Where is our "pattern change" ?

[WeatherX]

HIYO!

Weather x, looks good right?

http://raleighwx.ame...mbHGHTNA240.gif

Granted its smoothed by this point, but you can still see lower heights over greenland, the Davis Straights and eastern Canada. And while it's a robust PNA riding signal, the trough looks progressive on the exit side.

I believe maybe it was trials or someone else who said if possibly a s/w dropping down from the ridge can amplify enough to dig the trough a bit deeper. That's our best shot, because anything that would coke u p the coast would be quick moving.

Lol, now That's funny.

Yeah, it appears we'll have the ridging where we want it, some seasonably cold air, a touch of ridging in the NAO domain and there's been plenty of shortwaves available so far. Players are gathering and ready to take the field. Time to start getting excited.

[MJO812]

I hope the GFS is right with the pna ridge. It looks really nice.

[earthlight]

HIYO!

Weather x, looks good right?

http://raleighwx.americanwx.com/models/gfsensemble/06zgfsensemble500mbHGHTNA240.gif

Granted its smoothed by this point, but you can still see lower heights over greenland, the Davis Straights and eastern Canada. And while it's a robust PNA riding signal, the trough looks progressive on the exit side.

I believe maybe it was trials or someone else who said if possibly a s/w dropping down from the ridge can amplify enough to dig the trough a bit deeper. That's our best shot, because anything that would coke u p the coast would be quick moving.

You don't want lower heights over Greenland and the Davis Straight. You want the ridging there and higher heights/high latitude blocking.

Having the PV or a trough there is a +NAO

[TheTrials]

You don't want lower heights over Greenland and the Davis Straight. You want the ridging there and higher heights/high latitude blocking.

Having the PV or a trough there is a +NAO

werd.

[earthlight]

I hope the GFS is right with the pna ridge. It looks really nice.

I have seen too many medium range pattern changes modeled over the last two months to buy into this one right away.

I would like to see it for a few more days -- -!: not see it shift too far west or east or become a transient feature. We also have to watch the Atlantic. If the Atlantic and Greenland are terrible, forget it.

[MJO812]

Agree with you John. We need the NAO to stay near neutral or go negative .

[NaoPos]

You don't want lower heights over Greenland and the Davis Straight. You want the ridging there and higher heights/high latitude blocking.

Having the PV or a trough there is a +NAO

That's what I was saying. I'm not terribly excited about that pattern. Has potential, but it's low probability. I wast too enthused about the lower heights over the NAO regions. I do think the PNA spike is worth watching, but other than that, the overall pattern that weatherX showed on the ensembles isn't too promising. That's my fault if my thoughts were conveyed differently John.

[easternsnowman]

Pattern is not great but better than before and seaonably cold is good enough for snow.

[earthlight]

That's what I was saying. I'm not terribly excited about that pattern. Has potential, but it's low probability. I wast too enthused about the lower heights over the NAO regions. I do think the PNA spike is worth watching, but other than that, the overall pattern that weatherX showed on the ensembles isn't too promising. That's my fault if my thoughts were conveyed differently John.

Sorry - I misread the tone of the post. I read the top where you said "looks good, right?" and got thrown off. Not your fault.

Anyway I still think the pattern can be greatly improved as advertised. But it's certainly better than it has been. At our latitude we definitely need more help from the NAO than our neighbors to the north in SNE. If we want a sustained cold and stormy pattern it's almost a must.

But I think everybody here will deal with a big PNA and take our chances. Super bowl weekend could offer a surprise.

[earthlight]

Synoptically, we can look for amplification on the Pacific side as a saving grace in the mean time. Any Greenland or Davis Straight blocking that has been forecast to develop on all medium range guidance has not developed at all....and at this point I would not be banking on it to develop any time soon. The development of +PNA in the longer term could certainly support the potential for a storm...so long as the NAO region has not completely broken down into another +NAO state. The way it is now..and the way it is forecast to be through the term...is generally neutral...which could give the PNA some extra drive in the pattern.

For example, there may be the potential for trough amplification in the east on Super Bowl weekend. Most ideas haven't worked out so far this meteorological winter when trying to analyze pattern specifics in the medium range...but we are beginning to see most ensemble means indicate a favorably positioned +PNA with a ridge axis near Boise.

As we move forward, we can continue to watch this period for potential amplification out west and a resulting trough on the East Coast. But the amplitude of the trough, the progressive nature of the pattern, and the amount of cold air present are yet to be determined. These are things which are very important to watch as we get closer. If we're looking for a big snowstorm, we're probably going to need more help from the Atlantic side. But the 18z GFS ensembles show a pattern favorable for, at the very least, cold air and the chance for precipitation with shortwaves diving over the top of the Western US ridge.

We have seen the ensembles do this before...so I would urge caution. But as we are getting closer to the event..things are beginning to look more anomalous on all guidance...which can sometimes be a tip off to the validity of the idea. We will see.

[Isotherm]

Couple positive signals I'm seeing with regards to this particular PNA potential, and how it differs from prior periods this winter.

Here's the D 8-10 ECMWF/GFS forecats from back in early December. Note the position of the ridge along/just west of the US coastline, and also the high heights east of Hawaii, weak troughing over Japan.

Now, here's the D 8-10 ECMWF/GFS forecasts for early Feb:

Note in particular the deeper trough over/east of Japan, and the low height field east of Hawaii. If true, this teleconnects to the upper ridge pumping in W US and consequently a downstream trough in the East. The Japan and east of Hawaii signals are usually fairly reliable ones in terms of predicting trough episodes in the Eastern US.

Now, with regards to amplitude. that's a question as well. It does look like the next MJO wave will attempt to dive deeper into phase 6/7, possibly emerging in phase 8 by day 10-15, but I'm not convinced it gets there yet. Regardless, I'm very confident we'll see a pretty robust PNA pulse upwards given the evidence above. The Superbowl period could produce but I actually think the week after that (Feb 5-11) probably has the best potential we've seen so far this winter for something significant in the Northeast.

However, not much cold air to work with. The PNA ridge, although strong, won't get arctic air into the picture b/c we've still got a low height field over both AK and Greenland. No real -NAO in sight also means the temp pattern stays seasonable. So as I posted a few days ago, I still think Feb is seasonable, not a cold month, but not blowtorch either. Our best shot at something wintry is probably from the first to second weekend in February as that PNA pulse propagates eastward and short waves roll around the base of the trough, trying to dig in the East. I'm not expecting anything major due to the NAO state, but I do think this period offers potential for a significant event, which would be our biggest snow of the year.

[kevbo81]

great post isotherm