Last Thursday we told you about how we were keeping a close eye on a storm system that looked like it could bring big changes to the state. As this storm system starts to come into focus, we can now tell you what looks like COULD happen (emphasize on the could as we are still three days away and there are some factors that could play a role in changing this). The latest storm prediction center outlook has all of Iowa, parts of: Minnesota, Wisconsin and Illinois in this outlook. Since last Thursday, models have come into better alignment and confidence is high for a severe weather episode on Friday.
The western trough is forecast to move into the plains on Friday, with a rapidly deepening surface low near the Nebraska, Iowa border, Friday late afternoon, continuing northeast into Minnesota overnight. Dewpoints in the warm sector will already be in the upper 60s, ahead of the developing cold front trailing south from the surface low. A combination of steep midlevel lapse rates and a moist boundary layer will favor supercells producing tornadoes. The storm prediction center has also said a few of these could be possibly strong tornadoes. Very large hail is likely with these storms. Now if the cold front moves faster, or earlier initiation happens, then a damaging wind threat could take place.
Now the chance for tornadoes and possibly strong ones may be great eye candy for weather enthusiast, however, there are some factors that could put a halt to all of this. One of the things is that surface instability is weak do to cloud cover in the warm sector. Now if we clear out the clouds during the day Friday, then the environment would be favorable for damaging winds, large hail, and even the chance for tornadoes. The other factor is that we are still a few days away, so a lot can change between now and Friday. Fall storm systems are notorious for being busts, but on occasion, some systems are not.
We will continue to monitor this at the Iowa Storm Chasing Network as there is still a lot to be worked out. If there does look like a chance for tornadoes, we will be out in the field covering these storms for you. So check back here daily for the very latest.