On December 13th Donald C. Parker of Coral Gables, Florida, acquired a series of CCD images of Mars and noted a significant brightening in the Chryse region of the red planet. His observation of a large regional dust storm was reported in International Astronomical Union Circular 8256 and has been confirmed by observations made with the Thermal Emission Spectrometer onboard the Mars Global Surveyor spacecraft currently orbiting Mars. The dust cloud first appeared at the eastern end of Valles Marineris, moved southwest, and grew in strength. As of the 15th the most intense regions of the storm extend from Argyre Planitia west toward Solis Planum, but the dust also reaches north and covers the eastern half of Valles Marineris.
"I have images from December 9th showing Chryse bright in red, but with no obscurations of albedo features," Parker tells Sky & Telescope. "This is perhaps when the event got fired up. Weather did not permit me to image again until December 13th."
The angular diameter of Mars has shrunk significantly since its close approach to Earth last August. Still, according to Sky & Telescope associate editor Gary Seronik, the storm should be visible to anyone using a 6-inch (or larger) telescope. If the storm grows to near-global proportions, any scope should show that no surface markings are visible!