Mercury was at its point of greatest western elongation — its highest point of the year in the eastern sky — on Monday morning. Let's use the diagram below to again remind ourselves about the configurations - greatest eastern and western elongation:
The figure 1(b) shows the aspects for an inner planet, which Mercury is (as well as Venus). Note where the position denoted G.W.E. is relative to the Sun and the Earth.
Why would Mercury be difficult to have been seen on Monday despite having the highest altitude? Well, not merely because of any clouds but also its position relative to the eastern horizon at sunrise. Mercury is the smallest planet in the solar system, smaller than our Moon, so it's notoriously difficult to find for untrained eyes.