Major Thanksgiving Storm Will Be Diverted Offshore

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The major Thanksgiving storm that I made the call for a couple days ago will still happen- however, now the storm system will be forced offshore thanks to a positive NAO.

(Originally published November 10)This is a 500mb height anomaly forecast, valid a few days out. As you can see, there isn't much going on in the United States, so why am I showing you this? Well, we have to go to East Asia for that answer. If you look in the top left corner of the image, you will see a strong trough present in East Asia. It has been shown that there is a 6-10 day gap between what happens in East Asia and what happens in the East US. So, if we use this forecast (valid November 13) and apply the 6-10 day gap to it, we end up at November 22, or a day or two from Turkey Day.

We can also use the Lezak Recurring Cycle (LRC), which is, in the simplest of simple explanations, a repeating pattern that forms every fall and cycles through the winter. This pattern first forms in September-October. A strong storm system hit the Plains, Midwest and Great Lakes on October 2. If we use the expected 51 day gap between each cycle and add on a day or two to give the forecast a little wiggle room, we find this strong storm system hitting the Midwest/Great Lakes on November 21-23, which falls right on Thanksgiving!

However, this storm system will miss the United States. You see, while East Asia will be correct in a major storm hitting the East Coast, a positive NAO will get in the way of this system actually getting close to land. When you have the North Atlantic Oscillation (NAO) in a positive state, the jet stream is diverted east out to sea for storms that ride the Gulf Coast and are known as Nor'easters when the actually go up the East Coast (commonly seen in a negative NAO).

Despite this East Coast miss, the Plains may still find some precipitation in the forecast for Thanksgiving. This Hour 252 forecast of the GFS Ensembles on the evening of Thanksgiving depicts may individual ensemble members showing big depressions in the lines, which are storm systems. The lower the depressions, the stronger the storm system. Some members are even forecasting a big green circle. This means a cut-off low is present, which is a regular low pressure system that is no longer influenced by the jet stream.

In conclusion:
•The Major Thanksgiving storm will still verify- but it will be directed offshore.
•The Plains may get in on some wintry fun, however.
•Warmth expected for the South.

Andrew

El Nino May Get Quick Boost Soon

The Madden-Julian Oscillation (MJO) is moving into phases that are deemed conducive for El Nino development and sustaining. These phases are historically charted as Phases 6-1, while Phases 2-5 are known to help La Nina effects develop.

The latest MJO forecast, while pretty far out, is indicating that entrance into Phase 1 appears possible. Phase 1 of the MJO is known to bring cold and wet conditions to much of the East US. Considering it falls within the historically pro-El Nino region, I anticipate the El Nino to get a very quick boost of warmer waters and enhanced El Nino effects.

Despite this quick boost, if I extrapolate this proposed Phase 1 forecast out based on a developing MJO pattern, this boost would be quickly eliminated as the MJO would likely then transition more into phase 2/3 before possibly re-routing back into the circle in the middle (commonly called the Circle of Death), where the MJO is too weak to have any effect on the weather.

Andrew

Long Range Lookout: Stormy Start To December For East US

Hour 156

Hour 216

Hour 276

I am seeing a very stormy pattern emerging just after Thanksgiving and into the first days of December. Let's go into why I think this will happen.

A rule of thumb in forecasting the long range is that nearly everything has a correlation with something else (i.e., Factor 'A' has a correlation with Factor 'B', which has a correlation with Factor 'C', and so forth). One of these correlations includes East Asia. East Asia? Yes, East Asia. It has been shown that there is a 6-12 day gap between what happens in East Asia and what then happens in the East US. For example, if there were a big warm spell in East Asia thanks to a monster high pressure system, that same occurrence would happen in the East US 6-10 days later.

The above images are of 500mb height anomalies from 3 different forecast periods of the GFS Ensembles (GEFS). If you look in the upper left hand corner of these images, you will see a shade of blue encompassing none other than East Asia. I think you know what'll happen next.

If we apply this 6-12 day rule to the forecasted troughs (low pressure systems) in East Asia to the East US, we are likely to see a very stormy pattern begin immediately after Thanksgiving and persist through the end of November into December. This stormy pattern will bring unwanted troubles to the areas still reeling from Superstorm Sandy. The 'good' news is that this stormy period will not have any extreme storm systems like Sandy. However, bouts of heavy rain and snow are possible, if not likely, for much of the East going into the first week of December.

Andrew

Winter To Start Off Slow, Finish Very Active

The winter of 2012-2013 is most likely going to start off on the slow side before we get into a pretty active period to finish off the winter. Let's get into why I believe this will happen.

A big reason for this likelihood is something called the Rossby Wave. A Rossby wave is a storm system that emerges from the North Pole and moves to the southwest, something not usually seen in the Northern Hemisphere. The Rossby wave can be an event, where several of these storms will form and reform over the same area, typically setting up a pattern that can last for a good 4-6 weeks at a time. Unfortunately, this Rossby wave pattern has set up over the northeast Pacific, which has led to a stormy West US, and, consequently, a warm and dry East US. That is not something we want to see heading into the opening weeks of winter.

