Wednesday, May 1, 2013

Polar Vortex Collapses For Summer

Observed zonal winds on left
Hour 240 forecasted zonal winds on right
The polar vortex, the entity that ignited massive discussion earlier this winter, will be commencing its final collapse to enter its summer stage, and likely bringing an end to the unusually chilly spring in the long range.

Shown above is a combined image of observed zonal winds as of yesterday morning throughout the stratosphere (millibar levels shown on the left-hand side of the image), while the right image depicts zonal winds 10 days from now. Positive zonal wind values indicate the presence of a storm system (in this case, the polar vortex), while negative zonal wind values tell of an anticyclone (high pressure system) in the vicinity. The observed image of zonal wind values tells me that the polar vortex is weakly present from the 3 millibar level through the rest of the stratosphere. We see how the positive zonal wind anomalies extend well beyond the 100 millibar level that defines the border between the stratosphere and the troposphere. The forecast image shows that the positive zonal wind anomalies have been eradicated from the stratosphere, and it is this eradication that indicates the polar vortex has collapsed and entered its summer stage. When the polar vortex collapses in spring, high pressure takes over the stratosphere, ending the risk for sudden stratospheric warming events. In the fall, this high pressure system breaks down again and the polar vortex returns to re-ignite the risk of collapse in the winter, like we very nearly saw this past winter.

When the polar vortex takes its summer leave, we can anticipate the unusually chilly spring to end. The stratosphere was bubbling with anomalously warm areas of air in the upper stratosphere, meaning that the stratosphere was still in its winter stage. Because the stratosphere was in its winter stage, the lower atmosphere, including the troposphere was most likely still in a rather wintry stage. Because the stratosphere is getting into its summery phase, we can expect the surface weather to calm down as well.



Anonymous said...

Thank God! I thought this cold stuff would never end! Good riddens to it I will add! Time for sun & bbq’s! Oh, & beaches & boats!
Thank you so much Andrew for all you do! I & others appreciate you a great deal!
Happy Summer everyone!

Anonymous said...

Andrew, you hit the nail on the head there, I just noticed as I was enjoying the beautiful scenery beginning to emerge from the melting snows (about 10 inches of it managed to accumulate without melting) that the biggest sign that the severe cold is over was finally showing, that was that the trees are finally budding and some of them are even beginning to show their leaves, spring is finally arriving in Colorado, it's prettier than I have seen in years, meadows are filling with grass that in many places is already 6 inches tall, and flowers and tiny ferns are starting to poke through the soaked topsoils, small springs are getting bigger and bigger as runoff from our own snowmelt is recharging water supplies, and there shines a ray of hope after such a long duration of despair, and it is only a matter of time before our neighboring towns and lower elevations to the south and east of us finally begin to realize the same shining hope as us, let's just hope that the moisture will keep coming, and will also begin to favor those southeastern neighbors soon, because they desperately need it.

Anonymous said...

I don't know if noticed this, but I was checking the temperature anomalies for the stratosphere at 10 hPa and it looked like the bloom of warmth over the north Atlantic finally burst northward into the Arctic at the end of April. I had been assuming now for the past two weeks that he AO would trend back up to slightly positive after a dip into slightly negative (which we observed at the end of April). However, this sudden stratospheric warming leads me to believe the AO could crash to around -2 or so again. What are your thoughts? I know the stratosphere temp profile would naturally warm this time of year, but this has happened very suddenly, and there's still some very cold air over Canada that may want to creep south.