The Storm Prediction Center (SPC) has issued an Enhanced Risk of severe weather for parts of Illinois, Iowa and Missouri today.
Associated with the Enhanced Risk is a 10% Tornado Threat ring.
The SPC is basing this threat on the intensification of a surface low that will move northeast from southeastern Kansas throughout the day. The intensification will be due in part to the low’s path intersecting the left exit region of a jetstreak. This jetstreak will also boost shear in the warm sector of the system.
Synoptically speaking, the 0Z (Wednesday) 300 mb NAM chart (from Unisys) shows the trough dipping through the Great Plains, as well as the jetstreak, nosing into the Enhanced Risk area by this evening.
The 0Z (Wednesday) 500 mb NAM chart shows a strong vorticity maxima moving from Kansas to the northeast. This Positive Vorticity Advection (PVA) will ramp up the convection in the threat area by this evening.
The 0Z (Wednesday) 700 mb NAM chart shows extremely rapid vertical motion across Iowa and Illinois this evening. Storms that form in this region will grow vertically very quickly, and likely produce large hail.
The 0Z (Wednesday) 850 mb NAM chart shows strong Warm Air Advection (WAA) through Illinois and Iowa this evening. Notice the wind direction vectors blowing across the thermal gradient from warm to cold.
The 12Z upper air soundings do not show much yet. The severe threat will depend on the deepening of the low over Kansas.
TwisterData.com shows that, according to the RAP, there will be plenty of Convective Available Potential Energy (CAPE) by this evening in the warm sector of this mid-latitude cyclone.
TwisterData.com also shows that, according to the RAP, there will be 300 m^2/s^2 helicity (0-3 km) along the Iowa/Illinois border.
TwisterData.com also shows that, according to the RAP, there will be dewpoints in the low 60’s across the Enhanced Risk area. The dryline is not particularly strong, but there is a plume of moisture that extends into Illinois this evening.
Currently, the surface pressure (from the SPC Mesoscale Analysis Map) show the weak low pressure system over southeastern Kansas. The northeastern quadrant of this system will be the focus for severe weather this evening.
The RAP shows this system intensifying, both in pressure drop and in pressure gradient surrounding the system, over the next six hours, at least.
The RAP also shows that the Supercell Parameter goes to 8 over north-central Missouri over the next six hours. Storms will probably not initiate until later in the day, and this parameter will likely continue to climb throughout the afternoon.
Overall, I expect severe weather today. I would start out by targeting some place like Downing, MO, and anticipate moving east and north with the storm motion. I think that there is likely a threat after dark today, so even though the Iowa/Illinois border is a likely threat, it will be closer to dusk, and thus a poor time to chase. If I picked three locations today, I would pick:
1. Downing, MO
2. Farmington, IA
3. Burlington, IA
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC