Monday, September 22, 2008

First Fall Thunderstorms

A large line of thunderstorms has formed from the Canadian border through the Dakotas and into central Nebraska. A few of these storms have been severe warned for the possibility of both large hail and damaging winds. These storms should continue to move northeastward overnight tonight, as the cold front responsible for these storms also slowly slides eastward.

This cold front will continue to move eastward during the day tomorrow, reaching Iowa by the afternoon hours. This front will move across Iowa, and likely slow as the upper level features begin to pull off to the north. The front should exit the state during the early morning hours of Wednesday, taking a majority of the precipitation with it. Total rain amounts with the storms during the afternoon and overnight tomorrow could be fairly high, with plenty of moisture available and continued lift along the cold front. Anywhere from a half inch to an inch may be possible with the strongest storms. These strong storms may be able to produce an isolated strong wind gust during the afternoon hours, with a very small chance that a storm could reach severe limits given the limited instability and shear.

Although there is a limited severe threat, the timing across central Iowa may bring the thunderstorms through just after dusk. This means the potential for some lightning photography if the storms are cooperative, so I may have updates tomorrow evening on the storms if they are strong. Otherwise, look for some moderate to heavy rainfall tomorrow across the state from the morning hours through the afternoon in western Iowa; then over central Iowa overnight and through eastern Iowa by Noon on Wednesday.