Day 137: Upcoming Pattern Analogs

Posted by pmarsh on 17 May 2010 | 3 comments

Today is day 18 of VORTEX II and the armada once again deployed on thunderstorms in eastern New Mexico. These thunderstorms posed a low risk of tornadoes, but did give the armada a chance to practice deployment strategies in preparation for what appears to be another active pattern. More on this below.

How did the VORTEX II armada fair today? Well, at least five separate vehicles will need to replace windshields after today’s adventures. We probably won’t have a final count until sometime late tonight or tomorrow morning. The broken windshields were the result of hail up to the size of baseballs falling repeatedly on portions of the armada. If you are curious as to what this might look or sound like, then take a look at this video of the Oklahoma City hail storm that occurred yesterday. Warning, while the hail sound is loud, if you listen close enough you may hear some foul language.

So, above I mentioned the fact that we appear to be heading into a fairly active severe weather pattern. Above is a temperature forecast for the next 6-10 day. Instead of actually predicting what the high temperatures might be, this is a probability that a given location will experience a high temperature greater than normal for this time of year. In general, cool temperature indicates upper-level troughing and warmer temperatures indicate upper-level ridging.

If one were to translate the temperature forecast above into a forecast for mid-troposphere trough/ridge forecasts (below), we see that a trough is forecast for most of the western United States and a ridge is forecast for the eastern United States. This kind of pattern is conducive for extremely warm, moist air originating over the Caribbean Sea to move northwestward into the central United States. (For the more technical readers, this occurs because the persistent southwest flow at mid-levels results in a lee trough on the eastern slopes of the mountains that allows southeasterly winds to develop from the western Caribbean Sea into the northern plains.)

The warm, moist air is just one of the necessarily ingredients for severe thunderstorm development. We still need something to lift this warm, moist air into the troposphere to develop thunderstorms.

Typically on the east side of a large trough (such as the one forecast to develop over the western United States), minor shortwave troughs “eject” northeastward from the base of the trough to the crest of the ridge to the east. Ahead of each of these shortwave troughs rising motion is found. Without going into all the details, this rising motion that can act to lift the warm, moist air into the troposphere. Now, it is almost impossible to predict the exact timing of these shortwave troughs, but it is almost a sure bet to they will be there.

Like I discussed on 8 May 2010 (Day 128) for model forecasts, it is possible to construct analogs to previous events based on the forecasts above produced by the Climate Prediction Center (CPC). In the bottom right of the image below, analogs for this predicted pattern can be found. For convenience, I’ll post them below the image.

The analogs (click on the red ones to see the storm reports) are:

11 June 2005
17 May 1962
04 June 2005
27 May 1978
15 May 1999
23 May 1975
21 May 1991
07 June 2004
08 June 1984
14 May 1998

Most of these dates are either severe weather outbreaks themselves or are dates very near severe weather outbreaks. Like I said previously about analogs, you can’t take an analog as a specific forecast of what is going to happen. It should be used as a piece of guidance; it is merely one piece of information regarding a particular pattern’s potential. It’s a form of pattern recognition, and in this case the pattern appears to be an active one.