Wednesday, October 22, 2014

Extended Forecast Discussion (Part 1)

This is an extended forecast discussion for the time period of today until approximately one month from today. Due to the length and technicality of this post, there will be multiple parts to this discussion. Today's discussion will focus on the projections for weeks 1 and 2.

We're going to begin with a look at the Atmospheric Angular Momentum readings, or AAM.

ESRL
The image here shows atmospheric angular momentum transport anomalies over the past few months. We want to focus on the anomalies in the top-right corner, the last few days of recording. On this graphic, we see a swath of yellows and oranges seeming to push diagonally upward along the image. Those yellows and oranges define positive AAM transport anomalies, and they are beginning their long-awaited movement to the north, which will throw a big wrench in our weather pattern.

According to the oranges and yellows on the screen, the positive AAM anomaly transport values have made it as far north as about the 40N parallel. Because positive AAM anomalies generally can mean an enhanced jet stream, we might expect high pressure ridging to build northward with time as well, as the jet stream pushes north with the +AAM transport anomalies. This spells a predominantly warm weather period in the next few weeks, as this strong jet stream will eventually make it to the Arctic and keep the Arctic Oscillation (AO), and by extension the North Atlantic Oscillation (NAO) positive. Such a positive AO, which helps induce warm weather, is already on the forecast from the Climate Prediction Center, as shown below.

CPC
The spaghetti-like alignment of red ensemble forecast members above that neutral line suggests the positive Arctic Oscillation phase for the entire forecast period, which extends for 14 days from today.

We're already seeing the effects of the positive AAM transport anomalies in the mid-latitudes, as 250mb zonal winds across the Northern Hemisphere and Southern hemisphere are markedly positive (stronger than normal jet stream) around the 30-60N and 30-60S parallels in each respective hemisphere, per the graphic below.

ESRL
Let's transition for a moment to the tropics.

JMA
The graphic above shows Outgoing Longwave Radiation (OLR) anomalies across the tropics regions, in a global view. Here, we can identify areas of tropical forcing, where enhanced or suppressed convection may be driving or enhancing our weather pattern here at home. Glancing over this image, we do find a swath of negative OLR anomalies, indicating enhanced thunderstorm activity, placed south of India and a bit southwest of the subcontinent as well. This swath of convection has an entirely different meaning for our weather pattern, which will be discussed later on in this discussion. But for now, we'll analyze it as the Madden-Julian Oscillation (MJO).

The MJO states that enhanced or suppressed tropical convection over certain parts of the Equatorial Pacific basin or Indian Ocean can have different effects on the global weather pattern. In this case, when comparing observed negative OLR anomalies in the image above with the Bureau of Meteorology's average negative OLR placement for each MJO phase, we can determine what MJO phase we appear to be in. See if you can figure it out on your own.

BOM
If you guessed Phase 2 into Phase 3, you're right! Phase 2 and 3 MJO events typically see enhanced tropical convection just south of India, very similar to the enhanced tropical convection we're seeing now in that JMA graphic above.

Now that we know what phase we're in, let's see if we can identify how this phase MJO is driving our weather pattern.

Americanwx
The image above shows typical 500mb height anomalies for Phase 3 MJO events in the month of October. Blues indicate stormy and cool weather, while greens, yellows and reds highlight warm and quiet weather. In "normal" October Phase 3 MJO events (the word 'normal' placed in quotes, since no MJO phase is really ever 'normal'), we tend to see high pressure extending from the West US into the Central US, with a swath of negative height anomalies from Greenland to the East Coast. Interestingly enough, we're currently seeing that same scenario play out, though not as defined to the naked eye as you might want it to be. Regardless, we are seeing that progressive ridge formation from the West extending into the Central US, with some stormy East US weather as a result. Though we might not make it to Phase 3 of the MJO, and the MJO isn't the only part of these negative OLR anomalies, we're certainly observing Phase 3-like conditions. Consequentially, if this continues, we might expect a continuation of such warm spells in the next week or so in the US.

ESRL
Going back to the atmospheric angular momentum one last time today, I want to go over the relative AAM values we've seen in recent days. The chart above shows relative AAM anomalies, with greens depicting negative AAM areas and oranges showing positive AAM values. If we look at the bottom panel, we see an average anomaly across the globe of these AAM values, and this is where we want to focus our attention now. In recent days, the AAM has been trending more towards neutral territory, as the AAM was expected to shift into El Nino-like states of high (positive) AAM. Now, however, the AAM has stopped pushing positive, and has leveled off in negative territory. Add to that the AAM tendency is in negative territory once again, and it looks like we'll be more confined to La Nina-like, low AAM stages.

ESRL
AAM Tendency
I'll go more in-depth into this discussion tomorrow, with our Part 2 segment, but here's the first part of the summary for the next two weeks' outlook.

Summary

- Warm weather is expected to continue as MJO Phase 3-like conditions provide a base for ridging in the West, pushing east into the Central US with time.
- This warm weather will also be sustained as positive AAM transport anomalies push north into the mid-latitudes in the next few weeks.

We only got to cover the first week or so in today's post, so weeks 2 & 3 will likely be covered in Part 2.

Andrew

Monday, October 20, 2014

Initial Analysis Suggests Snowy Winter for Midwest, Plains

An initial examination of the conditions observed so far in October indicates we may see a snowy (or at least active) winter in the Midwest and Plains.

ESRL
The first factor going into this idea is one about cyclic weather patterns. The graphic above shows precipitation anomalies from September 20th of this year to as close to present day as I could get, in this case October 18th. Blues and purples correspond to wetter than normal conditions over this time period, while greens and yellows indicate the opposite. According to this image, we've seen the primary storm track set up shop over the Midwest and Great Lakes into the Central Plains, as the stretch of blues and purples show. The North Plains observed dry conditions, as did most of the Eastern Seaboard. The reason I'm discussing precipitation anomalies across the end of September into the first half of October is due to how the new Lezak Recurring Cycle (LRC) looks to be setting up.

The Lezak Recurring Cycle, developed by meteorologist Gary Lezak, states that the weather pattern which develops around October into November may 'repeat' on a steady interval, usually 40 and 60 days between 'cycles'. For instance, if we saw a very strong storm system in early October, and the cycle length was later determined to be around 52 days, we might expect that same piece of energy associated with that October strong storm to return in late November or early December. The same happens with ridges of high pressure, minor storm systems, etc.

Gary Lezak indicated a while ago that we were beginning to morph into the new LRC pattern, so it's quite plausible, if not likely, that the precipitation track in this image may show up again later on in November and early December, possibly bringing some wintry weather along (depending on the synoptic set-up at that time, of course).

WxMaps
The image above shows precipitation total projections for the next week or so on the top panel, precipitation projections for 7-14 days away, and precipitation anomalies for that first week's period. Glancing over the top image, it looks like the storm track is expected to shift north into the Plains in coming days, good news for snow fans in that area for when the LRC repeats later on this year. After that, the long-long range precipitation outlook in the middle panel suggests a return to a Midwest storm track. Today's updated precipitation outlook favors more of a Plains track, but the general idea of a rejuvenated Central US storm track is clear, and is something that will need to be watched closely as the LRC cycles later on in the winter.

To summarize:

- Indications from the Lezak Recurring Cycle currently favor a snowy winter ahead for the Midwest and Plains.

Andrew 

Sunday, October 19, 2014

October 28 - November 1 Potential Storm System

A storm system may impact the US around an October 28 - November 1 time period.

Tropical Tidbits
The image above shows the 500mb height anomaly chart from the ECMWF model, valid on the morning of October 22nd. In this image, we see a weak disturbance forecasted to shift into southern Japan, then following the arrow I placed on this image, as the trough moves northeast. When applying the Typhoon Rule concept, which states weather phenomena that occurs in Japan is replicated in the US about 6-10 days later, a storm system may be expected to affect the nation around an October 28th to November 1st timeframe.

ESRL
The image above shows forecasted anomalies for four different teleconnections. The forecast for the Pacific-North American (PNA) index is shown on the top-left, the North Atlantic Oscillation (NAO) is shown on the top-right, while the West Pacific Oscillation (WPO) and East Pacific Oscillation (EPO) forecasts can be viewed on the bottom-left and bottom-right panels, respectively. If we look at each teleconnection's outlook for the timeframe this storm may affect the US, we see the PNA may be negative, the NAO may be positive, the WPO negative and the EPO negative.

