Merge pull request #1055 from zbruick/el_lcl_1020

Prevent an EL below a LCL

metpy/calc/tests/test_thermo.py

@@ -589,6 +589,31 @@ def test_no_el_parcel_colder():
     assert assert_nan(el_temperature, temperatures.units)
 
 
+def test_el_below_lcl():
+    """Test LFC when there is positive area below the LCL (#1003)."""
+    p = [902.1554, 897.9034, 893.6506, 889.4047, 883.063, 874.6284, 866.2387, 857.887,
+         849.5506, 841.2686, 833.0042, 824.7891, 812.5049, 796.2104, 776.0027, 751.9025,
+         727.9612, 704.1409, 680.4028, 656.7156, 629.077, 597.4286, 565.6315, 533.5961,
+         501.2452, 468.493, 435.2486, 401.4239, 366.9387, 331.7026, 295.6319, 258.6428,
+         220.9178, 182.9384, 144.959, 106.9778, 69.00213] * units.hPa
+    t = [-3.039381, -3.703779, -4.15996, -4.562574, -5.131827, -5.856229, -6.568434,
+         -7.276881, -7.985013, -8.670911, -8.958063, -7.631381, -6.05927, -5.083627,
+         -5.11576, -5.687552, -5.453021, -4.981445, -5.236665, -6.324916, -8.434324,
+         -11.58795, -14.99297, -18.45947, -21.92021, -25.40522, -28.914, -32.78637,
+         -37.7179, -43.56836, -49.61077, -54.24449, -56.16666, -57.03775, -58.28041,
+         -60.86264, -64.21677] * units.degC
+    td = [-22.08774, -22.18181, -22.2508, -22.31323, -22.4024, -22.51582, -22.62526,
+          -22.72919, -22.82095, -22.86173, -22.49489, -21.66936, -21.67332, -21.94054,
+          -23.63561, -27.17466, -31.87395, -38.31725, -44.54717, -46.99218, -43.17544,
+          -37.40019, -34.3351, -36.42896, -42.1396, -46.95909, -49.36232, -48.94634,
+          -47.90178, -49.97902, -55.02753, -63.06276, -72.53742, -88.81377, -93.54573,
+          -92.92464, -91.57479] * units.degC
+    prof = parcel_profile(p, t[0], td[0]).to('degC')
+    el_p, el_t = el(p, t, td, prof)
+    assert assert_nan(el_p, p.units)
+    assert assert_nan(el_t, t.units)
+
+
 def test_wet_psychrometric_vapor_pressure():
     """Test calculation of vapor pressure from wet and dry bulb temperatures."""
     p = 1013.25 * units.mbar

metpy/calc/thermo.py

@@ -489,9 +489,11 @@ def el(pressure, temperature, dewpt, parcel_temperature_profile=None):
     if parcel_temperature_profile[-1] > temperature[-1]:
         return np.nan * pressure.units, np.nan * temperature.units
 
-    # Otherwise the last intersection (as long as there is one) is the EL
+    # Otherwise the last intersection (as long as there is one, and it's not
+    # below the LCL) is the EL
     x, y = find_intersections(pressure[1:], parcel_temperature_profile[1:], temperature[1:])
-    if len(x) > 0:
+    lcl_p, _ = lcl(pressure[0], temperature[0], dewpt[0])
+    if len(x) > 0 and x[-1] < lcl_p:
         return x[-1], y[-1]
     else:
         return np.nan * pressure.units, np.nan * temperature.units