Winter Outlook: Expected wet conditions to enhance river flood potential

The National Oceanic and Atmospheric Administration (NOAA) released its winter outlook Thursday, incorporating the weak La Nina that is now expected for at least part of the season.

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The official outlook is for near-normal average temperatures for the December-February time frame, with a better chances for above-normal precipitation this winter in the Northwest.

While a "La Nina Watch" was re-issued last week after a period in which "neutral" conditions were expected this winter, this La Nina is expected to be weak and possibly short-lived. It might not come about at all.

Flooding potential enhanced through the fall and winter

KIRO 7 meteorologists and the Pacific Northwest weather community were already expecting the possibility of a fall and winter that would be marked by a greater chance of river flooding. This is because more heavy rainfall events and a slightly-higher average snow level was expected. %

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(The snow level is the average elevation at which rain turns to snow in the mountains. A higher snow level means that more mountain precipitation would fall as rain instead of snow, enhancing river runoff.)

The slight "tipping of the scales" toward a weak La Nina does nothing to mitigate that concern. We have already had flood warnings this early fall, so people living and with interests along our rivers should make sure they are prepared for flood episodes through early 2017.

Doesn't La Nina mean more snow?

La Nina tends to produce more precipitation in the northwest, and that is what is expected this winter season, but La Nina also usually means cooler-than-normal temperatures are expected, on average.

But there's a catch. %

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Notice the NOAA outlook anticipates near normal average temperatures.

The temperature of the Pacific waters is expected to remain near or above normal in the coming months. The temperature of the Pacific has a major impact to our weather and climate in the Pacific Northwest -- a greater impact, as a whole, than anything else.

Since the Pacific is likely to be a bit warmer, our lowland snow potential is actually expected to be slightly below-average as we're more likely with a slightly warmer environment to get lowland rain than snow.

However, it's important to remember -- it just takes one big storm to make a "big snow season"!

Related: La Nina may come back this winter after all

In the mountains, we're already seeing healthy fall snow up at Whistler, which could open before Thanksgiving. As we continue to cool the atmosphere into the late fall, I expect that mountain snow could be enhanced this season, especially above the 5,000 foot elevation.

At lower elevations, the anticipated slightly higher-than-normal snow level could be troublesome, but with the expected above-average precipitation, we are still hoping for a good ski season.  And the expectation is for overall better conditions for our ski resorts than the past few difficult years!

Threat for fall windstorms remains

Despite dodging a significant windstorm Saturday, we are still on the lookout for the potential for strong wind events through our "windstorm season" in October and November.

The development of a weak La Nina for the winter season doesn't impact much the typical to slightly above-normal risk for wind events.

Here are some of the highlights from the NOAA Winter Outlook (December-February):

• Wetter than normal conditions are most likely in the northern Rockies, around the Great Lakes, in Hawaii and in western Alaska
• Drier than normal conditions are most likely across the entire southern U.S. and southern Alaska.

• Warmer than normal conditions are most likely across the southern U.S., extending northward through the central Rockies, in Hawaii, in western and northern Alaska and in northern New England.
• Cooler conditions are most likely across the northern tier from Montana to western Michigan.
• The rest of the country falls into the "equal chance" category, meaning that there is not a strong enough climate signal in these areas to shift the odds, so they have an equal chance for above-, near-, or below-normal temperatures and/or precipitation.
• Drought will likely persist through the winter in most regions currently experiencing drought, including much of California and the Southwest.
• Drought is expected to persist and spread in the southeastern U.S. and develop in the southern Plains.
• New England will see a mixed bag, with drought improvement in the western parts and persistence to the east.
• Drought improvement is anticipated in northern California, the northern Rockies, the northern Plains and parts of the Ohio Valley.

Cox Media Group