All of that tells me that when/if this potential storm begins to affect the United States, the jet stream may favor a storm track either north into the Plains, or down south along the Gulf Coast. The availability of cold air may vary, as the negative EPO favors cold air in the US, but the negative PNA restricts such cold air. If the storm goes along the South, it'll likely just push out to sea, as the positive NAO won't allow the storm to curve north along the East Coast, like a coastal Nor'easter storm. If it goes north into the Plains, the negative EPO may allow for some snowflakes to fly, but we'll re-examine that potential further on down the road.

Andrew

Friday, October 17, 2014

Long Range Discussion, Concerns About Winter (Part 2)

Today, to wrap up this post, I'll discuss my concerns about the coming winter in conjunction with some of the long range paraphernalia we went over yesterday. You can click here for the Part 1 full post (I highly suggest reading through it).

DMI
The chart above shows observed temperatures in the Arctic, specifically north of the 80th latitude parallel. The red line shows observed temperatures, while the green line displays the average temperature at a given time in the Arctic, allowing us to determine temperature anomalies. The constant blue line depicts the temperature at which water freezes (as this is a Kelvin scale, you chemistry buffs may recognize that freezing number to be 273 degrees K). On this image, we see how during the summer months, temperatures in the high Arctic remained almost completely below normal, though the temperatures were still above 273K. The hope for many was that this below-normal trend would persist into the fall and winter, so cold air would be in abundance come December. However, there's been a change of plans. Arctic temperatures are currently above normal, and have been above normal for nearly the last 100 days straight. That's nothing to shake a stick at. This warmer than normal Arctic air, though it may still be below freezing temperatures, is playing into my worries that cold air might be more scarce than what it typically is in the winter season. This will be discussed more later on.

CPC
The graphic above shows geopotential height anomalies since the middle of this past June. The top panel gives an indication of these geopotential height anomalies on a time-by-height graph, where reds depict positive height anomalies (warm weather, high pressure) and blues indicate negative height anomalies (cold weather, low pressure). Check out that big swath of reds only a few days after the start of October. We saw significant ridging in the troposphere and even into the stratosphere, disrupting the jet stream and sending the Arctic Oscillation plummeting.

Typically, when the Arctic Oscillation is negative, the jet stream becomes very wavy and enables pockets of cold air to be flushed south to lower latitudes. It's not uncommon for North America to see cold weather when the AO becomes negative. In a similar fashion, the jet stream is stronger than normal, and thus not as wavy/broken up during the positive AO phase. This leads to warmer than normal weather.

I want to analyze those first days of October, when the AO went well below normal, as the blue bar graph shows, in conjunction with a storm system that hit during this same timeframe.

HPC
This image shows observed surface conditions on October 3rd, 2014. On this day, we saw a strong storm system pushing northeast into Canada, taking with it heavy rain that had plagued swaths of the Central US in previous days. Noting that the Arctic Oscillation was beginning its freefall into negative territory, and a substantial cold front was in tow of the storm, we were in line to receive our first big cold blast of the season. Right?

Wrong.

That thick blue dashed line, which shows the line between liquid precipitation temperature profiles and snow temperature profiles (fancy ways of saying the 32-degree temperature line) only made it as far south as extreme NW Iowa the next morning. For a pretty hefty storm system, a pretty decent cold front, and a pretty negative AO, that was pretty surprising. Cold air did come south, but not nearly as far south as it should have.

HPC
Let's use another example. This surface analysis chart is from October 14th, showing a strong upper level low beginning to push eastward out of the Midwest. Check out how far north that warm front is. We have to look to northern parts of Manitoba and Saskatchewan to find that thick dashed blue freezing line! Sure, this was a closed low in the upper levels, which typically don't support such sweeping cold blasts like the first example storm does, but still; we should see freezing temperatures at least near the US/Canada border at this point of the season.

The reason why I'm worried about what's happened the last few weeks for this winter, is because our winter pattern is setting up right before our eyes.

