Chase Forecast No. 2 ~ 2025-03-19
You know that you’re craving for storms when you’re seriously considering a 12 hour drive west to Illinois for a cold-core setup. If you’re reading this now, that means I’ve made up my mind to commit to the Wednesday, March 19th, 2025 setup over Illinois. The writing of this forecast blog is the act of me processing my thoughts into coherent sentences that have ended in the conclusion that a 2,000 mile-round trip is worth it for some weak (but most importantly, likely photogenic) tornadoes.
Let’s start with the most limiting factor for this time of year; moisture. At first glance, dew points in the mid 50s (°F) isn’t really what gets the juices flowing (unless we’re talking about the proper High Plains). MLCAPE is seemingly a bit better, with a bullseye near 1500 J/kg, but what needs to be known to really have the ears perked up is what is going on at 500 mb. Extremely cold temps aloft with strong southerly flow is directly overtop the warm sector below of mid 60s surface temperatures contained south of a warm front.
This is a Jon Davies Cold-Core classic; ingredients look benign, but the pattern is everything that needs to be known. We’ve got that closed 500 mb upper low with a surface low slightly offset further east. A dryline out ahead of the main cold front will advance eastward providing the boundary needed to initiate storms. Further helping our case is a lobe of dry air aloft that’ll clear out morning cloud cover in order to further enhance instability at the surface. The story only gets more enticing with strong low and mid level lapse rates reaching into our warm sector, which support rapid and robust updraft development.
Beyond the thermodynamics, shear values are ideal to support tornadoes. Surface to 1 km SRH of 168 m^2/s^2 and 23 kt of shear is plenty in the lowest level of the atmosphere to get the job done.
Cutting this one short today to get everything together to drive out west! See Guyer/Davies’ paper here to learn more about Cold Core Tornado setups.
Cheers,
Ethan