Peoria, Ill. (WMBD) — As a heat dome/strong ridge of high pressure brings hot temperatures to the Central Plains, small disturbances called shortwaves will ride the northeastern edge of the ridge into Illinois. This will bring better chances of rain and storms to Central Illinois through the weekend.

The first wave, now located along the North Dakota/Canada border, will arrive in Illinois on Friday. This will force showers and storms to spread across Central Illinois late Thursday night and Friday morning. These storms will not be severe but could produce locally heavy rainfall. What happens next remains uncertain but could evolve into a severe weather event that could catch people off guard.

The first batch of rain is expected to wind down and come to an end by early afternoon. If skies are able to clear out and temperatures are able to recover in the wake of the morning rain, the atmosphere could destabilize enough for storms to redevelop by late afternoon or early evening (likely after 5 pm). Should storms develop the wind shear profiles will be quite impressive for July and would support severe storms with a damaging wind, hail and tornado threat.

So why the uncertainty?

While it’s been clear for some time that there will be periods of rain and storms from Friday through Sunday, the manner in which these storms move through the area comes down to small scale features that are difficult to discern more than 18 hours in advance. We often use Hi-Resolution models to find these features and try and iron out the details, but even they are not perfect.

As of 5 pm Thursday each model has a different solution as to how Friday will play out. Some models bring rain through Central Illinois for most of the day which in turn lowers the instability keeping our severe weather threat in check. Others show rain ending relatively early in the afternoon with the atmosphere destabilizing allowing for another round of storms to develop by early evening. Even the models that show this solution disagree as to where that second line of storms would develop, does it happen north of I-80 or closer to I-74?

Here are a few of these Hi-Resolution models, each with a different solution as to how Friday afternoon will play out.

Baron 3k Model (In House Model)

Our model shows showers and storms continuing across Central Illinois through about 1 pm Friday. While the rain moves out fairly quickly it keeps cloud over Central Illinois through much of the atmosphere keeping instability in check. It does eventually fire new storms, and while they could be severe, it keeps these storms north of I-80.

Hi-Res Rapid Refresh (HRRR)

This particular model is NOAA’s real-time, 3km resolution model, that updates hourly. It is designed to forecast the complexities of thunderstorms and does so by bringing in real time radar data. While this model does pretty good with existing thunderstorms, it can struggle with storms that have yet to develop. So, it’s not something that should be taken as gospel several hours in advance. For now, this model continues to bring showers and storms to Central Illinois throughout the entire day and even into evening. This would be the best case scenario as we would receive beneficial rain without the severe storms.

North American Mesoscale (NAM 3k)

This model is the hi-resolution version of NOAA’s 12km NAM model. While it is a higher resolution model designed for forecasting thunderstorms, it runs every 6 hours and is not infused with real time weather data. It also has a tendency to make dew points higher than they actually will be, leading to greater instability. The end result is that the model tends to be too bullish on thunderstorms. In this case, the model is clearing out the rain and clouds relatively early in the day leaving us with warmer afternoon temperatures and higher instability. As one would expect, the end result of this is widespread severe thunderstorms over Central Illinois by early evening. This solution should be taken with a grain of salt but does serve to show what the worst case scenario could be.

What do I think will happen?

To be clear, none of the models displayed above are going to be 100% accurate, they never are. However, they do offer us some tips as to what may play out. I suspect the morning rain will end between 1 and 3 pm Friday with some clearing skies not long after. This should allow the atmosphere to destabilize enough for storms to redevelop by early evening, likely near I-80 with these storms dropping south through midnight. They probably won’t be as widespread as the NAM 3k suggests, but these storms could be severe with damaging winds and hail. Should the more aggressive solutions play out the risk of a tornado would increase too.

For the time being the Storm Prediction Center has placed Central Illinois within a Marginal Risk (Level 1 threat) for severe storms. If it becomes apparent that skies will clear out, look for this threat to increase in future updates.

One the bright side, Central Illinois looks to receive a widespread 0.25″ to 0.75″ of rain with locally higher amounts possible. Should the severe storm threat increase, rainfall amounts of 1-2″ would be more common.