The general story seen across the state over the past few days would be warmer weather. High temperatures yesterday peaked into the 60’s and 70’s for many locations, a stark difference from the cold and winter weather that we have recently experienced. But as spring rolls around, we are also now looking at our first severe weather threat of the season.
A look at the radar early this morning showed scattered showers and thunderstorms over northern Iowa. Most of these have tamed down compared to the marginal hail threat that we saw this morning with a Severe Thunderstorm Warning for portions of Allamakee and Winneshiek counties. Overcast conditions are generally the story statewide. In the upper-levels, a longwave trough sits in the Central Rockies. At the surface, the low pressure system that we have been talking about in the past several days is currently meandering over north central Kansas, and this should shift to the northeast over east central Nebraska in the next few hours. This is, in all cases, the platform for our development today, with a warm front over Interstate 80 and a cold front to the south into the Southern Plains. Instability has already began to grow in southwest Iowa with 1500-2500 j/kg surface-based CAPE seen on mesoanalysis.
With deep-layer shear in place with some instability, large hail and damaging winds will be possible in areas with the best environment. As far as a tornado threat, there are two main areas of concern. The first, obviously, would be over the enhanced risk of severe weather in southwest to south central Iowa. Areas on the southeastern-edge of the low pressure center, ahead of a dry-line, will be in an environment aloft that will be supportive of rotating supercells. The secondary area would be with cells that form along and near the warm front around Interstate 80 in Central Iowa. While these storms will not be in the best thermodynamic environment, there is potential for a low-topped tornado threat as they interact with the frontal boundary. This is something to watch regardless of whether you’re in the elevated or enhanced risk of severe weather from the SPC.
Short-range weather models are currently showing initial development in the early-to-mid afternoon hours along the warm front on I-80. This is where the concern for some marginally large hail and tornadoes will be with cells by form. The main entertainment for the night will arrive closer to the mid-to-late afternoon hours as storms develop discretely near the low and ahead of the cold front in southwest Iowa. These storms may pack a punch with all threats at play, including an enhanced tornado threat. The overall severe threat will wane as we get past sunset, and storms should eventually turn linear and become primarily a heavy rain and lightning threat for eastern Iowa. We then turn to a winter weather threat in northwest Iowa for Saturday which we will discuss in our next post.
In any regard, make sure to pay attention to the weather situation and stay tuned to the Iowa Weather Network for the latest information.