


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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300 FXUS63 KLSX 100354 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1054 PM CDT Wed Jul 9 2025 .KEY MESSAGES... - There are multiple chances for showers and thunderstorms between Thursday and the middle of next week. Severe weather is not expected. - Friday will be the warmest day of the week as heat index values climb to around 100 degrees for most. The St. Louis metro area will see values closer to 105 degrees. && .SHORT TERM... (Through Late Thursday Night) Issued at 142 PM CDT Wed Jul 9 2025 Surface analysis shows a diffuse quasi-stationary front extending from the central Plains through central Iowa. This front will creep south into northeast Missouri/west-central Illinois through this afternoon and will have no noticeable impact on our sensible weather. However, the boundary has been a catalyst for convective initiation in Nebraska and the Dakotas today. As the nocturnal low-level jet ramps up tonight, these showers and thunderstorms will congeal into an MCS and follow the front into northeast Missouri. Scattered showers and thunderstorms from the MCS are forecast to arrive in the middle to late morning tomorrow and linger through the afternoon. The areal extent of convection will depend on the presence of any outflow boundaries laid out by the morning convection. Latest CAMs are keen on outflow boundaries playing a role in upstream convection tomorrow afternoon, and I`m not inclined to disagree given 1) that we`ll have up to 2000 J/kg of SBCAPE and 2) that outflow has played a large role in thunderstorm propagation this past week. Because of this and the chaotic nature of outflow boundaries, I`ve spread slight chance PoPs over the rest of the CWA tomorrow afternoon. With effective shear only around 15 kts, severe weather is not expected. Otherwise, tomorrow will be a seasonable day with lows near 70 degrees and highs around 90. Jaja && .LONG TERM... (Friday through Next Wednesday) Issued at 142 PM CDT Wed Jul 9 2025 A series of shortwaves will keep our weather pattern active until at least the middle of next week. The greatest chance for rain (up to 50%) will come Friday night into Saturday as a shortwave interacts with a stationary front in the vicinity of the CWA. Not everyone will see rain out of this due to the scattered nature of the convection. Those who do see rain, however, have the potential to brief heavy rainfall since PWATs will be hovering around 1.7" during this timeframe. This forecast is generally true through Wednesday. The front will linger in the area through Sunday providing another chance of showers and thunderstorms. Monday looks drier as the front moves off, but rain chances ramp up again on Tuesday as another shortwave triggers a cold front at the surface. A lack of sufficient effective shear each day (only 10 - 15 kts) will keep the potential for severe weather low. The temperature forecast through Wednesday will generally be seasonable with highs in the 80s to 90 degrees and lows in the 60s and 70s. Friday is expected to be the warmest day as heat index values climb to around 100 degrees for most and near 105 in the St. Louis metro area. Overall, nothing uncharacteristic for July. Jaja && .AVIATION... (For the 06z TAFs through 06z Thursday Night) Issued at 1045 PM CDT Wed Jul 9 2025 VFR conditions are expected to prevail for a majority of the 06Z TAF cycle. Clearing skies and light winds tonight may allow for some patchy river valley fog formation. While dense fog did occur yesterday in a few locations, much of this was likely caused by rain earlier in the day, which did not occur today. After a day of full sun and deep mixing, we don`t expect that coverage will be as widespread, and confidence is low that local terminals will be impacted again tonight. Otherwise, there is a low chance for showers and weak thunderstorms during the day, with highest chances (~40%) at UIN late in the afternoon. At other sites, lower probabilities (20% or less) exist, and this remains too low to included in the TAF at this time. Light southerly winds are also expected to prevail from tomorrow morning onward. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX