March 6, 2020
Here is how the severe weather event this week played out. I want report on what happened but also illustrate how difficult it can be to forecast severe weather. The forecasters at the SPC do a phenomenal job at forecasting severe weather. The fact is that we can't see or predict every aspect of the atmosphere. Small details that have a significant impact on the weather are often not resolved by our observation network or computer models.
The most significant weather occurred late Monday into early Tuesday, producing the Nashville EF-3 and Cookeville EF-4 tornadoes. You can read more about that here:
March 2-3, 2020 Tornadoes and Severe Weather. The SPC started talking about the possibility of severe weather this week as far back as
February 24th, refining their forecast as the event got closer. Below are some animations showing how the tornado, wind, and hail risk areas were updated throughout the day on the 2nd along with storm reports for each hazard type. It would be cool if the storm reports animated with time but they don't unfortunately.
Nashville was just on the edge of the 2% tornado risk area until the 1630Z update. Cookeville was always outside of the tornado risk area but not outside of the overall outlook area. Below is an animation of the Day 1 Convective Outlook as it was updated throughout the day.
Notice the expanding slight and marginal risk areas. The EF-3 and EF-4 tornadoes were unexpected events at least at the time that the last Day 1 Outlook was issued around
7 p.m. Had they been expected the SPC would have issued an outlook with at least an enhanced risk (orange) area with a black hatched area indicating significant severe weather was possible. You can read about how the SPC constructs convective outlooks here:
SPC Products.
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Tornado Watch was issued for Nashville and the surrounding area at 11:20 p.m. It is noteworthy that the probability information issued with the watch stated a 30% probability of 2 or more tornadoes and a 20% probability of EF2-EF-5 tornadoes so at the time of the watch strong tornadoes (EF-2 to EF-5) were not out of the question. The EF-3 tornado that hit Nashville touched down at 12:32 a.m. and was on the ground for nearly an hour producing a 60 mile-long damage path.
Putnam County, where Cookeville is located, was two counties to the east of the tornado watch area. Even though it wasn't in the watch zone it was indicated as being in a threat area in a
Mesoscale Discussion that was issued at 1:02 a.m. on the 3rd. The Cookeville tornado touched down at 1:49 a.m. and was on the ground for 8 minutes traveling about 8 miles. Thankfully is dissipated just to the west of Cookeville proper. Had it continued I don't even want to think about how high the death toll may have been.
Even though strong tornadoes weren't in the forecast the SPC did a good job monitoring the event and providing information as it evolved. It'll be interesting to find out what meteorological conditions created an environment supportive of strong tornadoes especially when this environment wasn't previously forecast. Unfortunately lives were lost and people were injured not to mention the property damage. Studies have shown this is more related to social issues such as building standards and hazard response than to warning time. We can all learn from this by assessing our risk level for the places we normally occupy such as our homes, places of employment, places of worship, etc. This assessment will be different for each of us depending on where we live and the common weather threats we can expect. If your not sure how to go about this let me know and I'll point you in the right direction.
The 3rd through the 5th didn't produce many extreme severe events as can be seen below. I had initially expected the 4th was going to be the worse day but that wasn't the case. Then it looked like there'd be some bad weather on the 5th but that didn't verify either.
Severe weather requires the right ingredients to come together at the right time. A subtle change can cause one or more ingredients to not materialize as expected resulting in an event that under-performs the forecast. Or as was the case in Tennessee the ingredients were stronger than expected and the event over-performs. The key takeaway is to have a plan and always be prepared when severe weather threatens.
Chris
