798 FXUS63 KLSX 051851 CCA AFDLSX Area Forecast Discussion...CORRECTED National Weather Service Saint Louis MO 151 PM CDT Sat Jul 5 2025 .KEY MESSAGES... - Widely scattered showers (20-30% chance) and a few sporadic thunderstorms (10% chance or less) will persist the remainder of the afternoon, with a few possible overnight as well. - Increased chances (30 to 60%) for showers and thunderstorms exist tomorrow afternoon, with a few microbursts and heavy downpours possible. While we don`t expect those hazards to be widespread, some minor wind damage and localized flooding can`t be ruled out. - A typical summertime pattern will persist for the next week, with repeated chances for scattered, mostly weak showers and thunderstorms almost daily and near average temperatures. && .SHORT TERM... (Through Late Sunday Night) Issued at 120 PM CDT Sat Jul 5 2025 The primary concern for the remainder of the day and into tomorrow continues to be the potential for showers and thunderstorms, along with potentially some isolated downbursts and heavy rain rates tomorrow afternoon. As we move past midday, some weak showers have already broken through a very weak cap across parts of central Missouri, with some more robust thunderstorm activity just to the northwest of there. These storms are likely being triggered by a combination of afternoon heating and cooling aloft from a very subtle mid/upper level shortwave evident on water vapor imagery. Instability is already moderate (1000-1500 J/kg ML CAPE) and will likely increase another 500 J/kg or so over the next few hours. However, wind shear is very meager, with effective shear values of only around 15 kt or so. As a result, this activity has not been particularly strong yet, and our local cells have not produced lightning as of 12:30. However, it should be noted that a slightly more substantial bowing segment has produced a bit of lightning just to the northwest, and we can`t rule out a few strikes over the next several hours. Otherwise though, strong/severe storms are not expected, aside from a limited potential for a microburst. This initial activity is likely to diminish as the sun sets, but another round of decaying showers and thunderstorms will be possible overnight as activity forming along an upstream cold front sinks into our area. Latest model trends suggest that this activity will be diminishing as it arrives, likely due to the loss of instability and continued very weak shear. While we will likely see at least some semblance of showers/storms overnight, impacts are expected to be minimal. By tomorrow afternoon, the aforementioned weak "cold" front will settle somewhere across the area, likely near or just north of the I- 70 corridor by mid afternoon. This boundary is likely to provide a more focused forcing mechanism for convection in a very weakly capped environment, although there may be even less upper level support than today. Meanwhile, moisture content is likely to increase, with precipitable water values surging to between 1.8 and 2.2 inches, per the HREF. Meanwhile, moderate instability will remain in place, perhaps reaching as high as 2000 J/kg of SBCAPE along the front by late afternoon. Model soundings also indicate shallow inverted V soundings with steep low level lapse rates, along with some potential for mid-level dry air entrainment that could enhance the downdraft potential. As such, it remains possible that we could see a few microbursts with this activity, although the even weaker effective shear (10kt or even less) will likely prevent storms from becoming organized. Meanwhile, bursts of heavy rain will also be possible, and we can`t rule out very localized flooding if cells can last for more than an hour or so in one spot. They won`t be moving very quickly and rain rates may be high, but with such weak wind shear it remains to be seen whether updrafts will be able to maintain themselves before they get cut off by their own outflow. This activity is likely to slowly drift to the southeast with the front during the evening and diminish in coverage, largely driven by their own outflow, but a few showers may linger through the night. BRC && .LONG TERM... (Monday through Next Saturday) Issued at 120 PM CDT Sat Jul 5 2025 From Monday onwards, a stagnant pattern and the previously mentioned weak frontal boundary are likely to result in additional chances for scattered showers and weak thunderstorms almost every day through the end of the work week. While the afternoons will likely be favored on most days, that may not always be the case every day. First, the stalled front is likely to remain across the area Monday, although there is a lot of uncertainty regarding how this boundary will be augmented by outflow from Sunday`s storms. In any case, another round of scattered showers and storms is likely to develop Monday afternoon wherever it settles, with similar potential hazards. Ensemble guidance suggests that this is most likely to occur along and south of I-70. Between Tuesday and Wednesday, a slightly more substantial shortwave may move across the upper Mississippi Valley region, triggering more widespread and slightly more organized storms to our northwest Tuesday afternoon. While we may see another round of weak afternoon pop-up showers locally during the afternoon, the better chances may actually be overnight through Wednesday morning. Given that this is still several days away and still rather weakly forced environment, this timing remains very tenuous. Beyond Wednesday morning, confidence in the day-to-day details remains low, but there is not much to suggest that the pattern will significantly change over the next week. LREF ensemble mean 500mb forecasts suggests that there may be a slight trend toward lowering heights and weak troughing late in the week, which may open the door for additional subtle shortwaves to move through the area, and these may provide some modest forcing enhancements for precipitation. As such, we will maintain the potential for scattered showers and thunderstorms each day through Saturday. Meanwhile, with little in the way of synoptic cold fronts or substantial changes in the overall pattern for the foreseeable future, the temperature forecast remains relatively steady for the next week, and right around seasonal averages. This will vary likely vary from day to day and from location to location depending on how showers and cloud cover evolve, but most should expect to see typical early July temperatures and moderate to high humidity for the next week. BRC && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1207 PM CDT Sat Jul 5 2025 Primary concern is the potential for showers and thunderstorms, which may impact terminals at various times throughout the 18Z period. Initial shower activity has already developed near COU/JEF at the start of the period, and this may briefly impact each of these terminals for the rest of the afternoon with bursts of heavy rain, lightning, and ceiling/visibility reductions generally to MVFR levels. A few of these storms may also impact UIN a few hours later in the afternoon as well. A brief lull in the activity is expected in the evening, but another round of decaying showers and storms will be possible at all terminals (including St. Louis area terminals) overnight, with similar hazards as well. Another round of showers and thunderstorms is expected tomorrow afternoon at all terminals, which is just beyond this TAF period for all sites except STL. Here we opted to add a mention of prevailing thunderstorms from 20Z tomorrow through the end of the period, with around a 60% chance of impacts to the terminal. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX