This won't be a very long post, I just wanted to make you guys aware of the fact that there could be a significant (for this time of year, at least) tornado outbreak over eastern Illinois, much of Indiana, and western Ohio this afternoon and evening. The Storm Prediction Center has issued a slight risk for severe weather for much of the Ohio Valley, and they seem to be fairly bullish on the possibility of a significant tornado outbreak once the storms fire up.
This is latest risk map from the SPC denoting the tornado threat for the day. The percentages convey the probability of one or more tornadoes within 25 miles of a point in the shaded area. The hatched area denotes a 10% chance of one or more EF2-EF5 tornadoes occurring within 25 miles of a point in the shaded area.
Here's some commentary from the SPC on their forecast, emphasis mine:
WAA/MOISTURE ADVECTION IN EXIT REGION OF LLJ N OF WARM FRONT APPEAR TO BE SUSTAINING THIS ACTIVITY WHICH WILL BE CAPABLE OF SOME HAIL AND PERHAPS LOCALLY DAMAGING WIND GUSTS. BY THIS AFTERNOON...CONTINUED WARMING/MOISTENING ACROSS THE WARM SECTOR WILL SUPPORT THE DEVELOPMENT OF SURFACE-BASED STORMS...INITIALLY FROM CNTRL/SRN IL INTO CNTRL IND. AMBIENT ENVIRONMENT WILL BE CHARACTERIZED BY MLCAPE VALUES OF 500-1000 J/KG...EFFECTIVE SRH OF 150-300 M2/S2 AND EFFECTIVE BULK SHEAR OF 50-70 KT...SUGGESTIVE OF SUPERCELLS AND BOWING STRUCTURES CAPABLE OF TORNADOES (SOME POSSIBLY STRONG)...DAMAGING WINDS AND HAIL.
Pretty much once the day's heating is sufficient enough to cause storms to start popping up, things will go downhill pretty quickly. The dynamics for bad storms are already setting up over parts of west-central Illinois (as predicted in the SPC's commentary), as shown by the supercell composite parameter and significant tornado parameter.
This is the supercell composite parameter from the SPC. It takes into account factors such as wind shear and instability to create a value that indicates the potential for supercell development in an area. The higher the number, the more likely the environment is to support a supercell. Values as of 1700z (1100AM Central) are already 8.
The significant tornado parameter shows how conducive the environment is to support significant tornadoes (EF2-EF5), with 1 being a significant value. Values as of 1700z (1100AM Central) were 3 across that same area of west-central Illinois.
This instability is expected to spread as the day moves on, with storms popping up by early this afternoon.
Since these areas are moderately-to-heavily populated (and many Kossacks live in this region of the country), I'll post a liveblog here on DailyKos and keep updating it as much as possible as long as the tornado threat continues.
Be sure to follow Severe Weather Liveblog here on DailyKos, and like my page on Facebook for severe weather updates on your wall when I'm not posting them here.
The Storm Prediction Center is updated immediately with information about severe weather, and you can find more localized information about today's severe weather by visiting the Central Illinois (Lincoln IL) NWS page, the Central Indiana (Indianapolis IN) NWS page, and the Western Ohio (Wilmington OH) NWS page.