The Lezak Recurring Cycle appears to be setting up its new components for the 2014-2015 winter season. While many in the Midwest should be excited that October's been a very wet month (that is, if you are a snow fan), the cold air is what I want to discuss. The lack of cold air now could mean a lack of cold air this winter, especially given the warmer than normal Arctic temperatures.
"But wait! Last October, the temperatures in the East US were warmer than normal, while the West was cold, and the following winter turned out to be exactly the opposite!" That's correct. However, take a look at the SST anomalies from October, and you'll see where that set-up came from.

ESRL
October 2013 SST anomalies
In the month of October 2013, we saw below normal sea surface temperature anomalies across the Gulf of Alaska, with the closest warmth displaced due south of the Aleutian Islands. These anomalies changed in time for winter, with well above normal SST anomalies evolving in the Gulf of Alaska. That's how we ended up with such a cold winter.
"The SST anomalies in the Gulf of Alaska are still well above normal, so we're in for another cold winter!" Not so fast.

ESRL
This graphic shows weekly sea surface temperature anomalies from October 5th to the 11th, 2014. I used a world-wide view here to better show what's happening in the West Pacific this year. In the Gulf of Alaska, we do still see intense warmth with those positive SST anomalies. But take a look at the waters east of Japan. In a flip from last year at this time, rather than a tongue of warm water anomalies pushing east, we now see a tongue of cold water anomalies pushing east.

The daily SST anomalies from today (October 16th) are far more sobering.

ESRL
Just like last year, but now flipped, we're seeing the SST anomalies from the West Pacific propagate into the East Pacific. Last fall, the warmer than normal anomalies transferred into the Gulf of Alaska to allow for a cold winter. This fall, colder than normal SST anomalies are transferring to the Gulf of Alaska. The consequences are yet to be seen, but I'm worried that cold winter prospects are on the fall.

Ridging over the Gulf of Alaska has been pretty consistent in the last 9-12 months or so. As a result, many believe this theme will persist, and will allow the warmer than normal Gulf of Alaska SST anomalies to stay put.

Unfortunately, that's not popular opinion anymore.

PSU
The chart above shows a mean 500mb height anomaly forecast from the GFS ensemble members, displayed by the big panel in the top-center. In this panel, warm colors translate to ridging/high pressure, resulting in warmer than normal conditions. Cool colors indicate troughing/low pressure, equalling stormy and cold weather. The small panels show individual 500mb contour forecasts for the given forecast time, in this case set at 12 hours out. In 12 hours (valid this evening), model guidance has a strong trough pressing into the Gulf of Alaska, something that's likely to happen quite a bit in the future (I'll discuss that later). You can bet that this stormy pattern in the near future won't help those warm water anomalies stay in the Gulf of Alaska. In fact, it would be logical to expect further cooling of the water temperatures in that region, as these storms move through.

PSU
But it doesn't stop there. The same forecast parameter from the GFS ensembles, now valid about 5 days from today, shows another strong trough placed squarely over the Gulf of Alaska. What do we see happening as a result in North America? A massive ridge of high pressure and warmth, except for the closed low in the Northeast. You get the picture by now- the medium range has a very stormy Gulf of Alaska, something that's likely to continue cooling the water temperatures there, further lowering the risk for a cold winter (talk about a change of thinking for the winter, huh?).

If this forecast comes true, as with the storm systems we discussed earlier, the very warm pattern outlooked due to the troughing in the Northeast Pacific may return in the LRC cycle this winter.

I briefly mentioned how this theme of a stormy Gulf of Alaska may continue into the future, so let's take time to examine that.

NOAA
This graphic shows typical atmospheric responses to the El Nino phenomenon, when warmer than normal water temperature anomalies surface in the waters just west of Ecuador. Note how the typical El Nino sees a stronger than normal Pacific Jet Stream, bringing the storm track into the South US with highlighted 'wet' conditions. We then see the Polar Jet Stream pushing south into southeast Canada after having to push north in response to warm weather. In the middle of these two jet streams, what do we find? That's right, persistent low pressure in the Gulf of Alaska. As we head into an expected El Nino this winter, this sort of pattern may appear more frequently.

It's not all good news for warm winter fans, however.

