Here it is! It’s taken me long enough, but I’m ready to release my official Fall 2012 forecast. I’ll issue my Winter 2012/2013 forecast in early December.
As always, before the forecast begins, there are a few things to remember. It’s only a matter of time before someone comments: “Meteorologists can’t even forecast 5 days out, what makes them think they can forecast 3 months out?” There is a clear difference between climatic averages and daily weather forecasting. One expounds on year to year averages (climatology) while the other predicts specifics usually no more than two weeks out (weather forecasters). Click here to read more about the difference.
In long range weather forecasting, some feel it is important to use analogs. Analogs are past years that exhibit some similar weather activity to the current year, and as a result weather forecasters try to match up the past with the present to see if there’s some type of correlation or pattern occurring. More often than not it’s just a guide, but sometimes history does repeat itself.
Other reliable pieces of data essential for producing a long range forecast is the ONI, or Oceanic Nino Index to track what El Nino, La Nina or neutral years in the past match up similarly to the present day. The records I have go all the way back to 1950. Solar activity can be another major factor to the weather over the years, but I haven’t weighted that heavily enough in my forecast mainly because of the lack of data. Lastly, I used the PDO readings (Pacific Decadal Oscillation) to finalize my findings.
So with all the above points in mind, let’s get our hands dirty
with some more specific, technical information.
I. CPC ANALOGS
Although hardly the most reliable or trustworthy analogs, I have been tracking the Climate Prediction Center (CPC) over the past month to get an idea of what kinds of analogs they’ve been matching their daily long range forecast updates with. Over the past month I have noticed a few recurring years (from most common to least common):
Again, the CPC analogs change every day, but these years have proven the most consistent.
II. THE OCEANIC NINO INDEX (EL NINO/LA NINA YEARS SINCE 1950)
As explained a while back, the ONI tells me what years were El Nino (red), La Nina (blue) or neutral (plain). Of course, the higher the number the stronger the event. I took my 4 most frequent analog years (1951, 1965, 2002 and 2006) and compared their ONI readings with our ONI trend. Both the winters of 2009-2010 and 2010-2011 were La Nina years and we are currently sitting at neutral, so I went out to find some years with 2 back-to-back La Nina’s followed by a neutral/weakly positive El Nino year. These are the years I found
- 1965-1966 (this one wasn’t preceded by a back-to-back Nina, but otherwise the numbers match well)
- 2006-2007 (similar story to 1965-1966)
III. STATE OF THE PDO (PACIFIC DECADAL OSCILLATION)
The PDO is the surface temperatures of the Pacific, north of 20° N. We are currently in a sharply cool (or negative) phase and we’ve been that way for almost 2 1/2 years straight! This plays a big part in our weather, so I set out to see which of the above analogs matched our current PDO phase (FYI, the PDO number for August was -1.93!) Although none of the analogs matched up quite to this years negativity, the remaining analogs seemed close enough, especially 1951 which registered a -1.37 reading in August.
IV. LONG RANGE FORECAST FOR FALL 2012
Whew! You’re still with me! Good for you! I hope you’ve learned as much as I have along the way. Long range forecasting is a fun, but tedious science. I consider myself a beginner, but the more I study and try my hand at long range forecasting, the better I expect to become. With that being said, my top 3 analogs for the Fall of 2012 in the Northwest is 1951, 1965 and 2006.
I have weighted my forecast heavily as a combination of those three years, although it obviously won’t play out as a carbon copy. These analogs just provide me with a credible basis. Also, just to note, the 1981-2010 temp/precip averages constitute what’s above, near or below average.
First off, here’s a composite map of my 3 main analogs.
TEMPERATURE TRENDS FROM OCTOBER-DECEMBER
PRECIPITATION TRENDS FROM OCTOBER-DECEMBER
So right off the bat, it looks like from October-December this year, we have a decent chance of averaging slightly above normal in the temperature department and near normal to slightly above normal in the precipitation department.
OCTOBER 2012- (Temperature Mean: 49°; 1° above average. Precipitation Average: 4.39”; 0.5” below average) Month Snow Chance: 0%
Contrary to a lot of fall forecasts out there, it just doesn’t look like the month for big temperature spreads or anomalies. Overall it looks like we’ll experience a much tamer and slightly warmer than normal October, on average. Expect the Cascades and Olympics to be seeing some snowfall this month as we could get several bouts with cold air, making the lowlands and the mountains chilly at times. Other than a few cold spurts, it’ll generally be a comfortable October, a month we usually have major wind or rain storms in.
NOVEMBER 2012- (Temperature Mean: 41.5°; 0.5° above average. Precipitation Average: 10.89”; 1.5” above average) Month Snow Chance: 40%
November will be our transition month. We’ll notice temperatures getting colder with many “first frosts” popping up around the peninsula. The most notable thing about November will be all the rain. Usually November is a wet month, but this year it’s projected to be quite wet. Temperatures will hover around normal for the month, but enough warmer, Pineapple Express-type rain storms could nudge the temperature up a tad. The jet stream will not have responded to the El Nino atmosphere quite yet, so expect a lot of cloudy, rainy days. The snow chance is up to 40%, meaning most of the month it will likely be too mild for snow, but we could have a few bouts of it towards the end of the month.
DECEMBER 2012- (Temperature Mean: 38°; 1° below average. Precipitation Average: 10.50”; 0.4” above average) Month Snow Chance: 80%
Even the research I’ve conducted corresponds well with a colder than average December. I’m not sure if I agree with the “much colder” than normal forecast put out by The Weather Channel, but either way it’ll be a chilly month. It’ll be drier than November, but still wetter than your average December. This will surely bode well for the mountains as well as lowland snow fans, as I see the very realistic potential for some arctic air intrusions/snow days during this month. It would be impossible to say how much, but with a forecast for above average precipitation, I’d say there’s a decent chance for SOME sticking snow.
*Left bar: temperatures; Right bar: precipitation
Well there you have it! It’s difficult and practically futile to predict any windstorms, snowstorms, ice storms, etc in these long range forecasts. All we need is a general idea of what it’s looking like all things considered. Of course there are other factors that play into our weather here, so it’ll be fun to check back and see how I did!
Please feel free to use the comment section below or shoot me an e-mail about what you see. Have a great day everyone!
P.S. I’ll post the updated 7 day forecast later tonight