Friday, April 23, 2010

Severe Weather Potential - April 23

Another day with potentially significant severe weather across both the Central Plains and into the Gulf Coast. Yesterday was quite impressive, with multiple cyclic tornadic storms over eastern Colorado and western Kansas, and several tornadic storms in the Texas Panhandle. Another severe weather setup is available today with a surface low located along the western Kansas/Nebraska borders, a warm front extends eastward across southern Nebraska and into southeast Iowa; and a dryline ahead of the cold front should be positioned over far eastern Kansas by this evening. The dryline should extend well south into the Arklatex region, providing a trigger for development from southern Nebraska to as far as northeast Texas. There is very good agreement that thunderstorms initiating in the Arklatex region will move eastward off of the boundary, but continue to pose a significant threat of severe weather given parcel profiles and strong shear present throughout the overnight. However, in the interest of forecasting sake I am focusing on the northern potential given its' likelihood to affect the Kansas City Metro this evening.

Morning convection is currently on its' way out of eastern Kansas, with cloud cover extending back further west to encompass much of eastern Kansas. This should clear out over the next few hours, allowing for sufficient destabilization ahead of the dryline and south of the warm front. This should yield 2000-2500 J/kg of surface based CAPE, and mixed-layer CAPE nearing 2000 J/kg. Deep layer shear values of 40-50 kts with a vector out of the west-southwest should allow for fairly discrete storm development along the dryline in extreme southeast Nebraska and northeast Kansas. As these storms move off of the dryline they will continue to encounter a favorable air mass and likely even better low level shear given stronger backing of the winds. A mid-level jet (500 hPa) will enter the area during the evening hours, likely increasing the deep layer sheer values and providing support for additional storm development. Storm motion given the storm relative wind fields should be to the northeast at 20-35 mph, with any right-movement yielding motions of east-northeast around 25 mph. Storms will likely have enough directional shear to rotate, yielding sufficient tornado potential to mention tornadoes possible with any supercells that do develop in this area. In addition to the tornado potential, ample instability will be available for large hail growth.

Storm initiation should occur by 00z (7pm) in eastern Kansas along or just ahead of the dryline, with storms continuing well into the overnight as they move northeast. Based upon current forecasts, thunderstorms should enter the Kansas City metro ~10pm and exit by 2am. Severe weather is likely with any thunderstorm this evening and into the early overnight. I work the evening shift at work, thus will not be chasing or be able to provide updates. `

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