Wiktionary shows whereäs as a valid alternative spelling of the word whereas (see here).
It gives the following quotations to illustrate the usage:
1 Permanent International Association of Navigation Congresses, Report of Proceedings — Milan (1905)
After a dry season, the influence of heavy rains becomes manifest more quickly and more progressively in the less wooded basin, whereäs the reverse is found in the basin which has a larger forest area.
2 Friedrich-Schiller-Universität Jena, Wissenschaftliche Zeitschrift (1984)
Notice that since the range of χ is limited by (5), whereäs that of x is unlimited, the transformation (6) does not cover the whole of the space-time represented by (1).
3 Hiroyuki Sonoki et alii, Heart and Vessels — Nipradilol, a new β-adrenergic blocker, reduces left ventricular remodeling following myocardial infarction in spontaneously hypertensive rats (1997)
...after MI, whereäs propranolol promotes it.
That was the only dictionary where I found the word (with that spelling) though. And a Google search for whereäs returns only 209 pages.
Is that really a valid spelling of the word whereas? If yes, where did it come from?