BUG: Fix passing degF values to some thermo calcs (Fixes Unidata#2005)

moist_lapse and wet_bulb_temperature were handling units manually for
various reasons--and weren't getting it quite right. Expand testing to
parameterize across the various temperature units to catch this going
forward.

Also update a test image that barely changed due to minute changes in
the moist_lapse calculation.

src/metpy/calc/thermo.py

@@ -313,7 +313,8 @@ def dt(t, p):
 
     pressure = pressure.to('mbar')
     reference_pressure = reference_pressure.to('mbar')
-    temperature = np.atleast_1d(temperature)
+    org_units = temperature.units
+    temperature = np.atleast_1d(temperature).to('kelvin')
 
     side = 'left'
 
@@ -342,7 +343,7 @@ def dt(t, p):
     if pres_decreasing:
         ret_temperatures = ret_temperatures[::-1]
 
-    return units.Quantity(ret_temperatures.T.squeeze(), temperature.units)
+    return units.Quantity(ret_temperatures.T.squeeze(), 'kelvin').to(org_units)
 
 
 @exporter.export
@@ -2998,13 +2999,13 @@ def wet_bulb_temperature(pressure, temperature, dewpoint):
         moist_adiabat_temperatures = moist_lapse(units.Quantity(press, pressure.units),
                                                  units.Quantity(ltemp, lcl_temp.units),
                                                  units.Quantity(lpress, lcl_press.units))
-        ret[...] = moist_adiabat_temperatures.magnitude
+        ret[...] = moist_adiabat_temperatures.m_as(temperature.units)
 
     # If we started with a scalar, return a scalar
     ret = it.operands[3]
     if ret.size == 1:
         ret = ret[0]
-    return units.Quantity(ret, moist_adiabat_temperatures.units)
+    return units.Quantity(ret, temperature.units)
 
 
 @exporter.export

tests/calc/test_thermo.py

@@ -113,18 +113,12 @@ def test_dry_lapse_2_levels():
     assert_array_almost_equal(temps, [293., 240.3583] * units.kelvin, 4)
 
 
-def test_moist_lapse():
-    """Test moist_lapse calculation."""
+@pytest.mark.parametrize('temp_units', ['degF', 'degC', 'K'])
+def test_moist_lapse(temp_units):
+    """Test moist_lapse with various temperature units."""
+    starting_temp = 19.85 * units.degC
     temp = moist_lapse(np.array([1000., 800., 600., 500., 400.]) * units.mbar,
-                       293. * units.kelvin)
-    true_temp = np.array([293, 284.64, 272.81, 264.42, 252.91]) * units.kelvin
-    assert_array_almost_equal(temp, true_temp, 2)
-
-
-def test_moist_lapse_degc():
-    """Test moist_lapse with Celsius temperatures."""
-    temp = moist_lapse(np.array([1000., 800., 600., 500., 400.]) * units.mbar,
-                       19.85 * units.degC)
+                       starting_temp.to(temp_units))
     true_temp = np.array([293, 284.64, 272.81, 264.42, 252.91]) * units.kelvin
     assert_array_almost_equal(temp, true_temp, 2)
 
@@ -1459,9 +1453,12 @@ def test_brunt_vaisala_period(bv_data):
     assert_almost_equal(bv_period, truth, 6)
 
 
-def test_wet_bulb_temperature():
+@pytest.mark.parametrize('temp_units', ['degF', 'degC', 'K'])
+def test_wet_bulb_temperature(temp_units):
     """Test wet bulb calculation with scalars."""
-    val = wet_bulb_temperature(1000 * units.hPa, 25 * units.degC, 15 * units.degC)
+    temp = 25 * units.degC
+    dewp = 15 * units.degC
+    val = wet_bulb_temperature(1000 * units.hPa, temp.to(temp_units), dewp.to(temp_units))
     truth = 18.3432116 * units.degC  # 18.59 from NWS calculator
     assert_almost_equal(val, truth, 5)
 
@@ -1499,7 +1496,8 @@ def test_wet_bulb_temperature_2d():
     assert_array_almost_equal(val, truth, 5)
 
 
-def test_wet_bulb_nan():
+@pytest.mark.parametrize('temp_units', ['degF', 'degC', 'K'])
+def test_wet_bulb_nan(temp_units):
     """Test wet bulb calculation with nans."""
     pressure = [1000.0, 975.0, 950.0, 925.0, 900.0, 850.0, 800.0, 750.0, 700.0, 650.0, 600.0,
                 550.0, 500.0, 450.0, 400.0, 350.0, 300.0, 250.0, 200.0, 150.0, 100.0, 70.0,
@@ -1521,7 +1519,7 @@ def test_wet_bulb_nan():
                    -48.2122467, -39.66942444, -34.30999451, -33.35002747, -23.31001892,
                    -14.55002441, -11.74678955, -25.58999634] * units.degC
 
-    val = wet_bulb_temperature(pressure, temperature, dewpoint)
+    val = wet_bulb_temperature(pressure, temperature.to(temp_units), dewpoint.to(temp_units))
     truth = [19.238071735308814, 18.033294139060633, 16.65179610640866, 14.341431051131467,
              10.713278865013098, 7.2703265785039, 4.63234087372236, 1.8324379627895773,
              -1.0154897545814394, -4.337334561885717, -8.23596994210175, -11.902727397896111,