6/11/07 FCST: MT/ND/SD/NE/MN

[Justin Turcotte]

Area currently highlighted in SPC SWODY3. Both NAM and GFS advertise highly unstable airmass over the Northern Plains on Monday with the NAM showing extreme instability over the Dakotas. Virtual temperature LI's as low as -16. Moisture gradually builds into the region through the weekend courtesy of southerly flow and evapotranspiration. There are plenty of flooded fields in ND after widespread rainfall of 2-4 inches from the last system. Juice shouldn't be a problem. Capping inversion will be. Models are pretty consistent advecting +10 to +12 H70 temps over the area. Convection is most likely along the surface trough in the High Plains during the afternoon where heating and convergence is maximized. Less certain is position of true surface warm front. NAM wants to place it in northern ND along edge of H70 cap. GFS appears to be further south. The NAM solution has been an effective tornado set-up for ND in the past when the cap does break.

 

[Bill Schintler]

Chase target for today, June 11

Chase target:
Glen Ullin, ND (48 miles west of Bismarck).

Timing:
Storm initiation: 6 PM CDT. Supercell storms will be likely early in storm evolution, and storms will evolve into a large convective complex overnight and travel east towards Bismarck.

Synopsis:
12Z BIS sounding indicated impressive dewpoints and moisture depth, along with a convective temperature of around 90F; while upstream soundings to the W showed steep mid-level lapse rates which will be advected into CNTRL ND during the afternoon hours. WV imagery indicated a S/WV with associated UVM over WRN SD traversing NE over the broad upper-ridge, and convection was initiating at 18Z N of the Black Hills in response to this feature. Meanwhile, A CU field was developing W of Bismarck, attesting to increasing moisture and LLVL mass convergence.

Discussion:
Convection will spread into the SWRN ND from the SW as the aforementioned S/WV arrives and convective temperatures are reached. Steep mid-level lapse rates in excess of 8.5C/km along with abundant LLV moisture will contribute towards MLCAPEs in excess of 2500J/kg. Deep-layer shear AOB 40 kts will aid in storm organization. By early evening, a veering 45kt LLJ on top of backing 20kt SFC flow will enhance hodograph curvatures through the cloud base level, resulting in rotating updrafts.

- bill
[FONT=&quot]1PM, 06/11/07[/FONT]