:: T-Storm on a Stick II
As hoped for, convection overnight and new modeling of the synoptic disturbance out west is giving a better picture of convection chances this afternoon through tonight. LLJ is hoisting more warm air advection into southern MN as progged by all previous modeling. This provided a nice push of CAPE between midnight and 2am in front of the shortwave mentioned in the previous post. Heavy rain and some small hail affected the TC Metro with the resultant squall line. As that line developed into an MCS over western WI, debris clouds/trailing stratus deck evolved over SC and SE MN. That deck is now slowly but surely eroding as we move past noon, hampered only by continually increasing moist advection from the south.
MADIS surface reports clearly depict warm front now advancing more rapidly northbound. Boundary traces back to a triple-point low centered over SD at 1000mb. North-northeast disecting southwest through the low is the cold boundary. NAM and latest RUC model runs agree on low moving along the cold boundary as warm front advances northeast, while another shortwave rolls off the CO front range and into the Sioux Empire by early this evening. Meanwhile, warm sector heating will build in earnest with highs well past 90°F acrs SW MN and NW IA. Resultant CAPE progged by RUC is well in 3000-4000J/kg range over central MN. Mid-level capping from WAA flow will most likely break from mixing and forcing efforts as warm front and shortwave move in unison across the area. Models suggest the cap break to occur between 21-23Z and in area from MOX-AXN-HCD-MOX, and then expanding southwesterly.
This grants some validity to MPX-NWS grids targeting the I-94 corridoor as init area for most severe storms. However, as shortwave pushes in, initiation will trend more to the southwest. Morning satellite loop showed cumulus streaks breaking out over SW MN inhibited from outflow of WI MCS. This indicates the cap is still in place, but that low-mid layer CAPE is building. Also, along the cool boundary that runs from PIR-JMS-FAR-BJI, some deeper sheer is occuring. Will expect TRSA development to continue along and around this area, but as it is outside of warm sector, severity will be limited. Effect of any storms evolving along that portion of the boundary will be to reinforce the front with cool outflow, and as it ejects into warm sector will reinforce the continued nocturnal development tonight.
Given the limited confidence on the cap actually breaking, I will introduce my forecast with a slightly lower potential grid, and will keep it on the short-term as this situation is in flux.
Lakeville forecast for rest of Monday...Mostly cloudy with a 50% chance of thunderstorms after 5pm. Some storms could be severe with large hail, heavy rain, and damaging wind. Then an 80% chance of showers and thunderstorms after 8pm. High 82. Low 62. Rain ending after 1am.