Friday, September 26, 2014

CFS Weeklies Determining Upcoming Winter Storm Track

The weekly outlook version of the CFS model, as well as 45-day precipitation forecasts from its four ensemble members, appear to be starting to figure out the upcoming winter storm track.

The image above shows two weeks' precipitation anomalies, one panel for each week. The top panel shows the first week's precipitation anomaly outlook, from September 26th to October 2nd, while the bottom panel shows anomalies for the October 3rd through 9th period. In the top panel, we see a general dry spell expected to linger throughout the East US, as strong ridging induced by a stormy West keeps weather systems at bay. It is this stormy West that will lead to above-normal precipitation anomalies in this same timeframe.

For the second week, valid from October 3rd to October 9th, we see the pattern change. Below-normal precipitation anomalies take hold in portions of the Western US, most notably the Pacific Northwest. Above-normal precipitation anomalies then take hold in the Central United States, including the Gulf Coast. These wet conditions will hit this region in a crucial time, as the new Lezak Recurring Cycle, or LRC, begins to take shape. I'll have more on that later on in this post.

This next graphic is the same as the one we just analyzed, but now valid for the Week 3 and Week 4 period. The top panel shows the precipitation anomaly forecast from October 10th to October 16th, while the bottom panel shows the anomalies from October 17th to October 23rd. During the first week, the latest CFS outlook has those below-normal precipitation anomalies persisting in the Pacific Northwest, now also being reciprocated in the Ohio Valley and South Plains. Wetter than normal conditions do prevail in the Northern Plains and Upper Midwest, through that's the only area that experiences such an anomaly throughout the country.

By the fourth week, we once again see above-normal precipitation anomalies return to the Midwest and Great Lakes, stretching into the Mid-Atlantic. Variable conditions look to exist across the Plains and most of the West, save for the Pacific Northwest.

All of this is pretty important to us, as this looks to occur during the month of October, when the new Lezak Recurring Cycle forms. Something I've discussed on here more than a few times is the concept of the Lezak Recurring Cycle, or LRC. The LRC was developed by meteorologist Gary Lezak, and discusses the idea that weather patterns which develop in October leave a 'footprint' of sorts that is repeated in a regular interval, between 40-60 days through the winter and following spring. In other words, the weather patterns that develop in October repeat themselves for the better chunk of the next year.

If we take that description of the LRC and look back at those panels of precipitation anomalies for the month of October, the general idea is that parts of the Midwest, Great Lakes, North Plains, and even East Coast could be in for a snowy winter.

Let's keep this model analysis going with additional (but different) CFS products.

This is the first of four images from the WxCaster site. In this graphic, we see the projected accumulated precipitation from one of four CFS ensemble members, all valid from today to November 9th. In other words, this image shows total precipitation from today to the ninth of November. Using our LRC guidelines, this should help capture most of the 'new' precipitation pattern as it unfolds in October and into November.

On this first graphic, this particular CFS member foresees a rather dry October and early November for the Midwest and Great Lakes, in opposition to the 16-member weekly panels we analyzed earlier. Instead, the heaviest precipitation is shunted north, into the Central and Northern Plains, or east into the Eastern Seaboard. Just going by this graphic alone, I would favor a snowy winter for the East Coast and Plains. Let's see what the other members say.

This second member shows a much different story than the first one. In this projection, the heaviest precipitation over the next 45 days is dropped on the Midwest and Great Lakes, in a similar fashion as the CFS weekly panels earlier in this post. The Northeast also would see a very wet October and November.

We now have two opposing ensemble members. We can't draw a conclusion from them just yet, so let's move ahead to the next member.

This third member is definitely more toned down than what the second member showed, but is more in line with that second member's geographical location of the anomalies compared to the first member. In this graphic, we see substantial precipitation extending from the South Plains into the Midwest and Ohio Valley, all the way into the Mid-Atlantic. This outlook does look similar to those weekly panels we discussed.

Our fourth and final member we will analyze takes the middle ground between these ensemble projections. According to this outlook, one track of very wet conditions for October and November would set up in the Plains, while another would hit the Midwest and Great Lakes. I might also be able to see a third area of wet conditions in the Mid-Atlantic and up the East Coast. Put it all together and this member definitely foresees an active LRC pattern ahead.

To summarize, while there are certainly discrepancies among model outlooks, and accuracy isn't that high with long range forecasts to begin with, it seems a trend favoring a wet October for parts of the Plains, Midwest, and East Coast may be in order. If this verifies, it could lead to a more secure winter storm track, quite possibly a snowy one.