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Monday, November 28, 2011

Why no winter yet...

12-9 - Still no pattern change, although models aren't showing blowtorch warmth either.  Around the 19th, we may get some normal air masses to settle in, which by then is all we for some white stuff.  Three to Four storm possibilities between now and Christmas.  First obviously going to the lakes, but a normal progression is to bring each one further and further south.  See first model run with storm on Christmas

12-8  Still no pattern change.  The end of the period still shows return to neutral, but that return keeps getting pushed off.  How long can an AO remain positive?

12-5 - Yesterday's outlook looked favorable for a pattern flip, but out of caution, I didn't post. I'd like to see 3 or more days of a sustained cold, in at least 3 days of model runs before I am convinced the end of the warm pattern is near. This mornings runs have the cold remaning transitory, and while they have the nao and ao approaching neutral, this is much higher than what it was yesterday. The AO currently is 5 right now, the highest I've seen - keeps the cold bottled up in the artic. The PNA however, has been consistently forcasted to go positive since the 12-1 post below, so there will be some cold entering from Western Canada, but it moves fast and modifies as it exits over the Rockies. For the east to be cold, need the cold air coming in east of the Rockies. Lots of talk about storms for this week - just not seeing it though. One cuts west, the trailer goes off east. Possible flurries or quick changeover as front comes through, but doubtful it sticks.

noon disco- NAM does show a snow event wed nite into thurs. Normally the NAM runs a bit north of the other models, but its something to watch now. CMC and GFS both have storms, but a little to far out to sea. 0z UKMET has a storm going right over us bringing rain. Opening separat post on event as more data is coming in.

12-1 update: this afternoon had ensembles for 12-15 with +pna, ao and nao heading -. GFS operational completely the opposite though. JB posted yesterday that "the ugliest pre dec 15 week in us since 2005 is on its way" HM posting that 60% of the country could be covered with snow and there will be an east coast storm next week. Now the models have been showing a storm in the dec 6-8 range, but its been cutting west of the Apps.


Below are the major winter indices: Artic Oscilation (AO), Pacific North America (PNA) and North Atlantic (NAO) as forecast by the GFS today. Typical cold patterns have a postive PNA to set the ridge in the East Pacific so cold air comes into CONUS. AO as negative to release the cold air from the pole and NAO negative to keep the cold air around. While the PNA is currently positive, the NAO is really high and AO is really high. Then PNA goes negative. Also note the error pattern on the NAO and AO. The bold line is the actual, grey line is the consensus. When looking at the 10 and 14 day charts, the typical bias since Sept 1 is that the predicted consensus is lower than the actual and for today its much lower. So until we can change at least the AO to a strong negative, no real brutal or sustained cold air masses.

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