Jay Anderson is a completely sound source:
From his website
home.cc.umanitoba.ca/~jander/
, which is well worth a look!
Overview
For most eclipses, weather prospects offer several choices: the 2006 total eclipse had a very promising climatology in Saharan Africa, Egypt, and southern Turkey for instance. This 2008 eclipse is more limiting in that the weather tends to be rather dismal along the majority of the track, even though the August 1 date comes at the peak of summer and summer sunshine. It is not until the path reaches southern Russian and northern China that the prospects for sunshine rise to values comparable to the last total eclipse.
China, near the cities of Hami and Jiuquan, has the best prospects - likely between 70 and 80% - while southern Siberia, between Novosibirsk and the Mongolian border, offers about a 60% gamble. Other locations tempt for their stunning scenery or travel off the beaten path, but eclipse-seekers in these areas will have to compromise on the weather prospects.
Specifically:
Siberia
As the path of the lunar shadow moves southward across central Russia, it encounters a moist landscape of rivers, bogs and small lakes. The surface provides a ready supply of moisture to be incorporated into passing weather systems. Most of these weather systems track north of the 60th parallel, but their associated frontal systems can sweep much farther south, even into China. The weather in the north has a very different character than that in the south. Above the 60th parallel, large weather systems with extensive mid- and upper-level cloud shields and steady precipitation are a common feature of the mid-summer months. Farther south, nearer to Novosibirsk, the weather systems become more convective in nature, with showers and thundershowers bringing the majority of the rainfall.
There is not a clear-cut distinction between the northern and southern cloud climates, but instead a gradual transition as latitudes decline. In the satellite data, mean cloudiness diminishes steadily, from 65% along the north coast near Nadym to 47% near Barnaul (Figure 1). South of Barnaul cloud cover increases by nearly 10% over the rugged Altay Mountains that mark the boundary between Russia and China. Surface observations show the percent of possible sunshine climbing from a mediocre 35% at Salekhard to a more promising 54% at Novosibirsk and 57% at Barnaul.
