diff --git a/src/ParticleDA.jl b/src/ParticleDA.jl
index 0caa9018..f0c09f4e 100644
--- a/src/ParticleDA.jl
+++ b/src/ParticleDA.jl
@@ -224,6 +224,41 @@ function copy_states!(particles::AbstractArray{T,4},
 
 end
 
+# Initialize arrays used by the filter
+function init_filter(filter_params::FilterParameters, model_data, nprt_per_rank::Int, T::Type)
+
+    if MPI.Comm_rank(MPI.COMM_WORLD) == filter_params.master_rank
+        weights = Vector{T}(undef, filter_params.nprt)
+    else
+        weights = Vector{T}(undef, nprt_per_rank)
+    end
+
+    resampling_indices = Vector{Int}(undef, filter_params.nprt)
+
+    # TODO: these variables should be set in a better way
+    nx, ny, n_state_var = model_data.model_params.nx, model_data.model_params.ny, model_data.model_params.n_state_var
+
+    statistics = Array{SummaryStat{T}, 3}(undef, nx, ny, n_state_var)
+    avg_arr = Array{T,3}(undef, nx, ny, n_state_var)
+    var_arr = Array{T,3}(undef, nx, ny, n_state_var)
+
+    # Memory buffer used during copy of the states
+    copy_buffer = Array{T,4}(undef, nx, ny, n_state_var, nprt_per_rank)
+
+    return FilterData(weights, resampling_indices, statistics, avg_arr, var_arr, copy_buffer)
+end
+
+struct FilterData{T, S, U, V, X}
+
+    weights::T
+    resampling_indices::U
+    statistics::S
+    avg_arr::V
+    var_arr::V
+    copy_buffer::X
+
+end
+
 struct BootstrapFilter end
 
 function run_particle_filter(init, filter_params::FilterParameters, model_params_dict::Dict, ::Type{BootstrapFilter})
@@ -251,38 +286,21 @@ function run_particle_filter(init, filter_params::FilterParameters, model_params
     @timeit_debug timer "Model initialization" model_data = init(model_params_dict, nprt_per_rank, my_rank)
 
     # TODO: put the body of this block in a function
-    @timeit_debug timer "Filter initialization" begin
-        # TODO: ideally this will be an argument of the function, to choose a
-        # different datatype.
-        T = Float64
-
-        if MPI.Comm_rank(MPI.COMM_WORLD) == filter_params.master_rank
-            weights = Vector{T}(undef, filter_params.nprt)
-        else
-            weights = Vector{T}(undef, nprt_per_rank)
-        end
-
-        resampling_indices = Vector{Int}(undef, filter_params.nprt)
-
-        # TODO: these variables should be set in a better way
-        nx, ny, n_state_var = model_data.model_params.nx, model_data.model_params.ny, model_data.model_params.n_state_var
-
-        statistics = Array{SummaryStat{T}, 3}(undef, nx, ny, n_state_var)
-        avg_arr = Array{T,3}(undef, nx, ny, n_state_var)
-        var_arr = Array{T,3}(undef, nx, ny, n_state_var)
-
-        # Memory buffer used during copy of the states
-        copy_buffer = Array{T}(undef, nx, ny, n_state_var, nprt_per_rank)
-    end
+    @timeit_debug timer "Filter initialization" filter_data = init_filter(filter_params, model_data, nprt_per_rank, Float64)
 
     @timeit_debug timer "get_particles" particles = get_particles(model_data)
-    @timeit_debug timer "Mean and Var" get_mean_and_var!(statistics, particles, filter_params.master_rank)
+    @timeit_debug timer "Mean and Var" get_mean_and_var!(filter_data.statistics, particles, filter_params.master_rank)
 
     # Write initial state (time = 0) + metadata
     if(filter_params.verbose && my_rank == filter_params.master_rank)
         @timeit_debug timer "IO" begin
-            unpack_statistics!(avg_arr, var_arr, statistics)
-            write_snapshot(filter_params.output_filename, model_data, avg_arr, var_arr, weights, 0)
+            unpack_statistics!(filter_data.avg_arr, filter_data.var_arr, filter_data.statistics)
+            write_snapshot(filter_params.output_filename,
+                           model_data,
+                           filter_data.avg_arr,
+                           filter_data.var_arr,
+                           filter_data.weights,
+                           0)
         end
     end
 
