-PNA,-NAO couplet

[CAD_Wedge_NC]

The LR models are wanting to keep us in a negative PNA and a negative NAO pattern for a while. This type of pattern has some interesting effects on our weather here in NC and the southeast as a whole. Just going off of memory and experience here....but the differences between a +PNA / -NAO couplet and a -PNA / -NAO have notable differences in the storm track for our area. I remember seeing a case study...... I believe it was from Allan's site, where the pattern we are in now favors the eastern / coastal areas for winter storms.

The NAO is negative in both cases. So, let's just focus on the differences in the PNA. During the negative phase of the PNA, you typically have an eastward displaced trough axis due to a fast flow off the Pacific that tries to push against the high lattitude blocking. The results of this are systems phasing to the east of the favored benchmark (that typically being the mouth of the Mississippi river) Therefore, when storms do go negative tilt, they only catch the eastern/southern areas with the precip shield.

Now, in the positive phase of the PNA, the energy off the Pacific is forced to ride up and over the ridge in the west and dive southward toward the gulf. This results in a storm track that is more common with winter storms in the interior SE while eastern/southern areas are too close to the LP track to see much in the way of winter weather.

In my opinion, these next two weeks might just be the best chance that our eastern/southern folks have all winter of seeing a significant winter event.

[shaggy]

The LR models are wanting to keep us in a negative PNA and a negative NAO pattern for a while. This tpye of pattern has some interesting effects on our weather here in NC and the southeast as a whole. Just going off of memory and experience here....but the differences between a +PNA / -NAO couplet and a -PNA / -NAO have notable differences in the storm track for our area. I remember seeing a case study...... I believe it was from Allan's site, where the pattern we are in now favors the eastern / coastal areas for winter storms.

The NAO is negative in both cases. So, let's just focus on the differences in the PNA. During the negative phase of the PNA, you typically have an eastward displaced trough axis due to a fast flow off the Pacific that tries to push against the high lattitude blocking. The results of this are systems phasing to the east of the favored benchmark (that typically being the mouth of the Mississippi river) Therefore, when storms do go negative tilt, they only catch the eastern/southern areas with the precip shield.

Now, in the positive phase of the PNA, the energy off the Pacific is forced to ride up and over the ridge in the west and dive southward toward the gulf. This results in a storm track that is more common with winter storms in the interior SE while eastern/southern areas are too close to the LP track to see much in the way of winter weather.

In my opinion, these next two weeks might just be the best chance that our eastern/southern folks have all winter of seeing a significant winter event.

After this little clipper I can't complain. It was my 4th accum. snowfall in the calendar year for 2010. If we can squeeze out another decent shot at snow in the next few weeks with this pattern then this winter could be a good one also. I don't expect much after the new year but anything we can get before then would be good!

[NC_hailstorm]

Watch the MJO.

It's starting to move again going to phase 4 now and forecated to go to 5 and 6 soon.

Phase 5 has been a warm phase(probably the warmest)in winter as long as I can remember so we should get a warmer spell in 7 to 10 days,it will be interesting to watch if the - AO can still deliver cold though in a moderate LaNina.It's just one piece of the puzzle so we'll see.

Just my opinion.

[SBUWX23]

Watch the MJO.

It's starting to move again going to phase 4 now and forecated to go to 5 and 6 soon.

Phase 5 has been a warm phase(probably the warmest)in winter as long as I can remember so we should get a warmer spell in 7 to 10 days,it will be interesting to watch if the - AO can still deliver cold though in a moderate LaNina.It's just one piece of the puzzle so we'll see.

Just my opinion.

I completely agree with you on the MJO signal. Its something that many people here do not know much about and its not only the phase of the NAO, AO, and PNA that are important.

[NCSNOW]

I'm all for anyone using this thread over the next few days to provide information in regards to winter outlooks and where we are headed, espeacilly Jan/Feb. I can see December is gonna turn out great, atleast right up until Christmas, thanks in large part to all the blocking. All I heard/read was doom & gloom due to La-Nina this fall, and to be honest I was part of the choir singing this chorus. I'm starting to hear rumors or post about JB and some others raising doubts or having cold feet. I already appreciate the previous post. I could have sworn I just read the other day where a poster on the main page was trashing the MJO and it staying in the 1-2 phase or not really becoming a factor anytime soon. The previous poster is right, I have heard 5 is usually a warm signal down the road. Just curious and hopefully others will step in and offer their 2 cents.

