It’s going to feel like January again

This is my first ever post to the CIMMSE blog, but I wanted to write about the potential cold coming next week, and I hope to begin to contribute much more in the future.

Over the last few days, many high temperature records have been broken across the southeast. Several locations across SC and NC have hit 80 degrees once or twice since Saturday, with a few locations approaching their all-time January high temperature records. Don’t forget…it is still January.

That being said…while we have been warm, many parts of the world have been quite cold, and I think we are about to return to the depths of winter with a very cold outbreak possible across the eastern half of the CONUS beginning next week.

Although I am not too familiar with stratospheric warming events, from what I understand, a reversal in the stratospheric winds from west to east occurs with warming temps high up the stratosphere. This leads to suppressed tropospheric thicknesses and weakening of the polar jet…which creates very cold outbreaks during the winter. I believe there are signals in place which point to one of these events across portions of our area next week.

The first image is an animation of 11-day moving average of 10 hPA temperature and associated anomalies:

temp10anim

(animation doesn’t appear to work here. link: http://www.cpc.ncep.noaa.gov/products/intraseasonal/temp10anim.shtml)

Note the incredible warming that has been ongoing across Asia the past few weeks. Asia is currently experiencing one of its coldest winters on record. It is clear that the stratospheric warming event is at least partially responsible for the extreme cold. At the same time…since the start of 2013 this warming has been expanding (while de-amplifying somewhat) towards the east and towards North America. This expansion of the warming towards North America will force the polar vortex to split and reload across Canada…setting up the cold pool which will drain slowly but significantly into the CONUS.

Guidance has shown high variability in the exact intensity of this cold event…but has shown almost no flip-flopping in its occurrence. In other words, although the level of cold has fluctuated significantly within different model runs, the cold air is ALWAYS in place. This is evident in figure 2 which shows the NCEP RMOP values for January 23rd:

mmap_2013011400_216

Note even though this is 9 days out, the measure of predictability is quite high with a deep 500mb low centered across the Hudson Bay and a strong full latitude trough across the eastern CONUS. Seeing this level of predictability by day 9 is quite impressive, and this upper pattern is consistent with cold air outbreaks across the east.

Additionally, we see in figure 3 the ECMWF ensemble mean SLP for D7 (1/21):

slp7

The key to take out of this is the massive area of plus-1036mb high pressure across NW Canada and extending into Alaska. This is the source region for this cold outbreak, and it should not be a stretch to foresee that cold dome sinking SE into the eastern CONUS beyond D7. This pattern appears it will somewhat correlate with the motion of the stratospheric warming discussed above too…and it would not be shocking to see temps 2-3 standard deviations below normal for late January. (For what it is worth, current progs suggest 850mb temps of -2 SD’s spreading into the CONUS by 1/22, but this may be underdone due to averaging of the ensemble members):

850SDonetwentytwo

If all of these parameters come into play concurrently, it would create the coldest air of the season across much of the eastern US. Of course, exactly how far south the extreme cold will impact is still very much in question, but at least partial intrusions of this cold will work into the Carolinas middle/late next week as pieces of energy rotate around the long wave trough to reinforce the cold air. The GFS, which admittedly has been most aggressive with this cold in certain runs (had -18C at 850mb on the 14/06z run into NC) has cut back on this with the 14/12z run…but we can still see both the expansive area being impacted by the event, as well as the strength of the cold:

coldairjw

Although the extreme cold (-18C) is no longer there…850mb temps do reach -10C across portions of NC and fall to less than 0C almost all the way to Georgia. This could support high temps only in the 30s across portions of NC and 40s into SC. Lows at night would be much colder with great radiational cooling occurring at night beneath the large high pressure.

I put this out there just for some thought. Even if the extreme cold does not reach this far south, it will still feel much more like winter than it has the past several days and will definitely be a reminder that it is still a long way to go until spring. The period from January 21 – 25 could be the coldest air we have seen in some time.

I appreciate any feedback/comments/thoughts on this.

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About Josh Weiss

General forecaster at NWS Wilmington, NC. Also serve as the fire weather program manager and regional coordinator for CoCoRaHS.
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5 Responses to It’s going to feel like January again

  1. blsmithwx says:

    Josh, I have seen some discussion of this on another forum, so I think your connection of the stratospheric warming and cold air outbreak is on track (assuming the time scales are related). The warming is thought to be related to a the Quasi-Bennial Oscillation (QBO). I struggled to find literature very quickly, but a Google search lead to this from NCAR.. http://climatedataguide.ucar.edu/guidance/qbo-quasi-biennial-oscillation. This is all new to me, but very interesting support for what you are seeing in the models.

