Marine Weather and Tide Forecast for Fairview Heights, IL

SHORT TERM
(Through Late Tuesday Night)
Issued at 352 PM CDT Sun May 17 2026

A deepening long wave trough over the Rockies is forcing cyclogenesis over the Great Plains this afternoon. The deepening low level cyclone is tightening the pressure gradient across the Mississippi Valley producing southerly flow and bringing warm humid air north from The Gulf. This will set the stage for several rounds of thunderstorms through Tuesday. The first round of storms is expected to develop late this afternoon/early this evening as a short wave moves into the central Plains which lifts a lobe of the surface low northeast. This increases convergence along the cold front over Kansas and Nebraska and fires off convection. Discrete storms are expected to grow upscale into an MCS which moves east overnight. Most CAMs show a broken line of weakening thunderstorms moving into our northeast and central Missouri counties between 09- 12Z. However a few (most notably the 12Z 4km NAM NEST) have the storms moving into Knox County as early as 06Z. Regardless of when they arrive, the GFS and RAP are showing enough MUCAPE across our area to maintain the convection as it continues east. Deep-layer shear is lacking at 20-25kts across most of the area, and forecast soundings indicate a fairly deep stable layer below the instability.
While some wind gusts to 50-60 mph will be possible initially across northeast Missouri, thing sub-severe gusts become more and more likely as the line continues east into Monday morning.

Still a good deal of uncertainty for Monday's forecast as some guidance moves the weakening showers and storms through quickly or dissipates them entirely by 18Z and others slow the storms down, but continue to march them southeast through the forecast area all day.
The lingering precip scenario looks less likely, but current high temperature forecasts in the mid to upper 80s will likely not be realized if clouds and showers linger through the day. Regardless, another upper level short wave breaks off the long wave over the Rockies and moves into the Great Plains during the afternoon and evening. This wave forces another low to develop on the surface front over the Great Plains, and it races northeast through Monday night. Another round of thunderstorms develops on the front over Kansas and Nebraska as the front begins to move, and they quickly grow upscale into QLCS. Much like tonight's line, this line will lose steam as it moves east, reaching our area between 06-09Z. The presentation of this line is not very impressive in most CAMs by the time it reaches our area. The most likely area for severe weather in our area should be northeast Missouri into west central Illinois where MUCAPE ranges from about 1800 J/Kg in the RAP to around 1200 J/Kg in the GFS. 0-6km shear isn't terribly impressive at around 25kts and there is a stable layer below the instability once again.

The final round of storms comes Tuesday as the cold front drifts into the area. Think the severe risk is conditional on how the overnight convection plays out as it moves through our area. A strong enough outflow boundary would wash out the instability ahead of the front and lingering clouds/showers could limit recovery. As it stands, the GFS develops around 2200 J/Kg MLCAPE ahead of the front during the afternoon and forecast soundings only show the tiniest bit of CINH. However the shear is still unimpressive at 20- 25kts. These parameters favor multi-cell clusters with the potential for damaging winds and large hail during the afternoon.
Guidance shows the front moving south of the CWA by 03Z Wednesday.

Carney

LONG TERM
(Wednesday through Next Sunday)
Issued at 352 PM CDT Sun May 17 2026

Briefly in the long term...cool high pressure builds into the Midwest Wednesday which brings drier weather to the region and temperatures fall back below normal. The deterministic NBM is forecasting highs in the mid 60s to low 70s Wednesday which is above the upper quartile of the LREF temperatures. However strong May sunshine may win out over cold advection so these temperatures are not unreasonable. Below normal temperatures continue Thursday with morning lows dropping into the mid 40s to around 50 and highs of 70- 75. Southerly flow and near to above normal temperatures with a chance for rain return Friday and Saturday as the surface high moves into southeast Canada and another trough moves into the Plains and Midwest.

Carney

AVIATION
(For the 00z TAFs through 00z Monday Evening)
Issued at 623 PM CDT Sun May 17 2026

Gusty southerly flow is expected to continue through much of the TAF period with VFR conditions persisting through late tonight.

Showers and thunderstorms develop over the Plains and Upper Midwest tonight, sinking southeast into the region between early Monday morning and Monday afternoon. Convective-allowing models show quite a spread in timing and evolution in intensity.
Convection tends to weaken in these scenarios, as instability wanes through the period of diurnal mins. Given the uncertainty, consistency is the best approach here. FM groups address -SHRA start/end times for highest precipitation potential (>60%) and TEMPO/PROB30 groups accounting for the uncertainty in ongoing thunderstorm timing/intensity. Overall, the threat from -TSRA should end between early to mid-afternoon Monday with lingering showers in the region. Cloud bases largely remain at VFR levels with MVFR conditions largely driven by visibility restrictions during heavy rainfall.

Conditions are expected through the later half of Monday with VFR conditions favored again toward the end of the period.

Maples

LSX WATCHES/WARNINGS/ADVISORIES
MO...None.
IL...None.