


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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883 FXUS63 KLSX 150747 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 247 AM CDT Tue Jul 15 2025 .KEY MESSAGES... - This week is expected to be seasonably warm with frequent chances for afternoon thunderstorms. - Heat and humidity build this weekend. && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 245 AM CDT Tue Jul 15 2025 We`re finally seeing some rumblings of change in the upper air pattern. A deeper trough moving into the Northern Rockies is helping to erode the western US ridge while also strengthening ridging over the southeast US. The last gasps of the persistent, weak, elongated trough over the south central US will be with us again today, providing yet another opportunity for afternoon showers and thunderstorms, mainly across the southeast half of the forecast area. But this trough is perhaps a bit weaker than previously expected, and overall convective coverage today may be similar to what was seen yesterday. With little to no shear, we`re expecting pulse type thunderstorms which produce locally heavy downpours in a moisture rich environment. But lack of storm organization and persistence should limit the severe or flash flooding threat. Storms should decrease in coverage through the evening. As the southeast US ridge becomes a bit more dominant it finally kicks out the lingering trough for Wednesday. The more pronounced trough over the Upper Midwest moves east and develops a more organized frontal boundary to our northwest. The result for us is we see temperatures rise a few degrees with a much lower chance of those afternoon pop up thunderstorms. With highs rising into the 90s area wide, we`ll see heat index values topping 100 degrees in many locations during the heat of the day. Kimble && .LONG TERM... (Wednesday Night through Monday) Issued at 245 AM CDT Tue Jul 15 2025 While the trough moves into the Great Lakes, a cold front will push southward behind it. Thunderstorms are expected to develop along this front late Wednesday into Wednesday night. While this activity develops to our north and west, there`s an increasing chance some of this moves into our northern forecast area Wednesday night. Wind shear does increase a bit, to about 20KT over northern MO. This will be enough to provide at least some potential for storms to organize into a convective cluster with a potential for damaging winds as highlighted in the Day2 SPC outlook. There`s also the potential for heavy rain and localized flash flooding as precipitable water values maximize near 2 inches once again. With a slow moving boundary in play, there`s a better chance that storms may be persistent in some areas, leading to swaths of higher rain totals. The front stalls in our area Thursday leading to a temperature gradient across the forecast area. While where that front sets up is uncertain, north of the front temperatures only reach the low to mid 80s, while south of the front it`s another hot and humid day in the 90s. The front will likely serve as a focus for shower and thunderstorm activity in the afternoon and evening. While shear decreases on Thursday, likely minimizing the severe weather risk, precipitable water remains high with a boundary in the area to focus potentially multiple rounds of storms, so we`ll still have at least some risk for flash flooding. The front remains near our area on Friday so we may see somewhat of a repeat performance with showers and thunderstorms. Ridging expands westward late this week, and by this weekend it will be centered over the south central US. This signals a shift toward warmer temperatures near the core of the ridge. While current forecasts are only a few degrees above normal, in the low to mid 90s for highs, the combination of heat and humidity will lead to heat index values considerably higher, well over 100 degrees Saturday, Sunday, and Monday. Northern areas will be near the periphery of the ridge and more likely to be impacted by passing shortwave troughs. These may bring periods of showers and thunderstorms and hold back temperatures a bit. However, confidence in building heat and humidity is greater across the southern and central portion of the forecast area. We may eventually need Heat Advisories during this time period. Kimble && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1005 PM CDT Mon Jul 14 2025 VFR conditions are expected at the start of the period, but patchy fog will be possible overnight through early tomorrow morning in river valley locations. While we do not expect fog to be as widespread or as dense as the previous night, some visibility reductions will be possible, with best chances at fog-prone terminals like SUS/JEF/CPS. Any fog that does develop tonight is likely to dissipate quickly tomorrow morning. While VFR conditions are expected through the rest of the morning, another round of scattered showers and thunderstorms is likely tomorrow, with best chances at St. Louis area terminals. While this activity will be scattered and some terminals may not be directly impacted, those terminals that do see a thunderstorm overhead will likely observe bursts of heavy rain, lightning, and occasionally gusty wind. Reduced visibility and ceiling categories would also be likely in that scenario. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX