Sunday, November 4, 2012

Special Long Range Lookout: Dreaded Eastern Ridge Showing Up

This is a Special Long Range Lookout, published November 4, 2012.

The dreaded Eastern US ridge pattern is showing up in the ensembles in the next 5-10 day timeframe. As a stormy pattern begins to shift westward into the Southwest and general Western US, and the environment around Greenland begins to become more stormy, a ridge of high pressure will be setting up across the eastern US in response to these two factors. The stormy West will be a negative Pacific-North American (PNA) pattern, which brings about a warmer pattern in the East. The stormy Greenland area will be a positive North Atlantic Oscillation (NAO), which helps a warming trend across the East. While this detrimental negative PNA will be quite strong, the positive NAO will be relatively weak, which means this won't be a locked-up warm pattern.

If this were winter, many in the East would be in some trouble. However, I can see that this is, in no way, the end of winter before its even started. Let's take a trip up to the Arctic. In the Arctic, we see a disorganized bunch of reds (high pressure) and blues (storm systems). This is good. If we have the ridges of high pressure holding their ground in the Arctic, it will ensure the prevention of a polar vortex forming. A polar vortex is the base of the Arctic Oscillation (AO), which is strong in the positive phase (cold air is locked up north, warm air prevails in the US) and weak in the negative phase (polar vortex breaks, cold air flows south).

Last winter, we had the polar vortex present and strong, which kept the cold air north in Canada and Alaska. Rarely did a ridge break in to that vortex that kicked cold air south. This fall, we have been observing a relatively quiet Arctic with the absence of the polar vortex, which is a good sign for this winter. While a ridge in the East may not be the best thing we want to see as we come in to the final days of fall, the absence of a polar vortex and the presence of at least one big ridge in the Arctic is certainly good news, and a welcome change from what we saw last winter.

In summary, the East is likely to see a few warm-ups in the next few weeks. However, the fact that the NAO will not be a strong positive and there is no polar vortex present is very good news in my eyes, especially the weakness of the positive NAO in the short term. If the +NAO remains weak, then the ridges in the East will be easily pushed off. Now, due to the strong negative PNA they will form again, but the ridge is unlikely to be sustained for longer than 3-6 days at a time thanks to the weak +NAO.

The people most likely to see snow in the next week or two will definitely be the Plains and Rockies, as the stormy pattern persists in that region.



KakHome said...

Very good, explanatory post. Covers many of the questions I was starting to have in my mind. :)

I sent a message on Accuweather (as Hertz) with just a check on interpretations and a few remaining questions. I'd appreciate a response there, but again this post makes me considerably clearer already than I would otherwise be. :)

KakHome said...

Thanks for respond to my message.

I have just a couple leftover questions which I sent in another message, which I'd appreciate a quick response to when possible. Otherwise I think I'm fairly clear on things. :)

mike paulocsak said...

Andrew.I think this will be short lived to a few weeks or so.Remember last year? Hopefully this is not the beginning of a warm winter for us like last winter was.Last winter will be remembered for years to come for many.

KakHome said...

It's true, also remember Andrew's post about snow cover in Siberia in October.

If that is to verify, winter will be most favored to kick into high gear in the East in the second half of the season. Not saying there can't be transient cold before that though, with the mean trough in the West "bleeding" some cold air into the East at times assuming the ridge doesn't get to the point in which it deflects fronts away from the East entirely. Andrew did say he doesn't expect that to happen, even though the ridge will rebuild in between fronts.

At least that is my best interpretation of all this.

KakHome said...

Visit Facebook BTW, Andrew has come up with when this warm pattern should end in the east.

(I prefer not to copy-paste anything he said on FB here without permission.)