A look at the radar early this morning shows very active weather activity throughout the region. We are now entering the second half of a 48 hour weather period that will be fueled by severe weather across much of the region, with large hail, damaging winds, and tornadoes all threats.
Plenty of action is being seen on the radar this morning. To the north, a decaying Mesoscale Convective System continues to push southeast across South Dakota. A Severe Thunderstorm Watch remains in effect for portions of northern South Dakota with that system. The majority of the severe threat there is diminishing with an isolated damaging wind threat the only concern. Southward, light-to-moderate showers and thunderstorms is pushing southeast from South Dakota into northwest Iowa. A Severe Thunderstorm Watch remains in effect in that area until 5:00 a.m. We expect that the severe threat is basically over in that area at this time.
A Severe Thunderstorm Watch is also in effect for much of the state through 7:00 a.m. A line of storms has fired from Sioux Falls to Mason City to Waterloo. A few 1″ hail cores have formed there, along with some of the scattered action to the south. Flash flooding is a large concern there, and a Flash Flood Watch remains in effect for much of the state through 10:00 a.m. tomorrow morning.
The forecast for today is a little bit tricky with many variables at play. The Storm Prediction Center currently has a moderate risk of severe weather for portions of east central Iowa with an enhanced risk expanding over much of eastern Iowa. A low pressure system and associated frontal boundary is expected to push northward into the state and set the stage for development of severe thunderstorms this afternoon.
The first obvious trick and wild card at play will be the morning convection that is all over the region. Confidence is not exactly 100% on how this activity will go this morning. Current short-term model solutions are suggesting that activity will dissipate or move out of the area by noon. We will likely see a lingering cloud shield left behind – how long this remains will be a big factor that will need to be monitored throughout the day. Our current expectation is, that alongside the storms moving out of the area, a strong “cap” on the environment will develop in the early afternoon as instability increases. This should keep a hold on new development until mid-afternoon, when a ripe environment fueled by high instability, strong shear courtesy of a powerful mid-level jet, plenty of lift and moisture, and winds veering with height will develop across northeast and east central Iowa.
It’s important to note that there will be a lot of things that could change throughout the day. If morning convection lays around too long, that will decrease the amount of instability available for us around the area, and therefore the severe weather threat would be somewhat limited. If things leave the area too quickly, which is unlikely at this point, the severe weather threat will be trampled by a very large cap, fueled by hot temperatures. In the end, the placement of the low pressure center and associated frontal boundary will be the biggest player in all of it, as that is where the whole stage will be setup.
As storms fire in the mid-afternoon, the initial storm mode will be discrete. With these discrete cells, all threats are possible within the ripe environment aforementioned. Large hail to golf ball size, damaging winds to 60-70 MPH, and strong tornadoes (with associated veering winds) are all possible. This risk will exist for a little while before a rapid transition to a linear mode takes place, with the threats transitioning to a widespread, intense damaging wind threat to 80 MPH. An isolated tornado will also be possible along any linear system.
Stay tuned to the Iowa Weather Network for the latest information!