plug: {Req.Test, Microwaveprop.Weather.RtmaClient}, retry: false]
 config :microwaveprop, solar_req_options: [plug: {Req.Test, Microwaveprop.Weather.SolarClient}]
 config :microwaveprop, srtm_req_options: [plug: {Req.Test, Microwaveprop.Terrain.Srtm}, retry: false]
 config :microwaveprop, start_freshness_monitor: false
diff --git a/lib/microwaveprop/weather/rtma_client.ex b/lib/microwaveprop/weather/rtma_client.ex
index 79797e5c..6ebb3fd3 100644
--- a/lib/microwaveprop/weather/rtma_client.ex
+++ b/lib/microwaveprop/weather/rtma_client.ex
@@ -72,7 +72,7 @@ defmodule Microwaveprop.Weather.RtmaClient do
   end
 
   defp fetch_idx(url) do
-    case Req.get(url, receive_timeout: 15_000) do
+    case Req.get(url, [receive_timeout: 15_000] ++ req_options()) do
       {:ok, %{status: 200, body: body}} -> {:ok, body}
       {:ok, %{status: status}} -> {:error, "RTMA idx HTTP #{status}"}
       {:error, reason} -> {:error, "RTMA idx failed: #{inspect(reason)}"}
@@ -118,9 +118,12 @@ defmodule Microwaveprop.Weather.RtmaClient do
       ranges
       |> Task.async_stream(
         fn {range_start, range_end} ->
-          Req.get(url,
-            headers: [{"Range", "bytes=#{range_start}-#{range_end}"}],
-            receive_timeout: 30_000
+          Req.get(
+            url,
+            [
+              headers: [{"Range", "bytes=#{range_start}-#{range_end}"}],
+              receive_timeout: 30_000
+            ] ++ req_options()
           )
         end,
         max_concurrency: 4,
@@ -159,4 +162,6 @@ defmodule Microwaveprop.Weather.RtmaClient do
 
   defp pa_to_mb(nil), do: nil
   defp pa_to_mb(pa), do: pa / 100.0
+
+  defp req_options, do: Application.get_env(:microwaveprop, :rtma_req_options, [])
 end
diff --git a/test/microwaveprop/weather/rtma_client_test.exs b/test/microwaveprop/weather/rtma_client_test.exs
new file mode 100644
index 00000000..d8dcae43
--- /dev/null
+++ b/test/microwaveprop/weather/rtma_client_test.exs
@@ -0,0 +1,214 @@
+defmodule Microwaveprop.Weather.RtmaClientTest do
+  use ExUnit.Case, async: true
+
+  alias Microwaveprop.Weather.RtmaClient
+
+  describe "rtma_url/1" do
+    test "builds the S3 URL for an RTMA analysis time" do
+      vt = ~U[2026-04-15 18:00:00Z]
+
+      assert RtmaClient.rtma_url(vt) ==
+               "https://noaa-rtma-pds.s3.amazonaws.com/rtma2p5.20260415/rtma2p5.t18z.2dvaranl_ndfd.grb2_wexp"
+    end
+
+    test "zero-pads single-digit hours" do
+      vt = ~U[2026-04-15 03:00:00Z]
+
+      assert RtmaClient.rtma_url(vt) ==
+               "https://noaa-rtma-pds.s3.amazonaws.com/rtma2p5.20260415/rtma2p5.t03z.2dvaranl_ndfd.grb2_wexp"
+    end
+
+    test "handles hour zero" do
+      vt = ~U[2026-04-15 00:00:00Z]
+
+      assert RtmaClient.rtma_url(vt) ==
+               "https://noaa-rtma-pds.s3.amazonaws.com/rtma2p5.20260415/rtma2p5.t00z.2dvaranl_ndfd.grb2_wexp"
+    end
+  end
+
+  describe "fetch_observation/3 — idx layer" do
+    test "returns {:error, _} when the idx fetch returns 404 (not yet published)" do
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 404, "not found")
+        else
+          Plug.Conn.send_resp(conn, 500, "idx should have short-circuited")
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      assert reason =~ "RTMA idx HTTP 404"
+    end
+
+    test "returns {:error, _} when the idx fetch returns a non-200 status" do
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 503, "unavailable")
+        else
+          Plug.Conn.send_resp(conn, 500, "unexpected")
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      assert reason =~ "RTMA idx HTTP 503"
+    end
+  end
+
+  describe "fetch_observation/3 — hour truncation" do
+    test "truncates minutes and seconds to the analysis hour in the request URL" do
+      test_pid = self()
+
+      Req.Test.stub(RtmaClient, fn conn ->
+        send(test_pid, {:request_path, conn.request_path, conn.method})
+        # Return an empty idx so downstream stages short-circuit on 0 ranges.
