ENH: More whatsnew documentation.

Author: rkern

doc/source/whatsnew/v0.19.0.txt

@@ -7,6 +7,10 @@ This is a major release from 0.18.1 and includes a small number of API changes,
 enhancements, and performance improvements along with a large number of bug fixes. We recommend that all
 users upgrade to this version.
 
+.. warning::
+
+    pandas >= 0.19.0 will no longer silence numpy ufunc warnings upon import, see :ref:`here <whatsnew_0190.errstate>`. (:issue:`13109`, :issue:`13145`)
+
 Highlights include:
 
 - :func:`merge_asof` for asof-style time-series joining, see :ref:`here <whatsnew_0190.enhancements.asof_merge>`
@@ -357,6 +361,15 @@ Google BigQuery Enhancements
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - The :func:`pandas.io.gbq.read_gbq` method has gained the ``dialect`` argument to allow users to specify whether to use BigQuery's legacy SQL or BigQuery's standard SQL. See the :ref:`docs <io.bigquery_reader>` for more details (:issue:`13615`).
 
+.. _whatsnew_0190.errstate:
+
+Fine-grained numpy errstate
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Previous versions of pandas would permanently silence numpy's ufunc error handling when ``pandas`` was imported (:issue:`13109`). Pandas did this in order to silence the warnings that would arise from using numpy ufuncs on missing data, which are usually represented as NaNs. Unfortunately, this silenced legitimate warnings arising in non-pandas code in the application. Starting with 0.19.0, pandas will use the ``numpy.errstate`` context manager to silence these warnings in a more fine-grained manner only around where these operations are actually used in the pandas codebase.
+
+After upgrading pandas, you may see "new" ``RuntimeWarnings`` being issued from your code. These are likely legitimate, and the underlying cause likely existed in the code when using previous versions of pandas that simply silenced the warning. Use `numpy.errstate <http://docs.scipy.org/doc/numpy/reference/generated/numpy.errstate.html>`__ around the source of the ``RuntimeWarning`` to control how these conditions are handled.
+
 .. _whatsnew_0190.enhancements.other:
 
 Other enhancements