Thursday, January 29, 2015

Weird Winter Weather

January 22, 2015

In early fall, sea surface temperature measurements for the eastern Pacific Ocean showed that a large area of unusually warm water was persisting at mid latitudes in the northern hemisphere. Historically unusual, perhaps, but the oceans have been soaking up a lot of heat in the past century, and it's bound to start coming out. Climatologists were also trying to decide if the equatorial Pacific Ocean was going to shift into a recognizable El Nino-Southern Oscillation (ENSO) pattern for surface water temperatures and winds, which also impacts higher latitudes. There had been moderately strong signals for months that an ENSO might start this fall or winter, but thus far this has not developed into a recognizable ENSO pattern.

The emerging seasonal prediction for this winter was that we would have a drier, warmer winter. Well, the warmer part is definitely correct. As for drier, the South Coast has seen a mix of conditions. On one hand, there have been blocks of days to weeks of dry weather. On the other hand, there has been a steady progression of atmospheric rivers, also called Pineapple Expresses, with a tendency to extremely intense rain 'events' or cloudbursts within these storms, as happened just a few weeks ago, when South Bend flooded, and a small creek in Naselle overflowed and blew out a culvert on Highway 4 at the Naselle Youth Camp. Rainfall was around 8 inches at the peak day of the storm, most of which fell in less than six hours.

We depend on consistency in weather patterns, and in seasons. Communities, timberlands, agriculture and outdoor recreation all rely on this consistency. Portland and Seattle metro areas store water reserves in high elevation lakes, which are fed by snow and glacier melt. With dry warm winters, the snowpack they rely on for summer water is not stored in the high Cascades. Regional soils recharge with long winter rains, flowing to streams and rivers for fish habitat and into soils to promote tree and crop growth. In our area, most residents have shallow wells, tapping the upper edge of the highest freshwater aquifer layer on the peninsula. If we don't get enough rainfall to fill local lakes and marshes to overflowing, then the aquifer doesn't recharge in winter. Low snow pack also means poor skiing, which impacts ski resorts in the Cascades and eastward. Major disruptions in winter precipitation affect many aspects of life in the Pacific Northwest. As for recent strandings of sea turtles on local beaches, and lingering brown pelicans, both species are farther north than normal because of that warm water offshore.

This winter has been notable for several atypical weather features:
Mild nights, often around 45 to 50 F, and few cold periods. Temperatures at sea level have rarely dropped below 27 F this winter. Yes, we had light frosts a few nights ago, but no hard frosts, no days to weeks of freezing temperatures or snow on the ground.
Periods of intense rain have occurred several times, when four or more inches fell in just a few hours.
Tornado warnings––now that is really outside the 'normal' box. I don't recall NOAA forecasting a tornado warning for our area at all, until this winter.

A change in the intensity of atmospheric rivers (AR) is another issue. Regional weather records don't go back very far, little more than 170 years in most cases. So it's interesting to look back at historic records for AR, given that as the climate warms, these huge warm storms are expected to intensify, e.g. be larger, last longer, and deliver more warm equatorial water to higher latitudes. Right now, AR deliver around thirty percent of the water that moves from the Equator to high latitudes, and this percentage is expected to increase to fifty percent or more in coming decades.

In the winter of 1861/2 there was a mega-AR, which become the thousand-year-storm standard for the West Coast. Abbreviated 'ARKstorm' (atmospheric river, 1000 years = K, storm), this AR blasted the West Coast from northern Mexico to southern British Columbia for 41 to 47 days. All major rivers flooded along the West Coast. The Los Angeles Basin and Central Valley went underwater, including the newly formed state capital of Sacramento, California. The Columbia and most of its tributaries flooded. Smaller rivers along the coast from northern California to Vancouver Island flooded. We haven't had a thousand-year storm since, but the odds of weather like this coming again, and soon, are likely.

The weather reality for this winter is much warmer air temperatures, with strong storms. Instead of long soaking days of rain, there are intense short bursts of precipitation that flood local streams and swamp communities. It's the new normal. As for the lack of cold weather––find a mesh hat and repellant. The mosquito hatch this spring and early summer should be tremendous. Likewise, slugs and snails will be more numerous, unless there is a very cold period before winter's end.

Safety note: If you do not have a NOAA weather radio at home, get one. Yes, they send out weekly tests, on Wednesdays, usually around noon, and yes, you do have to turn the test off or it stays on for hours. The plus is that you will hear the warnings for thunderstorms, tornadoes, and far-source tsunamis, and other hazard events, directly from the weather service and without any need to use computers or your phone. The radios are inexpensive and work right out of the box. County emergency services and local amateur radio operators can help reprogram them if needed. 

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