Latest Winter Forecast

Those predictions are educated guesses at best. Bastardi is pushing hard for a strong Nina and a colder than average winter around the country.
 
The MEI index was essentially neutral for 2 months but has moved to -.503, very mild La Nina territory in the recently released JUL/AUG MEI index http://www.esrl.noaa.gov/psd/people/kla ... table.html.

I am skeptical that Bastardi or anyone else can predict short term changes in El Nino/La Nina (ENSO). But past history is that it tends to be very stable through the northern winter. Therefore if the La Nina is somewhat stronger 2 months from now, we can expect to see effects during the upcoming winter.

Part of Bastardi's predictions relate to the Pacific Decadal Oscillation, which is in its cold phase. The cold PDO tends to accentuate La Ninas, as was certainly the case last year. However someone just sent me an interesting study of PDO/ENSO from 1924-1998. The combination of cold PDO and neutral ENSO tends to be drier than average over much of the West.
 
Nearly every time I see one of these "Model Predictions of ENSO from Aug 2011" type charts, the predictions are scattered close to equally above and below the current reading. The best "next month" guess for ENSO is always that it will stay the same as this month, as evidenced by month to month correlation of 96% in the MEI index. That correlation does have seasonal variation, being 98% or 97% from July through January, but dipping to 91% in April and May.

Over the past sixty years the average change in MEI from JUL/AUG to NOV/DEC is .322, with 80% of seasons seeing a change of less than .500. By contrast the average change from JAN/FEB to MAY/JUN is .817. Most of the time that larger change in the northern spring is a reversion toward neutral status.

While many researchers believe the MEI index is the most comprehensive measure of El Nino/La Nina, it is published with a time lag of about a month. So it's possible some more timely data is showing a continued move in the La Nina direction, prompting the winter predictions.
 
The same source as above e-mailed me a link to PDO readings: http://jisao.washington.edu/pdo/PDO.latest

It was easy to download that table into the same spreadsheet where I have the MEI table. Observations:
PDO and MEI are 58% correlated. So the same areas are favored by negative PDO as by La Nina. For many of the Northwest and Northern Rockies areas the PDO is even more strongly correlated with good snow years as La Nina. The flip side not so much. Southern California is strongly favored by El Nino but not much correlation with PDO.

The current PDO is very negative -1.86 as of July. So the Northwest/Northern Rockies skiers have reason to be optimistic even if the La Nina doesn't get any stronger. The short term (next 6 months) persistence of PDO is not as reliable as La Nina though.
 
Yea, as I've said before, IMHO, these long-term forecasts are, AT BEST, educated guesses as to what might happen. Futhermore, if you look at Accuweather's long-term forecast, it is sufficiently vague enough to encompass a wide variety of weather outcomes in any given region of the country. I make the same weather forecast every year for the Northeast - We'll have some cold weather, we'll have some not-so-cold weather, we'll get some snow storms, we'll get some snow storms turning to sleet turning to freezing rain, and then turning to rain (to be followed by a brutal cold snap, so everything freezes into rock solid ice), we'll get some rain storms, we'll have some windy days and not-so-windy days, etc. The bottom line is that the weather will vary greatly over the four months or so of winter around here.
 
SEP/OCT MEI was -.968, fairly strong but still below near record levels a year ago. PDO is -1.34. The 2 together still portend good snow for PNW and Northern Rockies of US and Canada. From a cursory look Sunday, November has been pretty good so far for those regions.
 
You must log in or register to reply here.
Back
Top