1:00 PM (Wednesday) | *Severe weather threat tomorrow/tomorrow night in the Deep South/Tennessee Valley*
Paul Dorian
A “negatively-tilted” upper-level wave will support strong upward motion on Thursday across the Mississippi and Tennessee Valleys contributing to a widespread severe weather outbreak. Map courtesy NOAA, tropicaltidbits.com
Overview
Last week, the first significant severe weather outbreak of the season so far took place in the Deep South/Tennessee Valley with more than 50 tornadoes recorded and tomorrow may bring a repeat performance in the same general region. On Thursday and Thursday night, there is the potential for an outbreak of severe thunderstorms across states like Mississippi, Alabama and Tennessee and the threat will include large hail, damaging wind gusts and several long-track strong tornadoes. Numerous ingredients will come together on Thursday to generate very strong upward motion in the atmosphere needed for a widespread severe weather outbreak. These ingredients will include a strong low-level jet streak, sharp surface temperature gradient, rapidly strengthening surface low pressure, and an influx of low-level very warm and humid air from the Gulf of Mexico into the Deep South/Tennessee Valley. The severe weather threat will shift into the Ohio Valley by late tomorrow night.
One of the ingredients on Thursday contributing to the severe weather threat will be a strong jet streak in the lower levels of the atmosphere (850 mb). Map courtesy Weather Bell Analytics, NOAA
Severe weather threat on Thursday/Thursday night
Strong upper-level low pressure will push eastward into the Lower Mississippi Valley on Thursday from its current position over the Southwest US. Also on Thursday, a cold frontal system will extend from Great Lakes to a weak surface low pressure system over Texas, but this low will intensify rapidly later tomorrow when the upper-level wave overhead becomes “negatively-tilted” (i.e., trough axis becomes oriented from northwest-to-southeast). As a result, upward motion in the atmosphere will intensify dramatically and this will result in rapid strengthening of the low pressure system as it pushes to the northeast later tomorrow.
A strong cold front on Thursday will separate cold air to the west (in blue) and very warm and humid air to the east (in red) and this temperature gradient will be sharpest across the Lower Mississippi Valley. Map of 850 mb temperature anomalies courtesy NOAA, tropicaltidbits.com
Additional atmospheric ingredients on Thursday that will contribute to the severe weather outbreak will include mid-level dry air and a substantial influx of very warm and humid low-level air into the Deep South/Tennessee Valley from the Gulf of Mexico. A low-level jet streak will get involved as well as it strengthens over the Mississippi and Tennessee Valleys adding to the threat for damaging wind gusts. All of these ingredients will contribute to the unstable atmospheric conditions which are likely to lead to this widespread severe weather outbreak – the second in as many weeks in the same general part of the nation.
The outlook for severe weather on Thursday and Thursday night is shown on this map as forecasted by NOAA’s Storm Prediction Center.
In terms of the threat of tornadoes, models support the notion of vertical wind profiles with very strong shear and this can lead to supercell thunderstorm formation with low-level “meso-cyclones” capable of producing strong tornadoes and large hail. Severe thunderstorm activity is likely to spread to the northeast through the Mississippi and Tennessee Valleys during the day and perhaps well into the evening hours on Thursday. Another area to watch tomorrow will be along and just ahead of the cold frontal system which can feature some linear structures capable of producing damaging wind gusts. The severe weather threat will push into the Ohio Valley later tomorrow night and then diminish somewhat on Friday as the system pushes towards the eastern seaboard.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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