


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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356 FXUS63 KLSX 290108 AFDLSX Area Forecast Discussion...Updated National Weather Service Saint Louis MO 808 PM CDT Sat Jun 28 2025 .UPDATE... Issued at 754 PM CDT Sat Jun 28 2025 Have issued a Flood Watch for late tonight and Sunday morning for Reynolds County. Parts of southeast Missouri including Reynolds county saw 1 to 3 inches of rain this afternoon. Satellite imagery is showing a nearly stationary MCV over south central Missouri that the CAMS show additional thunderstorms developing with late tonight into early Sunday morning. RAP soundings in southeast Missouri are showing PWATS near 2.0" with deep warm cloud depths which will support very efficient rainfall rates. The HRRR has 24 HR LPMM rainfall of 1-3" with the potential for higher amounts which could cause flash flooding with any training thunderstorms. Britt && .KEY MESSAGES... - Seasonably hot and humid conditions continue with periods of showers and thunderstorms through Monday. - A cold front on Monday brings a shift toward slightly cooler and much less humid conditions for midweek. && .SHORT TERM... (Through Late Sunday Night) Issued at 237 PM CDT Sat Jun 28 2025 Summer-like heat and humidity continues as we remain along the northern periphery of a broad, flat-topped ridge. Yesterday`s front has stalled and gotten a bit washed out in the low levels as the parent shortwave trough that drove it is now well east in New England. With the heat and humidity we`re seeing plenty of instability developing with convection mainly focused in a few clusters from southern Missouri eastward into KY and TN. The primary cluster affecting us today is associated with a remnant MCV just now entering southwestern Missouri. Most of the convection has been ahead of the MCV where subtle low level warm/moist advection toward the remnant front has encouraged more lift. Plenty of sun this morning also has led to strong instability this afternoon leading to broader convective coverage than what some high resolution guidance had been suggesting. We expect this activity to move VERY slowly to the east this afternoon as the overall wind flow is quite weak. Convection may propagate a little faster once larger outflow gets generated with the potential for new convection on the outflow mainly oriented to the east. Eventually, though, we`ll lose access to daytime heating and instability will wane this evening, leading to a decrease in convection as it inches to the east. While convection is expected to dissipate this evening, the MCV core itself will gradually move east as well. This is expected to generate new thunderstorm activity during the overnight hours over southwest Missouri moving into southeast Missouri Sunday morning. It will still be moving pretty slowly and we expect a gradual decrease in convection as the morning moves on. Lingering clouds may hold temperatures back a few degrees, but the humidity remains with us keeping those heat index values in the mid to upper 90s. Late Sunday afternoon into early Sunday evening, convection is expected to fire to our north along or just ahead of a developing cold front from Nebraska to Iowa. Guidance varies considerably on when and where along this boundary convection will develop, but the general consensus on a compact MCS developing and diving southward through the overnight is fairly well agreed upon. If this forms further west into Nebraska, then the area impacted will be across western Missouri. If it forms further east into central Iowa, then it stands a much better chance of dropping south through parts of northeast and central Missouri. This MCS does look capable of producing damaging winds across the region, but this threat decreases as storms head southward from their origin and as the available instability decreases overnight. The new Day2 outlook from SPC highlights this threat well. While a small portion of our area is included in this outlook, we`re holding off on messaging this more broadly just yet due to the uncertainty on the east/west location of where this MCS will track and whether it will maintain its severe weather potency as it moves south. Either way, though, the chances of rain associated with the nearby MCS increase overnight for most of the area. Kimble && .LONG TERM... (Monday through Next Saturday) Issued at 237 PM CDT Sat Jun 28 2025 Sunday night`s MCS will likely still have remnant showers associated with it Monday morning, but the next potential for thunderstorms will be associated with the cold front itself which will be dropping south through the region during the day on Monday. Considerable uncertainty exists on if this boundary will trigger additional convection Monday afternoon, with a lot of that uncertainty hinging on how much cloud cover from the morning MCS hinders destabilization ahead the front. If storms do form, though, they`ll have a little better shear to work with and stand a better chance of becoming severe. The Day3 Outlook now includes most of our area in a Marginal Risk due to this uncertain threat. Zooming out we see that this front is being driven by a much deeper trough dropping southeast out of the Pacific Northwest and tracking through the center of the country. This is what is enabling a full pattern change and a change in air mass for our region. While humidity lingers ahead of the front Monday, with rain chances continuing until the trough axis has fully passed through the area, the effects of the front`s passage will be fully noticeable by Tuesday. Dewpoints fall a good 10+ degrees back into the low to mid 60s. Plenty of sunshine will enable strong surface heating, so afternoon high temperatures will remain somewhat similar to what we saw the preceding few days, in the 80s, but it will feel much better. Low temperatures also drop into the 60s for the first time in a while. This air mass lasts through about Wednesday when the surface high pushes off to the east enabling a return southerly flow across the region. Ridging over the western US nudges eastward later in the week with a gradual warm up expected. Southerly flow also increases humidity across the area, with dewpoints rising back to 70 or higher by Friday, July 4. This combined with temperatures climbing back into the 90s will bring the heat index values back into the upper 90s to near 100 degrees for Independence Day. Although rain chances do start to creep back into the forecast later in the week with the arrival of the more humid, unstable air mass, these chances have come down a bit from previous forecasts as it is now more likely that we stay away from the influence of an eastern US trough and its associated frontal waves. Better rain chances may actually hold off until this weekend when a more pronounced trough rounds the top of the ridge sending a front toward us from the northwest. Kimble && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 628 PM CDT Sat Jun 28 2025 Showers and thunderstorms have moved away from the terminals and I now expect mainly dry weather until late tonight and early on Sunday when additional thunderstorms will move into the area from western Missouri. Confidence does not remain high with this chance, so will keep the PROB30 for COU/JEF between 09-15Z and STL/SUS/CPS between 12-18Z, There will be lower chances for redevelopment in the afternoon at all of the terminals, but confidence is too low to include at this time. Any of the heavier thunderstorms could bring MVFR/possible IFR ceilings and visibilities in brief heavy rain. Otherwise, winds are expected to stay below 10 knots outside of thunderstorms. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch from 1 AM CDT Sunday through Sunday afternoon for Reynolds MO. IL...None. && $$ WFO LSX