A Mesodiscussion is issued by the National Weather Service's Storm Prediction Center when there is a chance of a significant weather event impacting an area. These are routinely issued before weather watches or as updated to weather watches.
Mesoscale Discussion 0568 NWS Storm Prediction Center Norman OK 0736 PM CDT Wed Apr 26 2017 Areas affected...western Tennessee...northern Mississippi Concerning...Severe Thunderstorm Watch 166... Valid 270036Z - 270200Z The severe weather threat for Severe Thunderstorm Watch 166 continues. SUMMARY...A risk for primarily potentially damaging wind gusts continues at least another couple of hours with the squall line advancing across northern Mississippi and portions of western Tennessee. This may include areas in close proximity to, but east of watch 166, before activity weakens, but it is not yet certain that a new watch will be needed. DISCUSSION...As the significant short wave trough approaching the lower Mississippi Valley takes on an increasing negative tilt, stronger low-level convergence and mid-level forcing for ascent likely will become focused across northern Mississippi northward into the lower Ohio Valley during the next few hours. This is forecast to coincide with further strengthening of southerly 850 mb flow to 50+ kt ahead of the ongoing pre-frontal squall line which is now advancing east of the Mississippi River. However, the northward return of richer boundary layer moisture is becoming increasingly cut-off from this region, and the maintenance of vigorous boundary based storm development beyond the next couple of hours is increasingly unclear. The segment of the squall line north of Greenville MS into the vicinity of the MISSISSIPPI/Tennessee state border seems to provide the greatest risk for potentially damaging wind gusts through the 01-03z time frame, with at least some northeastward acceleration possible. ..Kerr.. 04/27/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...OHX...BMX...HUN...MEG...JAN... LAT...LON 36158881 36488844 36418745 34788792 33908807 33508891 33628998 34278996 34808962 36158881Read more
Mesoscale Discussion 0566 NWS Storm Prediction Center Norman OK 0702 PM CDT Wed Apr 26 2017 Areas affected...Parts of central/northeastern Louisiana...western/central Mississippi Concerning...Tornado Watch 164... Valid 270002Z - 270130Z The severe weather threat for Tornado Watch 164 continues. SUMMARY...The risk for a couple of tornadoes and potentially damaging wind gusts with storms overspreading the region will continue at least into the 9-10 pm CDT time frame. It is not certain that an additional watch will be needed to the east of watch 164, but trends will continue to be monitored for this possibility. DISCUSSION...Sustained vigorous thunderstorms within a pre-frontal squall line continue to advance eastward into/through the lower Mississippi Valley, as a supporting short wave trough pivots into an increasing negative tilt orientation as it approaches the region. New convective development is ongoing ahead of the line, but is generally confined to a narrow corridor ahead of it, before merging into or being overtaken by the line, as the leading edge of mid-level cooling contributes to a gradual west to east erosion of the plume of capping elevated mixed layer air. The leading edge of an inland returning plume of seasonably moist boundary layer air (characterized by surface dew points in the upper 60s/lower 70s) remains stalled over southern/eastern Louisiana and southwestern Mississippi, and the squall line appears likely to increasingly cut-off inland return of higher boundary layer moisture from the Gulf of Mexico. As it does, easterly inflow of less unstable air into the storms may tend to contribute to weakening of updrafts as early as 02-03Z, although it is possible that this may be counter balanced somewhat by at least some strengthening of southerly 850 mb flow (and low-level shear). Until convection begins to wane, a period of increasing risk for strong surface gusts remains possible into early evening, along with continued potential for a couple of tornadoes. ..Kerr.. 04/27/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MEG...JAN...LIX...LCH...SHV... LAT...LON 33469078 33969011 33888938 32978950 31949013 30499167 30179265 30449347 32549152 33469078Read more