Friday, 14 September 2012

Strong trough next 16 days, some model uncertainty in the long range

A constant barrage of fronts and troughs will threaten areas from west of the appalachians to the rockies.

Trough 1 at 108 hrs:
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GFS 7 day running mean departure with the first trough. Pretty much in agreement with the euro weeklies which has the centre of the cool over the western ohio valley/midwest. It has departures surpassing 4 blow normal for the 7 day mean.
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Second trough at hour 268 along with a front ahead of it on the 21st. Starts west and then progresses eastwards.
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Hour 240:
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For week two we can see that the lower temperature anomalies have shifted east quite a bit and are now centred over the great lakes region.

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Indicies back this up with a -NAO,-AO +PNA and -EPO:

Canadian keeps the trough positioning stronger and further west. It doesn't really move much or weaken over the 2 week period. The canadian migrates the trough eastwards slowly but doesn't lift it out as fast as the GFS. The canadian keeps it around until the end of its range 375 hours.
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The GFS is uncertain about the pattern past hour 288 with more of a zonal flow across NA. The euro on the other hand lifts the trough out by around the 26th like the GFS but then pops a strong ridge into the east centered in the midwest and great lakes. So we can see the uncertainty moving into the longer range as we get into october.

Heres the 16 day period as a whole on the GFS. Much Colder then normal departures seems very certain between all the modelling:
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