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:
(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:
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):
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):
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:
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.