Significant Cold Ahead For January-February

Significant cold is ahead for the months of January and February, especially late January into February. I'll explain what could cause this.

This chart of observed stratospheric temperatures for the years of 2011 and 2012 shows tat we have had two recent warming events, as shown in the red temperature line spikes on the far right of the graph. When these spikes occur, they are called Sudden Stratospheric Warmings, or SSW events. When an SSW occurs, warm air from lower levels of the atmosphere is forced up into the stratosphere. Because of the warm air being forced up, cold air originally in the stratosphere is displaced and forced down to fill the void left by the warm air now being pushed into the stratosphere. This is why we want SSW's to happen in the winter, so cold air can come down to the surface.

This ECMWF multi-panel graph forecast shows temperature forecasts for different latitudes. We see that the top 3 panels show significant and sudden warming of the upper stratosphere, including the 10mb and 30mb layers. This is a direct result of the sudden stratospheric warmings, and if these forecasts happen, it is certainly plausible that significant amounts of cold air will be displaced down into the troposphere (where we live). Even better news is how the two stratospheric layers do not directly cool down after the warming.

Even better news for cold air prospects is how the polar vortex is getting torn apart. For those unfamiliar with the polar vortex, it is the driving force behind the Arctic Oscillation and varies in its strengths. When it is weaker than normal, the polar vortex releases cold air down into the troposphere, much like the air displacement example shown above with the sudden stratospheric warming.

These two forecasts above of different isentropic layers show how decimated the polar vortex will be. The colors depict potential vorticity values, much like how high vorticity values signify low pressure systems at the tropospheric 500 millibar level. The two forecasts above show virtually no polar vortex to be found- the potential vorticity that IS present doesn't resemble a polar vortex in either of these two layers. This is exactly what I have been warning about- a polar vortex collapse. It seems to be happening in the upper stratosphere. If it propagates down to lower layers of the stratosphere, there's no telling what could happen.

Now, here's the big thing that will kick off the cold for mid-late January: CROSS POLAR FLOW.

The above image is for the lowest level of the stratosphere- the 100mb layer. I have outlined my best guess as to where the jet stream is. The plus sign signifies the North Pole. Using the outlined area, we see that the jet stream starts in Siberia, shoots north into the North Pole, and crashes south into the Plains, Great Lakes, Midwest, Ohio Valley and Northeast. The jet stream crossing the Polar region and then fleeing south into the US is called a cross polar flow and is commonly identified with the strongest cold air outbreaks in the US.

The stratospheric ECMWF is not the only model and atmospheric layer showing such a cross polar flow:

GGEM Ensembles showing Cross-Polar Flow in very long range

GFS Ensembles showing Cross-Polar Flow in very long range

Both the GFS ensembles and GGEM ensembles are showing cross-polar flow regimes setting up in the long range. This cross-polar flow is shown by high pressure pressing toward the North Pole, with low pressure then appearing across Canada and the US. Now, the GGEM Ensembles are indeed showing this cross-polar flow much better than the GFS ensembles. It is a very good sign to see two major ensemble systems showing cross-polar flow evolving, as well as the stratospheric ECMWF. If this happened, cold would invade the Lower 48 and would not be easily pushed out.

This is the zonal mean temperature forecast from the ECMWF model. I inserted an arrow into the 1mb - 5mb layers to signify what will happen now that this sudden stratospheric warming event is ongoing. That depression of light blue colors signifies cold air being forced down through the stratosphere in response to the sudden stratospheric warmings. Now, this air will warm as it pushes down through the stratosphere, but nonetheless, it is stratospheric air, meaning it will naturally still be colder than normal.

For the long range model forecasts, the CFS v2 monthly forecasts show a very cold January and February:

-Andrew