California’s historic drought is entering its fourth year, but downpours and atmospheric rivers  in December provided the state much-needed relief.

But how much could one month of rain do? Look at satellite imagery released last week by the National Oceanic and Atmospheric Administration (NOAA).

The image on the right, taken in January, shows significantly greener land coverage than the image on the left, taken just one year earlier. It’s a pretty startling difference — but, unfortunately, the drought-stricken state is by no means out of trouble.

According to water resource officials, for California to recover from the dry period, it would require 150 percent of its average rainfall. But what concerns officials the most is snowpack — the snow that accumulates on mountains and acts as a natural reservoir. As it melts, it feeds streams and groundwater.

According to an analysis by NOAA, the snowpack this year is much less than the year before. This is alarming because snowpack supplies one-third of California’s water used by residents and industry.