@@ -296,7 +314,7 @@ function run_particle_filter(init, filter_params::FilterParameters, model_params
 
         @timeit_debug timer "Particle State Update and Process Noise" model_observations = update_particles!(model_data, nprt_per_rank)
 
-        @timeit_debug timer "Weights" get_log_weights!(@view(weights[1:nprt_per_rank]),
+        @timeit_debug timer "Weights" get_log_weights!(@view(filter_data.weights[1:nprt_per_rank]),
                                                        truth_observations,
                                                        model_observations,
                                                        filter_params.weight_std)
@@ -308,33 +326,37 @@ function run_particle_filter(init, filter_params::FilterParameters, model_params
         # for their chunk of state.
         if my_rank == filter_params.master_rank
             @timeit_debug timer "MPI Gather" MPI.Gather!(MPI.IN_PLACE,
-                                                         UBuffer(weights, nprt_per_rank),
+                                                         UBuffer(filter_data.weights, nprt_per_rank),
                                                          filter_params.master_rank,
                                                          MPI.COMM_WORLD)
-            @timeit_debug timer "Weights" normalized_exp!(weights)
-            @timeit_debug timer "Resample" resample!(resampling_indices, weights)
+            @timeit_debug timer "Weights" normalized_exp!(filter_data.weights)
+            @timeit_debug timer "Resample" resample!(filter_data.resampling_indices, filter_data.weights)
 
         else
-            @timeit_debug timer "MPI Gather" MPI.Gather!(weights,
+            @timeit_debug timer "MPI Gather" MPI.Gather!(filter_data.weights,
                                                          nothing,
                                                          filter_params.master_rank,
                                                          MPI.COMM_WORLD)
         end
 
         # Broadcast resampled particle indices to all ranks
-        MPI.Bcast!(resampling_indices, filter_params.master_rank, MPI.COMM_WORLD)
+        MPI.Bcast!(filter_data.resampling_indices, filter_params.master_rank, MPI.COMM_WORLD)
 
         @timeit_debug timer "get_particles" particles = get_particles(model_data)
-        @timeit_debug timer "State Copy" copy_states!(particles, copy_buffer, resampling_indices, my_rank, nprt_per_rank)
+        @timeit_debug timer "State Copy" copy_states!(particles,
+                                                      filter_data.copy_buffer,
+                                                      filter_data.resampling_indices,
+                                                      my_rank,
+                                                      nprt_per_rank)
 
         @timeit_debug timer "get_particles" particles = get_particles(model_data)
-        @timeit_debug timer "Mean and Var" get_mean_and_var!(statistics, particles, filter_params.master_rank)
+        @timeit_debug timer "Mean and Var" get_mean_and_var!(filter_data.statistics, particles, filter_params.master_rank)
 
         if my_rank == filter_params.master_rank && filter_params.verbose
 
             @timeit_debug timer "IO" begin
-                unpack_statistics!(avg_arr, var_arr, statistics)
-                write_snapshot(filter_params.output_filename, model_data, avg_arr, var_arr, weights, it)
+                unpack_statistics!(filter_data.avg_arr, filter_data.var_arr, filter_data.statistics)
+                write_snapshot(filter_params.output_filename, model_data, filter_data.avg_arr, filter_data.var_arr, filter_data.weights, it)
             end
 
         end
@@ -370,9 +392,9 @@ function run_particle_filter(init, filter_params::FilterParameters, model_params
         end
     end
 
-    unpack_statistics!(avg_arr, var_arr, statistics)
+    unpack_statistics!(filter_data.avg_arr, filter_data.var_arr, filter_data.statistics)
 
-    return get_truth(model_data), avg_arr, var_arr
+    return get_truth(model_data), filter_data.avg_arr, filter_data.var_arr
 end
 
 # Initialise params struct with user-defined dict of values.