Tuesday, November 10, 2009

"...Use the time given to us."
- Attributed to Gandalf in Lord of the Rings: Fellowship of the Ring

6:00 AM WEDNESDAY, 11/11/09. This week, several climate factors and weather events in the western Hemisphere are interacting in ways which we believe continue to support our hypothesis outlined in earlier posts: Arrival of significant winter weather by 12/5 in the Mid-Atlantic. We also projecting the first major snow event to occur between Monday 11/30 and Saturday 12/5.

IMPACT OF IDA ON THE SHORT-TERM PATTERN [update 3: 11/11]
  • Transformation of Tropical Storm Ida into a Wed-Fri tropical rainstorm for the Southeast. [11/11 revision: Mid-Atlantic may NOT escape heavy rain, nor the impact of below-normal temperatures. Seems clear that Ida's remnants are "smacking down" a-plenty with much heavier rain than many were expecting. A note to climate historians-- the current surface map is a dead-ringer for the January 22, 1987 East Coast wallop-- snow from Atlanta to Boston]
  • While a high elevation snowstorm from Ida's remnants seems unlikely, it is more notable to observe how interaction between a storm to our south and high pressure to our north may produce an early preview of "cold air damming." Just look at the beautiful placement of that High pressure-- if only it was winter!  Weather watchers know full well the significance of seeing cold air damming develop this early in the season-- in Dec-Jan-Feb that phenomena often gives rise to freezing rain or significant snow
MONITORING BACKGROUND CLIMATE DATA
  • Rapid recovery of Arctic sea ice ( 7.71 million square km as of 10-26);
  • Expanding or stable snow cover in central Canada and Siberia;
  • El Nino signal continues to strengthen across equatorial Pacific [11/9 update- CPC reports the Aug-Sep-Oct average for the Oceanic Nino Index (ONI) was 0.9 C in the critical 3.4 region which impacts US winter weather patterns.
  • The 11/9 weekly departure for El Nino region 3.4 was a steaming 1.7 C!
  • Pacific Decadal Oscillation (PDO) weakly positive [Sep 09: 0.54, Oct 09: 0.27]
  • North Atlantic Oscillation (NAO) currently neutral, GFS outlooks suggest a negative trend develops in the 11/15-20 period, indicating a return to cooler weather.
AND WHAT ABOUT THE EARLY WEEK "INDIAN SUMMER" ?  The Sunday-Monday warm spell was timed perfectly, for it added another temperature imbalance early enough in the month which has the potential to over-correct to the cold side by late month.

THE ACCOUNTABILITY FACTOR  (POSTED 11/11) One of our readers posed a great question this week, and in the spirit of accountability to you, the customer, my (long) response is included below: 
Mr Foot,

I've seen at least one forecaster predict the recent rise in the el nino will bring above average temps in the east through December. What are your thoughts on that?
Sam
Dear Sam:
Thanks for your question. I too am a tad concerned about the continued rise of the Oceanic Nino Index (ONI) region 3.4 and in general all 4 ENSO regions continue their positive march. Comparing to analog years, a weak to moderate ONI (averaging in Dec-Jan-Feb between .9 and 1.5) combined with other factors has correlated with snowier-than-normal winters in the Eastern US. To quantify this data point, let's include the definition from CPC: "The ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. ONI is defined as the three-month running-mean SST departures in the Niño 3.4 region."

You can view the data I'm sharing here by clicking on the El Nino link in the post above, and scrolling to the last few pages. Clearly, El Nino years that went into the “strong” category (between 1.5 and 2.5) as in 1982-83 and 1997-98 directly correlated to abnormally warm winters and sparse snow events (save for the Feb 83 blizzard).

The 2002-03 analog has been widely circulated as a good comparison to what may occur this year, and I am seeing similar signals. In both October of 02 and this year, Nino values were on the rise… and in fact, October 02 ONI values were HIGHER than they are right now. For example, the Fall 2002 (ASO- Aug-Sep-Oct) values were already 1.1, where as currently we are standing at .9 and that year, ONI averages continued a steady rise straight to December, peaking at 1.5. Not until Jan-Feb was there a noticeable decrease to 1.4. The other teleconnection correlated to El Nino is of course the PDO (Pacific Decadal Oscillation).  Data shows the October 09 PDO value was .27 - barely positive. The Fall 2002 PDO values were much higher and continued so throughout the winter (Oct-0.42, Nov-1.51, Dec-2.10). Despite all that "warmth," the pattern was able to deliver multiple rounds of cold and snow starting in early December 2002 and continued right through to March 2003. For an early indication, we are seeing similar temperature imbalances now as compared to the Fall of 2002.

So to answer your question as to my thoughts on this...notwithstanding concerns about a strong Pacific jet, and apparent decrease of the cold reservoir in Canada, I believe the pattern is already set in motion to deliver an early -but brief- start to winter.  Ida did  throw a monkey wrench into the works, but another little-known factor that may turn in our favor is an upper level ridge just west of the Caspian Sea of central Asia. Once that ridge migrates to EAST of the Caspian, I believe it will have enough downstream influence to kick a piece of cold Siberian air across the pole. It is accurate to say El Nino dominates the pattern presently, but before long, enough cold air will catch up with us, and once that happens - it'll be showtime for East coast powderhounds.
Sincerely, Mr. Foot

A NOTE TO THE "THREE WEEKS" CROWD: In mid and late October, I posted that you had "(First five) then three weeks to complete your winterizing preparations." Though Mother Nature provided an extra day or two this weekend, here we are on Wed 11/10 and a more-weatherlike coastal storm has arrived courtesy of Ida's remnants. A "smackdown" snowstorm it is not, but another chink in the forecast armor it is. I won't say the arrival of Ida proves the whole forecast, but it's worthwhile pointing out we do have a nuisance to significant coastal storm roughly 10 days after it was projected on this site. So depsite Ida, I believe the pattern remains on schedule as outlined here.

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