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05/28/10 FCST: ND/MT

Chase Target for Friday, May 28:
New Town, ND (northwest portion of ND).

Timing and storm mode:
Isolated convection should initiate during the early evening hours, most likely after 8 PM CDT (7 MDT). The cap will be slightly stronger then it was Thursday, and a bust is possible given that significant upper-level forcing will remain well west of the area. Given convective initiation; supercells, along with a tornado or two, are likely. Storms will track towards the east at 15 mph. A poor road network exists in the area of Lake Sakakawea, influencing the target choice. New Town is situated near one of the few bridges crossing the lake.

Discussion:
Friday will be a comparable similar setup to Thursday, but shifted 150 miles to the east. An amplifying ERN CONUS ridge will slow EWD progression of a persistent trough over the WRN US. As a result, strongest forcing will remain well west of an impressive instability axis. Ongoing convection along and N of US-2 in NWRN ND will lift N into CAN by mid-morning, while reinforcing a baroclinic zone and possibly an OFB across the region. Low pressure, located over the SD/MT/WY tri-state area early in the day, will deepen while retrograding towards the SW. A secondary low will develop in NWRN ND. By 00Z, a quasi-stationary front will extend NNE of the low across the NWRN ND, providing the focus for convection by early evening. LLVL directional shear will be maximized along and NW of the boundary. Helicities will increase after 00Z as a SLY LLJ increases to 40 kts.

Dewpoints in the mid- to upper-60’s F will contribute towards MLCAPEs AOA 3000 J/kg. Looking at MDL initialization, both the NAM and GFS have initialized 1-2 C degrees too warm at H7, when compared with 00Z verification. Strong capping will persist Friday with warm H7 temperatures and an ULVL ridging in place, limiting aerial storm coverage once initiation occurs. It is possible that diurnal convection will fail to initiate entirely. MDLs indicate weak subsidence through 02Z, after which a couple of subtle vorticity maximas well E of the main trough approach the area. H7 omegas should increase to -3 to -4ub/s during this period. This lift may be offset by warming mid-levels, with H7 temperatures increasing from about 12 to 13 C during the same time frame.

- Bill

11:12 PM CDT, 05/27/10
 
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