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December 2012 Pattern Analysis


HailMan06

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Modelcasting will get you nowhere...that's why I think analyzing the anomalies on the Day 7 Euro is fruitless to begin wtih.

We're looking at a few weeks of disruptions to the PV/stratospheric vortex until we can get it dislodged or re-aligned ... and this could be timed with a better MJO and maybe less solar activity. The way things shook down in this regard over the last week or two has certainly ended the contest from now until around the holidays anywhere south of Philly in my opinion.

By the middle of Dec we could be looking at a -PNA gradient pattern if this breakdown of the vortex does begin to occur...with the positioning of the gradient then owing partly to the the NAO/Atlantic. But even then, this pattern is most favorable for N New England. If we get lucky we could see some front end wintry stuff.

But much still remains to be seen. The Euro strat maps look terrible through Day 7-10 right now.

Yeah I'm hesitant to buy into any one solution for the D7+ period. We see the drastic changes in the GFS even for something as near-term as the storm Mon-Tues. With that being said, I think it's clear enough to say the next 7-10 days will feature no wintry threats for our area. Good news is we start seeing the torch anomalies get erased in the Plains states by this weekend into next week, with a large scale Central US trough likely to develop in the medium range. This will put the baroclinic zone along the NW periphery of the SE ridge for the time being, meaning most snow/ice threats are likely to be confined to interior New England/Northeast. Remains to be seen when and exactly how far south that gradient presses in the D 7-15 range. I do like seeing colder temp anomalies entering the US though, and significant cold across Canada. In my winter outlook I mentioned the 52-53 season as the caveat year, a -NAO/AO but a terrible north pacific, but I'm not ready to go there for December yet. December 1952 featured strong neg height anomalies across the entire NPAC w/ zero semblance of ridging. If we can at least get the EPO to neutralize in the longer term, pump a bit of ridging into sern Alaska (the -PNA Western cold dump is likely to stay), then some of that cold can be directed further east.

The NAO is crucial as well and has been very poorly modelled beyond D 5-7. The negative AO is a lock as we've already tanked and look to remain negative, so that's one good thing. Unfortunately if we can't get the NAO to help us as well, the NPAC's going to rule the roost for awhile.

So the bottom line from me is I wouldn't write off the second half of December yet, but the pattern will favor the Plains and New England for the next week to 10 days. Beyond the 12th or so, I'm hesitant to make any calls about storm threats as modelling is very erratic out at that range w/ the global pattern. Will be interesting to see if the next Euro weeklies update on Thursday ditches the west based NAO idea or not.

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How would a strong west based block -NAO combine with an active pacific jet? We don't really need arctic air to get a snowstorm this time of year, a marginal airmass can actually be quite sufficient except for the immediate coast.

Very up and down with the temperatures for the rest of this week into next, should drop into the low 40s Thursday, then maybe more 60s for the weekend, could drop back into the 40s for a day, go up into the 60s with the cutter (looks impressive on latest gfs, strong wind potential maybe?), and then back into the upper 30s low 40s after the storm passes.

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If you're sitting here early this afternoon looking for a good sign, I suppose you could check out the 6z GEFS for a nice scenario. All of the cold bottled up over Alaska dumps east/southeast in a -PNA regime while the vortex is disrupted a bit allowing the -NAO ridge over Iceland to move farther west not only to Greenland but over the Davis Stragiht. This would likely bring about a -PNA driven gradient-type pattern that could hypothetically be favorable for some of us.

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Not sure exactly what forced this change on the GEFS but it's worth noting especially considering yesterdays Euro weeklies. The Pacific pattern flips to one that is much more favorable for bringing very cold air into the conus by Days 7 - 10 with the PV more favorably aligned. The blocking on the Atlantic side would come as a bonus at that point given the pattern developing after D 7.

http://www.meteo.psu...nsloopmref.html

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Yeah, I'm not sure what exactly is causing those changes, but it certainly is a good pattern depicted. And this is two GEFS runs in a row, and it's not THAT far out.

Perhaps we just get so many cutters/disturbances that act as wave breakers that we turn the NAO more negative and even more west based just from the troposphere. There can be times where we can generate a negative NAO via the troposphere without stratospheric support. It's just harder to do and wouldn't be as sustained.

Still don't really know much yet about the Pacific, but it always seemed like the Pacific was progged to change for the better somewhat. The uber PAC jet gets dislodged somewhat. Without any NAO help, it's probably a classic La Nina gradient pattern, maybe Dec 2008 style. But with it, that gradient shifts south. I'm not sure what to make of all this but it's nice to see.

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That said, I still don't really think the Pacific in itself will look good enough in that time frame to provide snow for us without help from the NAO.

The problem with the GEFS is that they keep building heights west back toward the Bering

instead of into Western Canada. Hopefully, we eventually see the heights building

more over the PNA region either later this month or next.

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The problem with the GEFS is that they keep building heights west back toward the Bering

instead of into Western Canada. Hopefully, we eventually see the heights building

more over the PNA region either later this month or next.

Even just building a bit into Alaska would be nice.

Anyway, the Euro ensemble mean at day 10 actually looks pretty good.

12zECMWFENS500mbHeightAnomalyNH240.gif

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As long as that ridge is that far off in the Pacific , the trough sits out on the west coast and the main piece never makes to it the east coast until after the 20 th .

The 10 day Euro keeps showing you SW flow and too much east coast ridging for my taste . Any storm that comes out likely cuts .

I would bet on the last week on Dec as the real potential for a winter pattern to develop .

Its possible it snows before then however , theres no locking the trough off in the east thru week 3.

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Euro ensembles today have the MJO coming back, in phases 1/2, by third week of December. So that might help us out in the Pacific again:

2n8spwi.jpg

Great observation.

And just a reminder: Here are the MJO phase 1 and 2 correlation composites to the 500mb pattern for December, respectively. Phase 1 also correlates to an improved NAO.

DecemberPhase1500mb.gif

DecemberPhase2500mb.gif

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