/Fig - 1/
Maps of SST's areas referenced above /Fig - 2/ and observed data:
/Fig - 2/
/Fig - 3/
The North Atlantic & Arctic Oscillation patterns of the past several months /Fig -5/ are shown here:
Fig - 5
I'lll discuss these more when we get closer to the Winter Outlook publish date (Nov). As you can see the North Atlantic Oscillation /NAO/ has been weakly negative much of the summer while the Arctic Oscillation /AO/ has been fairly neutral. Why such a hot summer with the NAO being negative? Just because the NAO was negative doesn't mean the implied cooler heights and surface air was delivered to the Great Lakes. Remember though; we did have an impressive Canadian Upper Low that forced somewhat cooler air at times into the region. That upper low was one of the polar upper air systems that was indeed reflective of the negative /NAO-/ at times this past summer. Meaning; in response to the NAO-, the cold upper low was able to meander far enough south and thus; infiltrate the Great Lakes and Northeast with refreshingly cooler, drier "Polar" oriented air. More about this soon in my summer review in September.
Back to the Autumn;
There are really no good indicators for trends this fall with basically; a downwind Neutral ENSO effect
across the Great Lakes and variable NAO/AO. With this kind of pattern we remain at the mercy of the
weakening summer ridge and the cold upper low (and thus; NAO/AO) in Canada; leading to an amplified and changeable pattern. Current model predictions of the NAO/AO are lousy. For example; just take a look at this model predictability of the NAO/PNA /Fig - 6/ during the Winters of 2000-05 for up to 15 days ahead.This is from an interesting paper by Ake Johansson in the Journal of Climate published in May of 2007.
Fig - 6
The skill in predicting the index of (left) the NAO and (right) the PNA as measured by the correlation coefficient (1) is shown with thick lines for the NCEP (black) and ECMWF (gray) models as a function of forecast lead time. The regular traditional centered anomaly correlation (AC) for both models are shown as thin lines with corresponding color shades in both panels. The skill of a persistence forecast of the two indices is shown as thin dotted lines. The data are from the extended winter months (1 November–31 March) of 2000–05. Correlations are multiplied by 100.
Looking at recent upper air trends, NAO/AO patterns along with neutral to weak El Nino patterns look for temperatures to average somewhat above normal for the Autumn. Since the downwind effects of El Nino really shouldn't be going for at least a month or two; little of the cooler and wetter autumn pattern normally associated with El Nino is anticipated till later this fall...especially since it will be weak.
Normal to below normal precipitation is expected this fall based again, on the same reasoning as above.
The crest of the full Harvest Moon will illuminate the sky on Saturday September 29 at 11:19 PM EDT
Halloween falls on a Wednesday this fall; October 31st, 2012
Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian