Monday, December 23, 2013

January 18-20 Potential Colorado Low / Panhandle Hook Winter Storm

This post will discuss the potential for a winter storm around the January 18-20 period. While this post may seem pretty far-fetched, I assure you that there is potential for a storm in this timeframe, and if you read on, you'll see why as well.

The latest 5 day 500mb height forecast from the Weather Prediction Center over Alaska shows a storm system entering the Bering Sea on December 30th, as the 'L' on the bottom center panel shows. Here is where we employ the Bering Sea Rule, a rule created by Joe Renken after his observation of storm patterns in the Bering Sea and the United States. It is stated that a storm system in the Bering Sea then results in a storm system for the United States approximately 2.5 to 3 weeks later, or 17-21 days later. If we see a storm system entering the Bering Sea on December 30th, we extrapolate that date to the Bering Sea Rule guideline of 17-21 days and end up with a storm timeframe of roughly January 16-20.

The Bering Sea Rule isn't the only long range piece of guidance we can use to detect a potential storm. Here, in a CFS four-member ensemble forecasts developed by Kyle MacRitchie, we see the long range projection of the Madden-Julian Oscillation, in its eight-phase phase space diagram. Using this graph, we see that the MJO is projected to enter Phase 5 around December 27th, which all ensemble members agree on. Now, we'll take a look at the Outgoing Longwave Radiation (OLR) composites in the mid-latitudes for a Phase 5 MJO.

This MJO composite, developed by Nicholas Schiraldi, shows OLR anomalies in the 30 day period before and the 30 day period after the MJO hits Phase 5. In this case, negative lag days on the left side of the image show the number of days before the MJO gets to Phase 5 territory, while positive lag days on the left legend depict the number of days after the MJO hits Phase 5. We can substitute the lag day of 0 for December 27th, as that is when the CFS forecast above predicts we will get into that Phase 5 MJO. Looking ahead, we will ignore the red circled portion (that is for an upcoming post) and will instead take a look at the black circled part of the graph, where you can see blues shaded in. A look at the longitudes at the bottom of the image tells us the strongest negative OLR anomalies will be centered between the 85 West and 100 West longitude lines. If we put that together with the indication that this OLR anomaly chart is valid for latitudes between 55N and 40N, we find that the latitude lines cover the entire United States from Canada to Mexico, while the 85W and 100W longitude lines cover the US from roughly the Central Plains to the Great Lakes. If we clarify that negative OLR anomalies mean stormy weather, and observe that the circled blues are moving north and east, we can deduce that a Phase 5 MJO results in a storm system crossing the US across the Plains, Midwest and Great Lakes in roughly a northeast (or even east-northeast) direction. If we glance at the lag days on the left for when this storm would occur, we find that the circled blues encompass lag days of +17 to +25, meaning the storm would hit anywhere in a 17 to 25 day timeframe after the MJO hits Phase 5. 17 to 25 days after the projected December 27th arrival of the MJO at Phase 5 puts this potential storm system in the January 15-23 period. Now, in order to cut down on the large timeframe, I decided to shorten the positive lag days to cover the strongest negative anomalies only, which gave me a projected storm timeframe of January 18-21.

So we now have two timeframes for a potential storm system. The Bering Sea Rule gives us a timeframe of January 16-20, while the MJO OLR Composites give us a broad timeframe of January 15-23, which I shortened to January 18-21. If we put those two dates together, we end up with a broad-brush timeframe of January 15-21, which covers all dates outlined by either one or both indices. If we shorten that January 15-21 period to only include dates that both indices highlight, we end up with a January 18-20 timeframe for this potential Plains/Midwest/Great Lakes storm system.

How do we know the track of this storm?

Well, we've already deduced from the OLR charts that the longitude and latitude markings would strongly suggest a Plains/Midwest/Great Lakes storm system, moving northeast as it crosses those regions. With that in mind, I took a look at a device created by Larry Cosgrove and found two plausible storm tracks.

Image created by Larry Cosgrove.
The first track possible is a Panhandle Hook (A) system. We can see that this system fits the bill that was outlined by the OLR charts. It originates in the Plains and move northeast through the Midwest and Great Lakes. These systems tend to bring heavy wintry precipitation to the Midwest, Great Lakes and upper Plains, and, if all goes right, these systems can attain massive amounts of moisture from the Gulf of Mexico to enhance these wintry precipitation prospects.

Image created by Larry Cosgrove.
The second track that also fits the bill is a Colorado Low (A). The system originates in the Plains and then moves northeast across the Midwest and Great Lakes before progressing into Canada. The MJO OLR charts confirm that this storm is also a possibility, and the last time I used the MJO OLR charts to make a long term prediction, the results were spectacular. Because this potential event is still about a month away, we don't know how the teleconnections will react to possibly force this storm in a different direction than what the MJO OLR composites predict will happen. However, by using all of the indices at my disposal above, I feel pretty confident that there is at least a decent potential of a storm system in the US for this timeframe. The strength of said system is to be determined, but there is definitely potential here.