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Active Galactic Nuclei (AGN) are the observed manifestation of the inflow of matter onto supermassive black holes. Winds driven away from black holes have also been observed comma which might play an important role in the evolution of black holes and their host galaxies. The obscuring wind is a rare breed of AGN winds comma which has been observed in only a few Seyfert 1 galaxies so far. This putative disk wind absorbs a large fraction of the soft X-ray photons. Contemporaneous blueshifted broad absorption troughs associated with UV and NIR resonance lines appear in association with the emergence of the soft X-ray obscuration. Obscuring winds are expected to be present in quasars (more massive and luminous AGN) with broad absorption lines. The accelerated UV-absorbing gas needs to be shielded from much of the UV-X-ray ionizing radiation. Aside from the well-known properties of broad absorption line (BAL) QSOs comma the transient appearance of obscuring winds in quasars with typically clear lines of sight has not been observed so far. Recent Swift X-ray data of the radio-quiet quasar MR 2251-178 suggest that the soft X-ray spectrum is significantly absorbed. Simultaneously comma a blueshifted broad absorption trough of He I 1.08 micron is developing in recent high-resolution NIR spectra observed with IRTF and Gemini. We propose to observe MR 2251-178 with HST-COS (1 orbit) to constrain the physical properties of the putative obscuring wind and to explore similarities and differences with Seyfert galaxies like NGC 5548 and NGC 3783.