The Storm Prediction Center (SPC) has issued an Enhanced Risk today for parts of Iowa and Missouri.
Associated with the Enhanced Risk (as well as with a Slight Risk) are two 5% Tornado Threat rings, both of which are over chase-able country.
Summarizing the SPC’s forecast, there is a shortwave trough ambling east that may interact with a surface low pressure system. The focus of severe weather will be along a warm front extending eastward from the low pressure system. The limiting factor will be how much diurnal heating will be possible given the thick cloud cover from yesterday’s Mesoscale Convective System (MCS).
The cloud cover is shown on the visible satellite imagery. Nebraska and Iowa are almost completely overcast, though there is some clearing at the very northwestern edge of the Enhanced Risk region.
The water vapor imagery shows a disturbance moving through the central Great Plains as well.
The 12Z soundings for the Enhanced Risk area are mostly washed out from the MCS this morning. I hope they release a 21Z or so sounding from Omaha or Davenport, but I’m not counting on it. What we can learn from the soundings is that the deep-layer shear is nearly high enough to support rotating storms (36 kts at Omaha, NE; 38 kts at Topeka, KS; 34 kts at Davenport, IA).
The SPC Mesoscale Analysis page shows that there is a 1002 mb low pressure system over north-central Kansas.
The surface observations show winds from the south across the threat area, and the warm front can be noted as the area where the winds shift slightly, and where the temperature jumps almost 20F. Currently, it extends from north central Kansas veering slightly north across Nebraska, and then settling over the Iowa/Missouri border. The winds are not strongly backed, which has been a key observation this year in the Great Plains. If winds come from the southeast, the tornado threat increases. Today the winds are more from the south, but with the threat being this far east, we may have moisture advection up the Mississippi and Missouri River Valleys, so I don’t think winds from the south will be a limitation today.
The surface-based Convective Available Potential Energy (CAPE) has a 4000 J/kg bull’s eye in west-central Missouri, though most of eastern Kansas is covered with greater than 3000 J/kg CAPE.
Both the peak at west-central Missouri and along the Kansas/Nebraska border near the warm front have normalized CAPE of 0.2.
The Lifted Index (LI) is most promising along the warm front as well.
On the Nebraska side, the Level of Free Convection (LFC) is near 1000 m. This is also promising, as you could almost punt a parcel of air into vertical motion.
If I were out chasing today, I would probably target somewhere near the Kansas/Nebraska border, ahead of the low pressure system, but just on the warm side of that warm front. Marysville, KS, to Sabetha, KS, looking to go north, as I expect storm motion (based on the 850 mb to 300 mb average wind) to track northeast. If storms begin to rotate, I expect them to break free and move more easterly. Beatrice, NE, would be a possibility. Regardless, I would anticipate a route north of St. Joseph, MO, as I followed these storms.
Thank you for reading my prediction.
The Severe Weather Outlook is from the Storm Prediction Center website.
The satellite imagery is from the NOAA Satellite and Information Service.
The surface observation and upper level charts are from Unisys Weather.