Tornado Digest

Tornado Digest: April delivers the first violent tornado of 2015, and tricky forecasts this week

Ian Livingston

Tornado highlights covering the week of April 5-April 11, and a brief look ahead.

An EF4 tornado near Rochelle, Illinois on April 9, 2015. (Jodi Mair via Flickr)
An EF4 tornado near Rochelle, Illinois on April 9, 2015. (Jodi Mair via Flickr)

As anticipated, last week was the most active of the season so far when it comes to severe weather. While parts of the severe weather episode did not perform as expected, others did and then some.

Among the barrage of about two dozen tornadoes April 8-9, the first violent twister of the 2015 season touched down to the northwest of Chicago on April 9, killing 2.

The upcoming week shouldn’t be a total snoozer, but it seems rather unlikely to produce anything quite on the level of events we just went through.

Tornado activity across the U.S. last week. Reports are filtered by SPC, preliminary, and not necessarily indicative of one tornado per report. (ustornadoes.com)
Tornado activity across the U.S. last week. Reports are filtered by SPC, preliminary, and not necessarily indicative of one tornado per report. (ustornadoes.com)

28 convective watches were issued during the week, up 10 from the week prior. Tornado watch issuance jumped by five to nine. Tornado warnings were more than double the week prior, as were tornado reports. Main impacts were across the southern Plains into the Lower Great Lakes and Midwest.

April 7: Plains, Midwest and California

(SPC event page)

A number of rotating storms passed through parts of the Midwest during the afternoon of April 7. Four EF1s touched down across Illinois, and two brief weak tornadoes also struck central Kentucky.

https://twitter.com/jackson_moss/status/585579908711239680

https://twitter.com/scottbrowning29/status/585592785580982273

Several tornado warnings were also issued in California near the capital region of the northern Central Valley. A few funnel clouds dotted the area.

Near nightfall, a handful of supercells formed in Kansas and Missouri. One or two brief tornadoes were reported.

April 8: Mostly Kansas

(SPC event page)

April 7 was expected to be “the day before the day” (in which some tornadoes occur ahead of the main event). In the end, April 8 may have ended up the day before the day.

The second moderate risk of the year, and the first for tornadoes (15% probabilities or higher), was issued by the Storm Prediction Center. Several tornadoes occurred, but it was much tamer than many expected overall. (sidenote: Mark Ellinwood was bearish enough I thought he might bust, but he did quite well with the forecast here).

Although a number of supercells formed across western Oklahoma and into Kansas late in the day, it was mostly one storm near the triple point in Kansas that did much in the way of producing tornadoes. Even then, most tornadoes were short-lived and weak, but several were quite photogenic.

Here’s some video of one of the longer-lived tornadoes near Medicine Lodge, Kansas from Skip Talbot.

It was a beautiful day for storm structure as well.

April 9: Illinois and the Midwest

(SPC event page)

What Wednesday (Apr 8) lacked in higher-end activity, Thursday (Apr 9) easily made up for.

While the risk level remained enhanced, which was a step down compared to the day prior, there was still high odds of a tornado event, one which could include strong tornadoes.

In Illinois alone, at least eight tornadoes occurred. One was the now very well-known Rochelle/Fairdale EF4. Two people were killed by this tornado which traveled for 28.7 miles. Its wind speeds were estimated to peak at 180 to 200 mph.

Videos of the violent tornado tell quite the firsthand tale. It was a beast.

The scene afterward was difficult to see, as it always is when a powerful tornado makes contact with civilization.

April 11: Southern High Plains

(SPC event page)

This one’s barely even worth a mention, but it was an early-season weekend chase day in the High Plains. And you just have to love the High Plains!

https://twitter.com/NWSKansasCity/status/587098487415672832

Mixed signals

A return to the pattern of old?

This week is starting off fairly quiet for tornado activity. Numerous severe thunderstorms did fire up across the country — focused across the Plains — on Sunday, but they were mainly wind and hail producers. More severe weather is anticipated today, again with a relatively low tornado threat.

Eyes now turn toward a slow-moving upper-level storm system slated to “cut off” over the four corners region midweek, before eventually moving out across the country toward the weekend. SPC has put up a marginal risk for Wednesday already on this system.

GFS forecast for Thursday evening shows a slow-moving upper low sitting west of the Plains. (Weather 5280 models)
GFS forecast for Thursday evening shows a slow-moving upper low sitting west of the Plains. (Weather 5280 models)

Systems like this, that are big and lumbering, are notoriously difficult to forecast.

Once the center of the upper low makes it to the 4 corners or east by Wednesday or Thursday (at least based on current expectations), there’s probably a daily chance of at least a little wave sparking off thunderstorms amidst at least marginally favorable wind shear.

Deep layer shear for Thursday evening. Supportive for severe weather in limited locations. (Twisterdata.com)
Deep layer shear for Thursday evening. Supportive for severe weather in limited locations. (Twisterdata.com)

From here, it looks like one big problem for widespread activity might be moisture availability. It seems Texas or into Oklahoma would be the favored region, though the southern High Plains more generally could face a severe or even tornado threat depending on how the system moves out.

GFS forecast dew points for Thursday evening. (College of DuPage)
GFS forecast dew points for Thursday evening. (College of DuPage)

Eventually, severe weather risks may progress east as we get into the weekend. Nothing is screaming big event at this point.

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Ian Livingston

Information lead and forecaster for the Washington Post's Capital Weather Gang.
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