Monitoring the Stratosphere in November

Well, we’d be wrong not to mention that we are all rejuvenating from releasing our winter forecast for 2015-16. We hoped you all enjoyed reading it –whether or not it was what you were hoping to hear. It took a lot of collaboration, research, and efforts between all of us here to put it together.

In the upcoming days, we plan for a series of technical posts for our premium subscribers to explore more on important topics from the winter forecast. For this post,  we discuss more about Stratospheric Warming.

There’s been a high volume of discussion within the weather community regarding snow cover extent over Eurasia, and it’s potential foreshadowing of Sudden Stratospheric Warming (SSW) events, which may be correlated to a negative Artic Oscillation phase (-AO), 2 to 3 weeks thereafter.  According to the automated graph below, snow cover is now expanding and running close to 2009 at this time. As some of you may already know, the winter following that was featured colder than normal temperatures with above normal snowfall for December; and then same again in February. We also had a minor stratospheric warming in event in November, before a major SSW later in January and February.

Snow Cover Extent from 2005-06 to this season in Eurasia as of November 2nd.

Snow Cover Extent from 2005-06 to this season in Eurasia as of November 2nd.

As we discussed in the winter forecast, one of first part of this process this month is the amount of poleward heat flux induced by the snow cover into the lower stratosphere. This starts the vertical propagation of warm waves into upper stratosphere. At this time, heat flux is forecast to drop below average and below of what we saw in early November last year.

Heat flux at 60 degress North and at 70 hPa forecast to fall well below average later this week.

Heat flux at 60 degress North and at 70 hPa level forecast to fall well below average in next 7-10 days.

The 12z/03 ECMWF model forecast below out to 10 days, shows temperatures at 10 hPA and 30 hpa dropping, with zonal winds increasing at 10 hPa and 30 hPA to between 30 m/s and 40 m/s. As we discussed in November outlook, this wind pattern is the opposite trend for a precursor to a stratospheric warming event. Another related factor is the EP-flux. These are stratospheric winds that support the propagation of warm wave anomalies that cause weakening of the stratospheric polar vortex. For this to occur effectively, the EP vectors (EPV) must be out the poleward direction or pointed to the right on graph below. The ECMWF forecasts the EP Vectors at 10 hPA are to remain equatorward or pointed to the left.  Looking at the GFS overnight at 10 hPa, there are no signs of warming or weakening of the stratospheric polar vortex through 15 days.

ECMWF model 10-30 hPA temperature forecast on the left graph. Wind and Flux forecast on right graph

ECMWF forecast cooling stratospheric temperatures on the left graph. Forecast increasing zonal winds, low heat flux and equatorward EPV at  on right graph.

6z GFS forecast10mb heights out to 384hr

6z GFS forecast 10mb temperatuers out to Nov 20th.  Polar vortex appears still strong near the north pole

We discussed earlier, in our November outlook for premium subscribers, and again in our winter forecast, the QBO influence on the stratospheric polar vortex. The 30mb QBO value for October was +13.38. This is the highest positive 30mb QBO value for October since records began in 1948. This value is above the +10 threshold, which lends even more support for a stronger vortex. We believe the +QBO will remain steady through early winter. Then possibly begin to decline in the positive values, during middle to late winter.

KP index values 5> show at geomagnetic storms

KP index values 5> show at least minor geomagnetic storms that enhance the the stratospheric polar vortex

We also discussed the effects of heightened solar activity — and solar storms — on the stratospheric polar vortex, including the fact that heightened activity tends to tighten or strengthen that vortex.  From Canada’s Space Weather Site, daily observed solar radio flux values is are currently running between 115.00 cm to 130.00 cm for first three days of this month. Back in November 2009 the average for the month was 73.66 cm. Higher solar activity (particularly with geomagnetic activity) enhances more strengthening of polar vortex. The KP index running up 5, also indicates geomagnetic storms. Some growing sunspots and coronal hole facing the earth could cause more geomagnetic storms in the upcoming days.

We will continue to monitor the stratosphere for any changes and continue to keep you updated here with detailed analysis, in the upcoming weeks. However, it doesn’t appear that we will be seeing a stratospheric warming event that would support -AO pattern very soon. Our thoughts from outlook for November look to be on track so far — with the current conditions and stratospheric vortex falling into line with our winter forecast as well.

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