Violent Weather for Nebraska & Iowa for This Evening

Severe weather is ongoing over Kentucky, Tennessee, Georgia, North & South Carolina, Virginia & West Virginia. More severe weather is expected in these areas through this afternoon & evening.

The area of most concern I have today/tonight is in Nebraska/Iowa. We could have violent, long-track tornadoes in these states later today or tonight. This should start to develop by dinner time. Here is the latest information from the Storm Prediction Center.

Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1121 am CDT Sat Apr 09 2011

Valid 091630z – 101200z

..there is a MDT risk of severe thunderstorms from extreme southeastern South Dakota northestern NE across southern Minnesota and northern Iowa into southwestern WI…

..there is a slight risk of severe thunderstorms surrounding the MDT risk from central MN/WI…southwestward across southeastern Nebraska into northwestern Texas…

..there is a slight risk of severe thunderstorms from eastern Kentucky/Tennessee southeastward into western NC
and SC/northestern Georgia…

Major western trough will start its eastward move with a very strong jet driving northeastward across the High Plains toward the upper MS valley overnight. Surface low developing over Central High plains will deepen northeastward across Nebraska by this evening moving into southwestern Minnesota by 12z sun. Strong southerly flow will continue to spread a moist and potentially very unstable air mass northward through the southern/Central Plains as warm front currently southern Nebraska to northern MO lifts northward.

Further east a well developed mesoscale convective system over lower Ohio Valley will turn S of east on the east side of ridge moving across central U.S. A moist and very unstable air mass downstream southeastward across Appalachians into
Carolinas coupled with the observed middle level jet of 50-60kt will support an active severe thunderstorm period this afternoon and evening.

..ern Kentucky/Tennessee southeastward through the Carolinas…
As the air mass heats downstream from the mesoscale convective system air mass expected to become strongly unstable southeastward across eastern Kentucky/Tennessee into Carolinas to the S of the backdoor cold front. Cold front currently against the mountains northern NC then southeastward along SC/NC border should slow and be the
northward limit of the greater severe thunderstorm threat this afternoon. The current line of severe thunderstorms associated with the mesoscale convective system Ohio River into northern Kentucky expected to redevelop southeastward into area of greatest instability this afternoon. With MLCAPES ranging upwards to 2500
j/kg and the 50-60kt of brn shear thunderstorms should increase and evolve into line segments and bows. Along with the wind damage concern…large hail will also accompany the strongest updrafts. Shear sufficient for supercell structures including a tornado threat…particularly with any more discrete storm that develops. One favored area would be the enhanced low level convergence vicnity backdoor front in the Carolinas.

Models are in good agreement regarding deepening the Central High plains surface low and tracking it east-northeastward into South Dakota/Nebraska by evening. Southerly low level winds in the warm sector will help to transport Gulf moisture northward and yield afternoon MLCAPE values of 2000-3000j/kg. A strong capping inversion will likely limit the number of surface-based storms that can form…with isolated development in vicinity of the dryline being the main concern
through 00z. Those storms that do form will likely be supercells capable of very large hail and damaging winds. Storms will have a risk of tornadoes as they interact with the warm front near the Minnesota/Iowa border late this afternoon and evening.

Have adjusted the MDT risk a little S into western Iowa/northestern Nebraska as high res models suggest surface storm initiation likely vicinity eastern NE/Iowa border by 00z. If so these storms would quickly become supercells and severe including very large hail along with tornadoes.

After 00z…the increasing low level jet will enhance warm advection and lift along and north of the warm front. This should result in an expanding area of severe storms capable of very large hail across the moderate risk area.


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