9:15 PM Fri, Apr 06, 2007 | Permalink
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What do a cooler than average tropical Pacific Ocean and an active Atlantic hurricane season have in common? They can be pre-cursors to a stormy winter in the Northwest. Cooler than normal sea surface temperatures in the eastern Tropical Pacific are part of what we call a "La Nina" pattern.
Sea Surface Temperature (SST) Anomaly map is courtesy of NOAA/DOC. Notice the streak of dark blue and purple color west of South America. Colder than average ocean temperatures here are a classic sign of a "La Nina".
As opposed to El Nino, when ocean temperatures in the same area are warmer than average. La Nina's tend to pile up heat and humidity in the western Pacific, which leads to an active and variable winter jet stream that often develops and delivers a lot of storms to the Northwest. But the same pattern in summer will help get Atlantic hurricanes cranked up, because it prevents a strong jet stream from arcing over the Atlantic. Strong winds aloft tend to rip hurricanes apart. Colorado State University's Dr William Gray's annual Atlantic hurricane forecast calls for a very active Atlantic hurricane season, based partly on the lack of El Nino conditions. We'll see how the Pacific behaves over the next few months. If a full-fledged La Nina develops and is sustained into fall, we can probably expect another rock and roll winter. Thankfully, it shouldn't have much of an impact on our normally excellent summers.
Thanks for watching and surfing KGW,
Matt Zaffino
Chief Meteorologist
KGW Northwest Newschannel 8
When do you think this winter will end? April 10 and another frost. What is the average last date for a frost in Beaverton/Hillsboro?