+        Plug.Conn.send_resp(conn, 200, "")
+      end)
+
+      # 18:47:33 must request the 18z (not 19z) analysis file — truncation
+      # is load-bearing for matching the stored row's hour-aligned valid_time.
+      assert {:error, _} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:47:33Z])
+
+      assert_received {:request_path, path, "GET"}
+      assert String.contains?(path, "rtma2p5.t18z")
+      refute String.contains?(path, "rtma2p5.t19z")
+    end
+
+    test "already-aligned hour passes through unchanged" do
+      test_pid = self()
+
+      Req.Test.stub(RtmaClient, fn conn ->
+        send(test_pid, {:request_path, conn.request_path})
+        Plug.Conn.send_resp(conn, 200, "")
+      end)
+
+      assert {:error, _} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 12:00:00Z])
+
+      assert_received {:request_path, path}
+      assert String.contains?(path, "rtma2p5.t12z")
+    end
+  end
+
+  describe "fetch_observation/3 — extract layer" do
+    # With an empty (or non-matching) idx body, `byte_ranges_for_fields/2`
+    # produces zero ranges, so `download_ranges/2` does no HTTP and returns
+    # {:ok, ""}, which the GRIB2 Extractor splits into an empty message
+    # list → {:ok, %{}} → {:error, "RTMA: no data..."} path.
+    test "returns {:error, 'RTMA: no data ...'} when the extractor yields no fields" do
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          # idx contains no wanted fields — produces zero byte-ranges.
+          Plug.Conn.send_resp(conn, 200, "1:0:d=2026041518:FOOBAR:nothing:anl:\n")
+        else
+          # Should not be reached because no ranges means no GET.
+          Plug.Conn.send_resp(conn, 500, "unexpected GRB request")
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      assert reason =~ "RTMA: no data"
+      # rlat/rlon are reported to 2.5 km precision (1/40°).
+      assert reason =~ "32.9"
+      assert reason =~ "-97.0"
+    end
+
+    test "returns {:error, 'RTMA: no data ...'} when grib bytes are non-GRIB garbage" do
+      # Serve an idx that DOES match wanted fields so byte-ranges are non-empty,
+      # then serve junk bytes on the ranged GET. The GRIB2 Extractor's
+      # split_messages/1 skips unknown bytes and returns an empty message list,
+      # so extract_point still yields the "no data" error.
+      idx = """
+      1:0:d=2026041518:TMP:2 m above ground:anl:
+      2:100:d=2026041518:DPT:2 m above ground:anl:
+      3:200:d=2026041518:PRES:surface:anl:
+      """
+
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 200, idx)
+        else
+          # 206 Partial Content with non-GRIB junk.
+          Plug.Conn.send_resp(conn, 206, :binary.copy(<<0>>, 1024))
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      assert reason =~ "RTMA: no data"
+    end
+  end
+
+  describe "fetch_observation/3 — malformed idx" do
+    test "crashes on a malformed idx line with a non-integer offset" do
+      # byte_ranges_for_fields/2 calls String.to_integer/1 on the offset
+      # field without a guard — a non-numeric offset is a programmer/server
+      # contract violation and the process raises. Characterize this so
+      # any future change to forgiving-parsing is intentional.
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 200, "1:notanumber:d=2026041518:TMP:2 m above ground:anl:\n")
+        else
+          Plug.Conn.send_resp(conn, 500, "unexpected")
+        end
+      end)
+
+      assert_raise ArgumentError, fn ->
+        RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+      end
+    end
+
+    test "tolerates an idx line with missing trailing fields (uses empty field name)" do
+      # A single-field line falls back to empty strings for var/level via
+      # Enum.at/3 defaults, so it simply doesn't match any wanted field.
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 200, "1:0\n")
+        else
+          Plug.Conn.send_resp(conn, 500, "unexpected")
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      # Empty idx body → zero ranges → empty GRIB → "no data" at extraction.
+      assert reason =~ "RTMA: no data"
+    end
+  end
+
+  describe "fetch_observation/3 — download layer" do
+    # download_ranges/2's Task.async_stream reduces over results; any
+    # non-200/206 downgrades the accumulator to {:error, _}. But a catch-all
+    # `_, acc -> acc` clause in the reducer silently swallows :exit/:timeout
+    # task results. If all tasks time out, the accumulator stays {:ok, []},
+    # which produces an empty binary and ultimately "RTMA: no data ...".
+    # Characterizing, not prescribing — tighten in a follow-up if desired.
