Day 2 Convective Outlook
American Severe Weather Forecast Center
12:30 AM CDT, Sunday, May 4, 2003
Valid: 05/12:00 UTC - 06/12:00 UTC
There is a Moderate Risk of severe thunderstorms Monday and Monday night from the Arklatex and Lower Mississippi Valley, eastward across much of the Tennessee Valley and northern Gulf Coast states.
Surrounding the Moderate Risk, there is a Slight Risk of severe thunderstorms Monday and Monday night from the Ohio Valley and Lower Great Lakes, southward to the Gulf Coast.
***Significant Severe Weather Episode Increasingly Likely from across the Lower MS/TN Valleys and Deep South***
National Synopsis
Shortwave trough now entering the Central High Plains will continue eastward into the Mid/Upper MS Valley early Monday then into the Ohio Valley and Lower Great Lakes by Monday afternoon. By late afternoon, the cold front accompanying the upper trough will extend from a surface low in the Upper MS Valley south-southwestward through the Mid MS Valley and into eastern Texas. Warm front will lift northward into the Ohio Valley.
Lower Mississippi Valley into the OH/TN Valleys and Deep South
Squall line may be in progress over part of this area early Monday from parts of eastern Texas northeastward through a portion of the TN/OH Valleys. Evolution of this activity leaves uncertainty regarding subsequent destabilization. Current thinking is that part of this activity may weaken by late morning as it shifts toward the Appalachians. Left over convective debris may limit heating over part of the area until afternoon. Best destabilization may occur from parts of eastern Texas northeastward through the Lower Mississippi Valley and parts of the Tennessee Valley as mid-level dry slot and steeper lapse rates overspread moist axis. Atmosphere should become quite unstable in this region where surface heating occurs with axis of MLCAPEs of 3000 to 3500 j/kg possible.
Additional storms should develop by afternoon along and ahead of surface front from eastern Texas, northeastward across the Lower MS Valley and TN/OH Valleys and Southeast. Storms may also develop along residual outflow boundaries from morning convection. It is also possible that some of the morning storms may intensify over the Southeastern U.S. as downstream atmosphere destabilizes. Mid-level jet will lift northeastward through the Lower MS/TN Valleys and into the Lower Ohio Valley overtop strong low-level jet during the day, creating favorable shear profiles for severe storms. Several modes of storms will be likely, including supercells and bow echoes. Lack of strong linear forcing mechanism in presence of weak to moderately capped environment across the warm sector would suggest that long lived supercells will be possible, given the degree of instability and shear progged. Aforementioned instability and shear combination, in conjuction with low LCL heights, will be favorable for a few long-tracked, strong tornadoes from any of the longer lived supercells. Activity may evolve into one or more MCSs overnight with a continued threat of severe weather. Large hail, damaging winds, and isolated tornadoes (still a few significant tornadoes possible from any discrete storms ahead of MCS activity or with embedded supercells) will be possible. Moderate Risk may be expanded further northward across the Ohio Valley in later outlooks. Also, as details concerning evolution of morning convection become more certain, parts of the Moderate Risk across the Lower MS/TN Valleys and Deep South may need to be upgraded to a High Risk in subsequent outlooks. However, current uncertainty regarding convective evolution and degree of destabilization further northward across the Ohio Valley preclude both an expansion of the Moderate Risk and any potential for a High Risk upgrade at the present time.
HAMMER