Typhoon Wipha and a major North America pattern change

[OKpowdah]

We're watching another potential major Typhoon recurving in the West Pacific, passing close to Japan by day 4 (Tuesday night ET).

 

The story begins though with just some simple extratropical cyclogenesis in the northern Sea of Japan and the amplification of downstream ridging. This ridge eventually breaks as it pinches another downstream disturbance, and then bridges with ridging over the eastern Pacific. The favored superposition of negative PV anomalies develops a very strong ridge on the west coast of North America toward Alaska.

 

As Wipha recurves, distributing upper level latent heat and negative PV downstream, we see a huge WPac ridge form, and a rapid acceleration of the jet. On the poleward exit side of the jet, another extratropical system rapidly intensifies near the Aleutians. As the huge ridge breaks, all the cyclonic vorticity on the poleward side of the jet gets dumped into this system over the Aleutians, forming a pretty stable trough over the North Pacific.

 

Day 5-9 (17th-21st): And so now we have the very distinct pattern of a large trough over the Aleutians and blocking ridge over western North America. As you might imagine, this could have some interesting implications over central and eastern North America, with a negative NAO in place over the north Atlantic. At the very least a period of below normal temperatures, and  an opportunity for snow in the Midwest.

 

 

 

 

 

 

 

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[Ginx snewx]

Check out my post in the WPAC tropical thread, this is not only a recurving TC it is a monster recurving TC size wise. A real pattern influence, great post Sam

[OKpowdah]

Check out my post in the WPAC tropical thread, this is not only a recurving TC it is a monster recurving TC size wise. A real pattern influence, great post Sam

 

True! It's a beast of a storm. Means a heck of a lot of LHR.

 

http://www.goes.noaa.gov/FULLDISK/MTIR.JPG

[Ginx snewx]

See WPAC thread

[Geos]

Great post OkPowdah!

[cny rider]

Thanks and a question from a relative newb.

You wrote:  As Wipha recurves, distributing upper level latent heat and negative PV downstream......

 

Can you explain why this is negative PV, not positive?  I think I am having trouble understanding that concept.

Thank you.

[OKpowdah]

Thanks and a question from a relative newb.

You wrote:  As Wipha recurves, distributing upper level latent heat and negative PV downstream......

 

Can you explain why this is negative PV, not positive?  I think I am having trouble understanding that concept.

Thank you.

 

Sure. So as we're interested in the upper level pattern, we're looking at potential vorticity in the top half of the atmosphere, and especially at the tropopause.

 

Hurricanes are warm core lows. By the relationship between temperature and thickness between pressure levels, this means the low weakens with height, and you actually have an upper level anticyclone at the top of the hurricane (note you can see anticyclonic outflow in the cirrus shield on satellite loops).

 

There are two components to potential vorticity: Vorticity obviously, and vertical stability. A stable environment (relatively warmer air above colder air) has higher PV (think of it as greater potential to stretch the column and create higher vorticity).

 

In hurricanes, first of all the warm core means that the column is less stable near the tropopause (above which becomes very stable in the stratosphere). So combined with the anticyclonic vorticity, there is a significant negative PV anomaly at the top of a hurricane.

 

PLUS, then with huge latent heat release in the upper half of the column, this destroys PV through that same stability relationship. So the system works together in supporting this negative PV at the top of the troposphere, which when advected outward by strong divergent winds aloft, can significantly amplify synoptic scale ridging downstream.

[cny rider]

Thank you.

[Met1985]

Great post about what could come down the road and what this might mean for us in the East. Again great read.

[LocoAko]

Nice stuff, Sam.

[Mike.Ventrice]

Thanks Sam,

 

Been watching this very closely. This happened last week and caused a huge drop in model skill performance, as the models flipped their predicted pattern by 180 degrees. This caused many models to perform poorly in the medium range, as shown in the plot below.

 

 

 

The models are showing this TC-extratropical interaction nicely, but it still worries me there could be some downstream errors translated across the U.S. I'm still in favor of the pattern shift, and have been for awhile.

[Drz1111]

Has anyone done a spectral analysis of that correlation plot? It looks for all the world that there's some periodic signal in there.  It would be interesting to know what it is, and then what happens semi-regularly that the models are missing....

[CoastalWx]

The pattern change and bad model performance started with that piece of energy cutting off NE of Hawaii as Sam noted. Now you get a REX block and a feedback with the Aleutian low in a happy place. Throw some TCs in and add to the fun.

[bluewave]

We have seen a tendency for stronger North Pacific blocking this year compared to the last 3 years to date.

 

 

[OKpowdah]

You can see the effect of the recurving TC nicely in this hovmoller of meridional wind (averaged 30-60N) forecast from GFS.

 

The effect of a recurving TC can be seen in the group velocity (so basically the wave envelope that amplifies the wave pattern). So when the phase pattern change is already in motion thanks to extratropical interactions in the central and eastern Pacific, the recurving TC basically acts to reinforce and to increase the amplitude of the wave pattern. At the same time producing a more stable blocking pattern than would've been.

 

Note where/when the wave pattern amplifies (right where Wipha is tracking) and how that envelope moves downstream, with a huge ridge anchored near 140W (east Pac) and the trough axis near 270W (Midwest).

 

[OKpowdah]

Thanks Sam,

 

Been watching this very closely. This happened last week and caused a huge drop in model skill performance, as the models flipped their predicted pattern by 180 degrees. This caused many models to perform poorly in the medium range, as shown in the plot below.

 

The models are showing this TC-extratropical interaction nicely, but it still worries me there could be some downstream errors translated across the U.S. I'm still in favor of the pattern shift, and have been for awhile.

 

Somebody shared this a few hours ago on listserv. At day 5 and day 6 there was some huge spread in the 500mb heights in the 6z GEFS. This is actually very similar to the cases that I see in ECMWF busts over Europe, where there's active wave activity interacting with a blocking pattern, and the error/uncertainty grows near the block, but further downstream the forecast is less affected.

 

The only situation I see, and I mentioned this in the New England subforum, is with that disturbance undercutting the ridge on the subtropical jet. Something to watch.

 

 

 

[Lorenzo]

Great post, that monster ridge all over the model output this morning. This at 216hrs on the ECM 00z.

 

 

Also with respect to this pattern, potential impacts on the stratosphere, where already there is some Wave 1 Activity filtering down. Last year the main hemispheric ridge feature developed over the Siberian Kamchatka peninsula and dictated everything. Looks like this one will do the same.

[HM]

 

Also with respect to this pattern, potential impacts on the stratosphere, where already there is some Wave 1 Activity filtering down. Last year the main hemispheric ridge feature developed over the Siberian Kamchatka peninsula and dictated everything. Looks like this one will do the same.

 

Thanks for the post and greetings from the West. The heat flux (and now momentum flux, even, with poleward EP vectors) is already underway with a classic tropospheric pattern in-place for successful upwelling. Throw in the poleward subtropical u=0 line and excess low-mid strat ozone and we've got a winter-like disturbance coming. Despite all of these events, I think the PV will have no problem organizing, like it usually does this time of year, and becoming even anomalously strong next month. I'm not sure if you agree; but, I can understand if you don't, given the conflicting signals.

[CoastalWx]

You can see the effect of the recurving TC nicely in this hovmoller of meridional wind (averaged 30-60N) forecast from GFS.

 

The effect of a recurving TC can be seen in the group velocity (so basically the wave envelope that amplifies the wave pattern). So when the phase pattern change is already in motion thanks to extratropical interactions in the central and eastern Pacific, the recurving TC basically acts to reinforce and to increase the amplitude of the wave pattern. At the same time producing a more stable blocking pattern than would've been.

 

Note where/when the wave pattern amplifies (right where Wipha is tracking) and how that envelope moves downstream, with a huge ridge anchored near 140W (east Pac) and the trough axis near 270W (Midwest).

 

Screen Shot 2013-10-14 at 2.59.03 PM.png

 

Look at how those meridional anomalies stay in place (don't really move much in longitude) yet other anomalies across the globe have that propagation east. That's going to cause some model fun.

[CoastalWx]

Thanks for the post and greetings from the West. The heat flux (and now momentum flux, even, with poleward EP vectors) is already underway with a classic tropospheric pattern in-place for successful upwelling. Throw in the poleward subtropical u=0 line and excess low-mid strat ozone and we've got a winter-like disturbance coming. Despite all of these events, I think the PV will have no problem organizing, like it usually does this time of year, and becoming even anomalously strong next month. I'm not sure if you agree; but, I can understand if you don't, given the conflicting signals.

 

What makes you so sure? Other than the QBO, curious of the  forcing mechanism to bring back a big PV..but of course heights in that area probably will lower from natural ebb and flow anyways, I doubt that pig ridge lasts all season....although the new Euro SIPS is tasty.

[Lorenzo]

HM -would be interested to know why you are thinking 'anomalously' strong, appreciate your expertise on this subject and welcome the ideas.

 

Am sure it is due a cold and vortexy episode due the the bashing around from earlier in the year, still that Aleutian low is looking well developed again so as you say mixed signals. Would be happy to see it ramp itself up very quickly only to have a big split later in the season.

[HM]

 

What makes you so sure? Other than the QBO, curious of the  forcing mechanism to bring back a big PV..but of course heights in that area probably will lower from natural ebb and flow anyways, I doubt that pig ridge lasts all season....although the new Euro SIPS is tasty.

 

The waves, while impressive, have nudged the "radiative-beginning" stages of a rapidly cooling vortex into the coldest part of the NH. The first disturbance came before the mid-level portion of the vortex even formed (quite unusal). In January that's fine and the same signal would mean a weakening NAM, but in October it will just allow parcels to radiatively cool much faster than if the vortex was just in climo-position (it is going to continue to rapidly cool this time of year and parcels are sitting/moving over Siberia more than normal). The MMC-tropical forcing will also become unfavorable soon and help force alignment from mesosphere down once we move into early November, aided by the QBO. The possibility of a wave 2 response is there but it still is October and it will succumb to the same fate as the wave 1 response (if not even weaker).

If it wasn't for the "near El Nino" last year (led to more ozone availability), subtropical u=0 line and bouts of strengthening MMC this year, I would be calling for a wall-to-wall warm/positive AO winter. These features will help to put a lid on that potential, most likely.

 

HM -would be interested to know why you are thinking 'anomalously' strong, appreciate your expertise on this subject and welcome the ideas.

 

Am sure it is due a cold and vortexy episode due the the bashing around from earlier in the year, still that Aleutian low is looking well developed again so as you say mixed signals. Would be happy to see it ramp itself up very quickly only to have a big split later in the season.

See above of course but yes the Wave 1 - Aleutian Low - response has been amazing. It has prompted the CPC analogs to list some rather impressive winters too, cold-wise. The problem is that you better have a good reason to suspect this feature will stick around. In most of the CPC-analog years listed, they certainly did have a good reason. Why would a typhoon-aided, convective/oceanic KW-aided, El Niño-like period in October (with residual W PAC walker uplift, intensifying the MMC further) stick around into the winter?

[NJwinter23]

Great discussion. For what it's worth, we are clearly seeing a strengthening +AO being modeled for days now entering Novy , it appears to be well in-line with the stratosphere forecast. Siberian snow is also slipping quite a bit here mid-month, but that can still recover in the next (most crucial) 2 weeks.

[CoastalWx]

The waves, while impressive, have nudged the "radiative-beginning" stages of a rapidly cooling vortex into the coldest part of the NH. The first disturbance came before the mid-level portion of the vortex even formed (quite unusal). In January that's fine and the same signal would mean a weakening NAM, but in October it will just allow parcels to radiatively cool much faster than if the vortex was just in climo-position (it is going to continue to rapidly cool this time of year and parcels are sitting/moving over Siberia more than normal). The MMC-tropical forcing will also become unfavorable soon and help force alignment from mesosphere down once we move into early November, aided by the QBO. The possibility of a wave 2 response is there but it still is October and it will succumb to the same fate as the wave 1 response (if not even weaker).

If it wasn't for the "near El Nino" last year (led to more ozone availability), subtropical u=0 line and bouts of strengthening MMC this year, I would be calling for a wall-to-wall warm/positive AO winter. These features will help to put a lid on that potential, most likely.

See above of course but yes the Wave 1 - Aleutian Low - response has been amazing. It has prompted the CPC analogs to list some rather impressive winters too, cold-wise. The problem is that you better have a good reason to suspect this feature will stick around. In most of the CPC-analog years listed, they certainly did have a good reason. Why would a typhoon-aided, convective/oceanic KW-aided, El Niño-like period in October (with residual W PAC walker uplift, intensifying the MMC further) stick around into the winter?

Yep, agree with your last thoughts. It's a temporary driven pattern for sure. Thanks for the comments. I made some points in our subforum about lower heights near AK as well, but I couldnt tell you what would happen post November. I feel like there are a multitude of thoughts right now.

[Lorenzo]

 The waves, while impressive, have nudged the "radiative-beginning" stages of a rapidly cooling vortex into the coldest part of the NH. The first disturbance came before the mid-level portion of the vortex even formed (quite unusal). In January that's fine and the same signal would mean a weakening NAM, but in October it will just allow parcels to radiatively cool much faster than if the vortex was just in climo-position (it is going to continue to rapidly cool this time of year and parcels are sitting/moving over Siberia more than normal). The MMC-tropical forcing will also become unfavorable soon and help force alignment from mesosphere down once we move into early November, aided by the QBO. The possibility of a wave 2 response is there but it still is October and it will succumb to the same fate as the wave 1 response (if not even weaker).

If it wasn't for the "near El Nino" last year (led to more ozone availability), subtropical u=0 line and bouts of strengthening MMC this year, I would be calling for a wall-to-wall warm/positive AO winter. These features will help to put a lid on that potential, most likely.

 

See above of course but yes the Wave 1 - Aleutian Low - response has been amazing. It has prompted the CPC analogs to list some rather impressive winters too, cold-wise. The problem is that you better have a good reason to suspect this feature will stick around. In most of the CPC-analog years listed, they certainly did have a good reason. Why would a typhoon-aided, convective/oceanic KW-aided, El Niño-like period in October (with residual W PAC walker uplift, intensifying the MMC further) stick around into the winter?

 

HM, Thanks again, great response, liked the sentence above, too many questions ! Still learning about the feedbacks associated between all the different features. MMC / subtropical u=0 line - not an acronyms I am familiar with.

 

I was interested to read the abstract in this paper from May as it creates another layer of interest. Tropospheric pre-cursors and now focused on also the mesosphere.

This is the first work to show that all major Sudden Stratospheric Warmings (SSWs) over the 20.5 year data record are preceded by USLM disturbances.

http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50289/abstract

 

The annual Strat. thread opened this week on netweather in UK, http://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/ wonder if there will be a similar one here? Sorry if this has gone off on a tangent from the original post re Wipha , Francisco however also looking potent for next couple of days.

[metagraphica]

Now that Wipha has recurved does anyone have thoughts on how Fransisco is going to effect all of this interaction?

[OKpowdah]

Now that Wipha has recurved does anyone have thoughts on how Fransisco is going to effect all of this interaction?

 

Reinforces the pattern over the north Pacific. 

 

Huge jet amplification, with cyclogenesis in the poleward exit region. Basically as long as we get these jet amplifications, we'll get significant cyclogenesis near the Aleutians, reinforcing the upper level trough there as well as the downstream ridge from the eastern Pacific to the west coast of North America.

 

 

Supported by current long range model forecasts, this particular recurvature may lead to at least a temporary unleashing of the arctic around the end of the month.

[Geos]

I take it Lekima will reinforce this pattern as well...? Track maps show it heading NW.

[phil882]

I take it Lekima will reinforce this pattern as well...? Track maps show it heading NW.

 

More or less... it won't be quite as direct of an impact as the ET of Francisco which is driving the Rossby Wave Train amplification, but the poleward -PV advection from the outflow of Lekima should only further enhance the polar jet. Both the ECMWF and GFS as a result show a reloading of the cold in the day 5-7 period across the Midwest as the wave packet resulting from this jet streak amplification swings into North America. 

 

I've made a quick animation below that shows the propagation of this wave packet. If you notice, the energy doesn't move at the phase velocity (the speed of individual rossby waves). Instead the wave packet created by the jet amplification due to WPAC TCs travels at the group velocity (which is double the phase velocity), and this serves to amplify individual rossby waves along the waveguide.

 

Thus, ET just off  the coast of Japan tends to reinforce a pattern that favors trough amplification and surface cyclogenesis in the Aleutian islands, subsequent ridgebuilding over far western North America, and finally general troughing over the eastern US. Of course the magnitude of individual events varies, but you can see now how recurving Typhoons have a direct teleconnection to our weather downstream.

 

[OKpowdah]

More or less... it won't be quite as direct of an impact as the ET of Francisco which is driving the Rossby Wave Train amplification, but the poleward -PV advection from the outflow of Lekima should only further enhance the polar jet. Both the ECMWF and GFS as a result show a reloading of the cold in the day 5-7 period across the Midwest as the wave packet resulting from this jet streak amplification swings into North America. 

 

I've made a quick animation below that shows the propagation of this wave packet. If you notice, the energy doesn't move at the phase velocity (the speed of individual rossby waves). Instead the wave packet created by the jet amplification due to WPAC TCs travels at the group velocity (which is double the phase velocity), and this serves to amplify individual rossby waves along the waveguide.

 

Thus, ET just off  the coast of Japan tends to reinforce a pattern that favors trough amplification and surface cyclogenesis in the Aleutian islands, subsequent ridgebuilding over far western North America, and finally general troughing over the eastern US. Of course the magnitude of individual events varies, but you can see now how recurving Typhoons have a direct teleconnection to our weather downstream.

 

That's a really great animation showing the propagation of the wave packet.

 

You can see it showing up well in the hovmoller

 

Pattern influence aside, it's interesting to see how Francisco and Lekima interact by day 5-6 northeast of Japan.