Last Friday through Sunday (April 13-15, 2018) were active severe weather days across the central, southern, and mid-Atlantic states, and sadly, there were two deaths related to tornadoes. I'll touch on the setting for these severe weather days later in this blog. But first, I'll briefly discuss an interesting storm chase to southwest Iowa on Friday, April 13 (see image above).
Near the Kansas City area where I live, Friday's storm environment didn't look very supportive of tornadoes. There wasn't much low-level wind shear (storm-relative helicity or SRH), and cloud bases looked to be too high with large temperature-dew point spreads around 20 degrees F or more. The best tornado potential on 4/13/18 was farther south in Arkansas, northern Louisiana, and northeast Texas. But in southwest Iowa, east of a surface low near a warm front/stationary front, things looked at least a little interesting.
So, my wife Shawna and I decided to take a quick trip north to the Iowa front to see if anything of note would happen there. We were rewarded with a tornado-warned storm, mesocyclone, and lowering that briefly tried to produce a tornado just north of the front, north-northeast of Hastings, Iowa:
And, of course, there was that cool funnel cloud as the second storm crossed the boundary :-).
On a much broader scale, the graphics below show the upper wind flow pattern and forecast environmental CAPE-SRH combinations (via the energy-helicity index, or EHI) for Friday evening April 13 (0000 UTC 4/14/18), and Sunday afternoon April 15 (2100 UTC 4/15/18). SPC storm reports for those two days are also shown (for brevity, Saturday April 14 is omitted):
Here's a couple photos of tornadoes from this 3-day tornado-producing storm system; one in southwest Arkansas near Umpire on Friday evening 4/13/18 (very large and ominous), and one near Greensboro, North Carolina on Sunday afternoon 4/15/18:
Unfortunately, a toddler was killed on Friday night in an EF1 tornado near Shreveport, Louisiana, and a man was killed near Greensboro, North Carolina from winds located just west of the EF2 tornado shown in the image above. Both deaths were from falling trees, a significant problem regarding both wind and tornadoes in the eastern half of the U.S., where trees are more numerous.
- Jon Davies 4/17/18
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