April Wind Fields + June Temps = Trouble

Chances for showers and thunderstorms will be increasing as we move through the week. Due to lack of moisture/instability, these should sub-severe for the most part at least until Saturday. It appears we’ll be more unstable by then with a greater chance for severe thunderstorms, although convective coverage is somewhat in doubt.

The main event looks to take shape on Sunday as a significant trough ejects eastward into the Plains. Models are in decent agreement on the overall pattern but there are still the usual differences with respect to timing. The GFS has been advertising a faster solution while most other models are slower. Regardless, this is a classic large scale setup for a significant severe weather event across our area. Models are taking a surface low from the central Plains toward Lake Superior and deepening it under 980 mb by Monday morning. Meanwhile, strong wind fields at all levels of the atmosphere will be overspreading the state as we move throughout the day on Sunday, creating strong vertical shear.  Here are some GFS maps to illustrate:

Other than timing, one of the main uncertainties at this point is the thermodynamic environment. Given the strong WAA regime, the models are almost certainly underdone with surface temps and much of the state should see temps reach or exceed 80 degrees on Sunday. Models are indicating good moisture, and unlike last weekend’s system, it won’t have to travel hundreds of miles in 12 hours to get here. The concern is how much downward mixing occurs and whether that and lack of evapotranspiration may keep the dewpoints a few degrees lower than currently shown. That is something to keep an eye on as we get closer.

Current guidance, namely the ECMWF/GFS, has been relatively consistent in showing the notorious 100 knot "barb of death" at 500 mb. This value has been associated with some of the bigger severe weather outbreaks in the past. They are also showing a very strong upper level jet punching into the area. There is little doubt about the impressive dynamics with this system. The eventual evolution of the trough as well as any mesoscale influences will dictate whether this is a major tornado outbreak or a major straight line wind event (or some combination of the two) but the ingredients look to be coming together for a significant or major severe weather event. Stay tuned...