Rainless streaks weeks or months in the making may fall this week as a big shift in the weather pattern unfolds in California and the Southwest.
Slow-moving low pressure, still well off shore as of Sunday, could serve up some weather surprises as it begins sparking widely separated showers and thunderstorms as early as Tuesday.
To be clear, odds for any widespread soaking rain are very low, as this weather system will begin with limited stores of moisture.
The offshore low will take a track to the east and southeast, ending up near the Southern California coast by Thursday.
Monday, little in the way of rain will fall, as the low will still be over open water off northern California.
Tuesday, as the weather system drifts nearer to the coast, scattered showers will begin to be sparked in the west, and a few thunderstorms along and near the Sierra Nevada.
Wednesday and Thursday, the low will gain access to moisture from northwestern Mexico. Showers and thunderstorms are likely to increase at this time over the southern half of the state, throughout the Sierra Nevada and into Nevada.
Furthermore, scattered thunderstorms may break out eastward to Utah and northern Arizona on Thursday.
Notwithstanding limitations to rain-generating moisture, this low pressure area will have enough vigor to gin up a few strong thunderstorms with localized downpours, powerful wind gusts, even hail, Wednesday and Thursday.
For most Californians, it would be the first rain to speak of since late spring or early summer.
No measurable rain has fallen in downtown Los Angeles since July 12, for instance. San Franciscans have to look back to June 4 to find the last measurable rain. In Fresno, one most go all the way back to April, as the 26th was the date of the last rain of significance here.
Dry, even rainless, summers the rule in most of California, which has a "Mediterranean" climate.
Although the far north can turn rainy in October, most of California normally has to wait until November for the season's first widespread rainstorms.
Seven homes have been red tagged, meaning do not occupy, and six others are under a voluntary evacuation order.
Though recovery continues from Superstorm Sandy, residents and homeowners on the Atlantic coast should prepare for another active season in 2013.
While there is a threat for a shower in spots in Baltimore, Md., on Saturday, it should not be a washout like the day of the Kentucky Derby.
The volcano is in a rather remote spot, and the biggest price will be to airlines caused by the ash.
Smoke from fires in the Yucatan Peninsula will affect parts of Texas and Louisiana over the weekend.
The potential for isolated severe weather will creep up in the Northern Plains, Texas and the Gulf States.
Mt. St. Helens (Washington) (1980)
Mt. St. Helens erupted; smoke plume rose to height of 80,000 ft. Visibility lowered to under a mile 400 miles downwind of the eruption. Five people died and over 2,000 had to be evacuated because of the mudslides and flooding that occurred when the snowpack melted. The cloud formed by the eruption reached the East Coast in three days and circled the world in 19 days.
Tornado in Burlington, OH. The storm leveled every structure in the town - houses, barns, walls and fences.
Lubbock, TX (2007)
1.39 inches of rain, a record for the date. (old record: 0.69 inches in 1926)