Wednesday, February 4, 2015

Wednesday Morning: A Closer Look at Early Week Storm Threat

Model runs keep getting interesting for early next week. Due to the complexity of the situation it is worthless to actually look at the surface output of any operational model. Instead, we must use ensembles to look at the overall pattern in place and ask ourselves what is possible here. At this time I would weight a high probability of snow effecting the whole region on Sunday night into Monday. Weather or not this ends up being light to moderate storm or a severe winter event still remains to be seen. I can not assign a high probability to a significant storm at this time but can acknowledge there is the possibility for a long duration event from Sunday night through Tuesday night.

Let me review why..

First off I like the pattern ahead of our potential storm system. We finally have a strong Greenland block or Negative NAO in place and we also have a healthly areas of low pressure in eastern Canada. This duo helps hold in an arctic high pressure system over the area and allowing approaching energy to potentially slow down and consolidate.

The more confident part of this forecast is part one of the storm which is northern jet stream energy entering the region on Sunday afternoon and night with light snows..


Moving back to 18,000 feet you can see the northern disturbance flowing into the area below..


We have a healthy ridge axis to the west in a favorable spot and you can see how that causes downstream amplification of our shortwave circled in black. Translation- this helps energy in the jet stream dive down and "dig" into a developing eastern trough and I tried to illustrate above.

Part two of this storm is the difficult part and deals with how this energy redevelops off the coast. If it stays off shore we only get snow from part one of this event and it will be light to moderate accumulations. However, if this energy "cuts off" from the jet stream in the perfect spot, then we are faced with a significant winter storm. 

You can see all the high pressure to the north of the developing low pressure that basically cradles it in place..


Obviously if that low develops in the right spot its not going anywhere and will live and die over our area causing significant snows. Models will keep flip flopping and flirting with this idea over the next few days. It will not be possible to forecast if this will happen until at least Friday or Saturday due to the complexity of the set up. In any event, here was one run of the Canadian model that was more aggressive with this from last night..


Thats all I have for now. I hope you guys see how its impossible to just say a big storm is coming or not. We have to sort a lot of factors out here but the potential is def there. 

More later.


3 comments:

  1. Willy, I'm too cheap to see the Euro long-range, but this AM's long-range GFS and Canadian hint that the Sunday-Monday snow event (4-5 inches in Newark/Paterson area, if I'm reading the charts right) will linger into Tuesday/Wednesday as a coastal storm, something like a Nor'easter. But both models show rising temps along with that, and thus change to rain. Interesting given that Andrew at Weather Centre talked about a storm here in Feb 10-15 range based on the 6-10 day Typhoon rule, relative to a low that was sitting east of Japan on Monday and Tuesday. There presently do appear to be some lows crossing the Pacific. The 7-10 day NOAA forecasts for NAO seem to stay positive, but PNA seems to have moved into negative zone. Doesn't that imply the Pacific ridge continuing to shoot cold air disturbances across the country at us, something like a bowling alley (Pacific Jet Lanes?) . . . but the NAO maybe keeps us from getting totally buried? Just my .02 SWAG. But then again, model guidance past 120 hours is SWAG country too, so I'm told. Jim G

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    1. Your exactly right the +PNA helps drive down the arctic air and clipper like systems but without a true -nao the pattern stays progressive or its much harder to get a big storm. A negative NAO slows the flow down allowing disturbances to combine and also holds cold air in place. Ahead of this next storm the NAO is going positive but the cut off nature of the low results in a block to the north from Arctic high so we have a very interesting set up to monitor.

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  2. OOOOPs, make that PNA + . . . . well, it seems negative to me, given that I'm not a big fan of snow. Jim G

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