9/8/05: FCST: IA

Well, looking at the latest 00Z NAM... I'm thinking there is a decent threat for severe weather across IA. Instability looks pretty good with CAPE >2000J/KG in the warm sector, also of interest are the 0-3km helicities in excess of 350m2/s2 over a rather large area overlapping instability... So, if the NAM turns out to be right, I wouldn't doubt supercells and bow echos in the least bit (bow echo and HP supercell environments overlap like this quite a bit). The NAM shows a rather breakable cap, with precip breaking out by mid-afternoon... So, assuming we get sufficiant convergance along the surface front (which we should) and storms are able to become SFC-based - then, I would say supercells with large hail and PERHAPS an isolated tornado or two are possible.
 
RE: FCST IA

Today:
Strong storms will move into the Cedar Rapids area around 3 PM CDT, and Iowa City around 4 PM. Primary severe threat will be winds to 70 mph.

Discussion:
Ongoing convection associated with an H5 S/WV trough entering SWRN MN has been maintained by elevated convergence at the nose of a 25kt LLJ. At the surface, a boundary was oriented roughly along US-20 in WRN IA, and along an EBS to CID line further to the east. By early afternoon, convection will become SFC based, and extrapolation of current radar trends brings precipitation into CID by 19Z and IOW around 20Z. Despite marginal mid-level lapse rates of around 7 degrees C/km, early afternoon SFC temperatures and dewpoints to 83/67 will contribute to MLCAPE’s to 1500J/kG. Additionally, deep layer shear to 45 kts along with (SFC-3km) SRH’s to 250m^2/s^2 just north of the aforementioned SFC boundary will result in a severe wind potential with bowing segments. A few embedded supercells will also be possible along the leading storms, leading to an enhanced severe potential.

- bill
 
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