Originally posted by Alex Lamers
I am surprised that SPC moved their moderate risk east of SE WI into Lake Michigan. I am expecting storms to develop and rapidly become capable of producing severe winds...mainly east of the Madison area. With LLJ 40-45 knots and ULJ focused right over the area...seems like it wouldn't be hard to transfer down some gusty winds.
I think best shot of tornadoes will be across E WI and NE IL where discrete modes will be present initially before linear mode takes over. BEST shot in that area would be over NE WI.
...Alex Lamers...
I think they moved the risk eastward because of instability concerns over parts of WI. RUC only shows CAPE climbing up to 1500J/KG over that area (temps currently only around 70F), with little in the way of directional shear. Speed shear is pretty impressive, and it will likely lead to severe thunderstorms.
Further east into central/northern lower MI - Winds are more backed, and are forecast to stay that way. As the afternoon progresses, helicity across that region is forecast to be in the 200-300m2/s2 range, with good directional shear. Temps are also currently flirting with 80F, and are forecast to hit 90-95F (at least here in southern lower MI). No doubt that CAPE will press the 3000J/KG mark across much of MI and parts of IN. My thinking is that storms will initiate in lower MI, associated with the second outflow boundary (currently across IL). Storms in WI will probably fire as the 500mb vorticity center plows into the region. I think the tornado threat would tend to follow the area of the best backed winds, which would be northern lower MI - and IL, if things remain backed.
Today's setup really needs outflow boundaries and low level jet convergence to get things going in the weakly capped environment. Further northwest, into WI and the western U.P. of MI - there is little in the way of outflow boundaries, and the trough/front associated with the low is providing very little convergence. Still, the vort center swinging through should be enough to provide good development across that area.
I have seen many setups like today, where you have CAPE in excess of 3000J/KG, and it only takes a little bit of forcing and a little bit of shear. Today, we have a little bit of forcing and quite a bit of shear... Things should get pretty lit up later today...
