Long Range Pattern Outlook #9

[notice]Instead of a discussion tonight, an update on the latest forecast for tomorrow night’s rain/wind/thunderstorms will be posted on the Twitter page. A more detailed discussion will be posted late on Wednesday morning.[/notice]

Brief Overview:

Today’s long range pattern outlook focuses on the medium range pattern going into early-mid February. Following the current mild temperatures, a colder pattern will return for the first week of February, with several minor snow potentials, followed by moderation in the pattern but with a lower likelihood of a significantly warmer than average pattern.



Pattern Outlook Archive

<< Pattern Outlook #8 – January 10, 2013
Pattern Outlook #9 – January 29, 2013


Expected Pattern Teleconnections:

  • NAO – positive to neutral
  • AO – positive to neutral
  • PNA– positive to neutral
  • EPO – positive to slightly negative


Overview of Current Pattern

Last week, one of the strongest cold air masses in the last few years affected the region. The magnitude of this trough and cold air mass was similar to that of other strong cold spells over the last few years, and as the previous pattern outlook expected, the onset of the colder pattern was delayed compared to initial expectations when the model guidance generally showed the cold starting around 1/17, which instead was only a short lasting cold surge limited to the interior Northeast followed by another round of unseasonable warmth on the 19-20th; however, the duration of the coldest temperatures was initially underestimated with the pattern outlook, and the duration of the colder temperatures, as well as the lack of cold in the previous winter and this one until January 20th, made this cold spell significant, with Central Park spending 5 consecutive days with temperatures entirely below 30 degrees. This cold pattern helped to significantly reduce the well above average temperature departures through mid January, with Central Park nearly 7 degrees warmer than average in the January 1-20 time frame. The original winter outlook expected colder than average temperatures in January but did not take into account the significant warmth observed in the first half of the month; as expected from the updated winter outlook, however, this cold was not enough to entirely remove the positive departures, and January is still expected to end up with temperatures at least 1 to 3 degrees warmer than average across the region. In just under 2 years, November 2012 remains the only month to feature widespread below average temperatures.

Despite this cold pattern, little storminess has been associated with it so far. There have not been any significant snowstorms to affect the area this season aside from the unusual early November snowstorm, and only a few minor snow events affected the area, including one on 1/16 north and west of NYC, one on 1/21 mostly in Long Island, and another on 1/25, which was the biggest accumulating snowstorm of the meteorological winter in Central Park thus far with a little over an inch. The storm currently over the central US headed towards the NYC area tomorrow, the most significant storm to affect the US since the start of the new year, is a rain, thunderstorm and unseasonable warmth producer across the entire eastern US.

Medium-Long Range Outlook

Scroll down to the bottom for a brief summary

The cold spell that started around 1/21 and continued through Monday has ended, with much warmer temperatures for this week. This is only a short lived moderation in the pattern, however, as over the last few days, a strong cold air mass built over Alaska and within the next few days will spill into the northern US as the storm currently over the central US rapidly intensifies while moving into Canada, pushing a strong cold front through the region with a trough returning into the eastern US. This cold air mass will not be as strong as that of last week, but will still result in at least slightly to moderately below average temperatures.

This pattern with a trough over the region will continue through at least the first 7 days of February with chilly temperatures staying in place. Despite the colder temperatures, however, the pattern again remains generally unfavorable for significant storms to affect the region. Ridging remains in place over the western US, with a trough over the East, but there is still a lack of blocking near Greenland, with a negative NAO pattern still struggling to develop. The trough axis remains too far east for significant coastal storms to develop and move up the coast; instead, the pattern generally favors weak low pressure systems diving southeast from Canada, racing east through the region before moving offshore and intensifying off the coast. This type of pattern is generally conductive for frequent light snow events across the region, with the potential for one of these storms to develop into a stronger storm with more widespread impacts across the region. There is still uncertainty regarding the timing, location and intensity of these weak systems which will also determine whether one of these storms ends up stronger, and if so then where, with the latest model guidance suggesting a stronger storm on the 5th-6th affecting the region with snow. More information will be posted on this with the daily discussions.

Not every cold pattern stays in place for a long time without moderating, and this will be no exception. Lower 500mb heights will return to the western US towards the 5-6th, with rising heights in the East resulting in another period of moderation in the pattern between at least the 7-12th. This time period at this time appears unlikely to contain significant warmth at this time, with the greatest positive temperature departures likely to focus towards the central US as opposed to the eastern US, but with warmer temperatures expected for the East compared to the first week of the month, potentially at least slightly above average. At this point, winter does not appear to immediately end; the month should continue to feature occasional periods of cold, especially with the MJO advancing into phases 8-1-2 by mid month, more favorable for colder temperatures in the East, but with the significant stratospheric warming from earlier in the winter weakening along with a potential continuation of a lack of -NAO blocking, the strongest cold of the winter has likely occurred last week. Despite this, occasional periods of cold are still expected along with increased storminess compared to the first half of the month, which will include some snow events in the region especially towards the middle of the month; although it is not impossible to observe a widespread significant snowstorm in the region, the large scale pattern overall appears to remain generally not too favorable, as with the rest of this season thus far, but such a possibility cannot be ruled out at this time range.

Summary: After the current temporary warm up, a colder pattern will return for the first 7 days of February, but not as cold as last week while also containing several minor snow potentials. Following the first week of the month, a period of moderation is likely but with the most positive temperature departures focusing west of the region. The rest of February is likely to feature at least occasional periods of cold and storminess, one potentially in mid February, but with the pattern generally not too favorable for significant cold and snowstorms. Overall, February is likely to end up near to slightly warmer than average, with near to possibly slightly above average precipitation.

Pattern Outlook #6 Verification

Verification for Pattern Outlook #5 will be added soon.


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