Surging 'atmospheric rivers' may soon flood parts of the Far West

Last winter, during a particularly strong wet and cool 'La Nina' sea-surface temperature event in the waters of the Pacific Ocean, we saw 'two' moist branches of the Maritime Polar Jet Stream slam into California and the Pacific Northwest coastlines bringing record rains and lowland flooding to the valleys and upwards of 20 feet of snow to the higher mountain locations.

These storms pushed inland from the Pacific about every two or three days and were accompanied by cooler than normal temperatures, the opposite 'extreme' from the juicy warm 'El Nino'-enhanced 'Pineapple Connections' that we usually see about twice a decade in the waters between California and Hawaii.

Last winter's two storm tracks pushed southward from the Gulf of Alaska and were far to the north of the Intertropical Convergence Zone. They also persisted far longer than normal into the early summer period. This delayed the planting of spring crops and the normal harvest of grains, fruits and vegetables in the Far West.

Many stations in northern and central California, for example, set all-time June precipitation records. The Lake Tahoe area, on the border between California and Nevada, enjoyed 'rare' July 4 holiday skiing and snowboarding. On July 31, one station in the Sierra Nevada Mountains at the 6,000 foot elevation still reported six feet of snow on the ground. The 'Going-To-The-Sun Highway' in Montana's Glacier National Park didn't open until July 12, a record-late date.

These two jet streams pushed eastward across the country north of I-80 producing torrential rains and a record number of April/May tornadoes, including the 'Big One' in Joplin, Mo., on Sunday, May 22, that killed nearly 150 people and caused more than $3 billion in property damage.

Severe flooding occurred from south-central Canada southward along the Missouri and Mississippi Rivers to Baton Rouge and New Orleans, La. Millions of acres of cropland were under water.

Later, in late June, Minot, N.D., a town of 41,000 people, saw the city's worst flooding on record. On Monday, June 27, the Souris River reached 14 feet above flood stage, topping the previous record set 130 years ago in 1881 by nearly 6 feet.

To the north in Canada, more than 14 million acres of summer crops were never planted due to record rains and widespread lowland flooding. Crop-damaging frosts hit many of these same areas in early September.

Locally in North Idaho, the Coeur d'Alene River briefly reached flood stage in June. The unusually chilly and wet spring likewise delayed both the planting and the ripening of spring crops.

On Labor Day, Sept. 5, Sharon and I were still picking raspberries and blueberries in the backyard. Believe it or not, our clematis vines were still producing blooms, more than a month later than usual!

Scientists tell us that we may see more torrential rains and flooding in the next several years from these 'superhighways of water vapor' in the Pacific Ocean that are often thousands of miles long and at least 300 to 500 miles wide.

According to NOAA, these destructive "atmospheric rivers" of heavy rains and snows, in a single day, can push up to 20 times the amount of water into the California coastline as the Mississippi River's daily discharge. In just six days late last winter, one atmospheric river of heavy rains stalled in California giving stations in the Sierra Nevada Mountains more than 26 inches of liquid precipitation and a record 15 feet of snow in just 144 hours.

We are well aware that these jet stream-fed atmospheric rivers are the primary cause of disastrous flooding in the West Coast states, the northern U.S. and parts of southern Canada.

While I'm certainly not expecting a deadly hurricane to hit the U.S. West Coast, I do see somewhere down the meteorological highway 'KATRINA-LIKE' flooding of Biblical proportions from an enormous atmospheric river trained particularly on California.

It's not the case of 'IF,' just 'WHEN' this will occur. Believe it!

NORTH IDAHO WEATHER REVIEW AND LONG-RANGE OUTLOOKS

As expected, the first 10 days of September were bone-dry and warm under the influence of a very strong ridge of high pressure camped over the Far West.

There were a half-dozen 'Sholeh Days' at or above 90 degrees during the period. This pushed our seasonal total of 90 degree plus afternoons this summer to 20, close to what Randy Mann and I predicted months ago.

The summer of 2011 started late following the third coolest and wettest spring on record since at least 1895 in Coeur d'Alene. But, the second half of the season since mid July has been exceptionally dry and approximately four degrees warmer than normal.

The warm and dry weather conditions are still likely to persist locally until at least early to mid October. Then, it all depends on whether our current 'La Nada' calm weather cycle turns into a mild 'El Nino,' or a chilly, snowy 'La Nina.' Only time will tell.

ADDED NOTE: Bob Hollingsworth of the Wolf Lodge reported that freezing temperatures "nipped his squash plants" around 6 a.m. on Saturday, Sept. 3, the apparent first local area frost of the season.

Cliff Harris is a climatologist who writes a weekly column for The Press. His opinions are his own. Email sfharris@roadrunner.com