Bismarck, ND Discussion

Synoptic Discussion

Little synoptic change over 24 hours.  Main upper level trough remains over the PacNW with broad SW flow aloft over the BIS CWA.  Fig 1 in the top right panel shows an associated surface low slowly progressing east. This is producing  south low-level flow ahead of the low that is producing moisture advection primarily over the eastern CWA. Currently surface dewpoints are in the mid 60 east of Bismarck so cloud breaks are allowing for instability to develop. Moisture and instability are in place and trigger mechanism looks to be associated with diabatic surface heating and eroding the low-level CAP.  Surface convergence will also come in play in the surface trough areas associated with the sfc low. These are located through the central Dakotas and extending into Montana and Wyoming. By 00z Wed a secondary forcing provide by a weak vorticity center may allow for already developed convection to rapidly develop. The HRRR (fig 2)also seems to initiate convection with the small perturbation around 20Z.  Overall will focus on eastern CWA for most potent and organized convection. --Cattywampus

Fig 1:

Fig 2:



Mesoscale Discussion

The CIMSS Layer CAPE and LI products show that instability has increased over the last few hours. CAPE and LIs are highest in the south central portion of the FA with values up to 1900 J/kg and -7 respectively. The CIMSS Layer PWAT is most favorable across the eastern half of the FA with values up to 1.35 inches. The SPC mesoscale analysis shows wind shear values up to 35kts in the south central portion of the FA, so believe convection will be organized. Large hail and locally damaging winds appear to be the main threats. CIMSS

-Helen Hunt