B737-800 Captain reported loss of ISFD (Integrated Standby Flight Display) and based on weather enroute and destination; elected to return to departure airport.

Narrative

Climbing through 16;000 feet just west of ZZZ1; our Integrated Standby Flight Display (ISFD) attitude indication went blank with a corresponding amber Attitude (ATT) flag annunciated. Given the duration of our flight to ZZZ2 and the fact that we were expecting IMC or over-the-the top conditions for the majority of the flight as well as forecasted low visibility with snow at ZZZ2 at our time of arrival; I determined that it was not safe to continue with the loss of such a critical instrument. We knew that the weather along the coast of Location A was clear VMC with only scattered clouds since we had just taken off from ZZZ so me and the first officer agreed that the safest course of action would be to return to ZZZ since we could remain clear of clouds in case we experienced any further degredation or failure of our primary flight instruments since we no longer had a backup attitude indicator. I notified dispatch and received an ammended release for the return to ZZZ. I then notified the flight attendants of our plan and then made a PA to the passengers. We did not declare an emergency and proceeded to land normally on runway XX at ZZZ. Upon arrival at the gate; I entered the discrepancy into the logbook and contacted maintenance control.Cause: When the failure occurred; I looked through the QRH for a checklist regarding a failed ISFD and; as far as I can tell; no such checklist exists. It would be helpful to future crews if a checklist for this failure was added to the QRH to help guide the diversion or continue decision that must be made. Interestingly enough; the MEL 34-XXX for an ISFD attitude display essentially says that a flight must be dispatched only in day VMC conditions and the aircraft has to remain clear of clouds at all times. This guidance should be added to a QRH checklist to help assist crews in the future that experience this failure.