add new method to time sort icing dicts, use it in `pirep_icing`

modules/icing/pireps.py

 import datetime
 from datetime import timezone
-from dateutil import tz
+import numpy as np
 import re
 from pathlib import Path
 import h5py
@@ -22,6 +22,34 @@ ATYPE = '/TP'
 RMK = '/RM'
 
 
+def time_sort_pirep_dict(the_dict):
+    new_dict = {}
+
+    keys = []
+    tidx = []
+    for ts in list(the_dict.keys()):
+        rpts = the_dict[ts]
+        for idx, tup in enumerate(rpts):
+            keys.append(ts)
+            tidx.append(idx)
+
+    sidxs = np.argsort(keys)
+    ice_keys = keys[sidxs]
+    ice_tidx = tidx[sidxs]
+
+    for idx, key in enumerate(ice_keys):
+        rpts = the_dict[key]
+        tup = rpts[ice_tidx[idx]]
+
+        n_rpts = new_dict.get(key)
+        if n_rpts is None:
+            n_rpts = []
+            new_dict[key] = n_rpts
+        n_rpts.append(tup)
+
+    return new_dict
+
+
 # Returns icing, no_icing (no icing observed), neg-icing (icing expected, but not observed)
 def pirep_icing(filename, lon_range=[-180, 180], lat_range=[-63, 63]):
 
@@ -158,6 +186,10 @@ def pirep_icing(filename, lon_range=[-180, 180], lat_range=[-63, 63]):
                 else:
                     rpts.append(tup)
 
+    ice_dict = time_sort_pirep_dict(ice_dict)
+    no_ice_dict = time_sort_pirep_dict(no_ice_dict)
+    neg_ice_dict = time_sort_pirep_dict(neg_ice_dict)
+
     return ice_dict, no_ice_dict, neg_ice_dict