*Blog Written at 11:30pm CST 11/17/13*
I will be the first one to admit that I was not totally convinced of a tornado outbreak on Sunday, November 17th, 2013 until the morning of. Though I was aware that there was going to be a severe weather outbreak, with possibly multiple tornadoes, I didn’t expect this many tornadoes and multiple strong (EF-3+) tornadoes. Because this event just recently occurred in the time of writing this blog, it may take up to a week or so before all tornadoes are accounted for. However, you can get a glimpse of the filtered tornado reports, along with other severe weather reports, below.
The set-up was quite remarkable for mid-November, especially for the Midwest, Great Lakes, and Ohio Valley. At the upper-levels, a significant synoptic trough was found over the central CONUS at 12z, 11/17. A powerful 100+ knot jetstreak at 300 hPa was located southwest to northeast from OK to central MO. This put the Midwest/Great Lakes area on the nose of the jetstreak with heavy difluence aloft as well. In the mid-levels, 12z soundings showed several shortwave troughs embedded in the synoptic trough in the central CONUS. These shortwaves would eventually round the base of the larger trough and influence the severe weather later in the day. At 850 hPa, a strong 40-50 knot low level jet (LLJ) was observed and advecting copious amounts of moisture from the Gulf of Mexico into the Tennessee and Ohio Valleys. And finally, at the surface, dewpoint temperatures reached upper 50s and even lower 60s across the Midwest to start the morning. By 16z a surface low pressure was located in southern WI, with a warm front that extended from the low to extreme northeast IN and a cold front that was located from the low, through central MO and points southwestward. IN and IL were both completely in the warm sector of the surface low at this time.
The setup above, alone, screams severe weather likely. However, the previous night I was looking at forecast soundings from GFS and NAM and I wasn’t really impressed by the thermodynamic setup. Obviously in hindsight, there was enough instability to cause a major tornado outbreak. While it’s true that you don’t need 2000+ J/kg CAPE for severe weather, it was my belief that much more instability was needed for a major tornado outbreak than what 00z 11/17 NAM & GFS models were outputting. Both models had 750-1000 J/kg for the majority of the severe weather risk area, with pockets of 1000-1500 J/kg. Again, this is more than enough for tornadoes, but I wasn’t really liking lapse rates and CAPE values being output by both models. Looking at the 12z 11/17 and additional soundings in the area, it’s obvious that the lapse rates were steep enough. Lesson learned for next time.
So here are all of the severe weather warnings issued on 11/17 from 12z to 0530z (6AM – 11:30PM CST). Image from corymottice.com :
Cory Mottice’s website also has the official preliminary tornado count and NWS surveyed tornado ratings.
As stated in the first paragraph of this blog, here are the preliminary, filtered tornado and severe thunderstorm REPORTS from the Storm Prediction Center as of 0625z (12:25am 11/18):