Saturday, January 19, 2013

Potential for US Polar Vortex Intrusion Increasing

I have determined that the risk for the polar vortex dropping well into the United States - no matter how small the chance - is increasing, and I'll explain why.

Displayed above are four separate forecast images from something called the GEFS Control. The GEFS Control forecast is a member of the GFS Ensembles, but, unlike regular ensemble members, its parameters are not changed. You may recall that ensemble members have their starting parameters changed (i.e. higher humidity than the actual humidity, lower temperature than the actual temperature, etc.), but the GEFS Control is not changed. Much like back in middle school and high school, the GEFS Control does not have its parameters changed, essentially the definition of a control factor in a middle school science experiment.

The GEFS Control is displaying 500mb height anomalies, where cold colors indicate low pressure areas and warm colors indicate high pressure areas. Areas of very bright green or even a gray color within that green is a polar vortice from the polar vortex, which will be splitting up in coming days and moving south, hence the basis of this post. The forecasts I picked out are within the last 6 runs of the GFS Ensemble, meaning 4 out of 6 of the past 6 runs are showing the polar vortex intruding on the US. The most obvious intrusion is the second image down, where the polar vortex is making its home in the Great Lakes. These forecasts should clear up with time.

But it's not just the GEFS Control forecasts, it's also the ESRL/PSD Ensembles. The PSD Ensembles are a group of ensembles not unlike the GFS Ensembles. They are run at the ESRL agency, a counterpart of the American NCEP agency. This is the forecast for Hour 360, also showing 500mb height anomalies. You can clearly see the polar vortex pushing south, as shown by the light blues in Canada and the North Plains. The depressed contour lines in that region also show that the vortex may be trying to make a move south. At this point, only the North Plains would experience the coldest of the cold. However, frequent clipper systems could bring cold air down to other regions of the US, but that potential has yet to be realized.

It does appear the potential for this actually happening is on the rise, but the potential is still low at this time- I want to see more models and ensembles catching on before I even think about raising a serious concern of this happening.


1 comment:

Anonymous said...

andrew, suggest you spend a little time and perform a postmortem on why the polar vortex collapse did not make it into the US starting early Feb. There were a number of people following your blog on that topic

anonymous Mike