Long Range Pattern Outlook #4

Brief Overview:

Tonight’s long range pattern outlook focuses on the second half of November, regarding the medium range pattern and the potential for a coastal storm, along with verification for the 1st pattern outlook from 10/6. The final winter outlook will be posted towards late November.




Pattern Outlook Archive

<< Pattern Outlook #3 – November 4, 2012
Pattern Outlook #4 – November 11, 2012
>> Pattern Outlook #5 – November 21, 2012


Expected Pattern Teleconnections:

  • NAO – positive, gradually moderating

  • AO – positive, gradually moderating

  • PNA– negative, becoming neutral late

  • EPO – negative to positive, becoming neutral late

Medium-Long Range Outlook:

The region remained in a chilly pattern through the first week of November, leading up to a nor’easter that brought an early season snowstorm to the region. Following the departure of the nor’easter, a pattern change evolved across North America as expected from the last pattern outlook, with the PNA turning negative with a strong trough over the western US, while the NAO has now transitioned to positive with much lower heights over Greenland. With these two variables in place, a strong ridge is currently present over the eastern half of the US, with widespread above average temperatures observed today.

The pattern will become more progressive across North America throughout the next few days with less amplification as a strong polar vortex settles down over the northern Canada region – this is somewhat similar to last year’s pattern, although there are still many differences which will also prevent this year from taking a similar route compared to last year, when a warm and snowless pattern was in place through the whole winter.

One of the similarities to last year with the pattern currently developing is that the cold air remains bottled up in Canada, and with the progressive and less amplified pattern in Canada the strong cold will have difficulty spilling into the US. Meanwhile, however, there will also be an area of lower heights near the SE US coast, implying increased clouds and potential storminess in that region, as the GEFS 500mb anomaly map from the PSU e-Wall shows to the left. This should lead to a pattern of above average temperatures in the northern half of the US extending into the central US with below average temperatures in the Southeast, perhaps extending further north into the Mid Atlantic, starting from the second half of this week and lasting through about late next week or beyond (11/21-24, perhaps until the end of the month). This may lead to a coastal storm perhaps reaching the Mid Atlantic as well around next week; while there is uncertainty with exactly how any storm in this time frame develops, the pattern argues for a suppressed track, with impact more likely in the Southeast and potentially in the Mid Atlantic, along with a lack of strong cold air which should prevent a widespread snowstorm. Despite the uncertainty, this storm potential has to be watched especially for coastal locations in the Mid Atlantic still recovering from hurricane Sandy.

For the NYC area, temperatures in this time period are generally likely to end up near to slightly above average, perhaps below average at times depending on where the coastal low sets up and how strong and north it is. The main question remains whether the NYC area ends up colder than average in November; so far, the first week of November has been much colder than average, with the first 11 days of the month 6.4 degrees colder than average in Central Park. While the area is currently observing warm temperatures, this warm spell is only brief, with temperatures otherwise much closer to average. More on this will be posted with the next pattern outlook, but there is finally an increasingly likely possibility that at least parts of the area may break the spell of consecutive warmer than average months stretching back to early 2011 with this month.

During this time period, the NAO will be persistently positive; this is a change from the persistent -NAO pattern that has been in place since late March, and is the strongest and longest lasting +NAO period of the last few months. There are still signs from the longer range models, however, that the NAO may trend back towards neutral and possibly negative late in the 15 day period, with some of the GEFS runs signaling the possibility of above average heights towards the Davis Strait. While at this time, a large pattern flip to a strong -NAO/-PNA/blocking pattern – which is what would lead to a cold and potentially stormy start to December – is not likely, with continued lower heights in the Gulf of Alaska also likely which may be an obstacle to a colder pattern without ridging/blocking in the Atlantic, gradual steps in the pattern towards a -NAO and perhaps a colder ending to the month are possible, with the current pattern unlikely to be anywhere near as warm and persistent as last year’s pattern was.

Pattern Outlook #1 Verification

Link to Pattern Outlook #1

Pattern Outlook #1, posted on October 6, expected changes in the pattern following the collapse of a block off the coast of western North America, with a low pressure tracking near or north of the area around 10/14-16, which would be followed by slightly cooler temperatures, with a greater probability of above average temperatures behind it along with the possibility for a colder ending to October.

The NAM posted above from 10/15 6 hours out, showing precipitation and pressures close to the initialized conditions, shows the low pressure tracking north of the region as expected; this was followed by slightly cooler temperatures, although the more persistent warmer pattern was delayed for another few days due to another storm on 10/18-20, which was unaccounted for with the original pattern outlook as it was beyond the foreseeable range. Following that storm, the pattern turned warmer for at least a week until the arrival of hurricane Sandy which was then followed by a colder pattern for the end of October, following the forecast from the pattern outlook, although Sandy was not predicted as it was well beyond the foreseeable range of that pattern outlook.

Leave a Reply