If I extrapolate (use observations to forecast the future) this Rossby wave pattern, this bad pattern in the East will end in the first couple weeks of December, as the pattern shuts down and moves on elsewhere. I am thinking that the shut down of this pattern will happen from early December to mid December, with the latest shut down date being the week before Christmas.

(This data was originally published on November 9) Observed snow cover in Siberia during the month of October is also supporting the idea of a back-loaded winter, something many winter weather lovers out there are dreading.

Something forecasters use in the fall months to help predict the upcoming winter is indeed Siberia. In October, the anomaly of snow cover over the region has been proven to correlate with observed Arctic Oscillation anomalies in the following winter. For example, if the month of October held a very below normal snow cover situation for Siberia, the Arctic Oscillation (AO) would most likely be on the positive side (warmer weather) for the winter.

If we apply this rule to the upcoming winter, I would expect a fairly warm November and most of December before some moderation in the AO occurs. This moderation from mostly positive would most likely happen around the Christmas timeframe. From there, the first week or two of January would hold continued moderation in the AO (not too positive, not too negative). However, later on in January and in February, Siberia is encouraging the idea of a strongly negative Arctic Oscillation. If this were to verify, we could see extreme cold in much of the nation- something that winter-season farmers may not want to see.

Solar activity will also play a role in this winter. A negative correlation has been found in geomagnetic activity (as shown above) and the Pacific North American index (PNA). A negative correlation means that when Factor 'A' goes up, Factor 'B' will go down. In this case, when geomagnetic activity goes up, the PNA index tends to go more negative, and we are already seeing this and will continue to see this in coming weeks.

Extrapolating previous ups and downs of the observed geomagnetic activity values in the chart above, the PNA should be the most negative in coming weeks before pushing towards positive territory by the beginning of December. The PNA should enter the positive phase by the first week or two of December, fitting in with what I have shown with Siberia and the Rossby waves.

In conclusion:
•November, much of December will be slow for snow.
•Plains, Rockies are snow hotspots for this period.
•Gradual change in last 2 weeks of December.
•January starts off modest, ends active and cold.
•February brings brutal cold, snow to the East US.

Andrew

Credit on the PNA/geomagnetic piece goes to blizzardof96 on the Accuweather Forums (see entire post here)

Major Thanksgiving Storm Likely For Midwest, Great Lakes

I am making the call for a major Thanksgiving storm system (likely with snow) to hit the Midwest, Great Lakes, and possibly the Plains and Northeast. Let's take a look at why I am now making this call.

This is a 500mb height anomaly forecast, valid a few days out. As you can see, there isn't much going on in the United States, so why am I showing you this? Well, we have to go to East Asia for that answer. If you look in the top left corner of the image, you will see a strong trough present in East Asia. It has been shown that there is a 6-10 day gap between what happens in East Asia and what happens in the East US. So, if we use this forecast (valid November 13) and apply the 6-10 day gap to it, we end up at November 22, or a day or two from Turkey Day.

We can also use the Lezak Recurring Cycle (LRC), which is, in the simplest of simple explanations, a repeating pattern that forms every fall and cycles through the winter. This pattern first forms in September-October. A strong storm system hit the Plains, Midwest and Great Lakes on October 2. If we use the expected 51 day gap between each cycle and add on a day or two to give the forecast a little wiggle room, we find this strong storm system hitting the Midwest/Great Lakes on November 21-23, which falls right on Thanksgiving!

I think it's time we turn to the models to see what they're saying. This is the morning forecast from the GFS model for Thanksgiving. This image shows precipitation over a 12 hour period, as well as MSLP lines. The pink line is the rain/snow line. Any precipitation above that line would be snow, and precip. below the line is likely to be rain. The GFS is forecasting a pretty strong storm system to be present across the Midwest/Great Lakes on the morning of Turkey Day. While the GFS has been juggling the position of this storm system, it has been forecasting a strong storm system in the general East US on Thanksgiving.

As you can see in the above forecast, there is a lot of color above the pink line. Yes, this would mean snow. However, because all I am confident in is the presence of a storm in the mentioned regions, I don't think now is the appropriate time to make calls on precipitation. However, if there is to be precipitation, it will most likely focus in on the Upper Midwest and Great Lakes.

This is likely to be the most accurate forecast for this system if we rely on the LRC, but any East US forecast with a strong storm system could verify if we use only the East Asian theory. Personally, I think it's a good idea to combine the two and use the GFS forecast above (which will definitely change in coming days).

Let's sum this all up:
•I am making a call for a storm system on Thanksgiving Day.
•This system will hit the Midwest, Great Lakes, and Northeast.
•Snow is likely, possibly heavy in some areas.
•Cold weather will follow the system.

Andrew