+    test "surfaces a non-200 status from the ranged GET as an error" do
+      idx = """
+      1:0:d=2026041518:TMP:2 m above ground:anl:
+      2:100:d=2026041518:DPT:2 m above ground:anl:
+      """
+
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 200, idx)
+        else
+          Plug.Conn.send_resp(conn, 500, "s3 blew up")
+        end
+      end)
+
+      assert {:error, reason} =
+               RtmaClient.fetch_observation(32.9, -97.0, ~U[2026-04-15 18:00:00Z])
+
+      assert reason =~ "RTMA download HTTP 500"
+    end
+  end
+end
diff --git a/test/microwaveprop/workers/rtma_fetch_worker_test.exs b/test/microwaveprop/workers/rtma_fetch_worker_test.exs
new file mode 100644
index 00000000..eeb498f2
--- /dev/null
+++ b/test/microwaveprop/workers/rtma_fetch_worker_test.exs
@@ -0,0 +1,107 @@
+defmodule Microwaveprop.Workers.RtmaFetchWorkerTest do
+  use Microwaveprop.DataCase, async: false
+  use Oban.Testing, repo: Microwaveprop.Repo
+
+  alias Microwaveprop.Weather.RtmaClient
+  alias Microwaveprop.Weather.RtmaObservation
+  alias Microwaveprop.Workers.RtmaFetchWorker
+
+  describe "perform/1" do
+    test "skips the fetch (no HTTP) when a matching row already exists in the snapped bounding box" do
+      valid_time = ~U[2026-04-15 18:00:00Z]
+
+      # Pre-populate a row at the snapped coordinates (32.9 → 32.9 at 1/40°,
+      # -97.0 → -97.0). The worker's bounding-box short-circuit must find it
+      # and return :ok without contacting RtmaClient.
+      %RtmaObservation{}
+      |> RtmaObservation.changeset(%{
+        lat: 32.9,
+        lon: -97.0,
+        valid_time: valid_time,
+        temp_c: 20.0
+      })
+      |> Repo.insert!()
+
+      Req.Test.stub(RtmaClient, fn _conn ->
+        raise "RtmaClient should not be contacted when an observation already exists"
+      end)
+
+      args = %{
+        "lat" => 32.9,
+        "lon" => -97.0,
+        "valid_time" => DateTime.to_iso8601(valid_time)
+      }
+
+      assert :ok = RtmaFetchWorker.perform(%Oban.Job{args: args})
+      assert Repo.aggregate(RtmaObservation, :count, :id) == 1
+    end
+
+    # With garbage-bytes-on-the-wire (no real GRIB2 fixture), the extractor
+    # yields no fields and RtmaClient returns {:error, "RTMA: no data ..."},
+    # which the worker surfaces as {:error, _}. This characterizes that the
+    # worker propagates the client error (and does NOT insert a blank row).
+    test "returns {:error, _} and inserts nothing when the client fails to extract" do
+      idx = """
+      1:0:d=2026041518:TMP:2 m above ground:anl:
+      2:100:d=2026041518:DPT:2 m above ground:anl:
+      """
+
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 200, idx)
+        else
+          Plug.Conn.send_resp(conn, 206, :binary.copy(<<0>>, 1024))
+        end
+      end)
+
+      args = %{
+        "lat" => 32.9,
+        "lon" => -97.0,
+        "valid_time" => "2026-04-15T18:00:00Z"
+      }
+
+      assert {:error, reason} = RtmaFetchWorker.perform(%Oban.Job{args: args})
+      assert reason =~ "RTMA: no data"
+      assert Repo.aggregate(RtmaObservation, :count, :id) == 0
+    end
+
+    test "returns {:error, _} when upstream idx returns 404" do
+      Req.Test.stub(RtmaClient, fn conn ->
+        if String.ends_with?(conn.request_path, ".idx") do
+          Plug.Conn.send_resp(conn, 404, "not yet published")
+        else
+          Plug.Conn.send_resp(conn, 500, "unexpected")
+        end
+      end)
+
+      args = %{
+        "lat" => 32.9,
+        "lon" => -97.0,
+        "valid_time" => "2026-04-15T18:00:00Z"
+      }
+
+      assert {:error, reason} = RtmaFetchWorker.perform(%Oban.Job{args: args})
+      assert reason =~ "RTMA idx HTTP 404"
+      assert Repo.aggregate(RtmaObservation, :count, :id) == 0
+    end
+
+    test "raises FunctionClauseError when args are missing required keys" do
+      # The worker only matches the shape with lat/lon/valid_time — missing
+      # keys must crash loudly rather than silently succeed. This pins the
+      # current fail-fast contract.
+      assert_raise FunctionClauseError, fn ->
+        RtmaFetchWorker.perform(%Oban.Job{args: %{}})
+      end
+    end
+
+    test "raises when valid_time is not an ISO8601 string" do
+      # DateTime.from_iso8601/1 returns {:error, _}, and the `{:ok, _, _} =`
+      # match raises — another fail-fast contract worth pinning.
+      assert_raise MatchError, fn ->
+        RtmaFetchWorker.perform(%Oban.Job{
+          args: %{"lat" => 32.9, "lon" => -97.0, "valid_time" => "not-a-timestamp"}
+        })
+      end
+    end
+  end
+end