RE: Poor performance in IA on 6/13
Wow, what a let down in the state of IA. Things just didn't come together very well at all. This storm almost looked like an early spring type system at first glance, the kind that produce low topped mini sups. I guess it ended up behaving quite similarily to one as well.
Several negatives in IA yesterday...
1) Morning guidance suggested that the first of a couple of shortwaves would affect the central part of the state by early afternoon. As the day played on, the mid/upper-level support arrived much later then predicted by the models, which left all but the western portions of IA in subsidence until the evening. This was visually evidenced by a CU field that developed in CNRTL IA early in the period which then did very little from the late morning on, despite decent insolation that was in progress.
2) A surface reflection of the advertised shortwave was predicted to develop across central IA by early afternoon in the form of a pressure trough/confluence line with surface moisture convergence along it and slightly backing winds to the east. This feature never developed, and most of the state continued with S to SWRLY surface winds during the afternoon and evening.
3) Once storms did get organized in the western part of the state and move eastward into the increased instability, the storm organization was primarily linear with a few “tail-end Charley’s†down towards the south end, one of which did produce a few TOR reports in SCNTRL IA. Overall, the storm organization relative to inflow from the surface through 850mb was poor because of the SWRLY component of inflow into a N/S-oriented storm line moving east.
4) Finally, instability was actually quite poor. The 18Z KDVN sounding was pathetic. Despite good moisture (surface dews AOA 65F), poor lapse rates made for terrible CAPE’s. This did improve slightly in the afternoon into the evening with cooling at 500mb with the approach of the upper trough. However, with cooler temperatures also advecting in at 700mb the lapse rates in the 700mb to 500mb layer didn’t improve much. If I recall correctly, the 00Z KDVN sounding only showed an MLCAPE of 425J/kg along with little or no inhibition.
- bill
