diff --git a/docs/src/index.md b/docs/src/index.md
index 0bf9913d..7465928f 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -68,7 +68,9 @@ be used by [`run_particle_filter`](@ref):
 ParticleDA.get_particles
 ParticleDA.get_truth
 ParticleDA.update_truth!
-ParticleDA.update_particles!
+ParticleDA.update_particle_dynamics!
+ParticleDA.update_particle_noise!
+ParticleDA.get_particle_observations!
 ParticleDA.write_snapshot
 ```
 
diff --git a/src/ParticleDA.jl b/src/ParticleDA.jl
index d47ef919..19a5c9a6 100644
--- a/src/ParticleDA.jl
+++ b/src/ParticleDA.jl
@@ -38,14 +38,32 @@ above signature, specifying the type of `model_data`.
 function update_truth! end
 
 """
-    ParticleDA.update_particles!(model_data, nprt_per_rank::Int) -> particles_observations
+    ParticleDA.update_particle_dynamics!(model_data, nprt_per_rank::Int)
 
-Update the particles using the dynamic of the model and return the vector of the
+Update the particles using the dynamic of the model.  `nprt_per_rank` is the
+number of particles per each MPI rank.  This method is intended to be extended
+by the user with the above signature, specifying the type of `model_data`.
+"""
+function update_particle_dynamics! end
+
+"""
+    ParticleDA.update_particle_noise!(model_data, nprt_per_rank::Int)
+
+Update the particles using the noise of the model and return the vector of the
 particles.  `nprt_per_rank` is the number of particles per each MPI rank.  This
 method is intended to be extended by the user with the above signature,
 specifying the type of `model_data`.
 """
-function update_particles! end
+function update_particle_noise! end
+
+"""
+    ParticleDA.get_particle_observations!(model_data, nprt_per_rank::Int) -> particles_observations
+
+Return the vector of the particles observations.  `nprt_per_rank` is the number
+of particles per each MPI rank.  This method is intended to be extended by the
+user with the above signature, specifying the type of `model_data`.
+"""
+function get_particle_observations! end
 
 """
     ParticleDA.write_snapshot(output_filename, model_data, avg_arr, var_arr, weights, it)
@@ -325,9 +343,11 @@ function run_particle_filter(init, filter_params::FilterParameters, model_params
         # Forecast: Update tsunami forecast and get observations from it
         # Parallelised with threads.
 
-        @timeit_debug timer "Particle State Update and Process Noise" model_observations = update_particles!(model_data, nprt_per_rank)
+        @timeit_debug timer "Particle Dynamics" update_particle_dynamics!(model_data, nprt_per_rank);
+        @timeit_debug timer "Particle Noise" update_particle_noise!(model_data, nprt_per_rank)
+        @timeit_debug timer "Particle Observations" model_observations = get_particle_observations!(model_data, nprt_per_rank)
 
-        @timeit_debug timer "Weights" get_log_weights!(@view(filter_data.weights[1:nprt_per_rank]),
+        @timeit_debug timer "Particle Weights" get_log_weights!(@view(filter_data.weights[1:nprt_per_rank]),
                                                        truth_observations,
                                                        model_observations,
                                                        filter_params.weight_std)
diff --git a/test/model/model.jl b/test/model/model.jl
index e838de8a..e994a44b 100644
--- a/test/model/model.jl
+++ b/test/model/model.jl
@@ -455,12 +455,15 @@ function ParticleDA.update_truth!(d::ModelData, _)
     return d.observations.truth
 end
 
-function ParticleDA.update_particles!(d::ModelData, nprt_per_rank)
+function ParticleDA.update_particle_dynamics!(d::ModelData, nprt_per_rank)
+    # Update dynamics
     Threads.@threads for ip in 1:nprt_per_rank
         tsunami_update!(@view(d.field_buffer[:, :, 1, threadid()]), @view(d.field_buffer[:, :, 2, threadid()]),
                         @view(d.states.particles[:, :, :, ip]), d.model_matrices, d.model_params)
-
     end
+end
+
+function ParticleDA.update_particle_noise!(d::ModelData, nprt_per_rank)
     # Add process noise
     add_random_field!(d.states.particles,
                       d.field_buffer,
@@ -468,7 +471,9 @@ function ParticleDA.update_particles!(d::ModelData, nprt_per_rank)
                       d.rng,
                       d.model_params.n_state_var,
                       nprt_per_rank)
+end
 
+function ParticleDA.get_particle_observations!(d::ModelData, nprt_per_rank)
     # get observations
     for ip in 1:nprt_per_rank
         get_obs!(@view(d.observations.model[:,ip]),