Yesterday in our first update we brought you, we told you about the potential for severe weather on Friday. The risk for severe weather included all of Iowa, with the main hazards being all three modes of severe weather. There was also the potential that some of the tornadoes on Friday, COULD be strong. All of this was dependent on if the timing was lined up perfectly.
Today, we add something new to our discussion. The storm prediction center has issued a slight risk for tomorrow, for parts of western Iowa. Scattered rain showers or thunderstorms are expected to be ongoing early in the day across northeastern Nebraska and eastern South Dakota. Conditions will become increasingly favorable for severe thunderstorms by late afternoon as shear and instability both increase. Forecast soundings show deep layer speed shear as well as low level veering for supercells. This should produce large hail initially, and eventually a damaging wind threat as cells merge into a MCS. There is a very small probability that a few tornadoes may form along the boundary. Otherwise, the main risks on Thursday will be large hail and damaging winds.
On Friday, severe storms are likely as low pressure deepens over southeastern Nebraska into Iowa during the afternoon or evening. A combination of ample instability, and veering and increasing winds with height, will favor supercells. Very large hail, a few tornadoes and damaging winds will all be possible. The strong forcing should allow severe storms to persist into the overnight hours, but it looks like they will line out instead of staying individual cells.
The main concern with this forecast is that our models have been very uncertain in the timing. Our models should start to get a better handle on the storm as it makes landfall in the pacific northwest coast later this afternoon.
October tornadoes are rare, however, they do happen. From 1980-2011, Iowa has seen 13 October tornadoes. On October 14th, 1966, a F-5 tornado struck the town of Belmond Iowa. Friday’s set up is starting to look similar to the system that produced the 1966 Belmond Iowa tornado. This does not mean that we will see tornadoes, but we will keep our eye on it and will continue to bring you daily updates.