6/15/06 FCST - A postmortem...
Today was a major disappointment… To start with, the upper support was poorly phased with the surface CF and instability axis. Many folks picked a chase target in the vicinity of the SD/ND border (Aberdeen or north of there). By early afternoon, it appeared as though most of the inhibition had eroded and convection was immanent. A cell went up west of Aberdeen which initially appeared promising. Before long, however, it fell apart. In retrospect, it appears as though subsidence had moved in the wake of a weak H7 wave. H7 temperatures in that area also rose by about 2 degrees C during that period, further increasing the inhibition. The 18Z LBF sounding indicated a convective temperature of 101F, which should have been representative of the environment further to the NE near ABR given similar SFC dewpoints and temperatures (T/Td of about 88/61), along with comparable H85 and H7 profiles and mid-level lapse rates. Even if that area had remained uncapped, chances are that it would have been a multicell mess given fairly high CAPEs juxtaposed with very weak low to mid-level flow (the stronger H85 and H7 flow remained well to the
south and east of NRN SD/SRN ND). I did not pick my target in that area for this reason.
I had picked a target further to the south at Chamberlain, SD. It had appeared that develping SFC low pressure just to the south of there in addition to stronger mid-level winds, due in part to a forecasted H5 speed max, would make this the preferred target location. By early afternoon, however, a number of things conspired against convection there:
1. A thick jet stream CI canopy working NE from NEB and CO. While this was indicative of large scale assent further upstream in SERN CO, the cloud cover served to reduce insolation.
2. A narrow axis of SFC dry air intrusion had worked N from NEB (ONL Td dropped from 57F to 51F in two hours beginning in the late morning). That area is in a serious drought, leading to poor evapotranspiration, and perhaps that was a factor?
3. The evolution of the aforementioned H5 streak was both slower and weaker then forecasted. The strongest assent associated with the entrance region of that max had only reached central NE by 00Z, which fired round of convection there to the north of ongoing storms in NWRN KS.
- bill