A rare total lunar eclipse will occur across the western U.S. late tonight. Known as the tetrad or "blood moon" the eclipse event begins around 11 p.m. Pacific time, with the period of total eclipse from about midnight through 1:30 a.m.
The satellite image in this graphic taken at 10 a.m. today shows a large area of cirrus clouds off the west coast (in red oval). This band of cirrus is expected to spread over eastern California and western Nevada tonight. It may limit viewing of the eclipse, depending on the thickness of the cloud cover.
Cool and dry conditions are expected during tonight's eclipse with temperatures mainly between 45 and 55 degrees for lower elevations, and in the 30s near the Sierra. Winds will be generally light, except on higher ridges where west winds of 10 to 20 mph are expected.
Tetrad is when the moon is completely covered by the earth’s projected umbral shadow for four eclipses in a row, as opposed to only partial eclipses that fall in the outer penumbra. Instead of going to complete darkness, the moon will glow red as it receives the refracted light that spills over the Earth’s circumference.