Rutgers
The image above shows snow cover anomalies over the Northern Hemisphere as of October 16th. In this image, focusing on Eurasia, we see well above normal snow cover over Russia. Some of you weather enthusiasts may be familiar with the work of Judah Cohen, who came up with the concept of the Snow Advance Index, or SAI. In a nutshell, the SAI says that if snow cover advancement during the month of October in a specific portion of Siberia is above normal, the Arctic Oscillation is then expected to be below normal for the following winter, and vice versa.
So far this month, snow cover has been well above normal, more-so than in recent years, in fact. The big question is, will this snow cover advancement continue? If it stops its progress right now, and doesn't increase for the rest of October, the big snow growth in early October will be moot, and the cold winter idea will once again be in jeopardy, more than it may be now. For the time being, however, this is a good sign for a cold winter ahead.

The above image shows anomalies of the October Pattern Index over the last several days, since the start of October. The OPI, the concept of which was brought about by a group of Italian scientists, says that monitoring of the atmosphere during the month of October can yield great hints at what the coming winter will bring. October is a month well-known for big winter-predictors showing their cards for the coming cold season (i.e. the LRC, and Judah Cohen's Snow Advance Index (SAI)), but it may interest many to know what the OPI may be one the best, if not the best up-and-coming predictor of the upcoming winter season out of the three mentioned above.

We've seen the OPI sustained completely in below-normal territory for the month of October thus far. For winter weather fans, that's an incredibly encouraging sign; verification for the OPI ranges around 90%. When the OPI is negative, the following winter may be expected to be cold and stormy. The opposite result may be observed when the OPI averages positive. We have yet to see what the OPI will do for the remainder of October, but this is a healthy sign of a cold winter ahead.

Concerns About Winter Summary

- Arctic temperatures are warmer than normal, which may limit cold air availability this winter.
- Even though the Arctic Oscillation was strongly negative, cold air still was not observed in force in North America. This raises the concern of the winter not seeing persistent cold air.
- Water temperatures in the Gulf of Alaska are cooling, which, if continuing through the fall into winter, may allow for cold weather possibilities to diminish.
- Stormy conditions are expected in the near future in the Gulf of Alaska, likely further cooling those warm SSTs.
- Such a stormy pattern in the Gulf of Alaska may persist due to the El Nino set-up in the atmosphere.
- Despite these factors, there are still components in favor of a cold winter.

All in all: I'm worried that the risk for a cold winter is on the fall.

Andrew

Thursday, October 16, 2014

Long Range Discussion, Concerns About Winter (Part 1)

Update: Click Here for the new Part 2 Post (ideally read after reading this post).

Today, we'll go over the latest outlook for the long range, and go over some new concerns I have about the coming winter. This is the first post of the two, dealing with the long range forecast portion. The winter concern post will come out tomorrow.

Let's first discuss the Global Wind Oscillation and Atmospheric Angular Momentum (GWO and AAM) concepts.

ESRL
The image above shows anomalies of the relative atmospheric angular momentum (AAM) since this past July to the present day. The image looks pretty complicated, and in reality it is, so we'll avoid any extremely difficult parts. In essence, positive AAM values can indicate enhanced areas of the jet stream, while negative values may indicate a weakened jet stream. As an example, take a look at the green swath around the 60N parallel in the first days after October. This green tells us of negative AAM anomalies in the area, so let's see if we can identify a cause behind it.

CPC
The graphic above shows geopotential height anomalies since the middle of this past June. The top panel gives an indication of these geopotential height anomalies on a time-by-height graph, where reds depict positive height anomalies (warm weather, high pressure) and blues indicate negative height anomalies (cold weather, low pressure). Check out that big swath of reds only a few days after the start of October. We saw significant ridging in the troposphere and even into the stratosphere, disrupting the jet stream and sending the Arctic Oscillation plummeting. As the jet stream significantly weakened with the ridging pushing through, the AAM reflected appropriately a negative AAM.

The overall AAM anomaly is shown by the bottom panel, and we can see how the AAM has been negative lately. However, it's been rising in recent days.

