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Winter '17 / '18 - Snowfall Forecast Contests
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Winter '16 / '17 - Snowfall Forecast Contests
18th Annual 'Regular Season'
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16th Annual 'Season-total'
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Tuesday, December 19, 2006

Waiting for -AO -- Stratospheric Warming

In some circles...the stratosphere was long known as the 'ignorosphere' in large part b/c all sensible wx was observed in the troposphere so why should anyone care what was going up there.

The stratosphere has been getting a little extra attention recently. Some say there are big changes are afoot that will lead to big changes underfoot.

The phenomenon of 'stratospheric warming' (SW) has been bandied about around MET town of late...along with the strong suggestion that it will induce significant changes in the current planetary flow regime. The change would bring an end the abnormal warmth and snow drought in the E as winter finally gets started.

The PV is currently quite evidence by the long run of +QBO. Arctic air over the NHEMI is constrained to high latitudes as a result. These synoptic conditions produce positive values for AO and NAO.

When SW over the Pole is observed...the PV is disrupted and its zonal flow weakens. The weakening PV allows arctic air to drain in to lower latitudes.

The time section of 30 mb air temperature shown below has been offered as evidence of an impending stratospheric warming event. Note the warming INVOF the International Date Line (180°W). SW progresses as the warm pool propagates into lower altitudes.

The stratosphere warms...not from warm advection...but from a lowering of the tropopause. Vertical propagation of low numbered Rossby waves are involved but we/re not getting into all that.

  1. Lower tropopause ==> falling / colder geo-heights
  2. Lower heights ==> colder air
  3. Colder air ==> builds hi-lat anticyclone
  4. Hi-lat anticyclone ==> hi-lat blocking
  5. Hi-lat blocking ==> -AO
  6. -AO ==> Trof E
  7. Trof-E ==> strong outbreaks of arctic air in the E
  8. Strong outbreaks of arctic air in the E ==> increased chances for storminess
  9. Increased chances for storminess ==> snowfall forecasting contests
Is there really evidence of a warming event?

The longitude analysis shown above seems to support that idea; however, the latitudinal time-section of the same data shown below indicates the warming in not occurring over the Pole where it would have to be in order for the AO / NAO sign to flip from positive to negative.

Since the warming is observed INVOF 65°N and not INVOF 90° doubtful this warming event will send the AO / NAO below 0.

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