TRICKY STORM FORECAST THIS WEEK

With rising temperatures this week into the 80s and increasing humidity as well, the pattern will become more reminiscent of a summertime storm regime as a frontal boundary stalls out over the region leading to a nearly daily chance of thunderstorms, especially later in the week Wednesday night onward. Overall models agree in potential for heavier rain across the Upper Midwest along the Iowa/Minnesota border region, and extending into Wisconsin and northern Illinois.

Machine-learning model guidance shows some potential for a strong to severe weather threat Wednesday and Thursday along this boundary where the greatest threat will likely be wind gusts with any organized activity. For the time being there are no Storm Prediction Center outlooks for severe weather, but this could and likely will change in the coming days.

WEDNESDAY'S STORMS

The NAM

The GFS

The Euro

Our first round of potential storms comes Wednesday evening. The NAM and GFS are both indicating thunderstorms affecting the area while the Euro is farther north with the potential storm activity. This would all be co-located with a boundary that remains stalled out over the region and is the focus for thunderstorm development.

The placement of the boundary will be critical for the risk of strong storms and heavy rainfall again Thursday. Areas along this boundary, both just north an south, will have the highest risk. The European places this boundary directly along the Iowa/Minnesota border Thursday.

Friday there is even more moisture, therefore instability, in place south of the boundary with dewpoints pushing into the upper 60s to near 70. The boundary Friday is also forecast to be farther north across southern Minnesota into southern Wisconsin. If this is accurate, this would likely direct any storm threat to be farther north.

Ensemble guidance can help us gauge the confidence in placement of the boundary and area most at risk of storms and potential heavy rain/severe weather. For Thursday the European Ensemble is pretty in line with the deterministic Euro with northern Iowa, southern Minnesota and southern Wisconsin in line for the heavy rain and strong storm threat. Probabilities of 0.5" of rain are pushing 60-70%.

For Friday, again the Ensemble guidance is pretty in line with the deterministic with the heavier rain and storm threat farther north into more of southern and central Minnesota and Wisconsin. The probabilities of 0.5" of rain are now 70-80%.

I do want to stress again despite the models seemingly being in agreement here, these systems are notoriously tricky to forecast and what happens one day will affect the next day as storm-induced outflow could push boundaries farther south than the lower resolution models can depict at this range.

While not in record territory, the overall moisture supply for this pattern is on the higher end of the scales. General moisture will be in the 90th percentile across the region with Friday's ample supply a bit higher than Thursday's.

The overall moisture transport is right along with norms for this time of year. Without this significant convergence crashing into the boundary it would help alleviate any significant flash flooding concerns, but this will be something to watch if we see repeated rounds of storms over the same areas.

South of the front we will see the heat building this week into next week. Wednesday forecast highs in the Quad Cities region are approaching 90° with mid/upper 80s continuing Thursday. Next week there remains another signal for long-lasting heat and potential for strong storms as well, which I talked in more detail yesterday. These forecast temperatures may be a few degrees too cool as it's a bit of an average and blend.

Certainly an interesting week of weather ahead and with drought conditions in place the rain is certainly welcome. Northern Illinois particularly is in worse shape with Severe Drought conditions in the latest drought monitor.

Have a great week everyone!

-Meteorologist Nick Stewart