gdal/python WriteArray working for 8-bit but not 16-bit

I’m trying to use GDAL/python API to open a raster, do some math, then write the two resulting arrays as rastes. One is to be an 8-bit raster and the other 16-bit signed. However, only the 8-bit raster is coming out correctly. The 16-bit raster comes back as a raster of 0′s. Here is the relevant code:

import numpy as np
import gdal
gdal.UseExceptions() # enable exceptions to report errors
drvtif = gdal.GetDriverByName("GTiff")

# open raster, read as array, do some math, return two arrays: arr1 and arr2

# arr1 and arr2 are both float32, though not necessary

print np.unique(arr1)
# prints [-15000, -10000, ..., 10000]
print np.unique(arr2)
# prints [1, 2, ..., 11]

# now write arr1 and arr2 as .tif:

outNDVI = '/path/to/outputs/output1.tif':
ndvidrv = drvtif.Create(outNDVI, ncols, nrows, 1, 3) # 3 = 16 bit signed
ndvidrv.SetGeoTransform(hc_gt)
ndvidrv.SetProjection(proj2)
ndvidrv.GetRasterBand(1).SetNoDataValue(-15000)
ndvidrv.GetRasterBand(1).WriteArray(arr1)
del ndvidrv

outQA = '/path/to/outputs/output2.tif'
qadrv = drvtif.Create(outQA, ncols, nrows, 1, 1) # 1= 8 bit
qadrv.SetGeoTransform(hc_gt)
qadrv.SetProjection(proj2)
## qadrv.GetRasterBand(1).SetNoDataValue(-15000)
qadrv.GetRasterBand(1).WriteArray(arr2)
del qadrv

outQA turns out as expected, with the correct range of values and correct projection, but outNDVI is just a raster of 0′s (in the correct projection). The values should range from -10000 to 10000 (with NoData= -15000).

Any thoughts?

Thanks

Deleting ndvidrv seemed to do the trick and I’ve updated above to reflect that.