Tuesday, April 24, 2012

The Tornado Chronicles: Cromwell and Creston, IA Tornado of April 14, 2012...

A strong tornado touched down near Cromwell and Creston, IA on Saturday evening, April 14, 2012. The tornado tracked Northeast for about 14 miles with a damage path width of 600 yards.

Based on the National Weather Service (NWS) survey, the tornado initiated at about 6:55 pm approximately 1.5 miles East of Cromwell and lifted at about 7:15 pm, 10 miles Northeast of Creston. The tornado was rated "high end" EF-2 intensity, based on the resulting damage.

Some of the most intense damage took place in Creston, where both the Medical Center and the Southwestern Community College were impacted.  Within the zoomed-in track on the image below, the yellow outline represents the approximate location of EF-2 damage, with the green outline representing the approximate location of EF-1 damage (the blue outline signifies EF-0 damage):

The following damage photos were taken by the NWS survey team in the Creston area:

Greater Regional Medical Center

Green Hills Education Center

Damage to a Home in Creston

Damage to Apartment Complex in Creston

Damage in the Apartment Parking Lot in Creston

The damage is also summed-up by this YouTube video:

Radar showed a strong tornadic signature in association with the parent thunderstorm, as shown on this velocity image below:

The red shadings indicate wind blowing away from the radar, while the green shadings indicate wind blowing toward the radar.   The radar is located off of the upper right portion of the image.

------------------------------Addendum 4/24/12:

Long time blog reader "Anthill Goddess" inquired (in comments) about the severe thunderstorm vs. tornado warning issue in association with this event.

I went back and researched the matter, and she is correct in that the Cromwell/Creston areas were initially placed under a severe thunderstorm warning, which was issued at 6:48pm:

According to the National Weather Service (NWS) damage survey (as noted at the top of the post), the tornado is estimated to have touched down at 6:55pm and estimated to have lifted at 7:15 pm, both in CDT.

The NWS issued a tornado warning on the storm at 7:11pm CDT:

...and issued the following follow-up statement to the original severe thunderstorm warning at 7:15 pm CDT (at the precise time that the tornado is estimated to have ended):

As you can see, in the follow-up statement issued at 7:15pm, the NWS regarded the damage in Creston as "wind damage", rather than that of a tornado.  This is curious, especially in light of the fact that a clear tornadic signature was indicated on radar (see last image in the original post above).  I won't go into that aspect of the situation any further in particular this posting, however you may certainly draw your own conclusions.

According to this article published on KCRG's website, the tornado sirens were never sounded in Creston.  A similar report was published on WOWT's website.  While neither of the reports cite a specific reason as to why the sirens weren't sounded, most emergency managers do so only when a tornado is actually spotted or a tornado warning is issued.  Since the text of the tornado warning issued at 7:11pm already placed the tornado 6 miles Northeast of Creston, they would likely not have sounded the sirens when the warning was issued since the indicated threat had already moved past town.

I have mentioned numerous times on this blog, and have reiterated in my Severe Weather Sheltering Guide, that you should never rely on outdoor tornado warning sirens as a cue to seek shelter.  Unless you are outside, you are not guaranteed to be able to hear them.  As this case shows, they may not even be sounded when a threat exists anyway, if a formal warning (or sighting) is not issued (or reported).

So what are you to do in this type of situation?  With regard to this particular overall severe weather event, the meteorological community had been talking all day (and in days prior) about a significant threat of severe weather - including tornadoes.  In situations like this, it would be wise to go ahead and treat even a severe thunderstorm warning as a tornado warning, that way you are in shelter should a tornado develop quickly and "without warning".

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Anthill_Goddess said...

Local coverage said that the sirens for Creston never blew but then said that the tornado "formed and dropped right over town". From what I'm seeing from your post, this tornado WAS on the ground well before coming into Creston. It was NOT a tornado warned storm until AFTER it had gone into Creston.

Rob White said...


See the "addendum" to the post (bottom section).

Thanks for your comments / observations, as always...