[CAD_Wedge_NC]

NC_Hailstorm is right. Not enough credit is given to the MJO. Probably due to the fact that it's not regarded by most as a factor in current local sensible weather. However it is a very good tool for LR pattern forcing.

[NCSNOW]

NC_Hailstorm is right. Not enough credit is given to the MJO. Probably due to the fact that it's not regarded by most as a factor in current local sensible weather. However it is a very good tool for LR pattern forcing.

Totally agree. Also I pinged a post to Robert a week or so ago stating the same thing you posted earlier in this thread. These La-Ninas over the past decade have proven more than once that when the cold does show up, the northern Jet stream tends be over-bearing and really supress the storm track. Probably a good case in point was the clipper like storm we just had Saturday. I know way to little about the MJO and really onl,y pay attention to it LR during tropical season. I'm sure it is as important in having an effect on weather the other 6 months out of year as well. It's really becoming exciting this year in trying to LR forecast (DJ,F) because we have such a unique combination of signals/teleconnections aligned in an arrangement thats uncommon I supose. Obviously the La-Nina is turning out like most thought it would up to this point, But The NAO staying negative the way it has this calendar year is something we haven't had the luxury of the past 10-20 years to my knowledge. If the NAO averages negative the next 85 days, then this would certainly throw a huge monkey wrench in alot of LR forecast I woulld think. It seems we just all bought into the LA-Nina signal,said here we go again and threw in the towel. Should be interetsing to see how this unfolds by early March.

[rduwx]

Totally agree. Also I pinged a post to Robert a week or so ago stating the same thing you posted earlier in this thread. These La-Ninas over the past decade have proven more than once that when the cold does show up, the northern Jet stream tends be over-bearing and really supress the storm track. Probably a good case in point was the clipper like storm we just had Saturday. I know way to little about the MJO and really onl,y pay attention to it LR during tropical season. I'm sure it is as important in having an effect on weather the other 6 months out of year as well. It's really becoming exciting this year in trying to LR forecast (DJ,F) because we have such a unique combination of signals/teleconnections aligned in an arrangement thats uncommon I supose. Obviously the La-Nina is turning out like most thought it would up to this point, But The NAO staying negative the way it has this calendar year is something we haven't had the luxury of the past 10-20 years to my knowledge. If the NAO averages negative the next 85 days, then this would certainly throw a huge monkey wrench in alot of LR forecast I woulld think. It seems we just all bought into the LA-Nina signal,said here we go again and threw in the towel. Should be interetsing to see how this unfolds by early March.

The models are showing a -nao in the future but it looks to me like it is an east based -nao. That's not going to help us as far as storm track is it? We need a west based -nao. This is more of a question than a statement. Is my thinking correct here?

[Nomad]

The models are showing a -nao in the future but it looks to me like it is an east based -nao. That's not going to help us as far as storm track is it? We need a west based -nao. This is more of a question than a statement. Is my thinking correct here?

You are correct. For us in the southeast, a west-based -nao is much preferable to an east-based -nao.

[rduwx]

You are correct. For us in the southeast, a west-based -nao is much preferable to an east-based -nao.

Thanks Nomad. I know a west based -nao is better for us and maybe I wasn't clear w/ my question. If we stay in an -nao in the future I can see where temps could be colder than expected in J-F but if it is an east based -nao it would be more of a cold and dry pattern. Is that correct?

[CAD_Wedge_NC]

You are correct. For us in the southeast, a west-based -nao is much preferable to an east-based -nao.

While I agree with you as far as storm track is concerned....... I remember reading a thread on Eastern a few years back where the east based vs. west based -NAO was argued. Believe it or not, data showed that an east based -NAO was colder in the east. Having said that....a lot depends on how strong the block is, and its' exact location. Bottom line.... I agree. A west based -NAO is preferred (at least in terms of winter storms)