It's the news rain fans, snow fans, and skiers love to hear: La Nina conditions have officially formed, meaning perhaps a cool and wet/snowy winter is in the offing around here.
NOAA made the announcement Thursday in regards to their forecast update to the Atlantic Hurricane season, but for the Pacific Northwest where hurricanes might as well be Bigfoot, we pay attention for different reasons.
La Nina is the term for the phenomenon where ocean waters cool in the equatorial region of Pacific Ocean. It's part of an oscillation with El Nino, which is when the waters warm. Both have great, but opposite effects on worldwide climate.
For the Pacific Northwest, La Ninas tend to bring cooler and wetter than normal conditions for autumn and winter. It doesn't necessarily mean a big, snowy winter (although 2008-09 was a La Nina winter) just that the odds of bringing cold and wet together at the same time are higher. But La Nina winters are typically big mountain snowpack winters, so ski resorts should fare pretty well if climate standards hold.
On the other hand, this does present greater risks for the Green River Valley and other river flood-prone areas. Last winter's El Nino played true to form of being warm and dry (remember our warm January?) and thus we never really had any kind of flooding event. That could change this winter. So those who live in the flood plains, don't let your guard down.
Scientists still aren't really sure yet what causes this back-and-forth tug of war between La Nina and El Nino, officially known as the "El Nino-Southern Oscillation" or ENSO, only that it repeats every 3-7 years, but rarely in the same way.
An average ENSO will probably see an El Nino winter, then perhaps 1-2 years of "neutral conditions" before a drift into La Nina for a winter, then reverse back to El Nino over another few years.
However, this year's shift was quite rapid. In fact, we blew right through the neutral stage, radically shifting from El Nino to La Nina in just the course of a few months this summer.
You can take a peek at this ENSO chart that shows El Nino and La Nina conditions since 1950. If the 3-month running average temperature in the part of the Pacific where this happens is 0.5C degrees or warmer than normal, then it's considered El Nino conditions. 0.5C or colder is La Nina. Anything in between is neutral. This chart has not yet been updated for August, but I'm guessing that number came out today at -0.5C or so and thus the La Nina declaration.
The chart shows there have been some years with quick turn-arounds -- 1973 (very wet Nov-Jan, cool Nov and Jan), 1988 (quite wet / avg temps) and 1998 (*very* wet Nov-Feb) come to mind. Most quick turn-arounds seemed to usher in a long La Nina pattern so we'll see how this goes.
More information on La Nina:
Why the East Coast and South care about La Nina:
La Nina conditions tend to make for active hurricane seasons, as the pattern limits wind shear in the tropics, which normally works against storm development. They are also concerned that the water temperatures in the Gulf of Mexico are at record warmth levels, so there is plenty of fuel for hurricanes to develop.
For the rest of the nation, it's take El Nino and reverse -- that means a likely dry winter across California, Texas and the south (except for hurricanes) and a wetter winter across the northern plains.
Our own hurricane?
While actual hurricanes are non-existent here due to our chilly ocean waters, the local weather community was abuzz on a strange item on the radar early this morning.
Take a peek at what was going on over Northern Vancouver Island:
Of course, it looked sort of like what an actual hurricane looks like on radar only ours just had some light rain. This was likely just related to low pressure still in the area. Cliff Mass' excellent blog featured this interesting "twist" today and has more on what likely caused it.