The Storm Prediction Center (SPC) has issued a Slight Risk today for the Eastern Great Plains.
Associated with the Slight Risk is a 5% Tornado Threat Ring.
The SPC is basing this threat on a complex weather situation today. There is a strong cold front will pass through the area. This will provide a forcing mechanism for storm development. This cold front will be colinear with a dryline, and all extending below a surface low pressure system over southeastern Nebraska this afternoon. There is a lot of uncertainty around this system, however.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows an upper level closed low, and a trough wrapping around this low. There is a jetstreak that is expected to eject into the threat area.
The 500 mb NAM chart shows plenty of vorticity in the northwestern part of the threat area. While the vorticity is strong, it is not strongly advecting, as the winds blow mostly parallel to the vorticity gradient.
The 700 mb NAM chart shows rapidly rising air much farther north and west than the 5% tornado threat ring. This is in response to the Positive Vorticity Advection (PVA) as well as the Warm Air Advection (WAA).
The 850 mb NAM chart shows clearly defined Cold Air Advection (CAA) approaching the threat area front he west (through central Kansas) and Warm Air Advection (WAA) through Missouri and Arkansas.
The 12Z upper air sounding from Springfield, MO, shows a damp sounding with a strong thermal inversion. In this case, the large thermal inversion is actually indicating the strong WAA that is approaching the threat area. While there is no Convective Available Potential Energy (CAPE) present this morning, there will be some later today. This is all happening under an area of strong low-level shear (53 kts) and adequate deep-layer shear (42 kts), with mostly directional shear at the low levels and speed shear aloft.
TwisterData.com shows that the CAPE will increase ahead of the cold front throughout the afternoon.
Currently, the surface observations (from the SPC Mesoscale Analysis Map) show the winds moving into the low pressure system, as well as the dewpoints in the low 50’s. Currently, there is no distinct dryline, though the cold front will form one.
Speaking of low pressure, examine the chart below and see if you can find the low pressure system. If not, that would be a good thing to work on in your professional development.
The Supercell Parameter shows that, by this afternoon, the supercell parameter will increase near the Kansas and Missouri border, as well as into southeastern Nebraska.
Overall, I expect that today will be a complicated storm day. There will be a lot of forcing, and often days where the dryline and cold front become colinear become nasty squall lines that are more mess than supercells. However, the low-level shear is incredible this morning, so even a non-severe storm could quickly escalate into a tornadic storm.
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