Peoria, Ill (WMBD) – The weather pattern is trending more active for the later half of the week with periods of showers and thunderstorms capable of very heavy rain and severe weather.
- Several inches of rain possible through Saturday
- Difficult to pin down the timing of the heaviest rain and the strongest storms
- Urban & river flooding likely
A frontal system will move across the Central and Northern Plains Wednesday night before very slowly moving across the Midwest from Thursday through Saturday. This will bring numerous rounds of showers and thunderstorm to Central Illinois through the weekend, unfortunately the timing of each individual wave is impossible to pin down more than 24 hours out. Now matter when the storms come through, the amount of water in the atmosphere would make these storms very effective rain producers with a conditional threat of severe weather.
Thursday and Thursday night
Our confidence is highest with this initial round of showers and thunderstorms that will move through Central Illinois Thursday morning and early afternoon. A complex of storms known as an MCS (Mesoscale Convective System) will develop across Nebraska this evening and track east through Iowa and Missouri tonight before arriving in Central Illinois Thursday morning. While these storms will be severe to our west, they are unlikely to be severe when they get to Illinois but may contain gusty winds and heavy downpours. Should these storms arrive later in the day, the storms could intensify and lead to an increased potential for severe weather, but the chance of this happening is low.
Cloud debris from the morning activity will likely lead to the atmosphere remaining capped for much of the afternoon. While the warm and humid conditions will likely lead to some pop-up storm development throughout the day, the cap should prevent storms from becoming severe.
Storm chances Thursday night are little less certain but with the presence of a low level jet and an approaching shortwave from the west, an increase in storm coverage Thursday night makes sense. Storms would likely initiate along an outflow boundary from the Thursday morning activity once the low level jet stream develops after sunset. It’s unclear where storms will initiate, but once storms develop they will be capable of producing torrential rain, damaging wind gusts and perhaps an isolated tornado as they lift north across the state.
The Storm Prediction Center (SPC) has placed far western Illinois in a Slight Risk (Level 2 Threat) with a Marginal Risk (Level 1 Threat) over the rest of the region. There is also a Slight Risk for flash flooding across much of the region.
Friday and Friday night
Thunderstorms will remain likely but there’s a lot of uncertainty in the storm timing and impacts since they will heavily depend on what ultimately happens Thursday night. While confidence in the details remain low, it stands to reason that this would be the day we see the greatest severe weather threat as a stronger shortwave lifts out of the Central Plains. Once again, the residual outflow boundary from the Thursday night activity will likely be the focal point for new thunderstorm develop Friday afternoon and evening.
No matter where the strongest storms develop, the presence of strong shear and instability suggest that damaging wind gusts and isolated tornadoes will be possible. The significant amount of moisture in the atmosphere will cause thunderstorms to produce very heavy rain that could lead to flash flooding. For now, SPC has placed Central Illinois within a Marginal Risk for severe weather. There is also a Slight Risk for flash flooding. We could see both of these risks increase in the coming days as the small scale features are better understood so stay tuned.
Details revolving around Saturday are scanty this far out as what happens Friday will determine what will ultimately happens. That said, scattered thunderstorms capable of heavy rain will remain possible. With sufficient wind shear in place, severe thunderstorms will be possible should there be enough instability.
This part of the forecast remains fluid as the placement of heaviest rain will depend on small scale features that can’t be resolved this far out. That said, it seems fair to expect 3-6 inches of rain across Central Illinois through Saturday, a notable increase from earlier projections. Some areas will likely exceed 6 inches of rainfall but it is impossible to know where that will be at this time. If you are in area that typically experiences flooding during heavy rain events, you should act now to protect your property.
River levels will also be on the rise next week once this storm system moves out of the region. All rivers are currently below flood stage but will need to be monitored for reaching flood stage next week.
While storm coverage will decrease, the presence of an upper-level trough will remain in place across the Midwest which will keep the chance for hit and miss thunderstorms capable of heavy downpours in the forecast through early next week.