April 29, 2010 Chase Forecast

Chase #1 of 2010!

Time of Departure: ~12:30PM
Initial Target: Herington, KS

Discussion: Initial low pressure system over Nebraska will swiftly progress northeast into northern Minnesota by late evening. A trailing cold front will surge east/southeast over MN/IA/NE and into northern Kansas during the evening, intersecting with a dryline positioned over central Kansas/Oklahoma. Largely linear forcing expected along the cold front in the Northern Plains preludes any significant tornado risk despite very strong shear values given the howling winds throughout all levels. Thunderstorms should initiate along this cold front during the evening hours, likely unzipping the front the entire way from southern Minnesota into southern Nebraska and along the Kansas/Nebraska border. As this occurs a secondary low is forecast to form in central Kansas, enforcing the dryline and providing a source for some localized backing of the winds. As this occurs it would appear likely that convective initiation should ensue given enhanced convergence. Bulk shear values are undoubtedly sufficient for supercells during the evening with an increase in shear likely with the low level jet increasing and proving south-southeast winds at the surface during the early overnight. Moisture is a concern given only mid to upper 40s exist widely in the area of interest, however continued strong southerly flow should provide ~60 surface dew points by 00z tomorrow. Widespread 1000-1500 J/kg of mixed-layer CAPE should exist, however fairly substantial capping inversion should limit any development without the aid of at least moderate surface convergence. Given surface temperatures of mid 80s and dew points ~60, high LCL values are also of concern for tornado potential. Nonetheless, the risk is there for at least a storm or two to develop along the dryline or for the cold front to initialize a storm near the intersection of the two boundaries.

It is for this purpose that the initial target be just south of the expected cold front and dryline intersection, being close enough for a tail-end charlie situation along the front or close enough to close quickly on any development to the south along the dryline. Will update by early afternoon with additional thoughts after viewing the 00z runs tonight and the 12z runs tomorrow morning; along with a look at the current conditions as a fellow co-worker and I depart.