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Big thaw triggers unusual wintertime alert

Most of us are familiar with the hazardous weather alerts given by the National Weather Service, ranging from winter storm warnings and flood advisories to severe thunderstorm watches.

Ever hear about a “hydrologic outlook” alert? If so, it was probably in spring or summer.

Not this time around.

Earlier this month, the weather service issued a hydrologic outlook for much of the Inland Northwest. Such alerts are issued to make people aware of two contrasting scenarios that might occur: flooding from too much precipitation; or a prolonged lack of precipitation that could cause drought conditions.

Here in the Inland Northwest, hydrologic outlook alerts associated with precipitation and snowmelt surges are typically associated with spring, not winter. At the same time that those famous April showers are occurring, warming temperatures are melting mountain snowpack.

But this year, it happened in mid-February. In a matter of a few days, the region went from freeze to thaw, causing water levels in streams and rivers to rise. Fueling the concentration of water was the melting of deep, dense snowpack in the Cascade Range and northern Rockies. Not only was it early for snow to be melting so rapidly, but unlike last winter, there were heaps of it to melt.

The weather service alert let people know to be on the lookout for possible flooding within the next few days, and that an official warning would be issued if conditions worsened. Thanks to cooler temperatures and dryer weather, they didn’t get worse.

Even so, this big, but thankfully brief, thaw demonstrated how a high pulse of water in one place can end up in a lower elevation someplace else. It also showed how a snow-fattened December can set the stage for rising creeks and rivers when the weather turns unusually balmy in February.

Nic Loyd is a meteorologist with Washington State University’s AgWeatherNet. Linda Weiford is a WSU news writer and weather geek.


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