DISCUSSION: On May 20th and 21st, a low-pressure system swept across the southern Central Plains and into the southern United States bringing tornadoes to parts of the Plains and Mississippi River Valley. The system began as an area of low pressure over the Colorado Rocky Mountains with a warm front stretching into New Mexico, through the middle of Texas, the most northwestern tip of Louisiana and into Arkansas. The warm front gradually moved slowly northward through Texas aided by a southerly wind which brought with it very warm moist air from the Gulf of Mexico.
The warm front interacted with the colder drier air in north Texas and southern Oklahoma that were influenced by a ridge of high pressure that was over Minnesota and Wisconsin on the morning of the 20th. The warm moist air from the South had Convective Available Potential Energy (CAPE) values above 2000 J/kg according to the soundings at locations such as Amarillo, Texas and Ft. Worth, Texas. CAPE is how much buoyancy is available in the atmosphere over a certain location with higher values leading to more severe thunderstorms, bigger hailstones and even tornadoes. The normal minimum amount of CAPE required for a tornado to be possible is about 2500 J/kg. The Storm Prediction Center (SPC) on the morning of the 20th had issued a convective outlook which included the highest risk level on their scale “High” to signify that there was a high level of confidence that widespread extreme thunderstorms and strong tornadoes are possible. The extremely high risk area covered parts of Oklahoma. According to the storm reports on the 20th, there were about 20 tornadoes reported with the strongest one being an EF-3 near Midland, Texas. There were some reported injuries but no deaths have been reported.
Then, on the 21st, the warm front proceeded to move to the South as it crossed Arkansas, Tennessee, and Kentucky towards Missouri and the Ohio River Valley. However, a cold front snuck in from the Rockies and connected with the low pressure system. The interaction between the two fronts led to the forming of an occluded front along the Kansas- Oklahoma border and grew as the cold front started to catch up with the warm front. Part of the warm front remained a warm front in Missouri into the night of the 21st, while the part of the warm front that was over Kentucky and Tennessee became a stationary front due to a blast of cooler air coming down from the Northeast as a cold front was passing through the Carolinas. On the 21st, the storm reports had tallied over 17 tornadoes across Kansas, Oklahoma, Missouri and Iowa with the strongest being an EF-3 in Bern, Kansas. One death has been reported from all these storms coming from the sole tornado in Iowa. This outbreak is just the beginning of a series of outbreaks that last through the end of May.
At the GWCC, we would like to remind you to be prepared for tornadoes. Some of our tips include getting a NOAA radio as well as batteries, flashlight, unperishable food and water. We recommend that if the National Weather Service (NWS) issues a tornado watch or warning that you either go to the basement or storm cellar, if you have one. If not available, then head to the lowest level possible in the house and get to one of the most inmost rooms without a window as a window would break and spray glass resulting in injury.
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©2019 Meteorologist JP Kalb