diff --git a/lib/xmet/thermo.py b/lib/xmet/thermo.py
index c382794..c1424a9 100644
--- a/lib/xmet/thermo.py
+++ b/lib/xmet/thermo.py
@@ -101,7 +101,8 @@ def moist_lapse_rate(temp: float, pressure: float) -> float:
 
 def loft_parcel(start_temp: float,
                 start_pressure: float,
-                lapse_rate: Callable):
+                lapse_rate: Callable,
+                step: float=10.0):
     """
     Loft a parcel of air from a given pressure, at a given temperature,
     yielding a Tuple containing the temperature and pressure of that parcel
@@ -136,7 +137,7 @@ def loft_parcel(start_temp: float,
 
         if pressure == PRESSURE_MIN:
             break
-        elif pressure - 10.0 < PRESSURE_MIN:
+        elif pressure - step < PRESSURE_MIN:
             pressure = PRESSURE_MIN
         else:
-            pressure -= 10.0
+            pressure -= step