A major severe weather outbreak is on tap for the central United States this afternoon, with a moderate risk for severe weather extending from Nebraska to Illinois. The threats today include the potential for strong tornadoes, extremely large hail, and damaging winds in excess of 75 MPH.
UPDATE: The SPC just issued a HIGH RISK for the imminent development of a derecho from Nebraska to Illinois. This is a life-threatening situation and everyone in and around the moderate and high risk zones needs to take immediate action now to prepare for severe weather over the next 6-12 hours.
The threat will come in the usual one-two punch that's typical of supercell events, with discrete supercells forming over eastern Nebraska this afternoon, merging into a squall line later this evening and racing eastward across the moderate risk area as a bow echo/squall line. The threat with the supercells will come in the form of very large hail and some potentially strong tornadoes, and the threat will slowly shift to a risk for damaging winds in excess of 70 MPH once the storms form into a line and start moving east.
Here's the tornado risk today. Remember that a 10% chance for tornadoes means that the odds of seeing a tornado within 25 miles of any point in the shaded area is 10 times higher than normal. The black hatching means that significant tornadoes (stronger than EF-2) are possible.
Here's the damaging wind threat today, which is enhanced from Nebraska to Illinois in anticipation of the development of a squall line. The black hatching means that winds in excess of 75 MPH are possible. The 60% zone means that the risk for damaging winds is 60 times higher than normal.
The hail threat will be elevated where supercells are present over Kansas and Nebraska. Large hail (golf ball size or larger) is possible in the black hatching.
At 12:40 PM CDT, there was a group of storms around a lone supercell in northern Nebraska that has a long history of producing copious amounts of golf ball size hail in its path. More storms are expected to form in the area over the coming hours as the supercell moves towards the southeast. The SPC says that it will issue a tornado watch by 2PM CDT.
Stay safe if you live in any of the areas at risk for severe weather today. Keep a close eye on the weather before you go to bed tonight, especially if you're downstream of the damaging wind risk. Straight-line winds are dangerous.
1:10 PM PT: UPDATE: The SPC just issued a high risk. Updating the diary shortly.