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Could the season’s biggest tornado outbreak of the season come on Saturday?

22 Apr 2014, 5:02 pm

At this point, you’ve probably already heard about how quiet of a tornado season it’s been to date. So far in 2014 as a whole, we’re barely over 100 tornadoes (109 unofficially) – and we’re normally at or above 400 by this time of year.

But that run of good luck could, unfortunately, be changing in the next few days. Here’s a look at where the severe threat could be concentrated over the next few days. The purple-shaded areas are where severe storms could come on Saturday and the green areas indicate Sunday’s greatest threat, with some overlap:

day48prob-1

First things first, the general flow aloft across the country over the next 10 days is gradually going to become more meridional – weatherism for “wavy” – a pattern more conducive to developing storm systems across the U.S. That’s step one.

Step two involves a strong “Colorado low” developing in the lee side of the Rocky Mountains on Saturday, and out ahead of it a strong cold front will mark the divide between a toasty and unusually warm air mass out ahead of it and chilly, almost winter-like air behind. That clash is a big part of what creates severe weather this time of year; warm, juicy air (typically from the Gulf of Mexico) will rise over the colder, denser air mass coming in, creating the lift necessary for big storms.

Step three involves those toasty temperatures, which will approach and probably eclipse 90 degrees in southern Kansas, western Oklahoma and Texas this weekend. That’s July-like weather in April. Factor in juicy air from the Gulf of Mexico (dew points could approach 70 in parts of the southern plains!) and you have all the energy-related components necessary for big storms. CAPE values (convective available potential energy, a measure of the instability of the atmosphere) will be approaching an astronomical 4000 joules per kilogram as a result. So – the energy to fuel big storms is clearly there. What about the rotation?

The map below (courtesy of twisterdata.com) shows helicity, or a somewhat general measure of shear (change of wind direction in both height and vorticity). In short, this map shows a wide swath of 500-700 m2/s2- extremely high values indicating a high degree of rotation in the atmosphere.

NAM_221_2014042218_F84_HLCY_3000_M_ABOVE_GROUND_0_M_ABOVE_GROUND

The final ingredient (although as Dr. Ryan Maue of WeatherBell said on Twitter yesterday- you need luck too) to all of this is a lack of a “cap” to block the air from rising, usually coming in the form of a warm air inversion that would keep cooler air parcels from continuing to rise. This forecast skew-T chart shows that we’re cap free in northern Oklahoma on Saturday:

NAM_218_2014042218_F84_37.0000N_99.5000W

The Storm Prediction Center (SPC) was unusually harsh in their summary of what could take place on Saturday and Sunday (Saturday looks, at least right now, like the stronger of the two days), noting that “strong tornadoes are possible” along with labeling it overall as a “significant multi-day severe event expected”.

While right now the potential exists for a widespread severe weather outbreak this weekend, we can’t overlook the threat for severe weather tomorrow and Thursday as well in the plains.

Stay tuned to WeatherNation for more on this potentially dangerous outbreak. Meteorologist Chris Bianchi.

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