TYLER, Texas — Severe weather season in the central and southern plains peaks in May. In terms of climate, this means that severe weather in East Texas hits its high point the first week of May.
The Storm Prediction Center takes historical weather data from the week of May 6, between the years 1982 to 2011, and found that there is a 4% - 5% chance of a tornado, high winds, or large hail.
Although those numbers do not sound like a high probability for severe weather, the statistics show a higher than 0% chance of severe weather occurring in East Texas this week.
We also know by using climatology that by the end of May, East Texas will start to experience some summer-time heat and humidity in addition to drying out. The best chance of severe weather by the end of May follows the seasonal jet stream shifts and moves north over Oklahoma and increases.
The Long Range Cycling Theory can help predict any severe weather for the current month of May, and try to identify some rough patches that could feature severe weather across East Texas.
This is the exact theory the CBS19 Weather Team used to accurately predict several severe weather set ups in April.
The weather pattern that developed last fall is still cycling, and we're entering the fourth cycle of this pattern. Looking back at the storms that cycled through the central and southern plains in October, February, and March can help with the prediction for May.
Part of the pattern that was apart of the March 21 tornado outbreak will be returning around May 22.
Here are the dates the CBS19 Weather Team has highlighted for potential severe weather in May:
- May 4 - 6: Featured an icy rain with the February cycle.
- May 9 - 11: This is one of the signature storms of the pattern that first appeared in late October, and then again in early March.
- May 13 - 16: Two of the previous three cycles have featured slow moving storm systems that have kept our weather unsettled with several days of rain.
- May 24 - 26: The March version of this storm produced our tornado outbreak.
Since the late-March version of this pattern produced a tornado outbreak, it is important to take a closer look at that set up, and try to diagnose whether that can happen again.
The map below shows the upper-level wind flow on March 21. It highlights the winds and thickness of the atmosphere were around 500mb, which is roughly 18,000 feet off the surface, or about half-way up through the atmosphere.
It is important to look at that area in specific, because often what happens at this level is reflected at the surface. If low pressure develops at this level, it is likely that there will be an area of surface low pressure, or a storm.
On March 21, an upper-level storm was transporting very humid air into East Texas. The winds aloft were also spreading out, or diverging, over our region. This created lots of lift, and in turn created changing wind direction and changing wind speeds from the surface up through the atmosphere. That natural twisting motion led to seven tornadoes in East Texas.
To determine if East Texas will have another tornado outbreak, we can apply a basic scientific principle: magnitude versus frequency.
Because there is an inverse relationship between the two, (the bigger the event, the fewer times it happens) it can be reasoned that we won't have a repeat of March 22 in East Texas.
The CBS19 Weather Experts believe a storm will form around May 24, but because of seasonal shifts of the upper level winds, the focus of the storm may follow climatology and center its strength across an area from the high plains through western Kansas and western Oklahoma.
Of course, we will continue to update the forecasts throughout the month and fine tune the timing as we get closer to each set up.