ESRL
The image above now shows the tendency of the AAM; among other things, it tells us whether the AAM wants to be in positive or negative territory. Lately, the AAM tendency has been in a positive state, and this is likely what the rising relative AAM is caused by. The tendency will take on a more significant role later on in this post.

ESRL
Take a look at the graphic above. Pretty complicated, right? Not quite. In the bottom left and right corners, as well as the top left and right corners, we see descriptions for regions that see convection in various stages of the Global Wind Oscillation (GWO). Phase 3 sees Indian Maritime convection, while the Dateline region observes tropical thunderstorms in Phase 5, and so on. More experienced weather junkies may realize these denotations are actually juxtaposing the Madden-Julian Oscillation (MJO) onto this GWO description.
As for the GWO itself, it does have eight phases, as the chart above entails. From another source in the ESRL, the GWO has been allotted into four primary phases. I've copied and pasted the four phase descriptions below:

The four primary phases of the GWO are described below, along with generally cold season (November-March) probable weather impacts for the USA. The GWO recurrence interval, or "time it takes to make a circuit", ranges from a broad 15-80 days. Two of the stages project strongly on El Nino and La Nina circulation states, which are also characterized by positive (Stage 3) and negative (Stage 1) global AAM anomalies, respectively.  Stages 2 and 4 are transitional.

Stage 1 (La-Nina like) – the global relative AAM anomaly is negative. The negative anomaly is primarily due to easterly upper level wind anomalies that extend from the Eastern Hemisphere tropics to the Western Hemisphere mid-latitudes. A retracted Pacific Ocean jet stream is a key feature in the total field.  Troughs are probable across the western USA with a ridge over the southeast.  High impact weather is favored across the Plains.

Stage 2 – the global relative AAM tendency is positive. This means that negative AAM is being removed from the atmosphere by surface friction and mountains. At the same time, westerly wind anomalies are intensifying in equatorial regions of the Western Hemisphere. Fast Rossby wave dispersion events in both hemispheres are a coherent feature of this stage and Stage 4.  A cold regime is probable across the central USA.

Stage 3 (El-Nino like) – the global relative AAM anomaly is positive. Westerly wind anomalies move into the Eastern Hemisphere, broaden in latitudinal extent and link up with deep westerly flow anomalies over the mid-latitude Western Hemisphere. An extended Pacific Ocean jet stream and southward shifted storm track is observed  favoring high impact weather events along the USA west coast.

Stage 4 – the global relative AAM tendency is negative. Positive (westerly) AAM anomalies are being removed by surface friction in the Western Hemisphere mid-latitudes and through mountain torques across the Northern Hemisphere topography. The next phase of the oscillation (if there is one) is represented by easterly wind anomalies intensifying over equatorial regions of the Western Hemisphere. This stage has enhanced subtropical jets and closed lows in the subtropics favoring rainfall events over the southwestern USA.
'Woah! Slow down! I don't know what this means!' is probably what some of you are thinking right now. Let's cut out the complicated parts and focus our attention on the underlined phrases above. In each stage, there's a description about the AAM and AAM tendency. We know what those mean, after discussing them above, so let's put it to use. Right now, the relative AAM is negative and the tendency of the AAM is positive. If we match that up with the underlined phrases, we find ourselves in a Stage 2 set-up, with the negative relative AAM described in Stage 1, but the positive AAM tendency described in Stage 2. Doing a quick evaluation, when we account for the fact that El Nino-like anomalies (Stage 3) are shown by high GWO values (Phases 5-8), and La Nina-like anomalies (Stage 1) display themselves in low GWO phases 1-4, we can estimate the GWO to currently be around Phase 3 or 4, given how Stage 2 (where we are now) is in between the high and low GWO phases.

As if that wasn't confusing enough already, we can actually forecast the AAM in the future!

ESRL
The graphic above now shows transport of the AAM. As if there aren't enough ways to examine the AAM, the transport of the AAM can allow us to delineate how AAM anomalies are making their way to the upper latitudes; I've drawn two arrows to illustrate this above. Notice how we currently see decently-strong positive AAM transports pushing northward. This tells us that we can expect a strengthening jet stream in the near future (if we recall positive AAM shows a strong jet stream), something confirmed by the forecast of the Arctic Oscillation, as we see below.

