Looking over the forecast models yesterday, it caught our attention, but there were too many variables that could throw the following forecast off, so we wait until today to talk about it. Today, the models continue to improve, and are backing our initial thoughts from yesterday.
A warm front will be lifting north out of Missouri late this evening, and will be moving into southern Iowa by early Wednesday morning. This warm front should spawn off a few showers and thunderstorms late this evening across southwest Iowa first, and eventually across southern Iowa by Wednesday morning. This is where things get iffy. As some of you might know, early morning convection (storms), often throw a major wrench in the forecast. Too much convection, can keep the warm front south.
Today, models are showing signs that there will be little convection overnight, which will allow the warm front to surge further to the north, and should eventually make it up to Interstate 80 by Wednesday afternoon. Why do we care so much about the warm front? Well south of the warm front is what we call the warm sector. This is where the heat and humidity builds in, allowing enough CAPE (instability) to develop. This instability is what is needed for storms to develop.
The warm front is crucial as along the warm front, the low level winds are backed out of the southeast, providing enough veering of the winds. If you go up vertical along the warm front, the winds are out of the southeast, and eventually the higher you get, will eventually be out of the west. This causes the turning of the atmosphere, which is what is needed to provide tornadoes.
As of right now, the greatest threats will be large hail and damaging wind gusts. However, we would not be surprised that if a storm can remain isolated and get rooted on the warm front, that there could be a tornado potential. So while the tornado threat is low, it is still appears possible.
Eventually a cold front will crash through the state by early evening Wednesday, which will cause storms to line out, which will create a squall line that will move across eastern Iowa. As for timing of storms, it appears storms will initially develop along the warm front after 3pm, and will quickly line out after 6pm. Storms will linger across southeast Iowa into Thursday morning, before eventually clearing out of the state.
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