Wednesday, January 4, 2017

Will California Dream Rains Become A Nightmare Soon?

Incredible amouts of precipitation predicted over
the next seven days in northern and central California.
A foot or more near the coast. The 20+ inches
in the Sierra Nevada translates to more than 20 feet
of snow in the next week. 
It's been a gloriously wet winter in California so far this year, with storm after storm coming in off the Pacific to dent the state's punishing six-year drought.

The drought is not over and southern and parts of central California in particular need more precipitation.

And they're going to get it, big time.

I alluded to this the other day: A moderate strength "atmospheric river" just hit central California over the past day or two dumping up to five inches of rain in some lowlands and a three to five  feet of snow in the Sierra Nevada.

It's looking increasingly likely that an even stronger atmospheric river is about ot hit California this weekend.

Atmospheric rivers are relatively narrow bands of very wet tropical or subtropical air that sometimes come ahore on the West Coast.

They're basically like giant fire hoses directing a hard stream of water, in the form of downpours or heavy mountain snow that hit a particular area for hours or days on end.

Like a fireman wielding a fire hose's blast of water from one flaming window to the next on a burning building,  the atmospheric river, when it sets up, can move up and down the West Coast.

Atmospheric rivers are relatively common in California, though they certainly have been lacking in the latest drought years.

Early indications are the upcoming atmospheric river this weekend could be relatively strong, which means the dreamy drought-denting rains and snows that have been drenching California over the past month or so could turn nightmarish.

A foot of rain could come down on parts of central and northern California over the next week. I also wouldn't be surprise if more than 15 feet of snow accumulates in parts of the Sierra Nevada, which have already gotten two to five feet in recent days.

That much precipitation in a few days could really set off some nasty flooding, mudslide, debris flows and urban flooding from overwhelmed drains.

This could be some of the worst flooding parts of California has seen in a decade or more.

Of course, this isn't totally set in stone yet, and we're not sure where the heaviest rain will set up. Still, the National Weather Service office in San Francisco is already starting to sound the alarm.

In a hydrological statement today, they said: "It is very likely that many flood-prone creeks and rivers of the Bay Area and Central Coast will rise above their banks."

 It does appear most of it will miss southern California, which is too bad, because they need the rain more than the north. But they will get some rain, on top of some that's already fallen over the past five weeks, so it's not as dire as it once was there.

Fifteen or 20 feet of snow in the Sierra sounds dire, too, but it's really not. The more snow that piles up the Sierra in the winter means better water supplies for California in the summer. The state relies in large part on meltwater from the Sierra for their warm season water supplies.

Despite above normal precipitation, the snow pack in the Sierra is a little below average right now, believe it or not. It's been so warm that a lot of the snow up there has been melting prematurely.

Another problem with the upcoming atmospheric river is it's a warm pattern. Snow will be limited to the highest elevations. Plus, rain will fall on some  upper elevations that just got snow. Melting snow combined with the rain could make flooding worse.

I'm sure all weather eyes will be on California for the next couple of weeks.


Once these atmospheric river storms hit California, they have to go somewhere. True, a lot of their moisture gets wrung out over the Golden State, but the storms move east from California, sometimes picking up new moisture from the Gulf of Mexico or Atlantic Ocean.

The first of these impulses is already starting to cross the Rocky Mountains, prompting widepread winter storm warnings in that region, all the way from Oregon to Colorado.

This initial storm will cross the central and southern United States just south of a strong push of Arctic air.

Once it gets to the southeastern United States, it could unleash some ice and snow in that region.

Despite the fake news and hype issued by some internet weather trolls, there's NOT going to be a Blizzard To End All Blizzards in North Carolina.

That's just people trying to get click views. Instead, there's the possibility of ice or snow in the Southeast Friday and Saturday. It only takes a little bit of wintry weather to really screw up things in that part of the country, so you ought to be careful if you're heading down there this weekend.

After that, more storms will parade across the country, but it's too soon to tell whether they will be big or small, or where exactly they'll hit.

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