


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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833 FXUS63 KLSX 122310 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 610 PM CDT Sat Jul 12 2025 .KEY MESSAGES... - Scattered showers and thunderstorms are forecast each day through late next week. There will be plenty of dry time. && .SHORT TERM... (Through Late Sunday Night) Issued at 225 PM CDT Sat Jul 12 2025 Recent surface analysis shows a pre-frontal trough pushing through southeast Missouri and southern Illinois this afternoon. This feature is quickly traversing these areas and is forecast to stall just beyond our border. As such, tonight will be mostly dry as ongoing convection is shoved out of the area. Portions of northeast Missouri and west-central Illinois will see a relatively cool night as well with lows dropping into the mid to upper 60s. This is due to a cold front ushering lower dewpoints into these areas. Rain chances return early tomorrow morning through tomorrow afternoon as a shortwave trough over the southern Plains ejects vorticity lobes into Missouri and Illinois. These lobes will interact with a stalled front to our south and produce showers and thunderstorms. Although showers are forecast areawide, the highest concentration of thunderstorms will generally be relegated south of I-70 where moisture and instability will not have been tampered with by the drier air to the north. With around 1500 J/kg of MLCAPE present, I cannot rule out a few thunderstorms capable of gusty winds, but strong thunderstorms are unlikely. Bulk shear values of up to 15 - 20 kts will support quick-lived pulse convection as opposed to organized thunderstorms. As we`ve seen earlier this week, cores will likely collapse before bulking up enough to produce strong winds. Otherwise, PWATs still in the 1.75 - 2" range will support locally heavy rainfall underneath these thunderstorms. Isolated flash flooding is a possibility in locations that experience multiple thunderstorms and/or have received abundant rainfall recently. Thunderstorm coverage will taper off through the evening with a dry forecast in store by midnight. A similar night to tonight is expected with widespread mid to upper 60s forecast for most. Jaja && .LONG TERM... (Monday through Next Saturday) Issued at 225 PM CDT Sat Jul 12 2025 There is a chance for showers and thunderstorms each day from Monday through late week, but plenty of dry time is expected. Coverage and location of convection will be dictated by the position of the aforementioned stalled front and the behavior of mid-level shortwaves and vorticity maxima. Global models begin to diverge on the pattern aloft as early as Monday which has implications regarding our rain chances for the week. What they do agree on is the presence of a near-cutoff low in the Oklahoma/Arkansas vicinity on 12z Monday. This feature is progged to head northeast through the mid-Mississippi Valley through the day on Monday, and that`s where the similarities end. Where exactly the feature starts the day, how strong it will be, how fast it traverses the mid-south, and where it tracks all differ. Most deterministic guidance favors a weaker, slower, and more equatorward tracking low which would result in rain chances confined to south of I-70 during the afternoon. However, there is some guidance that favors a stronger, faster, and more poleward shifting low. This solution would cause more locations to see showers and thunderstorms with them beginning earlier in the day. Although our forecast reflects the drier solution, both are possible at this juncture. Thunderstorm chances increase Tuesday as the cutoff low pushes the stalled surface boundary northward and back into our CWA. The low will continue to provide upper level support for convection during the day, but the details are muddled. The greatest chance will be in the afternoon when conditions are most favorable, but exact timing, location, and coverage all depend on the location and strength of the boundary. This will, in turn, be determined by convection on Monday and the behavior of the mid-level pattern. The same can be said for Wednesday and so on. This uncertainty is reflected in a growing NBM interquartile high temperature spread from Tuesday onward. By Thursday the spread is 8 degrees. This is a notable spread in July when the pattern is typically quiet and climatology forecasts are generally within a couple of degrees of being correct. Otherwise, high temperatures for next week are forecast to land generally in the mid-80s to low-90s each day with morning lows in the 60s and 70s. Jaja && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 604 PM CDT Sat Jul 12 2025 The primary concerns during the 00Z TAF period will be the potential for some patchy fog overnight tonight, followed by showers, lowering ceilings, and a few thunderstorms tomorrow morning through the afternoon. While a few very weak showers continue to percolate in the area this afternoon, mostly near UIN, VFR conditions are in place to start the period. Very light winds and residual humidity overnight may allow for some patchy fog development in low lying areas, most likely at SUS/JEF/CPS, with lower probability chances at COU and UIN as well. Showers are likely to move into central Missouri in the morning, followed shortly thereafter in the St. Louis area, and will continue on and off through the mid to late afternoon. A few thunderstorms are also possible, but are not likely to produce much more than lightning, bursts of heavy rain, and occasionally gusty winds. MVFR ceilings are also likely with these showers with a lower chance for dips to IFR levels as well. Visibility reductions due to heavy rain will also be possible. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX