Wednesday, April 27, 2011

Long Tracked Supercell Thunderstorms

The two day severe weather outbreak was largely contributed by two upper air disturbances that tracked through the Southern Plain states.

The reason why we saw severe weather with this spring storm was two fold. One was the fact we are later in the spring season. The fact we are late in April means that the days are longer and the sun angle is higher. That, in turn, leads to warmer temperatures and higher instability when these systems move in.

The other reason why we had two nights in a row of active weather had to do with storms firing along the dryline in North Central Texas. As you have heard by now, the dryline is a surface feature that separates the warm, humid air, from the warm and dry air. Often times, we get storms that fire up along dryline, and it is these storms, which traveled over 200 miles and made their way into East Texas.

Here is a timeline and a look at how the storms evolved on Monday afternoon and Monday evening.

Time 1: Supercells developed just east of Waco along the dryline and began their eastward trek.

Time 2: By 8pm, the two supercells, which have already produced a couple of tornadoes, now enter Houston county, affecting areas from Grapeland to Crockett. While no tornado was produced, strong winds and large hail caused damage near Crockett.

Time 3: At 9:40pm, the two supercells come together and merge over Houston, Trinity, Cherokee, and western Angelina counties. It is at this time when a brief tornado touched down just south of Wells, just north of Highway 103 and Highway 7.

Time 4: At 10:50pm, the supercells move into Angelina county, which prompts several tornado warnings. While no tornado was reported, strong winds did cause minor damage. The cell near Huntington moved over Zavalla, producing golf ball size hail shortly after this image.

Time 5: During the overnight hours, the two isolated supercells evolve into a cluster of thunderstorms that produced damaging winds and another isolated tornado near Onalaska and Lake Livingston.

This sequence is what occured on Monday night. Tuesday night was very similar as storms moved in from the west along the dryline. Thankfully, though, no tornadoes were reported with last night's storms.

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