CPC
Ensemble members have the Arctic Oscillation pushing positive, something I wouldn't be surprised to see with the positive AAM transports in coming days.

-----------

Let's take a step away from the AAM now and move on to other long range factors.

PSU
The graphic above shows a 500mb mean height anomaly forecast from the combined GFS ensemble members, with individual ensemble member height contours shown in the smaller panels. On this graphic, valid for 60 hours out, we can see a strong trough dropping into the Gulf of Alaska, as the deep blue colors indicate. A small cut-off low occupies the Southwest, with a weak ridge persisting in the Plains. A trough is on its way to the Atlantic, as seen in the Northeast in the graphic above.
If you were to examine a loop of the forecast from these GFS ensembles, you would see several bursts of ridging in the West and Central US that initially appear strong, but quickly weaken and push east. If you're a close reader, you'll take a look at the description of the GWO Stage 2 and realize that these quick-dissipating ridges are actually the 'Fast Rossby Wave dispersion events'.

The atmosphere's just one big web of connections and correlations...

PSU
Fast forwarding to the GFS ensemble height anomaly forecast valid 264 hours out, we now see that Gulf of Alaskan troughing has pushed east into the West Coast, thanks to sustained ridging in the Bering Sea. As such, the ridging previously in the West/Central US is now finding a home further east, in the Plains. The New England region is seen basking in below-normal temperatures with the negative height anomalies.
Take a look back at our AAM section and give Stage 3 a look. As I had indicated, we're forecasted to head into positive AAM territory, which is the equivalent of Stage 3 in the GWO. Note how the Stage 3 description tells of an extended Pacific Jet Stream, as well as high-impact weather events in the West US. It's no mistake that the long range GFS ensembles are showing a stormy West Coast, fitting in with that Stage 3 description.

I'll use these forecast images again in tomorrow's Part 2 post, which will go over my concerns about next winter; my post here is already too long to extend it into the second topic.

Tropical Tidbits
Let's give our brains a break and use some of our simpler tools in the long range. The image above shows the ECMWF 500mb height anomaly forecast over the Western Pacific, valid this morning (Thursday). Note the trough digging into Japan. Using the Typhoon Rule and 6-10 day correlation, we can expect a stormy period in the US 6-10 days from today, in an October 22nd to 26th period.

Tropical Tidbits
But all's not well that ends well, winter weather fans. The graphic above shows the same ECMWF height anomaly forecast in the West Pacific, now valid for 10 days out. We see a massive - emphasis on massive - ridge forecasted to cover the eastern part of Asia, including over Japan. If this forecast comes to fruition, we might expect to see a prolonged period of significant warmth in the November 1st to November 5th timeframe. Again, that's if this comes to fruition.

JMA
One final piece concerning this forecast. I mentioned the Madden-Julian Oscillation (MJO) earlier in this post, and wanted to discuss it for a moment. In the image above, we see Outgoing Longwave Radiation (OLR) anomalies in the color shadings, with 200mb velocity potential contours and divergence with the arrows. Negative OLR anomalies indicate stormy weather, and are displayed as blues on this graphic. Oranges depict positive OLR anomalies, highlighting quieter than normal tropical convection. Notice how the strongest divergence is located just west of South America... and it doesn't even appear to be focused along the Equator! This tells us that although tropical forcing is strongest in the Western Hemisphere, the MJO is anomalously weak, as it has been for the last several weeks, per the graphic below.

CPC
40 day observed MJO
The MJO isn't expected to be a significant factor now or in the near future, per model forecasts.

Long Range Forecast Summary

- The AAM is expected to shift to positive in coming days, as the AAM tendency remains positive and positive AAM transports are pushing to the upper latitudes.
- Due to the positive AAM occupying the upper latitudes, strengthening of the jet stream is expected. This will result in a positive AO, and thus warmer weather.
- The GWO is expected to push into Stage 3 with the positive AAM, which will allow an El Nino-like set-up to evolve. Stormy weather in the West US, with warmth in the Central can be expected in coming weeks.
- East Asian signals tell us of a brief stormy period to end October, with potential significant warmth to start November.

Remember to look for Part 2 tomorrow afternoon!

Andrew