    Barrett

  2. Hi Josh and all,

    Thanks for your post! I have heard a lot about this upcoming cold event, and the SSW. I’m no stratospheric dynamicist, but the papers I’ve read on the topic show an increase in the possibility of cold outbreaks following an SSW. However, they also caution against too much forecast application because it isn’t clear if the focus of the cold will be in Asia, Europe, North America, or elsewhere. There is an increased chance of a cold air outbreak following an SSW event, and Kolstad et al. (2010) cite a 50% increase in this possibility for North America, but the possibility increase is greater for Asia.

    Physically, I’ve always struggled with the idea that happenings in the stratosphere could exert “downward control” on the troposphere, just because of the much lower air density there. But there are several papers that advocate this view that appear reasonable, and the key is vertical propagation of wave activity.

    I like that fact that you mentioned the extreme warmth we’ve recently experienced. Yesterday, Rochester, NY was 68F, for example. There was little or no hype about the exceptional warmth, but I’m hearing a lot about the exceptional cold that is supposed to follow. I guess this is because we all tend to get more excited about cold than warmth in January! That said, if we were to experience cold anomalies that matched our recent warm anomalies in magnitude, we would be talking highs in the 20s and lows in the single digits in Raleigh, anyway. I very much doubt we’ll see that, but it sure would be exciting if we could. In Raleigh, we’ve now not set a record low temperature since November, 2008. We’re due!

    Following such warmth, with an amplified wave pattern, it would not be unusual for cold to follow. Whether the cold can be attributed to the SSW or not is another story. Downstream propagation of amplified Rossby wave energy might take place anyway. More locally, the recent loss of upstream snow cover may hamper our ability to bring very cold air into the southeast. I always like to see split flow, with confluence and a high to our north, an idea set-up for CAD.

    For those interested, the papers I mentioned above are:
    Thompson, D. W. J., M. P. Baldwin, and J. M. Wallace, 2002: Stratospheric Connection to Northern Hemisphere Wintertime Weather: Implications for Prediction. J. Climate, 15, 1421-1428.

    Kolstad, Breiteig, and Scaife, 2010: The association between stratospheric weak polar vortex events and cold air outbreaks in the Northern Hemisphere. Q. J. R. M. S., 136: 886-893.

    There are many, many additional papers, but these two seem to speak to the predictability issue more than some others.

    Thanks for the post, and best wishes,
    Gary

  3. Josh Weiss says:

    Thank you for your replies, guys.

    I am in no way an expert in SSW events and subsequent tropospheric cooling, only through the bit of literature I have read. The reason for this post is kind of 2-fold, both of which, Gary, you mentioned in your response. 1) Even if the true cold does not come to fruition, it will be significantly colder than what has been experienced recently and could have considerable public impact (heck even some of the flowers are starting to bloom!). 2) Agreed that in a highly amplified pattern a very cool period always follows a very warm period as it must…but in this case the guidance has been so adamant about a potential major cold event (and that RMOP map is pretty telling IMO) that it was worth mentioning and then discussing the evolution over time. Seeing 850mb temps approaching -20C this far south in a few model runs is nothing to “sneeze at,” if you’ll pardon the cliche. It may be impossible to specifically say that any cold outbreak is attributed to an SSW…but it certainly appears plausible which is the best I can do 🙂

    – Josh

  4. Thanks, Josh. Your point about a hard freeze after things have started blooming is a very good one. It sure would be nice if we had a nice snow cover to insulate the plants from the cold, should we get it! Cheers, Gary

  5. Nice read Josh. I’ll be very interested to see how much vigor this cold blast packs. Even with model insistence at times, it’s been difficult to get cold air to head south for very long this season. The SSW trends are really interesting, as are the model progs, but I think overall the pattern just makes more sense for a cold outbreak. I tell lots of non-weather folks all the time, if it’s way warmer than it should be here, it’s gotta be way colder than it should be elsewhere. Indeed that’s the case now, and our see-saw will flip flop soon enough. How much so, time will tell!

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